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49erFX Tuning Guide and guidance


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I was recently looking on line for tuning and general handling advice on the 49er FX. I'm thinking of adding one to my training fleet to give the women sailors in my group another level to aspire to. I figure I should get ahead of the game in learning any peculiarities about tuning or handling the boat

Most things seemed to be based around a 2012 guide put out by Mackay Boats.

One thing struck me as counter intuitive.

Their suggestion is you induce a fair amount of prebend with the uppers in light air, a little more in medium, but basically ease it right off in heavy.

But they don't really explain why.

Given that prebend will presumably flatten the sail, it strikes me as counter intuitive and certainly isn't what I've been doing with my current twin wire skiff.

So I suppose I was wondering

  • Why does it work this way? 
  • Is this generic to masthead spinnaker, double spreader, twin wire square headed skiffs, or is there something about the 49erFX rig that drives the approach

I also noted they suggested a lot more tension (loos gauge readings) on their D1 lowers/ checkstays than I'm used to using. I'm assuming these are measured before any vang is applied (or the sail is even hoisted) and again wouldn't mind some feedback on how specific this is to the 49erFX. Interestingly again, the tension is recommended to go up as the wind freshens - the opposite of what my old fashioned thinking might have suggested. So again, any explanation would be gratefully received (never too embarrassed to learn from being told why I'm wrong). 

Apart from that specific questions, I will be glad to be pointed to or provided with any good tuning, boat set up or boat handling materials that might help in my project.

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Hi mate,

If you don't pre-bend the top mast, then you end up with a hooked upper leach.

Given the size of the FX "head board" that's very slow, plus you also want to flatten the upper sail or you end up with too much camber and you can't get the flow to stick.   So you use Caps tension to open up the upper sail and the leach.

As the wind increases and you start to use more controls, especially down-haul, you need to come up on the caps so as to keep the mast head up on the CL.

Then as it gets fresher, one of your de-power mechanisums is to allow the mast tip to flick to leeward and spill the air, and to do that you need to ease the caps.

Interesting side bar, Sir JJ,  (Finish 2000 49er GM and Chinese coach) commented that they went through cap (shrouds) because they flogged about a lot and fatigued at the base of the eye-termianl at the mast head.    So they are letting the caps go a long way.

No issue under spinnaker because these people did not ease their mains all that much, so sure the tip went fwd and sideways but remained in control.   To be honest, the FX tip could probably survie without Caps.

That's one of the issue with having a 40-50% head length (as a % of foot length) which a FX has.     The 49er it's only 27-8% so it's far more in-control, has a greater range! 

49er/FX D1's go in at the the top of the ram vang, so they are a lot higher up, the angle is far more acute, so they need more tension to have the same result, the flip is that they hold the mast very positively higher up and there for are far more effective.

The guys in the AST alter their tensions every 2-3 knts of wind as you go up the scale, so there are a miriad of tweaks.    Given that they are all about to go to a new mast and possibly new sails, then it will all change, so the old numbers, which are pretty closely guraded should become available.    So if you are going to try and buy a old FX rig, it will be the Southern Spars mast and these guraded numbers will be just perfcet for you.

I will see if I can get you a set.

The new masts, will probably have similar numbers but there will be tweaks depending on % changes in sectional stiffness, and of-course new sails.   All retro fittable, so no shortage of spares.

                             jB

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1 hour ago, JulianB said:

Hi mate,

If you don't pre-bend the top mast, then you end up with a hooked upper leach.

Given the size of the FX "head board" that's very slow, plus you also want to flatten the upper sail or you end up with too much camber and you can't get the flow to stick.   So you use Caps tension to open up the upper sail and the leach.

As the wind increases and you start to use more controls, especially down-haul, you need to come up on the caps so as to keep the mast head up on the CL.

Then as it gets fresher, one of your de-power mechanisums is to allow the mast tip to flick to leeward and spill the air, and to do that you need to ease the caps.

Interesting side bar, Sir JJ,  (Finish 2000 49er GM and Chinese coach) commented that they went through cap (shrouds) because they flogged about a lot and fatigued at the base of the eye-termianl at the mast head.    So they are letting the caps go a long way.

No issue under spinnaker because these people did not ease their mains all that much, so sure the tip went fwd and sideways but remained in control.   To be honest, the FX tip could probably survie without Caps.

That's one of the issue with having a 40-50% head length (as a % of foot length) which a FX has.     The 49er it's only 27-8% so it's far more in-control, has a greater range! 

49er/FX D1's go in at the the top of the ram vang, so they are a lot higher up, the angle is far more acute, so they need more tension to have the same result, the flip is that they hold the mast very positively higher up and there for are far more effective.

The guys in the AST alter their tensions every 2-3 knts of wind as you go up the scale, so there are a miriad of tweaks.    Given that they are all about to go to a new mast and possibly new sails, then it will all change, so the old numbers, which are pretty closely guraded should become available.    So if you are going to try and buy a old FX rig, it will be the Southern Spars mast and these guraded numbers will be just perfcet for you.

I will see if I can get you a set.

The new masts, will probably have similar numbers but there will be tweaks depending on % changes in sectional stiffness, and of-course new sails.   All retro fittable, so no shortage of spares.

                             jB

Thank you Julian

That's a fantastic answer. Makes it really clear.

Very happy to get any update of the numbers.

I hope I can bring an acquisition of a FX off.

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Just fantastic!!!!

Our young coaches have just bought an FX and are getting her set up with the help of Harry Morton ... happy to share any intel we get down at Hunters Hill, and on buying an FX - it was a bit of a trek!!

Cheers

Chris

26F337BE-926B-483E-8070-B4E4272A39A0.jpeg

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On 6/11/2020 at 1:59 PM, Stanno said:

Just fantastic!!!!

Our young coaches have just bought an FX and are getting her set up with the help of Harry Morton ... happy to share any intel we get down at Hunters Hill, and on buying an FX - it was a bit of a trek!!

Cheers

Chris

 

Spoke to your coach Chris

That boat was a fantastic acquisition at a great all up price. I'm jealous :-)

I hope the sailors make good use of it.

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  • 3 weeks later...
On 6/10/2020 at 5:35 PM, JulianB said:

 

As the wind increases and you start to use more controls, especially down-haul, you need to come up on the caps so as to keep the mast head up on the CL.

Then as it gets fresher, one of your de-power mechanisums is to allow the mast tip to flick to leeward and spill the air, and to do that you need to ease the caps.

I

Hi Julian

I wonder if you could help me get my mind around one aspect of the quoted part of the answer.

I probably need to explain why I'm asking.

As you know by now, I take non sailors - mainly women - and convert them into high performance skiff sailors. After the first couple of graduates had raced for a year they said "you told us what to do, but not why."

So I introduced a winter lecture series that went into the full intricacies of skiff sailing - including for instance, preparing and explaining full vector diagrams of downwind apparent wind sailing. This was all backed up by comprehensive lecture notes.

Now I'm no Olympic level racer (or anything near it). I've spend a life time in skiffs, including about 5 years in the 18's, but I'm there for the fun, not the trophies - which is just as well :-)

So much of the higher level information is derived from those who know more than me; and to a very large extent from the books from your family. You might be interested to know the chapter on wind formation and behaviour was not just derived from your father's book, but a little over 20 years ago he was good enough to review the material and approve it for me as being a fair summation of his work; albeit simplified for younger sailors (teenagers at that time).

After a recent lecture, a couple of the sailors asked me if I'd do one on rig set up, how spreaders work and rig tensions. Surprisingly, these were the two most experienced sailors in the group - a sailmaker with extensive skiff experience and a championship level former junior sailor. I dealt with the topic superficially in an early lecture, but they now clearly want a lot more detail. In that context your answer above will make an interesting diversion (because it explains the non intuitive).

But as I think about the topic and what I have read here and elsewhere, I wonder if you could comment on one inconsistency.

In an earlier topic on mast tracks you basically suggested (in reference to a carbon track) "side bend bad", which is not entirely consistent with the above.

I'm assuming the difference is that with a large square head main, upper mast side bend is more acceptable at the upper wind range because it aligns the angle of bend with the twist of the upper main. Is that a fair approximation of the difference?

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Hi Mate, so how many pages do you want??????

I'm in Melbourne right now (how stupid am I), drive home tomorrow.

Let me come back to you on Friday but in short, while your seeking power and efficency mast bend to leeward is not a good thing.  The almost perfect boat/rig is the Tasar mast, when you over rotate it, the mast come out to windard, a near perfcet elipse, my father was not dumb, infact most "over" rotating masts do this, to some extent.

Once you get to the point where your over powered, in a skiff, then it's all about de-powering in the first instance, and minimising drag in the second instance.

With a FX, with it's longish head length, then the sum "or drags" falls heavily on allowing the tip to move to leeward to spill excess pressure.

With the 49er with it's smaller head board lenght, then it still pays to use a lot of downhaul, keep the mast head up (to windward) and feather it off.

Talk Friday,   jB

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15 hours ago, JulianB said:

Hi Mate, so how many pages do you want??????

I'm in Melbourne right now (how stupid am I), drive home tomorrow.

Let me come back to you on Friday but in short, while your seeking power and efficency mast bend to leeward is not a good thing. 

Bring on Friday

No page limit :-)

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Sorry guys, just came back from Melbourne, avoided Covid-19, and walked into a huge caldron of oppotunity.

Need another few hours, and it will come in 2-3 x 3 page instalments over a few days.

Got a bit carried away!

         jB

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Friday, 3 July 2020

Sydney Australia

Theory of skiff rigs.

Hi Rambler, you asked for it!

Sailing is all about drag minimisation,

You have a fixed amount of RM (Righting Moment) and you are exploiting that RM to generate lift to leeward (and sightly forward) in the sails, and lift to windward (and slightly forward) via yawl on the foils and the resulting combination of the 2 fwd. vectors minus drag = boatspeed.

My father used to say, a foil in the air, a foil in the water and a bit of low drag floatation!

Foil in the air/water, interestingly you can do the maths, it’s a x² law stuff, water is 812 times as dense as air, but your rig is operating in AWS where as your foil is operating at BS, so a 49er “say” has 22m² in the air, at 18 knts it has an AWS 29.5 knts and a BS of 14 knts. (see attachment #1, I’m re-cycling dwg’s)

So 29.5(knts)² x 22(m²) = 19,145 air widgets.

19,145/812 = 23.6 water widgets

14(knts)² x X (m²) = 23.6   And that = 23.6/14² = X

So X = 23.6/14²= 0.12m²  & at 14knts a 49er has lifted it centerboard 200mm but regardless it’s probably only operating on the 300-400mm from the keel-line downwards, boat has a cord of 325mm, so the .12/.325 = 360mm of the top of the board is actually doing any work.

(the board is 1.2m LOA, 350mm is in the case, 200 is lifted so there is only 1200-(350+200) = 650mm in the water and ½ of that doing anything is probably about right.  The reality is you could probably pull the centreboard up another 300mm and still maintain a yawl of sat 1.5° with a reasonable CoD.)

Every Naval Architect/Engineer is going to say CoL, AoA and CoD considerations and yes yes yes, but as a rule of thumb, it works and it’s fascinating!

So, get back on track, you want to do everything you can to maximise RM and minimise Drag.

Your question re tip flick is all to do with RM & Drag.

Re RM and the corresponding SCP (see attachment #2 from the 9eronline.com blog)

The important thing to remember about RM is once you leave the beach, the max RM you can generate is given, you simply can’t generate more, especially these days with people dress in rubber and not greasy wool jumper, (when you went under a wave, with a greasy wool jumper, you put on a “stone” (14lbs about 6 kgs)).

So to increase (or not decrease) BS you need to reduce drag or increase SCP.

SCP = Sail Carry Power, and it’s simply the ARM between the CLR [Centre of Lateral Resistance or the CoE [Centre of Effort]] of the centreboard and the CoE of the sails.

If you go back to 9eronlince.com and click on Library and then go to 49er sail working dynamics you will find a diagram spells that out, in the case of a 49er, at the design wind, the ARM is 4380mm.

Go one step further the RM of a 49er is crew weight = 165kgs (approx.) x distance of CoG [Centre of Gravity] of the crew from CoB [Centre of Buoyancy] of the hull.   

2.9m/2 (width of the boat) + approx. 1m (distance from your toes, to the CoG of your body) so it then =

165 x (2.9/2 +1) = 404 kgs/m if you now divide that by the arm which is 4.380m you get

404/4.380 = 92.3kgs/m² SCP

Interestingly SCP also =’s the sideload on the Centreboard and the sideload in the Rig (every reaction has an equal and opposite reaction)

You can increase SCP by lifting the Centreboard, or flattening out the tip of the main, easing the sheet, sheeting along the foot of the jib, easing the jib sheet, and feathering the rig (luffing briefly) etc etc etc.

You can also do it by allowing the tip of the mast to flick to leeward and re-distribute the pressure differential across the mainsail.

I will do the easy one first, lift the centreboard.

Pull the centreboard up 200mm and what happens, well if all other things are equal, (which they rarely are) then say ½ of that 200mm will decrease the ARM by 100mm so SCP is now 404/4.28 = 94.4kgs/m² so a 2.5% increase in effective power.     One of the big things about lifting the Centreboard is that not only do you increase SCP but you more than likely will reduce CoD of the Centerbaord (and wetted area) and if you have enough speed you won’t increase yawl, in-fact the increased speed, you may reduce it with the corresponding reductions in hull drag.

Far harder concept to get your head around is allowing the tip/mast head to flick to leeward.

First thing is a FX or 49er (hopefully a 29er) are being sailed up right, and if you now look at that boat from 22° to windward, if the boat is flat, then the rig is in fact canted about 5° to windward.

(there is a diagram of this somewhere in SA, I will go find it, or maybe someone else can)

Plus if the sailmaker has done a good job, and the crew has the right sort of controls set and right rig tensions, then the square head will be bladed-out nicely and making almost a 0° AoA to the AWA (at approx. 22°) so there will be very very little SWD [Span Wise Drift] so movement of the air upwards and over the mast head (which generates a tip vortex), (just have to include the photo out of Cape Town of the V60’s and their mast heads generating these vortexes) and that is pure drag, the tones and tones of air being spun into that vortex comes from your RM and SCP and that’s slowing you down.

Now with a FX, with it’s really long head length, yes it’s prone to generating a vortex, but empirically it would appear that in-terms of a bucket of drags, it’s less of a problem to allow the mast head to move to leeward, and by doing so, allowing the air pressure on the windward side of the main, from ½ way down the sail (that’s a guess) to move upwards getting greater and greater as you move towards the tip, and that in turn, sure it will generate a vortex, how big and how long living I don’t know, but given that they do it, it would suggest not for long, but the reduction is presure high in the rig, that in turn drops the CoE and that reduces the ARM and that then increases the SCP.  

 And that’s why they probably do it.    And very possibly without knowing why!

With a pin head rig, you never do it, the drag consequence is too great and the benefit to small.

Best pin-head rig is a over-rotating mast, (like a Tasar) and again a Tasar is sailed flat, so you more than likely have air moving down the rig in a breeze so allowing the upper leach to hang right off is low drag, increases SCP so it’s a bit like lifting a centreboard, as in everything is working for you, for your advantage.

With the 49er rig, with its far shorter mast head length, they tend not to do it, (let the head flick to leeward) they ease sheet tension just a little and again allow the upper leach to feather.   (need to stress lots of downhaul (approx. ½ tonne at the head board) and plenty of rig tension.

As you get longer and longer with the mast head length (look at some of the windsurfers) the top of the sail inverts.     (A windsurfer is a little different, in that it has a big head so if has lots of grunt downwind, where as a 49er/FX sets a spinnaker)

Let me get into that in a few days, probably enough to absorb right now.

What is the ideal mast head length is a really interesting debate.

The sailors tend to say a 49er has far more range than a FX and that may be the case now, but where will it be in 10 years’ time?   The FX coaches may have pulled another rabbit out of the hat by then, it’s simply too early to say.    And is more range a good thing or not.   On the 18teens where you have a selection of rigs, probably not, but then again, David MacDiarmid (NZL) has just won his 3rd JJ Giltinan with far shorter mast head lengths than his Australian counterparts.     No doubt there are other factors at play!

Also remember that it’s only 12 years since I watched my father light up (2008) watching Simon (Watin) and Harry (my son) sail the first 49er/skiff square-head and to his credit completely flick his 50 years of perfecting pin-heads and go hard on a new direction - squareheads.

image.png.fd5bb2add0f09bf93faa347d8494446c.png

image.png.37791ff37b2871a6ebf9950bc35320f8.png

image.png.c663e169cf4d8a9711a866f7e3c2e13b.png

 

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Awesome Julian!

 

Would love to hear some of the theory behind the Tasar rig as well at some point! 

We are having great growth in the class here in Seattle. Nearly 15 boats out this week with 3 world champions + many top 5 finishers among them. 

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On 7/4/2020 at 1:19 PM, JulianB said:

Friday, 3 July 2020

Sydney Australia

Foil in the air/water, interestingly you can do the maths, it’s a x² law stuff, water is 812 times as dense as air, but your rig is operating in AWS where as your foil is operating at BS, so a 49er “say” has 22m² in the air, at 18 knts it has an AWS 29.5 knts and a BS of 14 knts. (see attachment #1, I’m re-cycling dwg’s)

................................................

So X = 23.6/14²= 0.12m²  & at 14knts a 49er has lifted it centerboard 200mm but regardless it’s probably only operating on the 300-400mm from the keel-line downwards, boat has a cord of 325mm, so the .12/.325 = 360mm of the top of the board is actually doing any work.

(the board is 1.2m LOA, 350mm is in the case, 200 is lifted so there is only 1200-(350+200) = 650mm in the water and ½ of that doing anything is probably about right.  The reality is you could probably pull the centreboard up another 300mm and still maintain a yawl of sat 1.5° with a reasonable CoD.)

Every Naval Architect/Engineer is going to say CoL, AoA and CoD considerations and yes yes yes, but as a rule of thumb, it works and it’s fascinating!

So, get back on track, you want to do everything you can to maximise RM and minimise Drag.

Your question re tip flick is all to do with RM & Drag.

Re RM and the corresponding SCP (see attachment #2 from the 9eronline.com blog)

The important thing to remember about RM is once you leave the beach, the max RM you can generate is given, you simply can’t generate more, especially these days with people dress in rubber and not greasy wool jumper, (when you went under a wave, with a greasy wool jumper, you put on a “stone” (14lbs about 6 kgs)).

So to increase (or not decrease) BS you need to reduce drag or increase SCP.

SCP = Sail Carry Power, and it’s simply the ARM between the CLR [Centre of Lateral Resistance or the CoE [Centre of Effort]] of the centreboard and the CoE of the sails.

If you go back to 9eronlince.com and click on Library and then go to 49er sail working dynamics you will find a diagram spells that out, in the case of a 49er, at the design wind, the ARM is 4380mm.

Go one step further the RM of a 49er is crew weight = 165kgs (approx.) x distance of CoG [Centre of Gravity] of the crew from CoB [Centre of Buoyancy] of the hull.   

2.9m/2 (width of the boat) + approx. 1m (distance from your toes, to the CoG of your body) so it then =

165 x (2.9/2 +1) = 404 kgs/m if you now divide that by the arm which is 4.380m you get

404/4.380 = 92.3kgs/m² SCP

Interestingly SCP also =’s the sideload on the Centreboard and the sideload in the Rig (every reaction has an equal and opposite reaction)

You can increase SCP by lifting the Centreboard, or flattening out the tip of the main, easing the sheet, sheeting along the foot of the jib, easing the jib sheet, and feathering the rig (luffing briefly) etc etc etc.

You can also do it by allowing the tip of the mast to flick to leeward and re-distribute the pressure differential across the mainsail.

I will do the easy one first, lift the centreboard.

Pull the centreboard up 200mm and what happens, well if all other things are equal, (which they rarely are) then say ½ of that 200mm will decrease the ARM by 100mm so SCP is now 404/4.28 = 94.4kgs/m² so a 2.5% increase in effective power.     One of the big things about lifting the Centreboard is that not only do you increase SCP but you more than likely will reduce CoD of the Centerbaord (and wetted area) and if you have enough speed you won’t increase yawl, in-fact the increased speed, you may reduce it with the corresponding reductions in hull drag.

Far harder concept to get your head around is allowing the tip/mast head to flick to leeward.

First thing is a FX or 49er (hopefully a 29er) are being sailed up right, and if you now look at that boat from 22° to windward, if the boat is flat, then the rig is in fact canted about 5° to windward.

(there is a diagram of this somewhere in SA, I will go find it, or maybe someone else can)

Plus if the sailmaker has done a good job, and the crew has the right sort of controls set and right rig tensions, then the square head will be bladed-out nicely and making almost a 0° AoA to the AWA (at approx. 22°) so there will be very very little SWD [Span Wise Drift] so movement of the air upwards and over the mast head (which generates a tip vortex), (just have to include the photo out of Cape Town of the V60’s and their mast heads generating these vortexes) and that is pure drag, the tones and tones of air being spun into that vortex comes from your RM and SCP and that’s slowing you down.

Now with a FX, with it’s really long head length, yes it’s prone to generating a vortex, but empirically it would appear that in-terms of a bucket of drags, it’s less of a problem to allow the mast head to move to leeward, and by doing so, allowing the air pressure on the windward side of the main, from ½ way down the sail (that’s a guess) to move upwards getting greater and greater as you move towards the tip, and that in turn, sure it will generate a vortex, how big and how long living I don’t know, but given that they do it, it would suggest not for long, but the reduction is presure high in the rig, that in turn drops the CoE and that reduces the ARM and that then increases the SCP.  

 And that’s why they probably do it.    And very possibly without knowing why!

With a pin head rig, you never do it, the drag consequence is too great and the benefit to small.

Best pin-head rig is a over-rotating mast, (like a Tasar) and again a Tasar is sailed flat, so you more than likely have air moving down the rig in a breeze so allowing the upper leach to hang right off is low drag, increases SCP so it’s a bit like lifting a centreboard, as in everything is working for you, for your advantage.

With the 49er rig, with its far shorter mast head length, they tend not to do it, (let the head flick to leeward) they ease sheet tension just a little and again allow the upper leach to feather.   (need to stress lots of downhaul (approx. ½ tonne at the head board) and plenty of rig tension.

As you get longer and longer with the mast head length (look at some of the windsurfers) the top of the sail inverts.     (A windsurfer is a little different, in that it has a big head so if has lots of grunt downwind, where as a 49er/FX sets a spinnaker)

Let me get into that in a few days, probably enough to absorb right now.

What is the ideal mast head length is a really interesting debate.

The sailors tend to say a 49er has far more range than a FX and that may be the case now, but where will it be in 10 years’ time?   The FX coaches may have pulled another rabbit out of the hat by then, it’s simply too early to say.    And is more range a good thing or not.   On the 18teens where you have a selection of rigs, probably not, but then again, David MacDiarmid (NZL) has just won his 3rd JJ Giltinan with far shorter mast head lengths than his Australian counterparts.     No doubt there are other factors at play!

Also remember that it’s only 12 years since I watched my father light up (2008) watching Simon (Watin) and Harry (my son) sail the first 49er/skiff square-head and to his credit completely flick his 50 years of perfecting pin-heads and go hard on a new direction - squareheads.

 

 

 

 

Thanks for this first installment Julian.

I recognize some of it as being an elaboration of what was in one of your father's/ your books (they are lent out at the moment so I can't check) and answers some of the questions I had after reading that; especially the calculation of (I think it was) Sail Carrying Power (SCP) the formula of which wasn't entirely clear from the book - although the factors that went into it could be inferred.

Just to confirm my interpretations (and maybe help others wrestling with the formulas and concepts), my understanding is

BS is Boat speed

AWS is Apparent wind speed

While I can now see how ARM is measured, do the initials stand for anything or is the word 'arm' itself the concept (a bit like 'righting arm')

"Yawl" is what I might have thought of as side slip or leeway (expressed as a degree off course)?

I'm not quite understanding the "half of that doing anything" concept in relation to the centerboard, combined with the suggestion that only the 300 to 400 mm under the keel is the bit doing anything. This is a new concept to me; the suggestion that the bottom section of the board is ineffective?

I presume the 5 degree canter to windward at 22 degree apparent wind is the rake of the mast?

COD on the centerboard is Center of Drag? [This is definitely a question; not really a concept I've struggled with before - if that's what it is]

But there's some really interesting stuff in what you've written that goes well beyond what I've managed to absorb from previous writings (mainly your family's)

I'm really looking forward to the next installment.

Much as I asked your father to do all those years ago, If I was to take the sum of your writings and try and break it down and express it in a way that could be presented as a lecture to reasonably intelligent people, might you be willing to review it?

 

 

 

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2 hours ago, Rambler said:

Thanks for this first installment Julian.

I recognize some of it as being an elaboration of what was in one of your father's/ your books (they are lent out at the moment so I can't check) and answers some of the questions I had after reading that; especially the calculation of (I think it was) Sail Carrying Power (SCP) the formula of which wasn't entirely clear from the book - although the factors that went into it could be inferred.

Just to confirm my interpretations (and maybe help others wrestling with the formulas and concepts), my understanding is

BS is Boat speed

AWS is Apparent wind speed

While I can now see how ARM is measured, do the initials stand for anything or is the word 'arm' itself the concept (a bit like 'righting arm')

"Yawl" is what I might have thought of as side slip or leeway (expressed as a degree off course)?

I'm not quite understanding the "half of that doing anything" concept in relation to the centerboard, combined with the suggestion that only the 300 to 400 mm under the keel is the bit doing anything. This is a new concept to me; the suggestion that the bottom section of the board is ineffective?

I presume the 5 degree canter to windward at 22 degree apparent wind is the rake of the mast?

COD on the centerboard is Center of Drag? [This is definitely a question; not really a concept I've struggled with before - if that's what it is]

But there's some really interesting stuff in what you've written that goes well beyond what I've managed to absorb from previous writings (mainly your family's)

I'm really looking forward to the next installment.

Much as I asked your father to do all those years ago, If I was to take the sum of your writings and try and break it down and express it in a way that could be presented as a lecture to reasonably intelligent people, might you be willing to review it?

 

 

 

Thanks for this first instalment Julian.

My pleasure,

I recognize some of it as being an elaboration of what was in one of your father's/ your books (they are lent out at the moment so I can't check) and answers some of the questions I had after reading that; especially the calculation of (I think it was) Sail Carrying Power (SCP) the formula of which wasn't entirely clear from the book - although the factors that went into it could be inferred.

Just to confirm my interpretations (and maybe help others wrestling with the formulas and concepts), my understanding is

BS is Boat speed  YES

AWS is Apparent wind speed YES

While I can now see how ARM is measured, do the initials stand for anything or is the word 'arm' itself the concept (a bit like 'righting arm') Not that I am aware of, ARM = distance between CLR and CoE

"Yawl" is what I might have thought of as side slip or leeway (expressed as a degree off course)? Correct, it could be expressed as simply as HDG [Heading] vs CoG [Course over Ground] which these days seems to be set by GPS. It’s not a lot, if your Centreboard is doing a good job, most skiffs it will be 1.5-1.8° and WRT a skiff which is on-top of the water, as compared to a displacement boat which is in the water then Yawl drag is smallish, hang-on.

image.png.64eac620582a2ec87b697ff5e9d1a371.png

So we generated this graph, which is a 49er, sailing 14kgs light, so around 265kgs all-up weigh in 4th mode, so nose down 50 - 100mm.   The green line is generated by pulling it straight, the magenta line is at 2° off axis.    This was done in 2008, with Simon Watin  (nb1)

So Yawl drag of a 49er at hull-speed (5.6knts) will be the difference between 7.26kgs and 8.6kgs (I went back into the data to dig that out.)    That is a 18% drag increase to put it in perspective.

 Couple of points, skiffs, even Tasars the yawl drag is pretty low because they sit on top of the water, not in it.   The 2 bell-weather classes are the I14 and the 5o5 who spend a lot of resources getting gybing boards to work and they do it because it is important, and it works.

So they can opt for “in the water” with board gybed and minimising Yawl drag or they can jump up ontop of the water (planning to windward) at which point they rake their board aft a tad and the locks off the gybing function.

Pretty obviously a boat “in the water” will have a dramatically higher Yawl drag signature than a boat that is ontop of the water.   I have never measured the drag of a “in the water boat” or attempted to verify what the Yawl component is, so read into that what ever you wish!   (nb2)

Very few classes can Plane Up-wind (on top of the water) and even fewer body swung classes can, the Tasar being one that can.    And by plane up-wind, sure you can get your Laser and sail at a few degrees above abeam and plane, but in a meaningful manner, the word is up-wind, so to be able to Plane Up-wind you need to be able to generate a better VMG to the windward mark, by opting to allow the boat to crack off a few degrees and plane.   Yes a moth can (before they foiled), but it’s using wings, as dose a Contender  and Musto skiff (using trapez) etc.

And a lot of boats with trapeze can only effectively Plane to windward (and achieve increased (faster) VMG’s) when conditions are just so.   Just like a Tasar, plenty of wind is the key factor.

ISAF, now WS used to coin a term, they can plane to windward [with increased VMG] most of the time. So that would assume 50% or more and the 49er/FX are the only Olympic classes that can do that, 29er is the only Youth Class that can do that.    This was then the definition of High Performance!    That went out of favour pretty fast, so that has disappear from the WS tecahing, and possibly that is a good thing! 

 Tasar probably dose not meet that criteria as it needs conditions just so, lots of wind, to make it work, so it’s probably 15% of the time at best.   But it's probably is the only body swung class that can lay claim to being able to do it at all!

So ASP, I will come back to Tasar’s and it’s rig in a day or 2, and it’s the rig, it’s lightness and it shape (of the hull) that allows it to do this, but let me come back on track to Rambler.

I'm not quite understanding the "half of that doing anything" concept in relation to the centreboard, combined with the suggestion that only the 300 to 400 mm under the keel is the bit doing anything. This is a new concept to me; the suggestion that the bottom section of the board is ineffective?

OK, 49er Centreboard is 1.2m LOA, 350mm is in the case, so it’s 850mm into the water, CLR is say 45% of the way down it, 850 x 0.45 = 382mm.    Now pull that centreboard 200mm up, its now 650 into the water, 45% of 650 = 292mm.    I rounded it out to 100 for simplicity.   And the reality is there is less area low down, and there is less camber towards the tip (as a %) so the true effect will be closer to 100 than 89 (382-292 = 89-90mm)

I presume the 5 degree canter to windward at 22 degree apparent wind is the rake of the mast?

Yep, hard concept to grasp, let me re-do that dwg.   It’s easy for me in 3d, give me a few hours.

COD on the centreboard is Centre of Drag? [This is definitely a question; not really a concept I've struggled with before - if that's what it is]

CoD = Coefficient of Drag, it is rarely linear there are buckets and assorts of other stuff but from   -2.5 -> 3° it could be assumed to be pretty flat line, the bucket starts at about +/- 4°.

Let me dig out a graph and explain that when I come back with the 5° cant!

But there's some really interesting stuff in what you've written that goes well beyond what I've managed to absorb from previous writings (mainly your family's)

I'm really looking forward to the next instalment.

Much as I asked your father to do all those years ago, If I was to take the sum of your writings and try and break it down and express it in a way that could be presented as a lecture to reasonably intelligent people, might you be willing to review it?

I will look fwd to writing it.              jB

~~~~~~~~~~~~~~~~~~~~~~~~~~

Nb1, occasionally I get a person “debentured to me”.    I think it's happened 4 times.

Simon was from Revolution Island in the middle of the Indian Ocean, French.     He was one such person, by the time I meet him he was 23-24, had a few degrees under his belt, I remember being with Dina Kowalyshyn  (really smart Naval Architect, Amercan, presently chairs Equipment Committee at WS) at Orly Airport in Paris and this long hair crazy frog descended on us and Dina being really impressed.    Cut a long story short, Simon arrived in Sydney few months later, and spend 3-4 months with us!   I was his “professor” (what a joke, this guy was so smart) but he and dad hit it off beyond belief.  It was 2008, so dad was 88.     I remember one night where dad was doing maths in radians, and long hand, realms and realms of paper, and Simon was using MatLab.   Simon when one way and dad went the other, few glasses of Red later, lots of French swear words, and they ended-up within a few fractions of a 1% of each other.  Error was so small.  That empirically proved what we were doing had an extremely high level of credibility.  

That whole report is on 9eronline.com.      Last I heard he was working for VPLP in Breast.

Nb2, just re-reading this and it struck me that we all use centreboard that are way bigger than then need to be.   Especially on slower in the water boats.   Then I had a bit of an epiphany.

If you are in a “in the water boat” then the cost consequence of allowing the Yawl angle to increase very much is so devastating that carrying 20% more Centreboard area than what is needed is a small price to pay.   The extra drag from another 20% at 5-6-7 knots is trivial compare to a) the increase in Yawl drag from say 1.8 – 2.5° and b) the increase in CoD of the foil, when from 1.8 – 2.5°.  (I will post that bucket drag curve)   Again, I have never attempted to measure the Yawl drag of a “in the water boat” and when we did the extensive tow tests of 470’s 3-4 years ago we did not think of doing it then.   Pretty interesting paper out of the Wuhan Sports University re 470 hulls and the effect rudders have on them.    I got it off Scuttlebutt, those of you far more intelligent than I should have a read.   I probably need to re-read it!

Skiff's the sum goes the other way, at 10-11-12knts, the ability for the Centreboard to resist lee-way (Yawl) is a X² law, so a Laser probably has far more surface area than a 49er yet has a RM that is less than ¼ .  

Skiffs get very judicious about how far we pull the centreboard up, and it has a major bearing on overall speed.

Off the wind, with a skiff,  it’s already up, so getting it further up, is not so important, where as a in the water boat, getting the board up is paramount!      

Interesting, need to ponder that!

          Jb

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So in answer to your cant question.

I once again went to 9eronline.com and downloaded the rough 3d model of a 49er (done by Martin Billoch in Argentina approx. 2009)

And I then did 2 things, I worked out where the 33%, so the nominal CoE line of pressure (differential) was and projected that line onto the mainsail  (yellow line)

So below you have that line projected head-on and side-on to the mainsail.

Martin did a really nice job, the mainsail is twisted (washed out) at the tip, as it should be approx. 22°, so this would be a up-range wind scenario, with minimum vortex and therefore minimum drag.

image.png.5a50d26b316bdf1cc4c2fe5aed2b2ada.png

On the next page I have rotated the whole boat, rig, sails, foils around to 22°.

We know from the vector diagram (attachment #1) that the AWA [Apparent Wind Angle] is going to be somewhere from 21-24° in the normal course (excuse the pun) of sailing.

So with any sort of windward heel that 99% of the good 49er sailors do, the cant, so the angle between the red vertical line that I am dropping from the mast head and the cyan line that I have also started at the mast head, but is running through the heel of the mast, will be about 5°.   Dead flat, as this is showing its 4°.

image.png.3e719e25c710d0e4ed2938a27a4db7ee.png

I went a bit further with the yellow line, and it’s a lot more vertical, (2.4° positive cant) but it is also has a nice concave shape, which, along with wash-out/twist, reduced cambers and reduced cords high in the rig reduce, probably eliminate most of the time any tip vortex and therefore the resulting drag.

So this is how the wind see the rig.

WRT the FX and the tip flick, just visualise where the tip would be if you have 20mm less cap shroud tension.

image.thumb.png.0eaaa2ada27be60db955a44337f8d3be.png

Angle has ½ ved, plus the sail will have flattened off substantially because sideways bend adds to fore n aft bend, so the pressure will spill off the top of the main, you will get SWD [Span Wise Drift] upwards in discernible amounts from the top spreader up and that in turn will reduce leach load, it will reduce camber and all of those things will drop the CoE of the sails which will reduce the ARM and increase SCP.

Again, you need to see this from the winds POV, the sails are an obstruction, it wants to get around them in the lowest energy scenario that it possibly can.

The yellow line the line of pressure, is angled aft, so the air will naturally want to rise, but with firm Cap Shrouds, the tip comes out to windward, it's like a albatross with dropped wing tips, (and they have been doing this stuff for millions of year before us).

Don’t know how much or what but at some point the curved and canted rig to windward will cancel out the aft racked pressure line.

Pretty obviously the loose FX cap-shrouds dose it, so we must be very close to a tipping point!~

Its actually quite clever.

Now I have done all of this on a 49er, I have not done it on a FX.    I make no assertions and I can't back any of it up.   Very happy to hear other POV!

~~~~~~~~~~~~~~~~~

I promissed you some CoD and CoL graphs, the 1st graphs are for 0012 section, very similar to a Laser foil

image.png.3c717dc6d0e7c9c35e50a86785244eee.png

The commonality between the 2 graphs is the CoL, so Section Lift Coefficient which is the vertical scale on the LH graph, and the horizontal scale on the RH graph.

image.png.d4c417832fa0a849d11846400f92f3e8.png

Same book (it was publish before I was born) 6 pages earlier, a section not to dissimilar to a 49er/29er section.  (Tasar section is thinner)

Notice that the CoD comes down to 0.004 with the 0010-34 (49er) where as with the Laser section 0012 is 50% more at 0.006.

The 0012 section is far more tolerant, virtually has no bucket, there is not much penalty (WRT foil drag) whether you Yawl at 2-3-4°, and the big reason for that is it’s a turbulent section.

The 0010-34 has a very defined bucket, and that is where it has laminar flow, bit more precious, you have to be a little more “just so”, you had better be under 2°, better if your at 1.7-1.8° Yawl, but the reduction in drag is 50% (all other things being equal which as I said before rarely are.)

I am going to leave you for 2 days.   (I need to do some real work)

                  jB

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Thanks JB, Great stuff as usually.  A couple days will help get head around some of this.  Amazing art of invaluable info. here.  Takes awhile to absorb some off it, like your dad's books.  Thanks again, and keep it coming.

 

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Well, while waiting for Julian's additional words of wisdom and continuing to contemplate how and whether I might get a 49erFX as an additional training boat, one of my group - showing the enthusiasm and resourcefulness that has typified the women coming through the training - has got herself a training session skippering on an 18ft skiff.

 

It just shows why I'm so proud of them all and wanting to help take them further in their sailing.

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All at your leisure Julian

Your thoughts are appreciated but we recognize they're offered gratuitously and business takes priority. Time is not of the essence, even if we might occasionally make sure we're not completely forgotten.:)

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image.png.fd5bb2add0f09bf93faa347d8494446c.png

I was studying this diagram and was having trouble sorting out the three colours from the two TWS's

So 18kt TWS gives 14kt BS for 29.5 AWS at 25.4 degree AWAngle. Is the red 1.6 degrees the yawl for that equation?

And then is it 23kt AWS gives 16kt BS for a 34.4kt AWS at an unspecified AWA. But the higher 2.8 degree yawl (if that's what it is) doesn't seem right intuitively (for what my intuition is worth). And the red 31.4 AWS I can't place. It might be a post yawl AWS but I can't put it together.

I'm keen to work it out because it goes to the nub of a discussion I was having in an on line lecture last night; especially in light of Clare's experience in skippering an 18ft skiff (see above) where she was being instructed to feather the jib more than she was used to doing with the 15.

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Hi guys, sorry, it's likely to be another 24 hrs, it's got a bit more complicated.

Re the verctor diagram above, I mentioned I had re-cycled it!     I was using it to explain the effect of a gust/lift or a lull/header.

It's based on emperical numbers so these are real 49er speeds in real wind speeds in peak VMG [velocity Made Good] mode.

Black, is a 49er, 45° to the true wind doing 14knts of BS [Boat Speed] in 18knts of TWS[True wind Speed] and doing that it will have 29.5knts AWS[Apparent Wind Speed] with a AWA [Apparent Wing Angle] of 25.4°.

If the wind then increases by 5 knts, the boat WILL NOT imediatly reach it's new speed, it will take a few second to do that, and during those few seconds you will have

Blue, so the AWS goes from 29.5 - 34.4, remember this is a X² law so the potential aero widgets go from 29.5² to 34.4² = 870 -> 1183 which is a 36% increase in "force".    Obviously you have to do something or you capsize, one of the things you do is feather, or you ease the sheet.    Regardless of that, you will get a 2.8° swing via the vector, so your AWA will go from 25.4° -> 28.2° which will again increase the drive generated from the sails, which requires you to feather even more or ease sheets and the bottom line is you feel a 5-6-7° lift.

So the gust hangs around for 4-5 -6 secs and the 49er accelerates to it's new BS of approx 16knts and the gust fades, again the boat dose not imediatley drop back to a slower speed, it will take 2-3-4 secs to do that but what happens.

AWS drops from 34.4 -> 31.4 and that = 34.4² - 31.4² = 1183 -> 985 = 83% so you have just experienced a 17% reduction in force, and you have also got a vector swing of 1.6° to 23.8° AWA to add to your wow's.    Bottom line you feel a 4-5-6° knock (header)

So the queastion is what to do, and often it's squeeze on the sheets and "bend the knees" for 2-3-4 seconds until the 49er slows back down to 14knts and both AWS and AWA re-stabalise.

Sorry, GTG, see ya's all in 24!    jB

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1 hour ago, JulianB said:

Hi guys, sorry, it's likely to be another 24 hrs, it's got a bit more complicated.

Re the verctor diagram above, I mentioned I had re-cycled it!     I was using it to explain the effect of a gust/lift or a lull/header.

It's based on emperical numbers so these are real 49er speeds in real wind speeds in peak VMG [velocity Made Good] mode.

Black, is a 49er, 45° to the true wind doing 14knts of BS [Boat Speed] in 18knts of TWS[True wind Speed] and doing that it will have 29.5knts AWS[Apparent Wind Speed] with a AWA [Apparent Wing Angle] of 25.4°.

If the wind then increases by 5 knts, the boat WILL NOT imediatly reach it's new speed, it will take a few second to do that, and during those few seconds you will have

Blue, so the AWS goes from 29.5 - 34.4, remember this is a X² law so the potential aero widgets go from 29.5² to 34.4² = 870 -> 1183 which is a 36% increase in "force".    Obviously you have to do something or you capsize, one of the things you do is feather, or you ease the sheet.    Regardless of that, you will get a 2.8° swing via the vector, so your AWA will go from 25.4° -> 28.2° which will again increase the drive generated from the sails, which requires you to feather even more or ease sheets and the bottom line is you feel a 5-6-7° lift.

So the gust hangs around for 4-5 -6 secs and the 49er accelerates to it's new BS of approx 16knts and the gust fades, again the boat dose not imediatley drop back to a slower speed, it will take 2-3-4 secs to do that but what happens.

AWS drops from 34.4 -> 31.4 and that = 34.4² - 31.4² = 1183 -> 985 = 83% so you have just experienced a 17% reduction in force, and you have also got a vector swing of 1.6° to 23.8° AWA to add to your wow's.    Bottom line you feel a 4-5-6° knock (header)

So the queastion is what to do, and often it's squeeze on the sheets and "bend the knees" for 2-3-4 seconds until the 49er slows back down to 14knts and both AWS and AWA re-stabalise.

Sorry, GTG, see ya's all in 24!    jB

Great answer Julian

I deal with the apparent wind aspects of gusts and lulls in my talk, but this extra detail will blow their minds.

I think I understand it all, but I'll need to go back to the diagram and work it all out to be sure

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On 7/15/2020 at 6:02 PM, JulianB said:

 

Regardless of that, you will get a 2.8° swing via the vector, so your AWA will go from 25.4° -> 28.2° which will again increase the drive generated from the sails, which requires you to feather even more or ease sheets and the bottom line is you feel a 5-6-7° lift.

 

AWS drops from 34.4 -> 31.4 and that = 34.4² - 31.4² = 1183 -> 985 = 83% so you have just experienced a 17% reduction in force, and you have also got a vector swing of 1.6° to 23.8° AWA to add to your wow's.    Bottom line you feel a 4-5-6° knock (header)

 

Julian, I hope you don't mind me exploring your answers further. I suspect there are a few people reading this and quite interested in your explanations. I figure if I can't work it out well enough to explain to my trainees, then many of the readers will also be having problems.

I'm not sure I fully understand how a 2.8 degree vector swing translates to a 6 to 7 degree lift. Same on the other end of the gust.

Your father of course went to some length to get people out of the 'feather in a gust" to an "ease the sheet" approach. But I think it was either in your or your father's writings that it was also pointed out that a very large component of the gust force was delivered in the initial onslaught {all my books are lent out, so I can't go back to be more specific).

When training my students I teach them to luff into the lift provided by the gust (assuming of course it is coming from the base wind direction - not always the case on our river courses) and try and ease the main rather than lift and feather to reduce power; BUT, in light of the force of the initial impact on a large skiff rig, its better to lift and feather than to capsize if the main can't be eased fast or far enough.

Am I teaching the wrong gust technique?

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Hi mate, all depends on how far in depth you want me to go.

Absolutely 1000% correct, 80% of the guts of the gust is in the first 20%.   This all came from the Kingston (Canada) tower prior to the 1972 (???) Olympics.   Basically the Canadians put up this tower (its still there) and allowed free access to the data.   Where as most towers measured maybe at 1/2 hertz or 1/4 of a hertz, this tower measured at 4 hertz or some multiple of that and it clearly showed the inner working of a gust.

KISS

When a gust onslaught rolls across a boat sailing to windward well, then 2 things happen.

#1 the increase in the windspeed vector means that the AWA will err towards the TWA to a greater extent, and as you commented 2.8° (and that about right)

#2, the second thing that happens is that there is a increase in AWS, given that AWS is a multiple of BS and TWS, (if the BS stays the same and you increase the TWS, then you get a increase in the AWS.    As a very ball park rule of thumb, it you get a increase of 5knts (of TWS) then you will also get a increase of just a bit less than 5 knts in AWS)  in the very short term (2-3-4 secs).  And remember this is a X² law.      After that, you will get a increase in BS and that again will increase AWS, but reduce AWA.

So with the onslaught of the gust, you get a 2.8° lift (because TWS increase and AWA swings towards TWA).

But you also get a increase in AWS and that means you have to feather or spring sheets because you have increase force being generated by the sails ; because of greater windspeed!

Springing sheets is pretty slow. As you spring sheets, you increase twist, mast bends less so the mainsail fattens up, you reduce forestay tension, so you get more jib luff sag, the jib fattens, etc etc etc.     Its SLOW!!!!

Classic text book response happened with Mac (Charlie (Miesha) Diekman) and Mire, (Cameron (chemical) McDonald) but more so with Andrew (god) Hay and the irrepressible David (TF) Witt sailing the AAMI's.   We had those Pin-Head rigs so dialled in and we sailed 4 days a week with each other (and they (the crew) where paid to win, SO IT WAS IN THEIR INTEREST) that

~~~~~~~~~~~

When we saw a gust coming, and we had worked out which direction it was going to hit us from that gust at say -5 seconds, I would luff the boat 2-3°,

Gust - 3 seconds, we would all bend our legs a little (reduce RM) and the mainsheet tension would increase only 100-150mm,  

Gust -1 sec, by now we completely knew where it was coming from so we would adjust course to optimise AoA (Angle of Attack).

Gust onslaught, mainsheet would be tightened even further, boat would still be rolling to windward, maybe 5°, but most importantly it was rolling to windward so it had inertia.

Gust +2secconds we were 2-3° even higher again with very tight sheets so the Jib luff was even tighter than normal, so the entry was flat and the boat accelerated as the roll to windward was checked and starts to roll to leeward.

Gust + 4 secs, peak of the gust was past, bend the knees, still high at probably 2 knts above optimal "VMG".

Gust +6 secs, boat is slowing down and the roll that was to leeward  has stopped and just starting to roll back to windward.

Gust +8 Secs come back down to proper course (whatever that is) and back to full stretch, sailing nominal slight windward heel.

~~~~~~~~~~~~~

So you have just spent the last 8-12 seconds (and at say 12knts BS that’s approx a BL [Boat length] per second pointing an average of 4º higher (so 18ft x 10sec = 180ft x sin4º = 12ft) so ¾ of a BL to windward, and your doing approx. 2knts faster so that’s approx. 20ft further ahead.

So instead of suffering the gust, because you are already at 100% RM, and any increase in AWA or AWS, means you have to dump power, you set the boat up, so your at say 90-95% of max RM, with the rig moving the right way, so you had inertia also helping, as the gust hits, you go to max RM, your at the correct AoA,  with the sheet firm, so the boat is perfectly set up to handle the increase in wind = force, and you can even use inertia to maximise that benefit.

It’s an amazing feeling when you get it right.

Which anecdotal story do you want me to tell you to emphasise that???

                        jB

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24 minutes ago, JulianB said:

 

~~~~~~~~~~~

When we saw a gust coming, and we had worked out which direction it was going to hit us from that gust at say -5 seconds, I would luff the boat 2-3°,

Gust - 3 seconds, we would all bend our legs a little (reduce RM) and the mainsheet tension would increase only 100-150mm,  

Gust -1 sec, by now we completely knew where it was coming from so we would adjust course to optimise AoA (Angle of Attack).

Gust onslaught, mainsheet would be tightened even further, boat would still be rolling to windward, maybe 5°, but most importantly it was rolling to windward so it had inertia.

Gust +2secconds we were 2-3° even higher again with very tight sheets so the Jib luff was even tighter than normal, so the entry was flat and the boat accelerated as the roll to windward was checked and starts to roll to leeward.

Gust + 4 secs, peak of the gust was past, bend the knees, still high at probably 2 knts above optimal "VMG".

Gust +6 secs, boat is slowing down and the roll that was to leeward  has stopped and just starting to roll back to windward.

Gust +8 Secs come back down to proper course (whatever that is) and back to full stretch, sailing nominal slight windward heel.

 

                        jB

Oh dear

It sounds like I'm going to have to relearn everything! Much harder at my age. Just when I'd trained them all to keep the boat flat with the main too.:huh:

More so when I'm not doing 4 days a week sailing with my regular crew.

So do you think this translates more or less to a carbon mast/ square head set up boat such as, say a 49erFX or Javelin (to bracket the 15's with classes you know better)? Do you think the multi rig set up og an 18 (so that you're always carrying a sail area closer to optimum for the day) changes anything.

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No your not.

I just wrote 4 pages to answer you and all that you have to remember is KISS.

Easing sheet as a responce to a gust is a good thing.

Feathering is also a good thing.

A bit of both has a greater benifit than all of one or all of the other!

~~~~~~~~~~~~~~~~~~~~~~~~~

So the experience that I describe on the previous post, in both (nb1) cases was done with pin-head rigs on GRP hulls with alloy mast and FRP tips.

What square heads (nb2) do is make that a simple reality across the entire fleet because of the geometry of the rig is designed so that the rig wants to do it.

If you go look at a 49er or FX fleet, they are doing it without even really knowing it, and they are doing it all the way down into Bronze fleet, there is great depth, it's "natural" and it just feels great.    It just happens.

And it is true, the very good sailors in the 29er fleet, most are are doing it, but there is no depth, because with a pin-head rig, you have to make it happen!

What people fail to realise is the square head rigs are far better for the last ¾ ‘s (the WW) of the fleet than for the top ¼ (the RS) because everyone can do it, everyone has more fun and the RS don’t have it all their way, a guy down the back, can get up and mix it with the best!

Nb1

image.png.7c4dad553e0bfb5724c779479ebdc3ab.png

The importance of this photo is it was taken during exactly one of these processes, just out of frame is a much bigger 18teen, as it turned out, we sailed straight through his lee, then employed the strategy and simply out pointed and out footed him to the point where we made the mark which was only 300m in front and he did not.   It was the end of the big boat era (yet again) 1991 from memory.   It happened many times across 3 years.

Nb2, I get a bit thingy about square heads.     It’s not the actual shape of the square head, it how it works.   

1)      The head is actually over-square! Approx. 100º

2)      The mast bend drops from about 5.5% to 2ish% it’s that dramatic, and that in turn so dramatically simplifies things like rig adjustments, it just goes on and on!

3)      The top 2 battens become the control battens and they each do very different jobs, the Eulier crippling load of those 2 battens and their shape are very different!

4)      And unless you have 25+% headboard length (of the foot length) then you can’t make it happen.    There are no ½ square heads, you are or you are not.     As your headboard length gets longer and longer it become harder and harder to control and the mast has to get stiffer and stiffer (and heavier) and you just “loose the plot!

It's like driving a well designed car, it become so effortless, so much more and so many more opportunities plus the Biggy is the mast will most likely out live the boat. 6-year-old mast winning Olympics after being used daily for most of the previous 6 years is not unheard of!

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1 hour ago, JulianB said:

   The top 2 battens become the control battens and they each do very different jobs, the Eulier crippling load of those 2 battens and their shape are very different!

Hi, can you expand on that please? The Euler crippling load is the max compression the batten can take whilst staying straight, and is therefore a measure of batten stiffness - but how do you know what stiffness is needed?  I assume that the bigger the roach (or squarer the head) the stiffer the battens need to be but how do you quantify that at the design stage rather than just test them through trial and error?

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10 hours ago, JulianB said:

No your not.

I just wrote 4 pages to answer you and all that you have to remember is KISS.

Easing sheet as a responce to a gust is a good thing.

Feathering is also a good thing.

A bit of both has a greater benifit than all of one or all of the other!

Where's the "that a relief" emoji when you need oneB)

More seriously Julian, what I'm trying to pull out of this are training notes for twin wire skiff sailors (although maybe for any skiff sailors) that go into the science in an understandable way (I love your family's science) but in the end come down to practical, understandable instructions that WW's have a fair chance of implementing on the water.

I don't think anyone in my present group has the financial resources or time to go beyond WW level, but some (probably the majority) of them are ferociously competitive and ambitious. It is why I was contemplating getting a 49erFX training boat and started this discussion. Now Clare has set a new benchmark in being asked to try out on an 18ft skiff, there'll be others angling for the same opportunity.

 What I'm always concerned with is that, in teaching them enough to get by - and even do well - in a WW context, I don't want to teach them bad habits; merely things that need to be refined to take it to the next level. Clare's experience in the 18 certainly made me question whether I was doing well enough, but from what you say I don't think I was too far off the mark. What I've found in teaching adults who have no skippering history to steer a twin wire skiff is that they are quite surprised by the intensity of the concentration involved. "Watch the telltales" is a good way of getting them to focus, but given the viciousness of many of the gust onslaughts we get on the river, luffing has had to be part of the response repertoire just to survive. I just need to add some subtlety to the approach.  

Steering to windward has never been my strongest point (I make many places downwind - Cherubs and NS's were great teachers for getting the 'feel' of the best VMG downwind - but are more likely to lose them upwind), so are very willing to absorb superior knowledge.

Even as I type this, I'm thinking about how to bring this chapter (on steering to windward) together in my notes in a way that incorporates the full gamete of your valuable experience, while leaving them with a practical outcome they can implement. I hope you won't mind if I eventually email you some notes for your approval.

Mind you, you're not off the hook yet:rolleyes:

This started out as a discussion on setting up rigs and I've distracted you by leaping on a side comment of yours relating to apparent wind lifts. [If you're willing of course]

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Sosoomii, the thing to remember is this is only 10 years old technology so there will be lots of people who are far better at maths than I am and good with MatLab or any one of another 20 platforms who throw numbers at it and come up with a stream.   The big issue is BS in, then BS out.   I started a rig design program in 1981 on pre-cursor to excel, and I am guessing that it took 20 rigs to get it right and this was in the heady days of 18teen in Sydney where there where changes weekly to the boats, What Ben Lexan used to call the "hot house flowers" and the biggest issue is what bit of info do you use to seed your program.    With time, I gained a lot of confidence with mine so 25 years later with literally 1000's of input and probably another 2-300 rejected inputs we could sit down at a computer and design a rig that you would get made sight un-seen and it would need only a few tweaks once you got it on the water.

So what Euler crippling load, and what batten bend profile you put in a square head today is very much suck it and see.

49er rig is completely different to a FX rig, and that due to different sailmakers and different head lengths.

C-rigs are different again, because the mast is unstayed, and we altered the rate of response from the C5 -> C6 -> C8.   C5 is far more automatic, C8 you have more overall control.

But in essence the 1st batten is the trigger batten, by altering its stiffness and it's bend profile you can get the leach to stand up, with camber, stand up with very little camber or invert and de-power.        The other big factor is the rocking of the top panels to exploit the bias and wrap & weft.        

The 2nd batten is the camber batten and it sets up the top ½ of the sail.   The other battens, their bend profile is important but otherwise come along for the ride.

In terms of stiffness, 1st is say X-kgs, 2nd is 70% and the rest are 20-30%.   

Sorry but I can't give you X because if I do the world and her father will pillory me.

Over the last few years doing this and no doubt very shortly again, we will have very good sailmakers following very good sailors, tweaking rigs and they will have a quiver of battens with them.   While sailing it will not be un-known to stop, capsize a boat on top of the rib and replace or augment a batten, then go look at it, do it again, and that could happen 10 times a day.    The next day 2 new battens will appear, replace the battens from yesterday and the wheel turns again.

What will be really fascinating will be watching the FX sail designers handle the 49er profile and the opposite because they are very different sails, needing very different approaches.

Finally, ostensibly, the bigger the headboard length the stiffer the mast and the greater X/the stiffer the 1st batten will be, so yes, your right.

One of the reasons I pursue the shortest headboard length I think is practicable which is around 28%, is it allow the greatest flexibility, so the sail has the greatest range. 

This % (28%) in aerodynamic circles is a bit like a Fibonacci number, just keeps comes back like a bad penny.

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Hi Rambler, this is “my pleasure” emoji image.png.86311759da1cf56c9f99cdd616a82b96.png

Most people think that the wind slides across the surface of the world as one big homogenous mass.   It dose not, it rolls and churns and swings and twisted even before you get to headlands and valleys like the one your sailing on.

WRT going up-wind and down-wind, the wind oscillates in a relatively rhythmic pattern brought about by Coriolis and it’s well canvased in Dad’s book along with various other esteemed authors.

So normal 10-12knts summers day on the mid coast of NSW, you are likely to have a +/- 7º oscillation with a frequency of about +/- 3 mins.      And there are lots of variables and lots of changes, so this is just typical of Grafton, in a NE seabreeze, don’t read into it anything else!

If your now in a skiff, doing 10 knts upwind, your not going to meet those oscillations every 3mins, your going to meet them in ½ the time because your BS is close to the TWS, so your speed of closing is double.

So lets say the mean wind is 045º and your presently at 040º, you had better be on Pt tack because the wind is pulling left, but you have a bit of time to enjoy the ride.   Yes and no, angle wise yes, but laid on top of that is a gust lull sequence and given that a seabreeze is quite shallow there is probably a gust every 15-20secs and your having to mange that, you’re have an entry protocol and a exit protocol, you need to know where you are entering the gust so you can position the boat, yad yad yad.   Then the wind starts to come back to the mean (045º) so now you have to think about a tack, and obstacles, and where the buoy is, do you hang on for another 10 sec so you can make it in one leg, and how quickly is the wind coming back.

And if you’re in a race, other boats on the track that you have to give way to, plus the mad fisherman that ties himself to your windward mark, or right where you want to go.  etc etc.

It’s busy.   You probably have a 5-10 sec cycle, a scan happening, fortunately it become quite automatic and you start to “feel” the boat and act in some cases without thinking.

But regardless, no one is that good and you had better continually pick up on the pointers, so you stay in “sync!”

A very quick diversion, some years back, 49er crews went out with one of the crew (in turn) being blindfolded, the idea was to increase the communication between the crew and to try and make the process more automatic. So there you are as a skipper, in a 49er, you have to feel the boat upwind, that's pretty easy, but bearing away at the top mark and then holding the boat still while the crew sets the spinnaker and you take off, and your only "visual" ques are verbal ones from the crew.    Not sure if they still do it, but I watch some of this happen and they miss the big shifts, but the actual performance of the boat was impressive!     I have never done it, I hasten to add!

Then you get to the top mark.

Now instead of meeting these oscillations every 90secs, your moving in the same direction with them and at very close to the same speed, in most cases you are moving faster than the gust, so provided you get yourself on the right side of the shift to begin with, the only thing you need to worry about is where is the next gust and where is the mark.     You do have a AoA WRT the gusts but they are also moving in a similar direction as you so they are coming at a very manageable rate, and often the gust that will effect you is the one in front of you (sometimes). 

The only thing coming at you quicker is the leeward mark.

Completely different rate of decision making and a completely different set of values and priorities.

And it is true of a Laser as well as a 15ft skiff, just the gust that is going to affect you going down wind in a Laser will be from a vector +/-15º from the wind direction, and the direction its coming is far more critical to you than how you approach it.  So you have to think, do I gybe or hang on, and were's the next one.

The skiff, it’s a much bigger playground!

Upwind in a Laser, they are still coming at you more quickly but its 1 ½ times rather than 2 or 3 times and how you hits the gust and accelerate really dose not matter as you struggle to exceed HS [Hull Speed] so you just tend to pinch.

So yes, any boat spends 70-75% of its time going to windward and you had better be on the boil or it will be a painful 70-75% of your days sailing.

Downhill, much more fun, far less stress, (in some ways, but doing warp speed has it’s own set of challenges) and if that’s where you gained, then probably you where more decisive and pick up on the pointers, or even noticed the pointers more clearly!

And your more than welcome to posting my ramblings.    Feed back from those rambling makes me think and keeps me young.  Trying to explain difficult concepts at arm’s length stirs the grey matter and that must be good for you (and me).

As you know Anastasia has open the boarder so Deidre and I are planning a drive, no doubt we will transit Grafton.     If I do (wont be for 2 months, got Port Stephens and Mudgee already pencilled in) I will come and have a coffee with you at the Ramada.

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24 minutes ago, JulianB said:

.     If I do (wont be for 2 months, got Port Stephens and Mudgee already pencilled in) I will come and have a coffee with you at the Ramada.

I'll look forward to it Julian

On the right day, I'd be happy to introduce you to some of my group if it suited you; but no doubt will revolve around your travel plans.

In the mean time I'll look forward to whatever further installments you chose to deliver to us.

 

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1 hour ago, JulianB said:

 

So normal 10-12knts summers day on the mid coast of NSW, you are likely to have a +/- 7º oscillation with a frequency of about +/- 3 mins.      And there are lots of variables and lots of changes, so this is just typical of Grafton, in a NE seabreeze, don’t read into it anything else!

 

In his last book, your father talked about his 'theory' that gusts reflected the upper layer wind direction. The shudder quotes around 'theory' merely reflect the fact with the book lent out, I can't verify how firmly he expressed the idea. In some respects, I wasn't entirely convinced they were that predictable.

But in one area I've certainly seen it in action. A strong NE'er on a summer's day sends us upriver for racing (west of the Ramada). There the base wind somewhat funnels along the ENE flowing river; somewhat in that it still comes somewhat diagonally off the Northern bank. But the gusts come screaming down from above the superheated Northern landmass with an almost due Northerly twist.

12 knots gusting to 30 is often enough the case. You can throw all the main you want, but unless you screw the boat quickly up, not just to sail the gust, but to feather it, you're going to get very wet.

I always lament that, while in his last book your father discussed slow moving or static wind fades and pulses - a very common occurrences on the river and one that doesn't follow the cell idea he discussed in earlier books (and I don' think your father thought they did either) - he didn't describe what was causing them or what air flow was happening within them or at their margins.

 

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Rambler bloody good question and yes ASP I owe you an answer!  Sosoomii, your welcome!

Staying with the drag-minimisation approach, when you leave the beach, or the marina you have committed yourself to a set RM [Righting Moment] and by virtue of that, a pre-determined range of SCP [Sail Carrying power].     This is true of every sail driven boat from a sailboard all the way through to an AC or a mega yacht.     The only boats that push those boundaries and makes it a bit fuzzy are platforms like Vesta Rocket but even Paul Larsen went to all sorts of extremes to reduce drag!

I was extremely fortunate, I had a father who was an extraordinary pilot, with DFC’s to prove it and who was also into model aeronautics, just happened to come across his cache of certificates of World Records about 2 months ago, 7 in total, so I learnt to fly at a very early age, being the youngest,  every dinner time conversation was fluid dynamics, then I got stupid and started jumping off Long Reef with a hang glider strapped to my back, got a bit more adventurous at Stanwell Park and almost killed myself, so I progressed to real gliders, alloy/FRP ones, got my wings and had an extraordinary time.   Then Deidre (my wife) got pregnant and that was the end of that, have not been behind the controls of an aircraft for 30 years (age of my eldest son).

I attribute 2 things to my time soaring, 1# was a real comprehension of the 3d nature of the wind, the atmosphere and being able to look at the water ahead of me and understand what was happening and where that gust was actually coming from why the wind cycles.   I had years of empirical evidence, again mostly from Dad, but to experience it 1st hand just drove the point home & 2# I was already a minimalist but I became a drag (minimisation) freak.

I stopped soaring in 1989, the next 4-5 years I won everything in the 18teens and went on to dominate the design game, The B18, then the 49er, then the 29er, then Vivace, then the Skud and in fact the list goes on!   (And it possibly all started with the B14!)

I credit my stint Soaring as a tipping point WRT my dominance in sailing results and design.

So Rambler, you mentioned dad’s theory that gusts reflect upper layer wind direction, any pilot, and particularly a glider pilot will attest to the rolls in the atmosphere, and they can go up 1000’s and 1000’s of meters. 

As a glider pilot you occasionally hook into one of these, happens a lot in NZ, and the Land of the Long White Cloud, that cloud being formed by the uplift of the air as goes across the ridge of the island, and then downstream of it you have wave after wave after wave (just like on the water).

Here, we see “cloud streets” which are uprising air of a roll that happens to be going up through 0°C temp and these extend each way across a country like Australia for 1000’s of km’s.

I have not soared “streets” a lot, most of my soaring was localised thermals, what we referred to as the “stairway to heaven” in central NSW.     But I had a few occasions going long distances in constant rising air, bit like a surfboard rider on a really long shore break, plus have seen them 1000’s of times out the windows of aeroplanes and from the ground.

image.png.531a8293a9a11b0aceb7cae1f35745c8.png 

So above is a very generalised render of what I believe is happening.

Wind is going right to left, and the tube are spinning anti-clockwise!

Blue is the water, the air touching the water (gold), drags it downwind and creates waves but by definition it’s doing approx. ½ TWS (nominally at 10 or 20m elevation) .

You end up with these rolls/tubes of air rolling downwind.

Dad dedicated quite a few pages to this, and he concluded that in 10-12knts you had to be at 3ft (1m) before you broke the boundary layer.    So this lower tube or rolling air was about 6ft in Diameter (2m).   That whole tube of air is rolling down wind at about 60% of nominal windspeed, and Coriolis has screwed it 3°clockwise in the Nth Hemp, anti-clockwise in the great southern land.

Then you have a gap of about the same size, (6ft – 2m) because you have the top of the gold roll going down wind at above TWS, and you have the bottom of the Cyan roll almost stationary (WRT TWS).

Then you have the Cyan tube, doing the same thing, but it a lot bigger, 3-4m in Dia and it had less friction so it’s doing 80% of TWS.     Coriolis has screwed it another 3°

Then a bigger gap, more air, more energy to reorganise.

Then a bigger roll again, 10-12m in dia and this is doing nominal  windspeed

Another gap and then even a bigger tube again which is doing 110% of nominal windspeed.

A std east Coast Australia NE-er you would only have 4 rolls as it’s only 300ft (100m) thick.

Now you have to get conceptual!

You have all these tubes rolling away, down wind, and they are extending in some case 100’s of km sideways.  All screwed 3° constantly WRT the layer each side, 1st = 3°, 2nd at 6°, 3rd at 9° and so on.

Now there is going to be a set frequency at which air that is rolling at 100% nominal TWS, so say 20 knts in the green roll, lines up with air that is doing 80% of TWS but also going downwards in the Cyan roll, and its slowed down a little but not much, and then that in turn lines up with air 60% of TWS and also moving downward in the gold tune and it then slams onto the water surface in you classic “cats paw” pattern.

I look at it as a vertical street, it’s a path of opportunity where all the airmasses are moving in nominally the same direction and that opportunity will come and go at a fairly regular interval.

2 things come from this,

#1 is the air in the green (or even higher) rolls is moving a lot faster and has a lot more energy, so depending on how straight and opportunistic the path is, will depend on how hard it hits the water.

If it has an exceptionally smooth path to the surface, it could be 130% of (surface) wind speed.      If it has had a rough trip down it may only be 110%.

#2 it is also screwed 3-6-9° or even 12° from the surface air, and as it has more energy, so it is likely to maintain that direction because there is very little force trying to “straighten it up” (to surface wind direction).

So, with a quite high level of regularity and predictability you will get air moving from the upper levels, down vertical streets and those bodies of air, because they are moving faster than the surface air, will i) appear like gusts ii) be in most cases between 110-115% of the surface wind speed and iii) in most case will be come from the same screwed (by Coriolis) air mass, so if the first gust you meet is lifting on stb, then you can say with a pretty hi degree of certainty that all gust will lift on Stb.

I have drawn a black line of how I see this sort of gust, a vertical path that bring the higher speed air higher up, coming down from the upper levels.

Ramber, where you are, your sailing in a gutter (river valley is possible a less derogatory term) so the air 40-60m above you is moving a lot faster and probably at 6-10-15° left, plus you have voids, and therefor eddies swirling over your windward shore as the air flow over the top, and trips,  so if you had 10-15knts in the valley and a bit of upper faster moving air caught a eddy down, then 20-25knts is very believable with a 10-15° even 30° screw.

Also local eddies coming over windward banks can twist air to the left or the right with complete disregard for Coriolis plus they can drag down copious quantities of much faster moving air for extend periods of time.

I think I only sailed once in Grafton and I was incredibly young in a NS14, so that’s about as much as I can remember of your topography.

 

                          jB

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  • 3 months later...

Rambler, looking at transiting Grafton, heading nth prior to the 12th or heading sth, after the 13th (Dec)

If madam will let us Sydney-siders into QLD.

Hopefully sailing Wraith of Oden out of QCYC.

We should do coffee at least,

                    jB

Wraith of Odin - Classic Yacht Info

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Good discussion and high level from Julian here.

But really.. Kiss

If your skiff rig is at 100% tune (in the18 or the 49r) in the puff, the mainsheet should not ease:

See forestay stability. com etc

There is some footage from the last Giltinan of the Kiwi winners, mainsheet immovable at top range big sail...

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7 hours ago, JulianB said:

Rambler, looking at transiting Grafton, heading nth prior to the 12th or heading sth, after the 13th (Dec)

If madam will let us Sydney-siders into QLD.

Hopefully sailing Wraith of Oden out of QCYC.

We should do coffee at least,

                    jB

Wraith of Odin - Classic Yacht Info

Absolutely. Keep me posted. I'll email my telephone number to you.

I feel guilty raising this, but I've just had 7 new (never sailed before) women join my skiff training group. You indicated at one time you might have some old stock sailing pants in your ceiling that you'd like to get rid of.  :unsure:

Nice yacht

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7 hours ago, Frogman56 said:

 

If your skiff rig is at 100% tune (in the18 or the 49r) in the puff, the mainsheet should not ease:

See forestay stability. com etc

There is some footage from the last Giltinan of the Kiwi winners, mainsheet immovable at top range big sail...

Hi Frogman (or can I call you froggy)

Google search of "forestay stability..." didn't produce anything for me.

I like to learn. If there are other good materials, could you attach links please.

I can't say our 15's are at anything like that level. But then we have a single rig across all wind ranges - mind you, so do the 49ers, so can't use that as an excuse.

122835364_628356594497455_4260922742177953870_o.jpg?_nc_cat=101&ccb=2&_nc_sid=730e14&_nc_ohc=E_gbUnqicXoAX8xVHw5&_nc_ht=scontent.fsyd7-1.fna&oh=68dac9849184f14a9061afab348535ad&oe=5FDE1615Image may contain: sky, boat, ocean, outdoor, nature and water

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Rambler,

Oops... 

1. Forestay stabilty .com was a little joke. Reality tho, is that somewhere around 40% of the headstay load comes from the mainsheet... depending on lots of factors, to be sure.

2. The mains in the pics you sent are on the deep side. I do have some ok 18 pics at least and will dig one out and post in the next few days.

3. Froggy is a nicer label than most people use

,

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6 minutes ago, Frogman56 said:

Rambler,

Oops... 

1. Forestay stabilty .com was a little joke. Reality tho, is that somewhere around 40% of the headstay load comes from the mainsheet... depending on lots of factors, to be sure.

2. The mains in the pics you sent are on the deep side. I do have some ok 18 pics at least and will dig one out and post in the next few days.

3. Froggy is a nicer label than most people use

,

Oh dear. I'm a bit of a literalist. Make whatever conclusions you want from that.

It is interesting studying the photos. Its why I included them.

Easy enough to pick the 'this should have been tighter' problems from them afterwards. Harder to judge on the water but just studying the photos helps make you think about it next time.

And getting downhaul and cunno adjustments right are one thing. Getting the rig tension right for each day (not adjustable on the water) is a whole nother and I don't think we're anything close to really working that through..

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Interesting fact.

Each of the forward hands on the above boats is a female, between 25 and 40yo, who for all practical purposes, had never set foot on a sail boat before 2 years ago.

All are graduates of our training group. The boats were not designed for women; indeed, they're a bit light. Its just how the group has panned out.

The skipper of 09 is a woman who's just come back to sailing after a 20 year absence, although not previously in skiffs; again after a bit of a refresher and update in the training group

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  • 3 months later...
On 7/18/2020 at 1:57 AM, JulianB said:

 

But in essence the 1st batten is the trigger batten, by altering its stiffness and it's bend profile you can get the leach to stand up, with camber, stand up with very little camber or invert and de-power.        The other big factor is the rocking of the top panels to exploit the bias and wrap & weft.        

The 2nd batten is the camber batten and it sets up the top ½ of the sail.   The other battens, their bend profile is important but otherwise come along for the ride.

In terms of stiffness, 1st is say X-kgs, 2nd is 70% and the rest are 20-30%.   

 

Firstly thanks for taking the time to talk about this. I'm a bit late to the forum. I've heard you mention the trigger point on the batten many times before but this is the best description you have given that I have seen. I have a couple of things which it would be great if you can confirm. 

  1. I assume by stiffness you are talking kg/m (SI units) not batten manufacturers stiffness rating? So if batten 2 is 30% longer than batten 1 it is effectively 30% more flexible for a given batten section?  
  2. To stand up with camber a stiffer batten with more tension is required?
  3. To stand up with little camber a stiff batten with less tension is required? 
  4. A softer batten will invert more easily? 
  5. What are your thoughts on the interaction between cunningham and cap shroud tension and the trigger point of batten 1? 
    1. My thinking is depending on headboard length it  may be preferable to allow the batten to invert at a given point but then keep caps tight or run a stiffer batten and allow tip to drop to leeward 
    2. I'd be really interested to know your thoughts on this from the perspective of a heavier or lighter than average crew and how you could tweak the variables. 

If you could sum this all up in a few lines that would be appreciated :lol: (That bit's a joke) 

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I forgot about my Tasar question last year! Julian, at your leisure would you mind back-peddling and revisiting the design of the Tasar and its rig?

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3 hours ago, G-Shack said:

Firstly thanks for taking the time to talk about this. I'm a bit late to the forum. I've heard you mention the trigger point on the batten many times before but this is the best description you have given that I have seen. I have a couple of things which it would be great if you can confirm. 

  1. I assume by stiffness you are talking kg/m (SI units) not batten manufacturers stiffness rating? So if batten 2 is 30% longer than batten 1 it is effectively 30% more flexible for a given batten section?  
  2. To stand up with camber a stiffer batten with more tension is required?
  3. To stand up with little camber a stiff batten with less tension is required? 
  4. A softer batten will invert more easily? 
  5. What are your thoughts on the interaction between cunningham and cap shroud tension and the trigger point of batten 1? 
    1. My thinking is depending on headboard length it  may be preferable to allow the batten to invert at a given point but then keep caps tight or run a stiffer batten and allow tip to drop to leeward 
    2. I'd be really interested to know your thoughts on this from the perspective of a heavier or lighter than average crew and how you could tweak the variables. 

If you could sum this all up in a few lines that would be appreciated :lol: (That bit's a joke) 

WRT 1. The way I measure battens is to have them vertical, with the tip on the floor, put a spring balance on the other end and pull slowly down while watch the gague rise.   At a point (the Euler Crippling Load) the number will cease rising as the batten bends further and further., so you then back off, lift the scale until it just starts to fall (the reading), back and forward a few times until you find the sweat spot.     In China when they do this, when they find the sweet spot, they are doing this up against a wall with paper on it and they trace the curve of the batten.     When I do it, I have a camera set up and a remote, then I snap a photo.  

The number of the scale, the tension when its at the sweet sport, it could be 4.25kgs and the shape of the curve, we normall define that by % camber and % placment of max camber define the batten.     Then you need to make some statments WRT straight aft run, or heavy fwd curve.   My photo system, I then scan the photo into Rhino (3d program I use) and that defines all of that.

WRT 2. Ostensibly YES

WRT 3. Correct

WRT 4, Absoutly

5. holy shit, what a can of worms!    Give me a few hours.    It's more of a queastion of how to explain it, rather than what to explain.

                       jB

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Thanks for the response. Good method for the stiffness. I guess I could also push down on a set of weighing scales and get the same measurement. 

I need to think about how the camber at the sweet spot relates to the sail camber but I will await your thoughts on question 5 as I suspect it's going to be pretty interesting. 

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Yes, putting the tip of the batten on a good set of scales works very well also.

When we started doing this, which was in the early 80's, digital kitchen scaless did not exist, and my father was a man of consistancy, so we probably used a very old set of fishing scales, very likely in Lbs untill well into the 2000's.

But now with these really good kitchen scales going up to 7 - 10 kgs, it works well.

         jB

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On 3/19/2021 at 4:30 AM, G-Shack said:

What are your thoughts on the interaction between cunningham and cap shroud tension and the trigger point of batten 1? 

  1. My thinking is depending on headboard length it  may be preferable to allow the batten to invert at a given point but then keep caps tight or run a stiffer batten and allow tip to drop to leeward 
  2. I'd be really interested to know your thoughts on this from the perspective of a heavier or lighter than average crew and how you could tweak the variables. 

 

Downhaul tension is a primary trigger/control WRT the #1 batten, Cap shroud tension or lack of it is a very secondary control.

Pretty interestingly, we are presently knee deep in sail re-evaluation WRT the 49er and the FX, Jimmy, one of the skippers trailing the sails here in Sydney, he is well aware of the loose Caps WRT the FX to get it to flick off, and given that all the sails are now "more firm" giving the upping of the structural components, he is looking at using "more stretchy" dynema, so SK78 rather than SK99 to possibly breath some life into the otherwise "more firm" sails.   (this is WRT the 49er, not the FX)

Not sure it will work because the actual amount of load in Caps is quite small on a boat like the 49er.   So you may need to go to VBcord to get the desired result.

Tops of sails inverting when over pressed is common and not slow, one of my favorited 18teen photos is a 1991 shot of AAMI with the top 1/3 of the front of the main inverted (pin head)  and at the time of the shot, we where "hauling arse" under a bigger more favoured competitor who we completely hosed in 300-400m.

Tops of windsurfers and 49er flicking off to leeward works.

As I have said before, we are still in very un-chartered territory with Square heads, but the really big (as in long) head-boards so FX style require much stiffer and therefore heavier top-masts and corresponding top batten than there more moderate counterparts.

Very much as a matter of 1st principals, because it’s longer, (the #1 batten) it has to be stiffer and therefor heavier.

We are making the headboard on the 49er a little bigger to get some more flick, but a little is 50mm, still way under the size of the FX, and the real joy (also the draw back) of the 49er and the FX is the level of detail that happens and the on-going evolution in just the way they sail them and the extent to which teams develop completely different solution to similar problems.    The loose cap shrouds is but one, possibly VBcord caps may be another, it’s a lot of fun watching it all happen.

WRT weight variations, the biggest level you have, when you playing like we are now, is mast stiffness, so the amount of bend/curve and the resulting possition of the curve.    Finally the fairness of the curve.

Back in the late 80's and into the early 90s with pin-heads, we got very thingy about rates of bend and matching that to the size and rates of curves in the leach/roach.

But watching the way that these crews play with rig-tensions to set the boat up for their scenerio, so weight/height and therefor leverage/RM is fasinating, bit less horsepower but also less drag, provided you alter your rig to accomodate that seems pretty clever, and it would also appear to allow a wide range of body heights/weights to have very equal performance.

There are strengths and weaknesses in every crew, its just about playing to your strengths and trying to avoid the weaknesses.

~~~~~~~~~~~~~~~~~~~

Tasars will have to wait a bit longer, sorry. 

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Blimey its not even April! 3Di are approaching double the cost of panelled in most classes, and you generally don't even see the NS jockeys use them in most classes where you have choice. Moth and 18ft perhaps being exception. I wonder how they made the calculations re: longeivety?

Windows in 49er pics look big!

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If you buy a one off 3Di sail, it's expensive, as it should be, one off setup, design, etc etc etc.

Start buying 50-100 at a time, same set up & design cost, but only once, so they end up very cost effective.

The biggest thing the sailors wanted was consistency, and 3Di and it's moulds potentially offer that better than any other process.   

Equally weighted to Consistency was Vision.    49er sailors like to be able to see.

4th was Longevity, I think all the candidates offer Mains and Jibs that would last longer and yes we asked lots of questions, particularly of Moths (WRT 3Di) as they are similar loadings and those we asked said things like "tapes wear out before the laminate, and they are good tapes", or "you can use the one sail all year".

6th was Price, the attitude was pay ½ as much again for a sail that last 2 - 3times longer, your way ahead, not just in cost.   The reality we won’t even be paying 1 ¼ x's!     

Buy a one off 3Di sail, yep it's expensive, because one-off design, one-off mould set up, one off disposables.  

Buy 50-100 at a time, and factor in Consistency and Longevity, and your way ahead of the curve on so many fronts.

Add that to the new mast, that is cheaper and more consistent also, it’s all win-win.

Some really big names tested the sails, over saw the testing, or were part of the evaluation team, and bar JC and I abstaining (as we must) it was a unanimous decision.

The other really big winner is the environment, and that is a multiplier on so many fronts.    3rd less sails, less disposables, less wastage, less energy and less logistics.

But most importantly, less hassle!!

 

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1 hour ago, JulianB said:

Start buying 50-100 at a time, same set up & design cost, but only once, so they end up very cost effective.

So explain why class sails in nearly every dinghy class I have come across are about 3 times the price a local sail maker can do them for. 

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BOI guy

I am getting rather sick and tired of this.

If you want to play the SMOD game, you play by the people who sail those classes rules!

I think there are 150-180 WS Int classes, there are about 20-30 of those that are SMOD which in all but the case of the RS boats are really MMOD's. [Multi Manufacture One Design]

I don't know the number, but I would guess that 4-5 of the MMOD's account for more than 50% of boats sold in terms of $$$ per year.   (excluding big yachts, obviously)

So a very large proportion of the worlds sailing population chose to play the MMOD game.  And if you took out IODA which is closer to a MMOD than it is to an Open One-design then that number becomes overwhelming.

If you do that maths, there are lets say, 120 - 150 Int class that allow you to go down to your local sailmaker and buy a sail from them.     So if you don’t want to play the MMOD game, you don’t have to.

But if you want to play the MMOD game, then you need to play by everyone else’s rules, you can’t cherry pick and expect anyone else to respect you in the morning.

Shortly after the AKL/Geelong AMG’s of the 49er class some really impressive sailors formed a group to help select a sail manufacture, and one of the first jobs was assigning a weighting to what was important WRT that process.

Equal #1 was Consistency and Vision as already been stated. And weighted 100%

#4 was Longevity weight 50%

#6 was Cost weight 10%

That is the weighting, derived by those sailors based on the wishes of the people at those AGM’s  (AKL and Geelong) as to what they deemed important.

The cost of doing Consistency was probably 8%.

The cost of doing Vision is probably 4% & the

Cost of doing Longevity, up around 12%  (this was common across all sailmakers)

I do remember a Paul Elvstrom quote as being something like “you have only won if the guy you beat thinks you won”.  

Probably sums up the attitude of the 49er/FX, likely 29er, ILCA and most MMOD sailors.

If you want to play that game, you play by their rules, not by you’re rules.

If you want to go get local sailmakers and play another game, there are another 150 Int classes and possibly 10 times that number of regional classes to enjoy.

If you want me to go into the pros & cons of Single Source sail-making vs open sail making, I can do that, we have done those tests every 4 years for the last 20 years but that is a completely different debate.

But the 49er/FX sailor have made it abundantly clear that want to play the Single source sail making game, you got to remember it’s 18 months ago now, but I think the quote was “more of the same, just more consistent, they should last longer and if they cost a bit more, so be it!”

The person who said that, and in doing so summed up the assembled multitude, virtually unanimously, dissenters would have been less than hand full, ended up on the selection group, and has been true to their word.

 

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So basically this comes down to "purchasing power" and discounting, which is all good capitalism.

If the 49er class members want to pay 25% more (assuming it is only 25% more?) for something that they believe lasts twice as long (how that is concluisvely proven I don't know) then that absolutely makes sense - and probably is indicative of the fact that the vast amount of 49er sailing is done by olympians and olympic wannabes who will burn through a few sets of sails a year, rather that weekend warriors.

I must admit that, in all areas of business that I've been involved in, making stakeholders buy in to even subtly higher first costs even when proven to have lower through life cost (even when savings are in millions) is a very very hard sell - some of that is pure stinginess, some of that is short termism, some of that is attributable to the cost of capital. Cost of capital and opportunity cost at least is calculable.

Is there evidence of inconsistency of the panneled sails? They will all be laser cut out in big batches, and the likelihood of errors / variation in sticking of seams accruing over entire sails in a way to cause measurable inconsistency doesn't add up for me. Humans sticking seams is a stochastic process.  Which leaves material - the cloth and laminate is presumably QC tested leaving cloth manufacturer and possibly even by sailmaker - is there typically a large variation in mechanical property seen there batch to batch? I think I owned 20 or 30 laser sails over 10 years and I couldn't tell any difference between sails when new, apart from that they all got knackered quickly.

Is there some wider play here by NS to get more 3di adopted in smaller classes? Its pretty widespread in raceboats > 30 or 40ft. I kind of doubt it as I get the impression that outside of SMOD, most dinghy stuff is nuisance custom to a company big enough to have shareholders etc. 

So the thing that is interesting to me here is that a 3di North in most dinghy classes is approximately double the cost of panelled.

I just struggle to see how 3di or 3dl before it is a more consistent or scaleable tech than panelled - its not like they can suddenly make 20 sails in one hit like an injection moulding. The sail still needs pockets and corners and tabling by a human being. Equivalent economies of scale exist in panneled sails esp for SMODs.

So if the SMOD 3di is "only" 25% more expensive than an (already heavily value engineered) panneled sail, this implies that the near 100% markup in non SMOD is made up to a large extent by profiteering and differentiation. Which again is all perfectly legit capitalism.

I think that me and my i14 / 505 / moth / merlin rocket / melges 20 whatever comrades need to start wearing berets and form a cooperative to approach NS for bulk purchase for our OD sails if that will drive the cost down from double panelled to only +25%. Maybe we could integrate our cooperative with our 49er brothers and sister and then everyone wins. How hard could that be:P Four legs good, two legs bad!

 

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Firstly, 60% of all the sailors at any given 49er worlds are there for the kicks, not for the gold.

Rightly or wrongly, the 49er has become an aspirational boat, in the sense that they aspire to sail it, and some aspire to sail it well with no intention of Gold glory.

We could stochastic-aly verify that (you made me look up that word) but again the feedback from the sailors at the AGM, is more than enough for me.

Re  inconsistency.    These guys get bent out of shape over ¼% (as in 0.0025) and to them it’s very real.   

What I do believe is that 3Di and the claims made by North are about to be subjected to a level of scrutiny not experienced by many ever before.   

Re consistency, if you lay-up over a mold and by computer you should achieve greater consistency.   Even laying up a panel sail over a mould should increase consistency.

The big thing about what the 49er can do, that the 5o5 or I14 can’t do is have a 50-100 mainsail run with no variations allowed or even considered.

Set the machine up once, press the go button and extremely limited human intervention.

ILCA could do it,  and we know ILCA are watching closely.

                           jB

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On 6/10/2020 at 10:35 AM, JulianB said:

49er/FX D1's go in at the the top of the ram vang, so they are a lot higher up, the angle is far more acute, so they need more tension to have the same result, the flip is that they hold the mast very positively higher up and there for are far more effective.

Hi guys. I am a bit late to this forum, but it has been a great read. Was wondering if Julian could comment a bit more on how to use the lower shrouds?

I have been sailing 49er FX for almost a year now, but still can't wrap my head around the sail trim. On medium wind days the boat just flies, on stronger days we are struggling a bit to depower (after reading this I think that we should try easing the uppers more). But the real struggle is lighter wind (not very light, but light-ish), when we feel that we are lacking power. Pulling the vang on closes the leach, but also flattens the sail a lot, so we don't know where to stop. One theory is that we should increase the tension in the lowers to stop the lower mast from bending and so keeping the lower part of the sail fuller.. is this logic correct?

Also, another part that I would really love to understand deeper is the setup of battens. May the battens be one of the reasons we are lacking power (maybe not enough tension in the upper battens?) or are the batten tensions not as important as bending the mast the right way? Would appreciate it a lot if you commented on that too.

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Instead of mucking around with this, let me see if I can get you a set of numbers.   I promissed to do this some time ago, may have to wait until after the games, because people won't want this in the public domain prior to Tokyo.

 

                       jB

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Real numbers would be really great, but to be honest I am more interested in the Why rather than the What.

I have worked trough your fathers (and your) books, and the rigs used in 18footers and 49er seem to be such masterpieces. There is a lot of information, but I feel that I don't get the whole picture yet (or there are some gaps at least), as I'm not able to apply the knowledge in my sailing. That's why I turned to the internet. :)

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I presume you've at least found the McKay tuning guide here

https://www.mackayboats.com/mackayboats/assets/File/FX Tuning 010812.pdf

So you have there a bunch of numbers that might not be what the top of the fleet presently use, but give you a guide as to which way things move. Julian's promise to get the current numbers is nice, but in the mean time, let me offer the following propositions to answer your questions (which if they are wrong, Julian can correct if he feels the need)

The main shrouds increase their tension increased with increasing wind speed. That's pretty common across classes. Reduces forestay sag as the wind speed increases if nothing else. 

Because main shroud tension is increased by pulling back the side shrouds, to maintain the same amount of pre-bend on the mast the D1's are also tightened. Why not let them go looser to allow more lower bend? I'm sure you'll find the answer is that you want to spill the power in the upper sail, not the lower sail.

The answer on the non intuitive treatment of the uppers is contained in the first two posts.

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Karelchik

This is really how long is a piece of string and how detailed you want to get.

There are about 10+ variables that come into this, as into the design of the mast, and until you get to understand that, then how you tweak the mast with rig tension via the shrouds is a completely black art.

Give me a day or to to try and work out a way to simply explain it, without sending everyone off into a long and deep slumber.

It may take a few installments, the mast in it's simplest form is a mechanical spring that supports 2-3 elements of the rig (those being Main-Jib and occasional the Spinnaker) but as we have just spent a eternity tweaking the bend, and what one person wants is not the same as the other person.

Give me a few days, getting you the numbers is easy!   Explaining it is complex.

                            jB

 

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My issue with answering you is that I can be very simplistic and just talk about the mast, and in fact that is what I plan to do, but a mast in isolation, even a mast and mainsail in isolation is just that, you really need to think about them as a whole package especially WRT the Jib for up-wind sailing, sure spinnakers downwind but also placement of the foils and the iteration with the foils.

Just to digress for a moment, say you have too big a jib, and we are limiting ourselves to a skiff in this example, and by too big, say it's 30-31% of total Up-wind SA then you need to move your c'board further fwd than "the right amount" because as you go through a gust-lull sequence, easing the main, to relieve the pressure also allows f-stay to sag, and that in turn powers up the jib, so CoE moves forward, boat goes heavily out of balance, so you fight it with the rudder, and to try and over come all of that you will adopt a different rig set-up, and over time, you will alter the heights of things like F-Stays and mast stiffness to compensate.

So the mast and how you manage it, is a matter of the whole package, not just the mast.

But that is a far more complex conversation, and talking about the mast initially is as good a place to start as any.

~~~~~~~~~~~~~~~~~~~~~~~~

So a Mast and it's rigging and because they are joined at the hip (sailtrack) the mainsail.

5-6 things affect the mast, in order of importance

#1 F/Stay height

#2 Diameter of the tube and as part of that the lay-up

#3 Primary shrouds height as well as Trapeze wire height.

#4 D1's

#5 Spreader (the lower one, upper one really is superficial) &

#6 Heel tune

#1, Fore-stay height, ostensibly the 49er F-Stay height is in at about 71-72% and that's quite high, the reality is the D1's being high, make the effective F/Stay height around 68-69% and that's a pretty good number.

#2 Tube diameter, a 49er mast is about 62m OD at the butt, grows to 64mm at the 2 spreaders and then drops down to 21mm OD at the tip, it's a bit big if you think in terms of LE Rad vs Cord, it would have been better if it was say 55 - 53mmOD between the spreaders, and very likely the next iteration (8 years time) it will be. Max bend is about 1-1.2m below the hounds, and we alter the angle of the lay-up so that we achieve a) enough WT [wall thickness] to maintain stability (and this is especially true in the FX tip) and b) to ensure that there is enough material to do the job or resisting the bend and a controlled manner.

#3 The Primary shrouds attached to the mast a defined distance below the F-Stay and that dose 2 things, a) as the mast bends that action tightens the rigging as the distance between the Hounds and the deck reduces (due to the bending) and b) it locally stiffens the mast at the Hounds which as mentioned before has the highest bending moment in it whole length.

Trapeze wires are again a defined height above the Primary shrouds and that in turn pulls the mast head to windward.

#4 D1's, they are high, and they direct oppose the fwd thrust of the ram Vang, and again that are a set distance above the ram Vang to compensate for aft load on the boom, the idea is to keep the whole mast in column, particularly down low.

#5 The principal function of a spreader is exactly what it's name implies, it spreads the wire so that their angle of approach to the mast dose not fall below a critical level, for 1:7 std wire that critical AoA is 7-8°, what we call the "poke" so the sideways displacement is up around 10-11° so there is a fair bit of safety margin.     We also allow a bit of Lead, so that means that the mast rigged up with no mast bend, the wire is being pulled fwd, out of alignment about 30mm, this number goes right up when the mast starts bending but I still maintain that the primary function is spreading the wires, and 2ndry function, particularly of the top spreader is to stop the mast inverting.   But drop the main, boom hits the shrouds, the mast will fall down, period, so tie a knot!

Just digressing again for a moment, more 49er masts have failed aft, than fwd, more often than not, under spinnaker, gust goes away, crew squeezes the sheet on, spin rotates aft, mast falls down.   Early days it happened often, now people have learnt to get the weight of the trapeze and onto the shrouds so they (the Primary's) have some chance of supporting the mast.   &

#6, Heel tune, how the mast comes out of the step, sets up the lower mast bend, and in many ways the effectiveness of the D1's.

=> The other thing that most people forget is that if you are 2 stringing, and the boat is flat, or even heeled to windward, then it is the Leeward shrouds that are doing most of the work, and they will be significantly tighter than the windward ones.   The force being carried by the C'Board enhances this even further, it is trying to rotate the windward gunwale up-wards and the leeward gunwale downwards, if you then trapeze below the wing line to increase this rotation even more.

Just the action of the c'board alone, can make a +/-70kgs differential in windward to leeward shroud tensions, add to that the shift in CoB and under wing trapping, given that your probably running shrouds at say 300kgs, (base) it will be less as soon as you pull the main up the mast and even less again if your both on the wire, as you compress the mast, you can easily end up with a 3:1 tension differential, & it's not unknown to go up-wind with the windward shrouds loose. 

So after taking all that on-board, some idea's on what you want to achieve.

If the wind was steady, if it did not fluctuate much, then you would just about always be running rig tensions which would be 20-25% more than you presently do.   Major "want" would be to stabalise the f-stay, so you could set it's camber and twist up to be just so, and maximize it's potential, and you would also be running far tighter main-sheet, you would rarely ease it, so Vang and downhaul would also be set far more statically.

But because there are fluctuations in both speed and direction of the wind, and also the water, we therefore we opt for a far more fluid rig, and that includes rig tensions.  

An initial scenario.   Your pressed, going up wind, close to the design wind, main-sheet is eased a little, boat is carving thought the water well, your in good trim, but there is a light patch ahead, you both see it, and as it washes down, you bend the knees and pull the main-sheet on a bit harder.   Just think of all the things that change!    Pulling the main-sheet on a bit harder means, 1stly, the boom will bend less, then there will be less load in the Vang system, so instead of the Ram Vang pushing fwd 2 m up the mast and the boom pulling aft 1m up the mast they will be "more neutral" in terms of load so it's likely the lower mast will straighten, maybe only 5mm, but that will also lead to more camber lower down.   2nd order effects will be more leach tension, the actual clew of the main has been pulled down 20-30mm, so the leach stand up more, which is all good because it means the boat powers up a bit more, also a bit more drag, because your turning more air.

~~~~~~~~~~~~~~~~~~~~~~

I'm going to stop there for a bit because it's becoming long winded.

Let me know if it's what you are looking for???      jB

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Rambler,

thank you for explaining. Yes, I have seen the guide and that's what made mu curious. So the FX rig can be depowered with easing the caps, but how does the downhaul relate to this? Pulling the downhaul moves the mast head back, and as I understand this is not favourable in FX.

 

Julian, this is really great stuff -- thank you!

I don't quite get this part, could you elaborate? :

3 hours ago, JulianB said:

as the mast bends that action tightens the rigging as the distance between the Hounds and the deck reduces

And by this do you mean "straight"?

4 hours ago, JulianB said:

idea is to keep the whole mast in column



The mechanism - that pinching the sheet helps deepening the lower part of main - is cool. Out of sheer interest: how much does 5mm bend change actually change the depth of the mainsail? I guess it depends on the initial depth, but I'm just trying to get it in perspective.
The last example was very insightful. Pulling the sheet increases leach tension, which is good because it closes the leach, but am I right that it also adds bend to the upper-mast? And by that the upper sail should flatten. So in summary, the AoA of upper sail will increase, but sail itself will flatten, but that's okay because drive force will probably increase. Have I made a mistake somewhere? Excuse me if I did, I'm just trying to paint a picture of how these things are working together, and how powering/depowering works.

Also, more of these kind of examples would be appreciated a lot! :)

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Re F/stay - Primary shrouds interaction, the separation is about 150mm.

But to understand what is at play increase that to say 1/2m, (x4 approx) and then think about what happens when you go from a mast that is being bent at say 1% (mast is 8400mm LOA, so its a 84mm deflection) and increase it to 2.5- 3% (and those are pretty really numbers) the shrouds 500mm below the f/stay will resist the bending because that have to tighten or stretch to allow the mast to bend.   Over the years, particularly WRT the 18teens we refined those numbers, we tended to leave the Primary's as is, and have 2 f/stay positions, as little as 40mm apart.    Massive difference to bend and response.

And yes, keeping the mast in column, is ostensibly keeping it straight so it can manage the compression loads without going crazy.

Lower batten on a 49er is 2707mm LOA, camber is likely to be about 6% in a normal scenario, (I could get into a whole conversation about flat plate drag and the need for camber low down, so don't strap you out-haul), but if you have say 6% camber and then bring the mast back 5mm, either via D1's tension or increasing main-sheet/reducing vang, and you do the sum, you will increase camber from 6% to about 6.8%, its about 20-25mm of extra camber. CoL goes from 0.8 to 0.86, but the big change is because it's in the down-flow from the jib, it can stand a much higher AoA, due to the extra camber, most of which, (because you straightening the mast) will be close to the mast, so it will go "bull-nose!   I can't do the maths right now but the increase in Lift from the sail, if it was to be constant across the whole sail, is likely to go from 70-75kgs up around 80-82+kgs and if you then do the other sum, that is a increase of "weight" needed at the edge of the wing of about 15-17kgs, (if the wind stayed constant) but this is all about the wind reducing in a lull, so that increase in camber will to a greater or lesser extent off-set the reduction in velocity of airflow across the main. 

I'm being very rough, there are a mass of competing factors, and I am doping this without referring to any books or data, it's just gut feel.

                                     jB

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Thanks again Julian for an interesting reply!

So basically the pinching mechanism changes the mainsail shape so it can achieve greater AoA before stalling.. is that what you are saying? Also, can't really tell what "bull-nose" means :)

Do battens work the same, e.g increasing lower batten length by a small margin translates to relatively big a increase in camber? Would love to hear more about the battens and their contribution to the mix.

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So you asked why, and I have answered you with what (you are trying to achieve).

I need quite probably 2- 3 days, my wife is dragging me away (quite willingly) for the weekend back on Tuesday.

But most people set the boat for a given wind strength, 80% of people set it for the gust, 15% of the bottom end.

The smart 5% set the boat up so it's multi modal, so exactly what I have explain is going in one direction, a reduction in windspeed.

The flip is equally important, that being a increase in windspeed, and really you only have the mainsheet, and if your really judicious, the jib sheet at a gust by gust level.

This is why it's so important, what boat you sailed before, in the past, people could "cross over" and some still do, but it's become less and less frequent because the level is getting higher and higher.

~~~~~~~~~~~~~~~~~~

Bull nose means like the nose of a bull, lots of camber forward.   Like a old aircraft wing, even an original 747 compare to a 747 400.    Really round at the front!

~~~~~~~~~~~~~~~~~~

49er sails, the sails have significant tension-al material so loading the batten up more and more won't make a whole lots of difference.   Once they are the right tension, then that's sort of it, and that's because its a Mylar sail, Dacron is a whole different ball park, the new 3Di sails will probably be even less responsive to differing battens tensions.

Talk in a few days,    jB

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  • 2 weeks later...

Rambler, probably drop in on you on the way home if thats ok, so it will be Tuesday 29th.

Way up looks a bit action packed, only sailed the boat once so far, not idea preperation!

                 jB

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3 hours ago, JulianB said:

Rambler, probably drop in on you on the way home if thats ok, so it will be Tuesday 29th.

Way up looks a bit action packed, only sailed the boat once so far, not idea preperation!

                 jB

I thought that would be easier for you. I agree, time a stop for a trip up is difficult unless you're stopping over night somewhere and that's before thinking about preparation.

Let me know when you have a sense of a timetable for the trip back.

I'm not seeking to hold you to anything, but at one stage you thought you had a supply of sailing pants in your attic that you might have been willing to pass on for the benefit of the trainees.

PS: I'll PM  you with my phone number

Cheers

Rambler

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I think I may still have some, but they are all L or XL, so not going to suit you ladies.

But let me go look.

Leaving SYD, 18;00 ish, driving through the night Wednesday (23rd, as in 1 weeks time) straight through, probably transiting Balina 03:00 Thursday am.

Driving back on Tuesday 29th, should be there around lunch time.

                   jB

 

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  • 1 month later...

Dear Julian

Could you talk about how to adjust the position of max draft of 49er/FX mainsail? On the jib the trick should be tightening the forestay and the jib halyard to move MDP forward, but regarding the main I'm not sure what to do.

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Hi, sorry, but I have more than a bit on!

Stupid me, too many projects and a few complications.

Let me think, but in it's most basic, 

Down low  -> downhaul and D1's push camber fwd.

Outhaul or lack of D1's moves camber aft.

Up-top -> down haul will pull camber fwd.

Cap-shroud tension will move it aft.

                    jB

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