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Why do the eighteens use square headed rigs? Some of them even have the aft corner of the head (is there a name for the fourth corner created by the square head?) above the mast. I can understand the automatic gust response, but I’d think that you’d lose leech control, and it’s certainly farther from the optimum elliptical wing shape that the high roach pin-headed rigs have, like on the older 18’s, 29ers, and older IACCs

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More sail area to fit under the box rule. With the wind shear, more twist isn't an issue. The sails respond well when matched with the rig properly. They do, however, have a lot of drag and load up quite a bit when the boats are sub planing speeds. I think square head sails require better mast/rig tuning. The twist is controlled more with the cunningham and mast bend than the boom vang.

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Why not a longer boom? I’ve never heard of a foot length requirement?

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The top of the square top may or may not be above the top of the mast - remember there is a lot of bend going on creating an illusion.... or at least that was its own very convoluted discussion when the 18';s went to the extreme end of the squaretop several years ago. 

My understanding from older threads and general discussion, i'm not an engineier, is that: 1) aspect ratio is king. The lower the aspect ratio, the more efficient the air foil. By making the leach profile vertical, you help to increase the aspect ratio. 2) gust response - a square top can help with depowering a little bit as the gust hits initially. And of course, sail area is sail area.  

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Also, it seems like the gust response would be limited if there were sufficient batten tension

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my understanding was that they needed to measure in under the mast tip but once rig tension got put on thing got a little creative

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Connor, the 18s are built to a rule that forces that to happen. Beware. A boat built free of the rule would not benefit from that extreme.
Look at lots of other classes but you need to read the rules too. For example: IC, A class cat, moth, ufo etc.

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Yup. If mastlength not restricted, the squaretop would be more or less parallel to the waterline. They are good for gust response/tolerance when fully sorted.

Luff round and batten stiffness needs to be accurate though.  e. g. 5mm change in luff curve at the 7/8 height would be very significant.

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The masts are measured, the sails are not. Just getting max area from the legal mast height.

The one big regatta has been getting later and later in ths season when the winds are lighter, and its always on Sydney Harbour where headlands and traffic make the winds even more variable, so everyone has been making the sails bigger and bigger to maximize performance for the JJs.

When they get a big blow early in the season  many crew struggle with the small rig as its bigger than they need in a solid 25kt NE or Southerly.

 

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11 hours ago, inebriated said:

http://bethwaite360.com/blog/

read this from @JulianB

good shit

Haha a GP18 faster than today's foiling moth? Bullshit. Was not long ago that the JB was telling everyone that squareheads were just fashion and were wrong. The peak of his belief that sail area = bad = drag was designing rigs for an 18 that were about 20% smaller than everyone else. Guess what? Hopeless! Lots of his stuff is interesting and some of it is right. but woven into it is complete bullshit.

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Nice work Tinga!

Julian quotes some complete nonsense (in particular) about his b18 setting the 'course record' for the sydney ne 18 course.

Just ignoring that was in a n/nnw wind. Etc etc. We didn't call his old man Frank the Wank for nothing, either.

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37 minutes ago, Frogman56 said:

Nice work Tinga!

Julian quotes some complete nonsense (in particular) about his b18 setting the 'course record' for the sydney ne 18 course.

Just ignoring that was in a n/nnw wind. Etc etc. We didn't call his old man Frank the Wank for nothing, either.

i guess you know more than him then?

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Inebriated,

No comment, really.

But i probably know enuff.

Just trying to help sort the gold from the dross.

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2 hours ago, Frogman56 said:

Nice work Tinga!

Julian quotes some complete nonsense (in particular) about his b18 setting the 'course record' for the sydney ne 18 course.

Just ignoring that was in a n/nnw wind. Etc etc. We didn't call his old man Frank the Wank for nothing, either.

Charming.  Have you made a positive contribution to sailing?  Would live to hear all about it.

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Yup, tis charming. But then so are (were) Frank & Julian!

But no brochure or bullshit from me.

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Just now, Frogman56 said:

Yup, tis charming. But then so are (were) Frank & Julian!

But no brochure or bullshit from me.

please explain it seeing as we have no brochure

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If you required a dissection of Franks publications that would be possible. But lengthy. Would three major carveups suffice?

That might be quite entertaining...?

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2 hours ago, Frogman56 said:

If you required a dissection of Franks publications that would be possible. But lengthy. Would three major carveups suffice?

That might be quite entertaining...?

nah, wouldn't mind an explanation of what you've done for the sport though

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Perhaps just 40+ years of participation, across skiff, od keelboats, offshore. Designed and developed mainly above the deck. Coached, mentored a few. 30 cat 1s. No injuries! Sufficient?

(Oops cupla guys with broken ribs offshore)

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I think the Bethwaites generally know what they’re talking about- they’ve designed some bloody good boats 

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Just a thought, has anybody ever put an end-plate on the top of a square top sail?

From what i've read about aircraft wings they are used to reduce drag & increase efficiency. Would that work on a sail?

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The square top on a fractional rig works a bit like an endplate.

The more nearly vertical main luff above the headstay reduces upwash to some degree. At 'design windspeed' (i.e. full hike and slightly flattened) the highest part of the squaretop should then be a ~ zero aoa, i.e. aligned with apparent.

So the aero load tapering and the diminished upwash both act to to reduce the tip vortex.

Capiche?

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3 hours ago, Martin T said:

Just a thought, has anybody ever put an end-plate on the top of a square top sail?

From what i've read about aircraft wings they are used to reduce drag & increase efficiency. Would that work on a sail?

They’ve tried it on the jib

look up 18 ft skiff wing jib

they said it goes faster but with harder moding 

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What about an end plated boom? Not the deck end plate, but a separate winglet attached to the boom?

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That would look like the A class mains. But hard in crewed boat to tack or gybe!

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Frank the wank by some who has done what?  

It's pretty hollow unless you put up some credible counterpoints of view, and particularly gutless given he is not here to defend himself!

Re Square Heads, I was there when Chris Cairns initially was developing them and what he was doing was impressive (with the Tornado).

Fashion statement probably has to do with the ridiculous sized ones being sported on the Sydney 18teen at present, and the Kiwi win proves the point, their (Kiwi) ones where smaller and far more efficient, so the Sydney ones are a fashion statement and are ridiculous and oversize.

Personally, being with my father and watching my son Harry and Simon Watin taking a 49er up-wind sporting a square head after having Dad do what he did best, hard empirical testing, and the resulting refinement, to the point where it did everything near perfectly was a moment I won't forget for a while.   The overwhelming adoption of the square head on the 49er by the sailors, demand that sent Southern Spars into a tailspin is all the endorsement I need. Some feeble words buried deep in Sailing Anarchy, again gutless.

Re doing the NE course in under 50 mins, there are 2 magazine articles, Kazi (Japanese) and Aust Sailing both recording the fact, plus Bob Ross referred to it in this years JJ Giltinan event book, again.  As to it being an N/NNE-er, my recollection was one long gybe from the Beashal Bouy into Talor bay and an equally deep gybe, so deep we had to get the kite off early to make the Explosives #2 mark off Clark, that would suggest a near perfect NE-er and it was a heat of the JJ Giltinan, so comments re N/NNE wind don't stack up and do the race officials a huge disservice.    And wind direction is probably irrelevant anyway, still plenty of tacks and gybes.   

My strongest memory is Dad came up after the race and gave me a huge hug, and that was it!   What normally happened is he told me 10 things I could have done better.    Not a word that day.

Re foiling moth or MC32's doing the course in that time.    I have dined well on people who have attempted to better the time, and that includes some very notable names.  I am unaware of any who have done so.    If you know someone, then lets all hear about it.  It will happen one day, but with the rise of the Bay to Bay and the Cenglomiglia, the Bandor, etc etc, that iconic course and whatever the record stands for is less relevant.         

Just for the record, these were not GP 18teens, these where B18 Mk1 hulls, GRP (as in Glass) laminate, gelcoat, foam core with carbon cross in the hull, Alloy lower mast, GRP topmast, 17ft wings.  Yes they sailed in the GP, but this boat did not, we did not sail the GP that year, we did it in 1990-91, and 1992-93, this was not the AAMI most of you know, it was in fact All-States.   The GP 18teens where a few years later.   Yes they all had pinhead rigs.

Remember this was January 1992, not sure moths where even foiling then, what would have happened if the GP 18teen continued who knows but making comparisons with 2000(s) Moths with 1992 18teens stretches credulity. 

 

 

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22 hours ago, Martin T said:

Just a thought, has anybody ever put an end-plate on the top of a square top sail?

From what i've read about aircraft wings they are used to reduce drag & increase efficiency. Would that work on a sail?

My understanding is that the big challenge is the need for it to operate on either tack. These things have pros and cons, but you'll notice they are all asymmetrical. a sailboat rig needs to be symmetrical, so there has to be an almost useless drag creating plate on the wrong side as well as the useful one on the right side. Then when you add to that that most classes will require them to be measured in as sail area and factor in the effects of twist then it seems to me it will take someone very clever indeed to make it work.

In addition there's much lower hanging fruit at the other end of the sail which is commonly an aero disaster area. Even that's subject to tradeoffs. Convinced about FBs evaluation of the "cuff" at the bottom of the 49er sail, I made a detachable one for the bottom of my IC rig to clean up that area and get the aero interactions. It lasted about two races. It meant that I couldn't see the jib clew, which in turn completely psyched me out about jib settings and trim, which I regard as crucial. It so distracted me from the task of sailing the boat better that it seemed to me it was doing more harm than good to my race performance. Probably that could have been addressed somehow, but I never managed to get round to doing it.  

Of course we're now seeing a lot of attention to that area on Moths, and previously on the Cs.

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21 hours ago, Frogman56 said:

That would look like the A class mains. But hard in crewed boat to tack or gybe!

I meant as in a boom fitting, not the deck end plate on the A cats and moths

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20 years ago, we played around with a fence, 2nd top batten, use a lycra type material with a bit of shock cord, so it popped up on the windward side, laid flat against the sail on the leeward side.   Jim's comment re cost/benefit equation ring true.  On a skiff sailed flat, (which we where doing it on) not much point, on a yacht or a dinghy, sailed on a heel, more benefit.    With square heads, it's easier to do.   We have been playing with end-plates on square head for 2 years now, interesting results, but to date, not conclusive. 

What has really blown us away is the effect of the cuff luff and the disproportionate increase in pressure differential low down.   Again, Jim's comment re cost/benefit rings true, huge gains to be made at the bottom of the sail, what the A-Class, Moths and AC boats are doing is impressive and relevant.   The old Park Avenue Boom, that was 1930, there's a photo in Marchaj, as mentioned above, is pretty extraordinary, but given that boat (Enterprise) sailed well-heeled, it probably was not as effective as it could have been.

Going back to the cuff-luff and 49ers, if the boat is sailed flat, and the main sheeted hard in there is considerable downward flow (counter span-wise drift) but as soon as you spring the sheet 50-100mm it disappears completely, the whole rig cleans up.    Stumbled across this by accident, but it's significant!

 

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3 hours ago, JulianB said:

20 years ago, we played around with a fence, 2nd top batten, use a lycra type material with a bit of shock cord, so it popped up on the windward side, laid flat against the sail on the leeward side.   Jim's comment re cost/benefit equation ring true.  On a skiff sailed flat, (which we where doing it on) not much point, on a yacht or a dinghy, sailed on a heel, more benefit.    With square heads, it's easier to do.   We have been playing with end-plates on square head for 2 years now, interesting results, but to date, not conclusive. 

What has really blown us away is the effect of the cuff luff and the disproportionate increase in pressure differential low down.   Again, Jim's comment re cost/benefit rings true, huge gains to be made at the bottom of the sail, what the A-Class, Moths and AC boats are doing is impressive and relevant.   The old Park Avenue Boom, that was 1930, there's a photo in Marchaj, as mentioned above, is pretty extraordinary, but given that boat (Enterprise) sailed well-heeled, it probably was not as effective as it could have been.

Going back to the cuff-luff and 49ers, if the boat is sailed flat, and the main sheeted hard in there is considerable downward flow (counter span-wise drift) but as soon as you spring the sheet 50-100mm it disappears completely, the whole rig cleans up.    Stumbled across this by accident, but it's significant!

 

What causes this? The cuff only seems to clean up the gooseneck area, and the open back of the cuff surely causes minor vortices. Perhaps if the back end of the cuff was sewn together?  What happens when the cuff is distorted by the boom angle?

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This ended up being a topic of conversation between Dad and some eminent people at MIT.

I was busy holding everything together, and it was Dad's golden time, so the details are sketchy but the gist is, a considerable amount  of the pressure differential, the lift, be it a bird, a plane, a rudder in the air or the water or a sail, happens in the front 25% of the section.    So by extending the sail downwards in that area sets the sail up so the "counter span-wise drift" in the case of a skiff, downwards flow from the high pressure directly above the foot of the sail, can't escape, so it has to flow horizontal across the sail.   It goes without saying that the better you end plate it, so vertical fences, or bring the sail all the way to the deck for as far aft as you can the better you will end plate it.    Get an effective end-plate, and you double the efficiency (CoL) or 1/2ve the drag (CoD) but in most cases a combination of both.     This is sometimes refereed to as doubling the Aspect Ratio [AR].    That part is pretty clear.   What we also knew is the pressure differential of a skiff tends to be pretty low compared to say a Cat.   Its pretty light, largish sails, so the kgs/m-sq is not that hi,  about 3.6kgs/m-sq, where as a cat and the AC boats are probably running double or triple that.     So it works really well on a 49er or a 29er, especially when you have sprung the sheet.   On a A-class you probably need to seal it a whole lot better.    Moth runs pretty low Kgs/m-sq also so they can probably get away with a LE cuff and thats a good thing because tacking the boat is pretty important.    Jim's comments re cost/benefit ratio.   Ergonomics trumps sail efficiency often.

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A bit off -topic perhaps , but does anyone know what happened to the squarehead main made to fit laser masts that was marketed by intensity sails (for only a couple of months, apparently)? Was going to buy one for my franken-force 5 but when I went back to the  Intensity sails website it had disappeared. Did it just not sell well  or did they encounter some legal issues? I really wanted to try it out.

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Wouldn’t the batten tension have to be really low to get the automatic gust response? It seems like the ‘gust onslaught’ that FB talks about wouldn’t be powerful enough to luff the top if there was sufficient batten tension, but if there wasn’t as much batten tension it seems like useless weight/drag/sail area aloft. 

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8 hours ago, edward mason said:

A bit off -topic perhaps , but does anyone know what happened to the squarehead main made to fit laser masts that was marketed by intensity sails (for only a couple of months, apparently)? Was going to buy one for my franken-force 5 but when I went back to the  Intensity sails website it had disappeared. Did it just not sell well  or did they encounter some legal issues? I really wanted to try it out.

Intensity is intensely reponsive to emails. Just ask. 

 

edit- it's still there

http://www.intensitysails.com/insapohesafo.html

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In a pinhead rig, like the 29er, its the combination between the mast bend and the rate of increase of the cord that's important.  Get that right and batten tensions are critical to sail depth but very 2ndly to de-powering.

With a square head rig, (49er, 18teen, etc) the top to battens are critical in terms of stiffness, also referred to as Euler Crippling load, so it's more batten stiffness than tension that is key.

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Julian, I think you mean Euler Buckling, which defines the " critical load" for column in compression.

as you point out, there were lots of ways to pursue getting the mainsail to react properly for a given stability of boat. When the 18s "only had two rules" the rigs could get taller when people wanted to add area, with limited rig height, you do stupid things just to get more sail area. Big flat sails being better than small full sails, the advances in materials and sail design make these things possible.

The second point is that there are many variables which combine to skin this cat. I learned a great deal about how to optimize rigs from an old guy named Lou Whitman, who built very nifty pre-stressed wooden spars that could be induced to flex at different rates depending on rig tension and luff tension.  He would plane off parts and add different woods to tune the spar to a sail cut, modify the sail cut and then change the mast again.  He was something like 75 years old when I met him, and it took me about two years to ever beat him upwind. He wasn't genoeous with his technique and  acquired knowledge, and was harshly critical of my attempts to learn and experiment. Things like "we tried that in '53 and it was a failure," " save yourself some heartache" and my favorite," you're trying to give us the benefit of your experience, but you haven't got any!"  But I did figure it out. The problem was how to achieve what he was doing with endless tweaking of sails and masts with stuff I could repeatable build and sell. So we played with panel rotation, roach profile, hounds height, and cloth specification to get sails that worked .

the Swedish IC team all built their own sails. They had a ritual of progressively pulling on downhaul vang, mainsheet and rocking the boat in the dolly. There was a particular way the sail " turned inside out" that was indicative of how the sail would twist and de power and when. If it wasn't right, adjustment to battens, seams and stitching followed very much in the mode of what Julian describes. One design sailors don't do this work. They get "tuning guides" from sailmakers and coaches and slavishly conform to them. It was a different world, which was lots of fun.

Square head is not magic, it is one of the various roach profiles. A Class cats have gone back to pin heads because they want to keep the center of pressure low with the stability losses inherent with foiling. 

Various attempts to end plat the tops of sails have been tried, it is hard to get right, and if not right, it is weight and drag right where you want it least.  Things like this take lots of effort and time.

SHC

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Steve, we agree, wonders will never cease.

Buckling vs Crippling, same dude, 17th century, us antipodeans ain't the same as you merican's.

And ain't that a blessing both ways!

Hope you well, we probably should have a drink sometime in the not too distant future!

    jB

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5 hours ago, Dex Sawash said:

Intensity is intensely reponsive to emails. Just ask. 

 

edit- it's still there

http://www.intensitysails.com/insapohesafo.html

I've been using one of Intensity's "Power Head" square-top Laser sails for a couple of years now and love it.   Shape holds up and has plenty of power.

 

 

 

 

 

 

 

 

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Never heard "crippling" in that context, where as " buckling out of column" is something that has crippled me on  more than one occasion.

Things aren't good here in the Home of the Brave.  Episode 5 " The Assholes Strike Back....." is kind of how I see it.

SHC

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On 4/1/2018 at 3:08 PM, Connor.kainalu said:

I meant as in a boom fitting, not the deck end plate on the A cats and moths

Slice the crew instead of merely knocking them about?

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On 01/04/2018 at 11:33 PM, knobblyoldjimbo said:

Wasn't that the Park Lane boom as used on J boats in the olden days? 

I always felt the Park Lane boom was a bit small to get much benefit in proportion to the sail.

Julian's comment about pressure differential is interesting. Its a concept I've never thought much about, but it makes complete sense that different boats vary. The question is why, and also how much do sloop rigs change things. There must be significant differences between a sloop rig where the foredeck endplates,  one where the foredeck is a bit more open and the worst case, the catamarans. I wonder if Cat folks are considering whether their chute/snuffer things have potential for endplating jibs.

The other thing I'd be interested to hear opinions on are the weight tradeoffs. When you look at those extreme 18 rigs it seems to me that you've got big heavy battens and stiffer and thus heavier mast up where it does most harm. Are the numbers likely to be significant? Trouble is the 18 rigs are now as rule influenced as anything on the planet, there aren't many pure design rigs left - if indeed there can be such a thing.

It would be interesting if someone could figure out a way of closing the deck gap that could be opened out for manouvers/handling. After all there are classes where the one design sail no longer fits the boat due to increasing mast rake, so they have to release the kicker to tack, so presumably releasing something else to tack would be feasible...

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Once again I get pedantic.

It's a Park AVENUE boom.  Named after the famous Park Avenue in New York City.

As a 9 year old, my mother was walked down Enterprise's Park Avenue Boom holding Starling Burgess' hand.  There were probably advantages to the set up that were more significant than the supposed end plating. For example getting enough shape in the bottom of the mainsail, something that was hard to achieve with the materials of the day.

It makes intuitive sense to get mainsail luff behind the fattest part of the jib. But as all development classes, short of the classic skiffs, have sail area restrictions, you have to determine if area in one place is more effective than area in another.  I have always worked on the premise that area up high worked harder than area down low. After all the wind aloft is stronger and force varies at the difference of the square, so if I had area to add, i do it on top.  So if I had to measure the cuff, it would take some real convincing not to add that area to the top of the roach. Nevertheless, on all my IC sail plans, the tack of the main is as close to the deck as I can arrange.

On the other hand, the in PANAIR results we saw running the C Class wing sealed to the trampoline sealed to the hulls showed such significant reductions in induced drag (in the order of 30%) that i felt it couldn't be ignored. There were two other benefits.  The center of effort lowered more readily in response to twist, making de-powering by twist more effective.  And the vertical force under the leeward side of the trampoline went from less than nothing to being able to pick up half the weight of the boat.   I really though this was too good to be true, but the direction was clear. Never got a satisfactory seal in order to see if it really worked.

Dave is right, though, you have to REALLY seal the foot to get the advantage.

SHC

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1 hour ago, Steve Clark said:

[snip] So if I had to measure the cuff, it would take some real convincing not to add that area to the top of the roach. Nevertheless, on all my IC sail plans, the tack of the main is as close to the deck as I can arrange.

On the other hand, the in PANAIR results we saw running the C Class wing sealed to the trampoline sealed to the hulls showed such significant reductions in induced drag (in the order of 30%) that i felt it couldn't be ignored.[snip]

My imaginary dream IC rig had a level deck back to the front of the sliding seat and both jib and the front part of the main deck sweeping. Unfortunately I couldn't figure out a way to implement it without hideous compromises in other areas that killed more than was cured.

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So why, in classes that aren’t as rule restricted (as in one designs or ORC maxis) are square heads becoming increasingly popular?

Also, I think people aren’t really sealing their main feet to their booms is because of that pesky “spar area will be included in the sail area”

maybe a system where the foot splits, and sits on the boom, or becomes a cuff, like on the 9ers.  The problem with extending it forward to be a cuff is that ‘double luff’ rule.

how big of an end plate do you need to get an increase in efficiency? And what shape? I’ve been looking as some nasa stuff about non endplated continuous wings (circular and the like) and they said that a box configuration was most effective. It would be interesting to see if you could do that with a main and jib, or a schooner rig. I’ll link the article if I can find it

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21 minutes ago, Connor.kainalu said:

<SNIP>maybe a system where the foot splits, and sits on the boom, or becomes a cuff, like on the 9ers.  The problem with extending it forward to be a cuff is that ‘double luff’ rule.

how big of an end plate do you need to get an increase in efficiency? And what shape? I’ve been looking as some nasa stuff about non endplated continuous wings (circular and the like) and they said that a box configuration was most effective. It would be interesting to see if you could do that with a main and jib, or a schooner rig. I’ll link the article if I can find it

K.I.S.S.

Why?
1. Fashion

2. Handling
3. Knowledge
Never underestimate the influence of (1).
2: see what 49er sailors have discussed. Better sailability for their difficult to keep upright boat.

3. Sailmakers who are on the literal cutting edge know things about these sails. You are leveraging that knowlege. 15 years ago you would have been the science experiement.

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1 hour ago, Rasputin22 said:

I think Conner is referring to BOXWING configurations

image.jpeg.e30c1e0f8ea7661af1a8be272d571e5c.jpeg

Yeah 

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Airport2030_PUB_DLRK_11-09-27.pdf

not the NASA paper, but detailed and interesting.

Also, it’s more up to date, the NASA one was written in the eighties.

Essentially, I think it allows a higher overall aspect ratio with a shorter wingspan 

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Again, a tad off topic, but when we did the 49er on foils (www.youtube.com/watch?v=bPPUwvUwEN8) the main lifting foil was an H configuration and we got almost double the CoL that Bora could get with his Moth.    So that would suggest the above has some merit.

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Steve, intrigued by your comment that the A-class is going back Pin-head.

I was watching Attenborough's life in cities with Peligrin hawks diving in NYC to catch pigeons.     Very pin-head or narrow elliptical tipped wings.

And let's face it, these guys (birds) have been at this a lot longer than we have or probably will ever get the opportunity to be at it.

So I am going to make a couple of bold statements.

#1, if you're going to hang a spinnaker off the top of the mast, you have so much structure up there to do that, it tips the scales towards square heads.

      i) if you're not going to hang a spinnaker off the top, then the argument is nowhere near as compelling.

#2  but our recent tests (in Austria) show that a square head 29er was far more forgiving and far smoother than it's pin-head counterpart.

#3 also our recent work here in Aust, with single handers also show far smoother and forgivingness with square heads.

      i) but the reduction in mast weight between the Alloy and carbon is well over 50% (with the single hander)  (29er reduction is far less, 25% max because of all the wires and crap)

     ii) the CoE position with the square head was about the same as the pin-head & the (carbon) mast ended up being 300mm (1ft) shorter in a 5.2m span.

So what I am thinking is this is all about CoL, and sail loading.

49er, 18teen,VOR even a Nacra, no-brainer, moderately low kgs/m² and hanging the spin off the top, scales heavily tilted towards squareheads.

29er, Cherubs, even single handers where the kgs/m² is lowish, ergonomically tilted towards square heads.

A-Class, C-class and maybe IC's where the CoL is a lot higher and kgs/m² also higher, pin-heads come back into favour.

What would be very interesting is if the A-class sailors opted for non-max length masts (they may have already).   When I sailed 18teens, we never had a max length mast, but our sum was different, we were chasing a very defined kgs/m² which was a trigger, maybe we are just too obsessive with length/black bands, etc.    Moth's maybe re-inventing the wheel yet again.    Again, present Aust 18teen with their obsessive square heads, are a fashion statement and quite absurd!

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11 hours ago, JulianB said:

#2  but our recent tests (in Austria) show that a square head 29er was far more forgiving and far smoother than it's pin-head counterpart.

#3 also our recent work here in Aust, with single handers also show far smoother and forgivingness with square heads.

Julian, do you think there's any difference in the way the sails depower and blade off? My guess is that what we want, ideally, is a sail where anything up to the top third of the sail will flatten off and blade out as the gust hits, but the leach of the rest of the sail will stand up so that pointing etc is unaffected. Full battens help with this of course, but in my experience the lower leech still sags to an extent. In your experience does the way the sail depowers change, and how would you think this affects usability?

The other thing that puzzles me is how the current fashion in the UK for square head sails with short battens on singlehanders works, I don't pretend to understand those at all.

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Julian: 

 Catamarans lose righting moment when they start foiling.  In part because the center of effort goes up by the amount you rise above the water, and the side force from the board remains pretty close to the same place.  The lift vector off the daggerboard is also probably closer to centerline than the center of buoyancy of the leeward hull.  For most of my experience, catamarans  have been doing everything to fly a hull sooner and were starved for power down wind. Around the track, being heavy was always a disadvantage, you would lose twice as much down wind as you could gain upwind.  Foiling seems to have turned that on it's head.   Current obsession is it's getting the CoE as low as possible once you are flying. Which explains the very endplated rigs.

I agree with your thinking that a certain amount of sail behind the mast makes sense at the tip just to reduce the drag of the tip. If that area is just following along, it still helps to mitigate some of the tip vortices.  I guess that's what all the colored pictures show. When asked about tip treatments, Burt Rutan said," I don't care, just make it longer."

More to Conner's point, there are lots of variables and each may have their place is the tool kit. Mast design, sail plan, cloth selection and thread orientation and stretch, are all mixed and matched to get to a good result. I don't believe there is a single silver bullet which is always right except for the really obvious things like having a smooth bottom and not dragging extra shit around...so it is always a process of iterative refinement. Breakthroughs are very rare, and often are preceded by long periods of iterative refinement which reaches  what I call a Toggle Moment where all the assumptions have to be updated.  

SHC

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On 4/3/2018 at 11:41 AM, Steve Clark said:

A Class cats have gone back to pin heads because they want to keep the center of pressure low with the stability losses inherent with foiling. 

 

22 hours ago, JulianB said:

Steve, intrigued by your comment that the A-class is going back Pin-head.

Be very careful with comments like this. A's are not going back to pin heads. Before foiling, square head sizes had increased to around 900mm, depending on sailmaker and this has come down since foiling started. The last worlds was won with a 500mm square head. Since then, some sailmakers are trying smaller heads at about 300-350mm but the world champ seems to be going the other way as I believe his new sail used last weekend had a 650mm head.

It seems the problem with going for a smaller head is that it is far harder to get the sail to twist the way you want and it doesn't blade off as nicely, and you lose out in the lighter stuff.

23 hours ago, JulianB said:

What would be very interesting is if the A-class sailors opted for non-max length masts (they may have already).

Development on this has been underway for some time. To start with, there is no max length of mast, although everybody had settled on the same height.The first short rig was seen about 18 months ago with 600mm cut off, developed by Andrew Landenberger. Stevie Brewin developed a rig with 750mm cut off (say 10%) and won various events but despite using it at the lead up event to the worlds, he switched back to the tall rig for the main event because he wasn't confident in light winds. He sailed with a short rig again at the Queensland State titles, as did the second place boat. A mid fleeter used a short rig at our nationals and I seemed to always be battling with him and couldn't tell any difference in our speed.

Smaller square heads and shorter rigs are all about the same thing, reducing the CoE of the rig. It will be interesting to see where this phase of development goes, although the picture will continue to be blurred by the significant differences on performance of the main designs and the main sailors such as Stevie, Mischa and Glenn who can win with whatever they put up.

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22 hours ago, fastyacht said:

the best thing about curent 18s is they channel the Chasse-marée vibe.

cc8f69ac21385e50b00553aec3737bd5.jpg

 

These are the comments I come to SA for :D

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The head length of a 49er mainsail is 743mm, foot length is 2816mm so it 26% approx.

I know North like them up around 42%

Harry, (my son) tells me the rig on Asko (best performing Aust boat in the last worlds) is great between 9-11knts, very notchy.

Problems below that powering up, problems above that with mid leach blowing out (he used a few more expletives) and the head being basically uncontrollable. 

If they sailed light it was even worse.   It's a North rig.

We also see this with the FX main.     As I have said before when they are good, they are very good, and the trick is to extend the "good" range.

Steve, J foils on cats, I guess it is the hull width rule that stops them turning them around (put the J outwards) but I have been watching the Narca's sailing out of MHYC where I beer-can race every Wednesday and your right, they even look wobbly when they get up, with the CoL (foils) moving well inside the CoB (hull) so loss of RM is quite dramatic.

We have got some pretty interesting tracking number of the Nacra's, no doubt they will get faster, but max speed in Sopot Poland a few months back in 25-30knts of wind was 28knts.   The same day in Arhus, 49er was coming downhill at 26knts in 20knts of wind.

Begs the question, when we originally did the 49er we over-killed the laminate, its got about 470gms of glass outside, 300gms inside.  Drop that down to GP - 18teen scantlings,  250gms on the outside and 175gms on the inside, stay with S glass (bloody tough) or go Aramid/Carbon, loose that weight plus the weight of the resin, do roll over gunwales, PU cored wings, etc etc, and the weight could drop from 130kgs all up to something under 100kgs (that's a fully rigged/foiled 49er weight, everything but the crew).

So do you cut the weight out first, and make it a very different CX49er (can't call it a 49er) or do we go foils [XF49er] (we did 28knts in 18knts of wind, pre the video, with me crewing)?

Interesting dilemma.  Losing 30kgs of dead weight results in an increase or decrease in live weight.   Need to know before you do it, so you can tweak the hull in anticipation.

It's impressive to hear the A-class is playing with smaller mast lengths.   If its any comfort, with the 18teen, our light air speed was legendary, we would win races by legs in under 7-8 knots with our smaller masts of very similar magnitude, so that should not be an impediment to you.

          jB

 

 

 

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Hi Jim, sorry, I don't think I fully answer you.

I think there are square heads and there are exaggerated headboards.

The Devoit and the Aero are the latter.

For me, the difference is all in the 2 control battens, and their placement, because that is the trigger system by which the square head works.

Before anyone says I am sledging the Aero/Devoit, also agree with truncated ellipses,  and that's what these are, more so that square heads.  Truncated ellipses are particularly good when it comes to centerboards up-range, so the old 18teen #2 and #3 centreboard, where more like an F18 wing than a Peligrin hawk.   Maybe they have extended that to a sail.    I have never seen a Devoit, and only an Aero without ts sail up at close range (in the real world, sure I have seen them at Alexander Place) so I can't comment. 

So when Dad and I were following the 49er sailed by Harry (same one) & Simon, early 2000's, what we were impressed by was the triggering of the mast head, it transitioned from power-up mode to de-power mode on demand and effortlessly.    The principal control is downhaul, a bit of extra downhaul you bow-string the mast a little more,  and it triggers earlier, little less, and it stands up for longer.    Anecdotally, we saw that as they where initially sold, sailors use far more downhaul, pulling the headboard cringle out of the sail initially, and then when the FX girls wanted 6:1 downhauls because 4:1 was not enough, the boys said me to, and we started destroying the luff panels just above the cuff from excess load.

(yes we have fixed both problems, now its luff tensions in the spinnaker as we have made them flatter and smaller, so the boats are going faster and lower, it never ends)

So the sailors have gone from Vang control, which sets up the whole mast as a spring, to downhaul control, which tension the luff of the sail to trigger the masthead.

Getting the Euler buckling/crippling load of those top 2 battens right is 90% of the game.   You can then opt for high mode/pointing, not much downhaul, lots of leach control and high/slow (relatively, you still doing 10-11knts in a 49er) mode, or max VMG, bit more downhaul, which is getting the head to lay off, and if the boats flat or slightly to windward, that will form an effective end plate, increase AR with all the benefits, boat speed jumps, etc etc etc.      

The trick is to get the combination of D1 tension right so the downhaul does what you want it to do, on call.

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Peregrine falcons flare their feathers at the wingtop to control flow. So not really like a "pinhead."
d759a968284946d081cefdad8a489866.jpg
The tern is the truly slender-wingtip bird. But of course they too can do flaring with feathers that we sailors can only dream of.
35486495006_a623839d3a_b.jpg


 

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When they are not flaring to slowed down, they are pretty pinhead-y to me.

Image result for peregrine hawksImage result for peregrine hawksImage result for peregrine hawksImage result for peregrine hawks

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Yes, indeed. But when they need lift at hi AOA they can get it in spades in a way that we can't. Instead of carrying around a bunch of sail out there that they have to "feather" away when a "gust" hits, they just fold it up to a pinpoint.

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They can also do stuff with "lateral" bend we an only dream of...

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Can someone do the Reynolds number comparisons, please?

I'm running short of time before I go to China.

      Jb

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Only in dinghy anarchy would an anonymous user needlessly denigrating a designers late father produce such a fruitful discussion of sail design. It's a testament to the civility of this forum.

DRc

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Posted (edited)

Fuck off kid.

Your Dad.

SHC

PM follows with details.

Edited by Steve Clark
Make funnier
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On April 6, 2018 at 4:54 PM, JulianB said:

Steve, intrigued by your comment that the A-class is going back Pin-head.

I was watching Attenborough's life in cities with Peligrin hawks diving in NYC to catch pigeons.     Very pin-head or narrow elliptical tipped wings.

And let's face it, these guys (birds) have been at this a lot longer than we have or probably will ever get the opportunity to be at it.

So I am going to make a couple of bold statements.

#1, if you're going to hang a spinnaker off the top of the mast, you have so much structure up there to do that, it tips the scales towards square heads.

      i) if you're not going to hang a spinnaker off the top, then the argument is nowhere near as compelling.

#2  but our recent tests (in Austria) show that a square head 29er was far more forgiving and far smoother than it's pin-head counterpart.

#3 also our recent work here in Aust, with single handers also show far smoother and forgivingness with square heads.

      i) but the reduction in mast weight between the Alloy and carbon is well over 50% (with the single hander)  (29er reduction is far less, 25% max because of all the wires and crap)

     ii) the CoE position with the square head was about the same as the pin-head & the (carbon) mast ended up being 300mm (1ft) shorter in a 5.2m span.

So what I am thinking is this is all about CoL, and sail loading.

49er, 18teen,VOR even a Nacra, no-brainer, moderately low kgs/m² and hanging the spin off the top, scales heavily tilted towards squareheads.

29er, Cherubs, even single handers where the kgs/m² is lowish, ergonomically tilted towards square heads.

A-Class, C-class and maybe IC's where the CoL is a lot higher and kgs/m² also higher, pin-heads come back into favour.

What would be very interesting is if the A-class sailors opted for non-max length masts (they may have already).   When I sailed 18teens, we never had a max length mast, but our sum was different, we were chasing a very defined kgs/m² which was a trigger, maybe we are just too obsessive with length/black bands, etc.    Moth's maybe re-inventing the wheel yet again.    Again, present Aust 18teen with their obsessive square heads, are a fashion statement and quite absurd!

Maybe it has something to do with mast stiffness?  Or kinetics?

If this intrigues, google 

'Can Tip Vortexes Enhance Lift of a Flapping Wing?'  AIAA Journal 47(2):289-293

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On April 1, 2018 at 3:31 AM, JimC said:

My understanding is that the big challenge is the need for it to operate on either tack. These things have pros and cons, but you'll notice they are all asymmetrical. a sailboat rig needs to be symmetrical, so there has to be an almost useless drag creating plate on the wrong side as well as the useful one on the right side. Then when you add to that that most classes will require them to be measured in as sail area and factor in the effects of twist then it seems to me it will take someone very clever indeed to make it work.

In addition there's much lower hanging fruit at the other end of the sail which is commonly an aero disaster area. Even that's subject to tradeoffs. Convinced about FBs evaluation of the "cuff" at the bottom of the 49er sail, I made a detachable one for the bottom of my IC rig to clean up that area and get the aero interactions. It lasted about two races. It meant that I couldn't see the jib clew, which in turn completely psyched me out about jib settings and trim, which I regard as crucial. It so distracted me from the task of sailing the boat better that it seemed to me it was doing more harm than good to my race performance. Probably that could have been addressed somehow, but I never managed to get round to doing it.  

Of course we're now seeing a lot of attention to that area on Moths, and previously on the Cs.

I'm not clever enough.  I tried it on the top of a windsurfer square head.  I put a bunch of tell tails around the pneumatic fence (2 thin balloons, 1" diameter, one on each side on top of the squarehead.  IIRR, it was a Reynolds Trisail).  As far as I could tell, the flow never settled down enough to do much except get knotted up around the fence.  Or the telltales would stand straight out from the sail!  The trailing edge/corner long tell tail at the downwind corner end of the head only twirled like it was in a trailing tip vortex a couple of times.  So I tried a fence that would weathervane vertically.  Then the telltales would try to slip under the fence on the weather side.  When the balloons weren't trying to point straight up (!).  If I tightened the fence enough to stop this, the fence wouldn't weathervane to the flow.  This was on shore.  It got weirder on the water.

On the dipping lug I tried on a different project, I put a long tell tail on the trailing top edge, which indicated much better results- I think the top spar kind of acted like a fence, but I was too busy to really watch the thing carefully.   Maybe if the top spar was shaped like a Park Avenue boom?  That sail kicked like a mule.  Scary.  Besides, ounces up top there add up.

 

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Hi,  I'd just like to add that the elliptical spanwise lift distribution is only ideal when the span is held to be the limiting design factor.

However, if the span bending moment is held to be the limiting design factor, then the bell shaped spanwise lift distribution is the ideal (minimum induced drag).

The later was pioneered by the Horton Brothers but was largely ignored by USA engineering as the Hortens designed for Germany during WW2, but is clearly the more efficient design as it is based on the true real world limiting factor of span moment in fixed wing aircraft and in sailing conditions above the designed wind speed.

The Hortons (students of Prandtl developer of the lifting line theory) are famed for their tailless flying wing designs developed in Argentina after the war.  The Bell shaped lift distribution allows aircraft to carry a greater wing span for the same bending moment (or heeling moment in the case of sailboats), reduces span load and induced drag and cancels the negative yaw effect of aileron controls.  Computer modeling of their designs shows they are as good as anything that could be done today.

The square top sail was developed to improve automatic gust response, twisting of the peak on Sydney 18 ft skiffs. You can read about that in Frank Bethwaite's " High Performance Sailing".  Raising the aft corner of the tip (raking the tip) slightly reduces induced drag over that of a square tip.  I think I 1st read a technical report on this some 40 years ago.

Ken

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Has anyone tried building masts that are already bent ?(which I think is different than prebend, which (I think) is induced by rig tension)

 

Would changing luff profiles make the sail any faster?  Is there a way to do it in a real world situation without screwing up mast bend?

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6 hours ago, Connor.kainalu said:

Has anyone tried building masts that are already bent ?(which I think is different than prebend, which (I think) is induced by rig tension)

89037_2.jpg

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11 hours ago, tillerman said:

89037_2.jpg

The 4.7 section is bent to balance the helm on a laser with a smaller sail. It wouldn’t hurt to have the radial section bent a bit too, in heavy air I have to pull the board up a bit 

 

I meant to have a changed luff shape for aerodynamic purposes

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18 hours ago, Connor.kainalu said:

Has anyone tried building masts that are already bent ?(which I think is different than prebend, which (I think) is induced by rig tension)

Not sure about dinghys but take a look at some 30 square meter rigs and a couple 12 meters from 1980 (UK boat and then Australia).

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On 7/21/2018 at 7:01 AM, Connor.kainalu said:

Has anyone tried building masts that are already bent ?

Many class rules in development classes prohibit deliberately bent spars, which suggests that back in the day it must have been done and found undesirable.

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16 hours ago, JimC said:

Many class rules in development classes prohibit deliberately bent spars, which suggests that back in the day it must have been done and found undesirable fast but expensive.

I wonder if my "fify" is more like it?

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Rig plan from 14' skiffs in victoria in 1948. Masts were laminated spruce. Pre bent.

14 ' skiff rig plan 1948.jpg

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22 hours ago, fastyacht said:

I wonder if my "fify" is more like it?

The FIFY thing to me is misquoting, and just bad manners. However for many classes fast but expensive is a subset of undesirable. There is, after all, limited need to prohibit slow but expensive.

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On 7/21/2018 at 8:18 PM, Connor.kainalu said:

The 4.7 section is bent to balance the helm on a laser with a smaller sail. It wouldn’t hurt to have the radial section bent a bit too, in heavy air I have to pull the board up a bit 

 

I meant to have a changed luff shape for aerodynamic purposes

This is very easy to do, but it has to be done with full length battens. A rotating cuff with a few inches of support where the batten hits the mast is needed.  The batten pocket is slightly over-tightened to force camber into the leading edge of the sail. The only down side is that the main sheet has to be yanked hard one time to rotate the camber inducer to the correct tack. You hear a loud pop when it rotates over. I suspect the effort to move the camber inducer is the reason it's not popular with dinghys.

The big benefit is that the leading edge camber allows you to point really high, as high as a boat with a jib. The side benefits are never getting stuck in irons and no flapping in the breeze.

Both North Sails and Gaastra Sails have had this in production since 1995.

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On 3/27/2018 at 3:11 PM, Connor.kainalu said:

Why do the eighteens use square headed rigs? Some of them even have the aft corner of the head (is there a name for the fourth corner created by the square head?) above the mast. I can understand the automatic gust response, but I’d think that you’d lose leech control, and it’s certainly farther from the optimum elliptical wing shape that the high roach pin-headed rigs have, like on the older 18’s, 29ers, and older IACCs

Elliptical wing shape is certainly not the ideal shape

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On 7/24/2018 at 10:47 AM, Eddie_E said:

This is very easy to do, but it has to be done with full length battens. A rotating cuff with a few inches of support where the batten hits the mast is needed.  The batten pocket is slightly over-tightened to force camber into the leading edge of the sail. The only down side is that the main sheet has to be yanked hard one time to rotate the camber inducer to the correct tack. You hear a loud pop when it rotates over. I suspect the effort to move the camber inducer is the reason it's not popular with dinghys.

The big benefit is that the leading edge camber allows you to point really high, as high as a boat with a jib. The side benefits are never getting stuck in irons and no flapping in the breeze.

Both North Sails and Gaastra Sails have had this in production since 1995.

I remember camber inducers in the late 80s. Unless my memory is failing me (which it could be).

On 7/24/2018 at 4:32 PM, Christian said:

Elliptical wing shape is certainly not the ideal shape

The eliptical load distribution not necessarily = eliptical planform...

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That was done by Jono Whitty, its a couple of years old now has has not been continued with.

I think Jono was over-taken by conservatism (his coach, not Jono) and it didn't get a real run for it money.

But regardless, it's been discarded, like many good ideas that re-surface latter.    There would have been other complexities inc, controlling AoA at the head of the jib, you would have to couple it with the jib-sheet, and the present day 18teens are bereft of $$ to try new stuff.

Not sure this will but watch and wait!

jb

 

 

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On 7/24/2018 at 5:47 PM, Eddie_E said:

This is very easy to do, but it has to be done with full length battens. A rotating cuff with a few inches of support where the batten hits the mast is needed.  The batten pocket is slightly over-tightened to force camber into the leading edge of the sail. The only down side is that the main sheet has to be yanked hard one time to rotate the camber inducer to the correct tack. You hear a loud pop when it rotates over. I suspect the effort to move the camber inducer is the reason it's not popular with dinghys.

The big benefit is that the leading edge camber allows you to point really high, as high as a boat with a jib. The side benefits are never getting stuck in irons and no flapping in the breeze.

Both North Sails and Gaastra Sails have had this in production since 1995.

Ahh, old windsurfing tech.   First RAF (rotating air foils) with just the battens, then Camber Inducers with bigger luff pockets.   Rotating square heads.   I even had an Aeroforce 8m with split battens, camber inducers and a luff pocket that extended back over the first third of the sail.   The Aeroforce sail had great top end, but was finicky in lighter air, very easy to stall and heavy.   All of this was in the early 80s on boards, even wing masts (I can picture the mast and then name - I think started with an M.)

- Stumbling

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On 9/21/2018 at 3:27 PM, stumblingthunder said:

Ahh, old windsurfing tech.   First RAF (rotating air foils) with just the battens, then Camber Inducers with bigger luff pockets.   Rotating square heads.   I even had an Aeroforce 8m with split battens, camber inducers and a luff pocket that extended back over the first third of the sail.   The Aeroforce sail had great top end, but was finicky in lighter air, very easy to stall and heavy.   All of this was in the early 80s on boards, even wing masts (I can picture the mast and then name - I think started with an M.)

- Stumbling

See, I knew I wasn't imagining things. I designed a dinghy in 87 or 88 that had camber inducers and a wishbone boom. Never finished building it. I stole the idea from the windsurfers. I thought they were really onto something. (They were!)

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