89er

[JulianB]

Some of you are eager for me to continue, you seen to not like a week or more with no ramblings from a obviously delusional man, so here goes.

I would like to touch on 2 things.

• On the ferry (18teen) last Sunday and also in local banter, some are making comparisons with the Cape 31. I think that is unfair for a few reasons.
• Never sailed against the Cape 31, sure we beat boats that beat the Cape, but head-to-head, it’s never happened.
• They are very very different boats, one can sail the Fastnet, the other is ½ tone, dialed in to do a completely different style of sailing. &
• Neither the Cape or the 89er are anywhere near “wound out” yet, there is a lot left in the tank interms of development and improvement.

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

Far more interesting is the rigging and the extent to which rig tensions dramatically alter the performance of the boat.

To date, I have not touched any of the splices in the rigging of the 89er, I probably need at some stage to alter the splice in the Primary Shrouds, solely because I dropped another 15mm of rake into it, so mast comes back, I probably have lost 5mm of range on the Primaries (and also on the Caps). I probably also have lost 3mm on the D2’s, but so far, it has not affected rig tensions and my ability to manipulate the rig, other then one occasion where we had to use a 6mm pin to give us that bit more tension, rather than the 12mm wide carbon batten that we use.

So the DM20 rigging has been faultless, it probably out performed the Dyform wire if I listened to the comments from Skeeter which is similar weight and near identical rigging.

Yes it shrinks/recoils when you de-rig, but within 5-10mins of re-loading it goes back to exactly where it was before you un-rigged last time.

Further if you actually go measure “wire/Dyform” it’s recoil and recovery are very probably greater than DM20. That has been my experience, given the DM20 I have used and the way I have managed it.

We have no backstays or runners. Caps are M3, Primaries are M5, D2’s & D1’s are M4. Sure forestay is M6, but that’s for idiot factor, it could really be M4 structurally if I wanted to replace it regularly.

In PL, we were probably sailing at 550 – 580 kgs dressed of crew weight [CW], and just about all of us (sportsboats) where carrying 30-40kgs of water, as in it was coming over the decks and ending up in the bilge and no opportunity to get it out.

That’s a tad above target, and as Steve has commented prior, all this has a bearing on RM and SCP and there for foil loading. In PL, conditions where so steady state that we could identify yaw wake and as commented before I am very confident, fully loaded at 7.4-7.6 knts we were inside the bucket.

The other big thing that we found is that CW is it had a very big effect on appropriate rig tensions [RT].

So what we are now doing is trying to target ½ tone of CW (dressed) so that we can dial in RT, and get a play book on what to do when and why.

Our std OP [operating procedure] is to back the rig off after sailing. I think this is just good husbandry and we have to back of the D2’s because we use the D2 chainplates as the lift point for the crane, but we also back off the primaries probably 15-18 turns (per side).

Early in the piece we did leave the rig fully loaded for almost 2 weeks to measure creep in the DM20, I have mentioned this before and we measured it by testing the load in the primaries, and as mentioned before, after an initial settling, there was no discernible creep.

Now, I believe that the “resting” primaries load is sub 100kgs per side.

Base load, on the primaries is 25 on a PT-2 Loogs gauge and that is very close to ½ tone (506kgs)

So prior to going sailing, on the way out to the start or at the dock, one or 2 of the crew wind on x turns until they get 25 on the Loogs gauge. That is about 15-16 turns. What ever it is, and it’s equal on each side, we put ½ that (number of turns) on the D2’s, (from a base of just taught) but more so we ensure that the distance between the ends of the 2 threads (in the turnbuckle) are the same distance apart on both sides, and that becomes our base setting. Still early days, and I have not defined that measurement. I have set of plastic callipers which are super useful, and I have little doubt that before we venture to Airle Beach I will have a bit off alloy made to simplify finding this base setting for the D2’s.

When I talk about base setting, I am more than likely talking about the DW setting. If we have 580kgs of CW then DW will likely be 12 knts, if we have 500kgs of CW then DW is likely to be around 10 knts.

So from there, every 2 knts of wind, we tend to wind the primaries up 1 turn per side and that is true all the way up to say 25knts. Put some numbers around that, 25 = ½ tone, 28 = ¾ tone, 31 = 1 tone.

In PL, we got to 31 and some.

As I have commented a few times, I over speced the Turnbuckles so we can do this on the fly, so I ask, Jack or Alex for another 2 turns on the Primaries, they do it on the windward side while everyone is hiking hard, no backing off! When we tack which may be 30 secs or 3 mins, they put another 2 turns on the old Leeward, now the new windward side, again once everyone is across and hopefully hiking hard.

But what is super important is that if the wind drops, you need to back off the RT.

Both Skeeter and ourselves in PL, between the 2nd last and last race, wound on another turn in anticipation of increased wind. The opposite occurred and Skeeter probably got theirs off earlier, and they certainly hung on (to us) for longer. I was a bit dumb!

I’m going to stop there for a bit, come back to D2’s and Caps and how I go about adjusting those away from base.



jB

 

[Snowden]

• Never sailed against the Cape 31, sure we beat boats that beat the Cape, but head-to-head, it’s never happened.
• They are very very different boats, one can sail the Fastnet, the other is ½ tone, dialed in to do a completely different style of sailing.

Which one? I don't think the Cape can.

 

[pqbon]

Which one? I don't think the Cape can.

I'm pretty sure the Cape can't -- it is built as to near shore standards as a class B.

 

[JulianB]

So as I may have commented, I have never seen a Cape 31 in the flesh, certainly know about them, my mate, Philip Blaum (RSA, VP of WS) has had one for years and he speak highly of them, but to draw comparisons between the 2 boats is a little stupid, especially given they have never meet!

 

[JulianB]

D2’s, D1’s & Caps

We are still too early in the learn how to sail it mode to really understand what we are doing with the mast.

D1’s I always suspected that the D1’s would be set and forget, and so far, that is a lot of what we are doing. The rational is that the D2’s coming in 300mm below the main spreader a) carry a lot of the mast staying factor, b) are a lot further up so are a lot more effective, far greater arm, & c) have a direct effect on the mid section of the mainsail.

So what I had been doing is setting the D1’s so they are i) on CL and ii) just taught once the primary shrouds are wound on, then lock them off.

What I am now doing with the D1’s is i) & ii) but then backing them off a set amount. Presently that amount is about 4 turns, then I lock them off. As an aside they are now firmish, once we back the primaries off but that’s not the rational. The rational is when the primaries are on, that if we chose to use vang, then the lower mast needs some give, it needs to be able to rock fwd under vang load and by letting them go a set amount, we are allowing that and we are also allowing the D2’s to be more effective.

Time will tell if it’s 4 turns (per side) or 2 or 3.25, don’t know. What I do know is if they are tight, then 1) mast is well locked up down low, 2) D2’s are less effective & 3) no where near the sort of control that I want in the lower main.

But at present it’s 4 turns off, ( from taught with 25 on the primaries) and we then lock them off, and they are not adjusted week in, week out!

D2’s I have the same Bluewave Turnbuckles on these as I do have on the primaries so they are very easily adjustable under full load at any time.

Because of the geometry of the rigging, as we come on the primaries, if we do nothing to the D2’s they effectively loosen ½ a turn (per full turn of tightening the primaries,) so in many ways they tend to be automatic in that if we need more Primary tension, it’s because we have more wind, and flattening of the mid main, to stop back-winding and also just to flatten off the main a bit more and generate less drag, tends to all happen with the one action (tightening the primaries).

But with more wind, you occasional get more chop, or you get tide against wind or tide with wind (this is very Syd Harbour and San Fran and Brisbane and Airlie and, and) so it’s not all sugar and roses.

The 1st indicator for us, is the movement of the mainsheet, we find ourselves springing mainsheet beyond the easing of the traveller/hawse.

Let me embellish.

The jib and the upper main (above the jib) are all meeting the same air coming from the same direction so they should be set about the same, Sure upper main can be a little flatter, possibly a slightly lower (wider) AoA° because it’s higher up, possibly more WS, and you really want to be driving off you lower sails more than your upper but ostensibly, they should be the same.

So we tend to set the jib, so the LE tuffs all break at the same time (upper ones 1-2° degrees earlier) and we do that by moving the jib up and down the FS, and we set the Jib Sheet Angle to give us our BS that we are targeting and then the person with the dummies stick steers to those Jib tuffs and to a target BS. To get the upper mainsail to set appropriately we need a fair bit of mainsheet tension especially with a square head, and so that we can maintain the mainsheet tension (which the fine tune is 8:1) we then set the hawse angle, so it may be down 100mm and that in turn = 1° which may not seem a lot, but dropping 1° in 8° (jib sheet angle) is 13% so it’s not to be sneezed at!

And if by doing that, we can maintain mainsheet tension to +/-30mm which in turn means that the top of the mainsail, above the jib is probably “barn dooring” +/-2° then that is probably acceptable.

Barn-dooring means the whole top of the main moves as one, like opening or closing a barn-door as opposed to it twisting off and fattening up in the process.

Sure there will be a bit of twist, and you want that also, what you don’t want is the fattening up as you ease the mainsheet.

If your easing the mainsheet its because you have too much power, the last thing you want is for the top of the main to go from say 8% camber to 12% camber.

What you do want is the whole top of the main to blade off as one “barn-door” movement.

That is the real beauty of the squarehead mainsail geometry, that is what makes it so good. If you have a Maka, or a Lecte or a Kelly (and those are the ones I know who “get it”) and you have a general idea of what is happening then the square head, just makes it so much better, it’s unbelievable.

When we went from the pin head 49er main to the squarehead 49er main back when we barely knew what we where doing, the squarehead with more area, same crew, was so much easier, so much more simple and so much more rewarding that it became a chalk and cheese decision.

And I think what I have written above is the guts of that rational.

I just had one of those moments. Had to go back and Italic that, that’s a gem!

It’s one of the reason I love doing this stuff.

Also best place to hide something is in plain view! (hehehe )

Back to D2’s.

When we see that mainsheet moving +/-50mm then we know we need to do something.

On DP the 2 primary mainsheet block “engage” by that I mean they come so close its really easy to judge how much mainsheet tension your running. That is very deliberate, we alter the hawse length to make sure that this happens.

The other thing that happens if you ease the mainsheet say 100mm (+/-50mm) is you start altering FS tension, and again , last thing you want when you spring the mainsheet is the FS to over loosen because then you get FS sag and the jib rounds up.

Learnt this lesson on the Farr40. You tend to use mainsheet to set the mainsail twist and depth, and you then bring the backstay up so if you dump the main, the backstay “catches the mast” as it goes fwd which a) flattens the main and b) stops the jib rounding up excessively.

I do remember on the AAMI’s back in the early to mid 90’s we had a sock around the boom so the mainsheet would not drop down and gorot the skipper (me) and we put a black mark on the mainsheet so basically when that mark started to disappear inside the sock, time to de-power, when it started being 100mm infront of the sock, time to power-up.

Same-same but different!

D2’s, getting side tracked, our principal de-power and power-up tool is D2’s, one to 2 turns on or off the D2’s completely alters the whole lower main, (it also alters the upper main at the same time) so we will alter the D2’s by 1 turn, and the effect is dramatic and instantaneous.

The other tell-tale sign is back winding of the lower main. If you are confident in your jib trim and jib-sheet angle, and you start getting excessive backwinding (a bit is OK) then easing the D2’s will flatten the lower main and reduce drag.

Yes dropping the traveller/hawse more than about 200mm/2° exacerbates lower main backwinding so we are mindful that down traveller has it’s limits, but again, the ease with which we can alter the D2’s makes that pretty painless.

Caps;- As soon as you firm the caps you loose elasticity in the mast! We have approx. 70mm of movement in the caps, in that we can tighten/loosen them with one string pull. But we are mindful of watching the leeward cap, because as soon as it goes firm, there goes some level of responsiveness in the mast.

But, last Saturday, pretty steady wind, we had already dropped 2 turns of D2’s, lower main was very flat, so we started to increase Caps tension. The initial action of this is to bring the masthead to windward, and that’s not a bad thing because of instead of a gust driving the main and the resulting bend of the mast in the direction of the AWA (22° of CL to leeward) it can only move the mast aft, along the CL, that means the initial action of the Caps is to increase mast stiffness and also increase the amount to which the leach stands up, but the squarehead then kicks in and blades of, so you get what used to be called bias movement that flattens the head off.

Sure, as it got fresher and fresh, and we increased tension more and more, the Caps start actively increasing mast bend and dare I say “artificially” flattening the main.

Couple of minor points here, I use M3 DM20 for the caps.

If I was brave, and maybe in the future I will go for M3 SK99 or even SK78 caps, same UTS but a lot more yield, so the Caps, could become far more useful.

Pretty sure that is I went to say M4 DM20, I would kill the whole game.

Pretty pics from the weekend

To be fair to GT, this is right after the finish, so yep, 20° of heel, and the shot before it is right before the finish, as again we are slacking off.
But keeping the boat flat is a full time job, and as a skipper, the crew get a bit over your insistence of keeping it flat.

jB

 

[JulianB]

Although I alluded to reductions in foil tip loss, perhaps this would only be relevant in centreboarded boats. A bulbed keel may not see much of it, if at all?

Sidecar, this came up yesterday, it would be interesting to work out how big a bulb needed to be to be an effective end-plate.

Some where in the back of my brain Dad is telling me 2 thicknesses so if the tip of my fin is 30mm thick, I need to extend out 60mm, obviously more front and back.

so 60 + 30 + 60 = 150mm

My present bulb is 160mm Dia, about 1.2m LOA.

These (2 are mine, 2 are Tubbies) are 120mm Dia and 0.7m long. They weight 32kgs each so a pair is 74kgs. Thinking is probably can't go much smaller, infact possibly pushing the lower limit, but we can carry 20-30kgs in the tip of the fin to compile with ISO Reg 3 and we can feather off the tip so the PD/lift is reduced.

Be interested in your's and anyone else's thought on how big dose a bulb have to be to effectively end-plate???

jB

 

[Sidecar]

Judging by your endplate prototypes on top of the Wing‘s mainsail, perhaps very little at all is necessary.

Effectively, what you are trying to do is to achieve a required keel RM (for ISO standards) in as short a keel as possible (to minimise heeling moment) to generate the necessary side force resistance whilst also having the least frontal and surface area drag.

Stretching it a bit, but effectively using Scheel keel Principles. I don’t know how much hydrodynamic research went into his patent, but if you wade through it, his “optimum” ratio between keel thickness and thickening/bulb width seems to be 2.144, so close enough to your father’s thoughts on the matter.

I would have thought all other things being near enough equal, the cross section, plan profile/ side profile of your torpedo bulb is far from ideal for reducing tip induced drag. Which is why, way back in your thread somewhere, I alluded to the cross section of an Me 262 fuselage, ie shark shaped triangular.

It will take a few days, but as an intellectual exercise, I would be happy to draw up a suggestion for a ~ 74 kg lead bulb if you are curious.

My boat doesn’t have a keel, and relying on just the two rudders, the boat can’t sail to windward and is unmanageable (don’t ask me how I know). But with a chine runner on I can go to windward pretty well with good speed (~10-11 knots in ~12 knots TWS). You have seen the video. The runner being a tiny fraction of the frontal area and half the surface area of the original 2m x 0.4m x 0.04m (bottom half elliptical profile) centreboard.

It wouldn’t work on your boat because it is too wide and too shallow.

 

[sheeting yarns]

Sheeting Yarns, the moth you are showing is a Mach2, got to be 10 years old with the wishbone and the alike. All the moths at this years RYA show, had very sharp TE/HB angles.
Also, a moth probably has down flow (because its heeled to windward) so there is little or no point in a end plate as it aint going to help , only hinder.
Possibly why they have got very thingy about the cuff at the bottom, because the flow is rotated downwards across the whole sail. Windsurfing is another case in point.

jB

The only reason they are not rounding the gaff batten leech is the manufacturing cost. It is not trivial to add reinforcing which needs to be strong enough to stop the head and top leech from fluttering where the radius occurs and the batten pocket finishing is also more complex.

 

[JulianB]

Do any sort of vector, there is downward span-wise-drift across a Moth sail.
Not sure any other boat has downwards span-wise drift.
And all these boats have sharp TE/HB angles, not sure of the reason, not sure it's relevant, have not put much thought into whether it should be rounded or sharp, but I assume plenty of others have.

WRT putting a end-plate on the top of DP's mainsail, can't see the connection!

 

[DickDastardly]

So as I may have commented, I have never seen a Cape 31 in the flesh, certainly know about them, my mate, Philip Blaum (RSA, VP of WS) has had one for years and he speak highly of them, but to draw comparisons between the 2 boats is a little stupid, especially given they have never meet!

There’s one sailing outta MHYC…

 

[JulianB]

There’s one sailing outta MHYC…

I will look Wednesday

 

[JulianB]

Sidecar, you seem to be good at this stuff and I would love a 2nd opinion.

I have commissioned a new fin because I want to try a flexible TE fin.

I have done this a few times before, and it’s worked.

So this is a rough approximation of the section of the Fin (black)

And Red is where it will end up if I engage the flexible TE process.

What would you (or anyone else that would like to take a stab at it)

• think my CoL would go from -> to (assuming 2.5° AoA)
• Would there be a reduction in surface area/span possible &
• What is the AoA variation/reduction.

I have taken some stabs at it, in the past, just interested in getting a 2nd, 3rd of 4th opinion.

jB

 

[Sidecar]

Julian

I am no expert and have little experience on foil numbers. Sadly Tom Speer is no longer with us, he would have advised you in a heartbeat.

My guess at the numbers:

Symmetrical foil:
AoA: 0.0 degrees, CoL: 0.00. AoA: 2.5 degrees, CoL: ~ 0.27.

Asymmetric foil:
AoA: 0.0 degrees, CoL: ~ 0.10. AoA: 2.5 degrees, CoL: ~ 0.45.

You would get higher CoL numbers on the asymmetric condition if the front half was asymmetric as well, maybe ~ 0.30 to ~ 0.60 for the respective AoA’s.

If you are going to the trouble of making a flexing foil, maybe it would be a waste in terms of tip loss/drag when the trailing edge moves off centre due to the circular bulb sections? Perhaps you also need a bulb which has a flat top aft? I will add a suggestion to the bulb info, which is nearly done.

I will send you some AutoCad files (or would you prefer DXF?) for your perusal and comment before it goes public.

 

[JulianB]

Julian

I am no expert and have little experience on foil numbers. Sadly Tom Speer is no longer with us, he would have advised you in a heartbeat.

My guess at the numbers:

Symmetrical foil:
AoA: 0.0 degrees, CoL: 0.00. AoA: 2.5 degrees, CoL: ~ 0.27.

Asymmetric foil:
AoA: 0.0 degrees, CoL: ~ 0.10. AoA: 2.5 degrees, CoL: ~ 0.45.

You would get higher CoL numbers on the asymmetric condition if the front half was asymmetric as well, maybe ~ 0.30 to ~ 0.60 for the respective AoA’s.

If you are going to the trouble of making a flexing foil, maybe it would be a waste in terms of tip loss/drag when the trailing edge moves off centre due to the circular bulb sections? Perhaps you also need a bulb which has a flat top aft? I will add a suggestion to the bulb info, which is nearly done.

I will send you some AutoCad files (or would you prefer DXF?) for your perusal and comment before it goes public.

Hi Rob, thanks a bunch, your numbers/assumptions are higher than mine.
Front 1/2 is structural, so it ain't moving and it has to tack (obviously) so just trying to get the best of both worlds.

I will punch 0.45 into my foil program see what size it comes out at. Be nice if I can reduce the Span.

igs. stp. dfx. 3dm. I can make sense of any of them.

Top of the bulb was going to have a flat to accommodate a) necking laws and b) TE movement.

 

[Sidecar]

Front 1/2 is structural, so it ain't moving and it has to tack (obviously) so just trying to get the best of both worlds.

Understood that, I was just explaining why I thought the CoL’s for the asymmetric setup weren’t very high. I am not surprised that your assumptions are lower than mine, you know a lot more about this stuff than I do….

 

[sailhmb]

Interesting design mod. Is the TE flexing feature passive or active?

 

[JulianB]

Sidecar, this is me playing (@ 4am, can't sleep)

Red is what I am thinking of, the plot underneath is a e67-il, it's the closest I can find. Both 12% sections yad yad yad.

These are the plot.

So my cautions are, these are aerodynamic, we are hydrodynamic.
As you pointed out, no asymmetric-icy in the front 1/2, so I am assuming a huge discount on lift.
When I went digging for something with similar front 1/2 much closer to your 0.45
My RN calculator says I'm close to 2m, also finding that hard to believe.

I'm assuming 20c water, yad yad yad.

This is a CL - Alpha plot of a section sort of close to mine (symmetrical) so your near spot on at 0.27 (at 2.5°)

CD - Alpha is likely to stay the same at 0.005 either sections, so the big advantage is a possible smaller fin and a significant reduction in yaw drag.

Bottom line, is your likely to achieve a 150-160% increase in CoL by doing this if we can minimise TE drag.

If a 49er is 4.5% ( yaw drag, and I need to go back and check that) the 89er is going to be 120-150% of that, so say 6%. Hydro drag of a 49er at 7.5knts is 44% of the whole package, so I'm guessing the 89er it will be a bit greater than that, say 50% then a 3% reduction is massive, huge (if we can negate yaw drag).

Could really be fun to do this.

As I may have commented before, I have already done this, but never had 1st hand feedback, it's always been at arms length, 1st time was in Germany.

Really like to play myself.

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

sailhmb, let me get my head around if I am going to do this, (I really want to) then I happy to get into how I plan to do it.

​

Need to do a few experiments, and then I need to be brave.

I also need to do ISO reg 3 with 74kg bulb and make sure the boat comes back up "long" before Airlie because that is going to get factored into this also.

 

[neuronz]

Julian

I am no expert and have little experience on foil numbers. Sadly Tom Speer is no longer with us, he would have advised you in a heartbeat.

My guess at the numbers:

Symmetrical foil:
AoA: 0.0 degrees, CoL: 0.00. AoA: 2.5 degrees, CoL: ~ 0.27.

Asymmetric foil:
AoA: 0.0 degrees, CoL: ~ 0.10. AoA: 2.5 degrees, CoL: ~ 0.45.

You would get higher CoL numbers on the asymmetric condition if the front half was asymmetric as well, maybe ~ 0.30 to ~ 0.60 for the respective AoA’s.

If you are going to the trouble of making a flexing foil, maybe it would be a waste in terms of tip loss/drag when the trailing edge moves off centre due to the circular bulb sections? Perhaps you also need a bulb which has a flat top aft? I will add a suggestion to the bulb info, which is nearly done.

I will send you some AutoCad files (or would you prefer DXF?) for your perusal and comment before it goes public.

Lift curve slope rule of thumb is about 0.1 per degree of angle of attack if I recall correctly. Going asymmetric mostly shifts your angle of zero lift so creates an offset.

The only way to create a real gain (read reduction in area) here is if the asymmetric section has a higher permissable coefficient of lift while staying inside the drag bucket.
Since your righting moment does not change the keel actually needs to produce slightly more lift as you are unloading the hull. However this is probably offset by the slight increase in speed since producing lift with the hull is draggy. There are some aerodynamic benefits as well, but bottom line is if the asymmetric section does not have a wider drag bucket you cannot reduce area since you need to produce the same lift and if you cannot tolerate a higher lift coefficient from a drag point of view you end up with the same area.

 

[Sidecar]

Dormoy details below. Also have a look at Fage & Collins and N-9 sections

 

[Sidecar]

I think you need to go back to the beginning Re keels/bulbs and ISO RM.

You need to tip your boat over and determine (doesn’t matter which bulb you use and determine the exact RM you need to pass ISO. A heavier bulb will need less righting arm than a lighter one. That will give you an idea of the foil span you have to play with, all other things being equal.

If the keel was bulbless, the accepted practice is to taper the span profile towards the tip and reduce the %age chord thickness with it to minimise tip drag loss. If you have a bulb which already should be doing this, and better, then you no longer have to taper the profile or reduce the %age chord thickness? Which means more foil area, more lift, which should mean that you can quid pro quo reduce span, down to the righting arm limit.

Looking at the foil sections on line, it struck me that, up to some point of course, the thinner you can make the %age chord thickness, and the blunter you can make the forward sections, the better the CoL/DR to do the job..

Over to you.