Q 4 : fixed Luff length on genaker

Introduction :
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<br>It is found by several F16HT group members personally and julian Bethwaite (Designer 18 foot skiffs and 40-er skiff) that luff length is more important in genaker performance than raw surface area. In effect the aspect ratio is important. Proposal is to fix the F16HT genaker to a high aspect maximum surface area (say 17 sq.mtr = 180 sq. ft.). The genaker is used while solo sailing as well as sailing with a crew. Wetted surface calculations (approximations) have shown that this genaker ratio F16ht/F18 = 17/21 sq.mtr. closely approximates the ratio for wetted surface area. The last is all important in light to medium air races. Remember that mast length is NOT fixed under the draft F16HT rules. The maximum allowed mainsail area is linked to the mainsail luff length via a formula. This new value (parameter) called RATED MAINSAILAREA is a indication of true sailpower and is fixed. The same could be done for the genaker.
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<br>Question :
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<br>Would you as a sailor like to see luff length restrictions in the F16HT rule framework ? If yes, in what form ?
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<br>Please answer with Yes or NO in the subejct line and your reasoning in the main message
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<br>Wouter
<br><br><br>

Wouter-
<br>I think the simplest would be to just apply a "no longer than" rule, but I would not know where to set that too SO, to begin with I think making 17 square meter the max size and then using some form of "rated sail area" to equalize things will allow some "experimentation" so that an "ideal" length could be determined. However, I would not like to see the class turn into one where "the person who shows up with the most masts/sails/etc." wins (that is, running a spi to the masthead knowing it will result in mast failures some fairly large percentage of the time BUT will result in regatta victories more often due to some speed advantage in MOST conditions).
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<br>MO,
<br>Kirt<br><br>Kirt Simmons
<br>Taipan #159, "A" cat US 48

Yes, I would like too see a maximum luff length. Maybe it is smart to ask what the sailmakers think is an optimal shape genaker and calculate back the luff length when the total genaker area is 17 (?) sq.mtr.
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<br>Another option. Specify where on the mast the genaker luff may come. And fixing this point via load calculation. This as an answer to Kirt -failure- remark.
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<br>If these are to complicated I'll say 17 sq.mtr. max size and a maximum luff length that puts the genaker halveway between the masthead and hounds. This will limit loads and allow some freedom to experiment.
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<br>Later on we can maybe use an aspect (efficiency) formula a la Texel like Wouter proposed for the mainsail area.
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<br>Anonimous4
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I'd like to see the main focus to be on developing better gennaker sail shapes. Limiting the size and luff length really directs attention to shape straight away.
<br>Maybe I'm wrong but I think, given the limited experience with gennakers on Cats, it will help both the sailmaker and the sailor by just putting an upper limit on these two aspects of the sail.
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<br> Has there been any consideration given to limiting pole length and gate height?
<br> Not suggesting they be limited just woendering if it has been considered and what people think.
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<br>Phill<br><br>

If we are to maintain an open class, then I would vote for a sail size of 17SqM period. I love experimenting with sail shapes and the within the 17SqM rule, we can all find that sail shape that each of us prefers. That will enable us to refine the gennaker/spinnaker shapes to those that work best with each type of boat considering that each type may vary in mast length, composition, cross section, etc.
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<br>Jon Hamlet
<br>Taipn 4.9 #217<br><br>

Jon,
<br>You hit on a good point. Ie mast length.
<br>Of the boats that could be considered potential participants the mast length variation is 3.5ft. I think the Isotope is 26ft and the BIM is 29.5ft.
<br>It is possible the BIm will be able to carry a much longer gennaker luff.
<br>Do you think the Bim will have an advantage because of a longer gennaker luff?
<br>Should we be concerned?
<br>I suppose the question may be should we be looking at setting up a framework that encourages development or a frame work that keeps boats equal even if it is limitting their potential?
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<br>I'm not advocating one or the other just interested in what people think.<br><br>

Gentlemen,
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<br>The pole length is fixed in the (draft of the) rules. It is fixed at the length at which it most forward point is 0,8 meters passed the very tip of the bow. This rule is part of the Texel rating system aswell as the FFV system and I think the ISAF small cat system. In any case the same rule applies on the F18 and iF20's. This is the means reason for having the same rule in the F16 HT. Side effect is that this limits excessive leehelm.
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<br>Still this rule is also open for input.
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<br>And what is the " Gate" ?
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<br>Wouter<br><br>

Indeed a good Phill, Jon we need to think of something to safeguard against inequality.
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<br>The mast height and mainsail area are made equal from design to design by having a efficiency formula calculate the real sailforce produced and fix the last. The formula use the luff length of the mainsail area to calculate it's aspect ratio and thus have a measure (empirical formula ?) of effeciency.
<br>We know this works for it is at the basis of both the Texel, FFV and ISAF small cat measurement handicap systems.
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<br>By deregulating the genaker luff length a similar setup must be implemented to keep the downwind performance equal.
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<br>I.E. Smaller mast (less luff length) more genaker area and visa versa.
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<br>This approach can well be to complicated in the beginning.
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<br>I have no perfect answer myself on this one Only right one I can think of right now is too rule that :
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<br>The genaker head must be halve way between the masthead and hounds. And fix the maximum genaker size.
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<br>This too venturi the same percentage of mainsail on all cats.
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<br>Still, I need a few days to think about this. But I'm quite sure that not regulating the luff length is a equality breaker.
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<br>Reagrds,
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<br>Wouter
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<br>
<br><br><br>

My views on the spinnaker are this:
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<br>I would go for the biggest one we can use, currently the 16ft cats going fast the in the UK are using 17.5 sq m and 18 sq m sails. And there is no doubt we lose out to the f18 in lighter airs due to their increased area.
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<br>If we are baseing the rule around Texel handicap system the max size sail we can use is 18sq m. There is no difference in the handicap whether we use 16, 17 or 18 sq m so lets use 18. The max size for 18ft cats is 21 sq m and for 20 ft cats is 25sq m, and guess what f18 use 21 and f20 use 25. As far as pole length is concerned I agree to limit the pole to 80 cm beyond bow, if we use Texel. However if you base the rule around ISAF, pole length is not regulated and I would go bigger because it is faster, sheeting points can go forward (neater), and costs no more to make.
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<br>For the luff length I agree that longer is faster(we want faster don't we) and if we control mast length then we can control spinnaker luff length by having a max height of halyard point, I would suggest about 300mm below top of mast. If we are having carbon masts (which we should) the manufacturers will reinforce the masts so that they do not fail.
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mate,
<br>It would be easier to fix the max pole length forward of the bow and max draw height of the genacker..
<br>To try and equate an area to compensate for loss of luff will be close to impossible.. Too much area and the result is a break effect and not equalisation.. Any area aft of the pivot point is wasted in my experience..
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<br>ps enjoy the play skiffs..<br><br>

John said :And there is no doubt we lose out to the f18 in lighter airs due to their increased area.
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<br>But on the F16HT site I've read a document that would put the F16 HT (at 105 kg, not at the minimum of 100 kg) at an advantage on wetted surface. Wouter claims this to be all important at light airs. I have copy-paste the important bit:
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<br>Ratio wetted surface = sq. rt. (0,77 / (5,5/ 5) ) = sq. rt. ( 0,77 / 1,1 ) = sq. rt. ( 0,7) = 0,8367 = 84 % (F16HT to F18)
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<br>Ratio wetted surface = 84 %
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<br>Compare to :
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<br>Ratio mainsail area F16/F18 = 14,5 / 17 = 0,8529 = 85 %
<br>Ratio sail area (main + jib) F16/F18 = 18,5 / 21,15 = 0,8747 = 87 %
<br>Ratio Rated Mainsail Area F16/F18 = 12,77 / 14,80 = 0,8628 = 86 %
<br>Ratio rated sail area (main + jib) F16/F18 = 16,51 / 18,79 = 0,8787 = 88 %
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<br>Genaker F16 / F18 = 17 / 21 = 0,8095 = 81 %
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<br>John, do you think that the given calculation is wrong ? Or can it be that the 16 footers you are referring to differ from the F16HT in this respect ?
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<br>Anonimous4<br><br>

I think that Steward has made a good point. why not, as he put it , :
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<br>*********
<br>fix the max pole length forward of the bow and max draw height of the genacker
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<br>We have done the first if I understand the wording of the draft rules correctly.
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<br>And I assume the draw means something like "vertical projection" of the genaker luff analogue to wingspan on swept wing aircraft.
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<br>A rule fixing this would be simple, easy to understand and truelly equal to all while being independend of things like mast height and mast rake. So now we have lost one argument which was forcing us to fix the maximum mast height.
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<br>Anonimous4<br><br>

I've recalculated, I stand by the numbers given go to :
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<br>http://www.geocities.com/F16HTclass/F16HT_to_F18_equality.html
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<br>Can John P. explain ?
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<br>Wouter
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There is no seperate rule for max. genaker size for 1-up boats. This was asked as while back on the forum. The rule still is :
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<br>-------
<br>Maximum spinnaker area
<br>Boats up to 16 ft. < 4.87 m.: 17 m 2
<br>from 16 up to 19 ft. > 4.87 m. <= 5.80 m.: 21 m 2
<br>from 19 up to 22 ft. > 5.80 m. <= 6.71 m.: 25 m 2
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<br>Theoretically F16 HP could fly a 21 sq. mtr. genaker but as we all know this size is not a succes on the short little over 16 ft. platform.
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<br>The 17 sq. mtr. kites have performed much better.
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<br>The 83 % rule suggest a new size of 0,83 * 21 sq.mtr(F18) = 17,43 sq. mtr.
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<br>The old 17 sq.mtr. was at 81 %, ... , well in my opinion we can keep the 17 sq. mtr. and not loose out to F18.
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<br>I propose to keep with teh 17 sq.mtr. for that is what some of us already have and see what the results are after a season of sailing.
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<br>Wouter<br><br>

Setting draw height would allow both tight and loose luffs. Thus allow for some experimenting with full headed genakers like the skiffs have and maybe enter the field of semi planing catamarans. (Not full planing for that needs hard chines, I know Bill R.)
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<br>Will give more performance at the top speed range where a 16 footer will normally loose out.
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<br>Wouter<br><br>

John,
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<br>I agree with You on this point, lets go for a maximim reasonable spi area, for Texel Rating this is 21m^2.
<br>I would suggest to set this also as limit for the F16 HP class.
<br>In fact it's hardly more expensive than an 17^m, time will tell what the best area will be.
<br>I heard a story about the (New)Tornado spi' ; at first they were 25^m, there were complains that they collapsed too soon, and smaller spi's were used. But.. very soon the spi was redesigned, and now a lot of the Tornado sailers again go for the 25^2 spi, as it handles well now.
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<br>This could also be the case for the F16 class
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<br>Geert
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Texel says
<br>Maximum spinnaker area
<br>Boats up to 16 ft. < 4.87 m.: 17 m 2
<br>from 16 up to 19 ft. > 4.87 m. <= 5.80 m.: 21 m 2
<br>from 19 up to 22 ft. > 5.80 m. <= 6.71 m.: 25 m 2
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<br>So I don't understand where your 18 sq. mtr. comes from.
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<br>The reasons on which the group decided on a start with 17 sq.mtr. a few weeks ago are however :
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<br>-1- The 21 sq.mtr was found to handle worse and have disporportionally higher sheet loads (found by 4 of the groupmembers , 2 USA and 1 EU and 1 Aus).
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<br>-2- Furthermore Taipan america has decided on offering 17 sq.mtr. if Kirt's info is correct. Taipan Aus (Goodall) is in doubt wether to go for 17 sq. or 21 sq.mtr. But it will be one of these. Most groupmembers have 17 sq. mtrs. already ( at least 4 of them) and one member has gone even smaller as a result of his experience with bigger kites on Taipan 5.7.
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<br>-3- 17 sq.mtr. comes closer to the 83 % rule than 21 sq.mtr or even 18 sq.mtr. 83 % * 21 = 17,43 sq. mtr.
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<br>-4- BIM 16 has a 12 sq. mtr. kite It might well go up to 17 sq. mtr, and a little more luff length but. 21 sq. mtr. will be to much.
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<br>-5- It is a Formula 16 foot class (even though it is a little longer than actuall 16 foot) Texel 16 foot max is 17 sq.mtr. we wanted to stay with the spirit of the rule.
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<br>-6- The F16 HP is setup such that the solo class uses the same materials as the 2-up configuration, this includes the genaker. This to provide the class with an easy switch from 1-up to 2-up without extra investment. Going to 21 sq.mtr will severly hamper this. The switch is together with the F18 equality are the two "selling" arguments of the F16 HP, without it the class will be hard pressed to get out of the experiment phase.
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<br>-7- 17 sq. mtr. is what the soloboats I-17 and FX-one use, so it was considered to a good (max) size for the F16HP 1-up. Especially with the lower sheetloads.
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<br>-8- And deregulating size will lead to confusion during possible future F16 HP get togethers.
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<br>-9- Well known sailmaker in NL was reluctant to go bigger than 19 sq. mtr. on my P18 for he said :"the is not enough room to optimally fit 21 sq. mtr. in the dimensions of the boat". So taking into account that the pole tip to sideshrouds on the F16HP is about 91 % of the P18 (F18) makes any gen over 91 % * 21 = 19,13 sq. mtr. less effecient than the F18 gen, when aspect ratio is assumpted to be important (Bethwaite)
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<br>-10- Grandfather boats whose masts are 8,5 on average to 9 mtr. of F18 => 94,4 % => 94,4 % * 19,13 sq. mtr. = 18 sq. mtr to have same efficiency (aspect ratio). But then again this is not a real necessity but by a large part a choice (equal to F18). F16HP will therefor have a higher aspect ratio even when the 83 % rule is observed so it already has a small advantage over the F18.
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<br>-11- F18 weight (140kg) to gen. power ratio with 21 sq. mtr. >= 15,23
<br>F18 ,, (115 kg) ,, ,, ,, ,, 19 sq. mtr. >= 15,52
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<br>-12- F16 HP weight (140kg) to power ratio with 17 sq. mtr. >= 14,11 (IS less weight per gen. sailarea, better accelleration)
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<br>-13- Therefor the F16 HP already had a 8,4 % higher acceleration when coming out of a gibe. That is with equally efficient genakers producing proportionally equal thrust. Going bigger will offset this alot.
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<br>-14- No other solo or two up catamaran design has gone higher than 17 sq.mtr. as far as we know (Stealth ?)
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<br>These were the reasons to limit the gen size to 17 sq. mtr.
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<br>There is a strong tendency to vote in a clause that allows the F16 HP rule to be opened up more later, after the class has established itself but for the beginning it was voted to go for more control so that we have a good change of actually starting the class. And also to make it is easy and relative inexpensive for people to swithed to F16 HP.
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<br>With these points in mind I would like to stress that really convincing arguments are needed to reverse the 17 sq. mtr, decision now.
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<br>Wouter
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<br>This
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Geert,
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<br>Even though I'm personally very interested in maximizing the F16 HP class in the way of performance, I am at the same time very involved in getting this class of the ground. With respect to genaker size these two come into direct conflict.
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<br>As we know Texl rating is not descriminative when it comes done to genakers. It recognizes but three situations; you have a genaker or you don't and the genaker is less or equal than max allowed under Texel. Point is; it does not rate genakers in the same way as it would do with overall weight and jib/mainsail area's.
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<br>We can allow some flexibility in overall weight and sailarea's because we know how that can be corrected by the other dimensions on the boat. This way we can correct heavy boats by allowing them more jib area and thus make them equal to F18 again. We can't however do that with genaker size and luff length.
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<br>Result : following the Texel rule and allowing the F16HP to carry a 21 sq.mtr. with nearly equal to F18 luff would give the F16HP an unequal advantage and destroy the F18 equality aspect which we are using to attract new blood and thus get the class excepted and thriving. Unregulating the genaker area would also sever the link between 1-up and 2-up sailing for which 17 sq.mtr. could well be the max size that can be handled.
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<br>Ofcourse maximizing under the Texel rule is very interesting to a one -off sailor but not it is not in the interest of creating a class. Sorry.
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<br>I propose to keep the current rule of 17 sq.mtr. and expanded it with a max draw height at 91 % of the F18's
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<br>This would satisfy two of wishes at the same time of which one was also expressed by you.
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<br>First being : Not to make the drawheight to high in order to not load the grandfathered mast to height by forcing them to go masthead
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<br>Second being : real equality to F18's and not only on handicap rating.
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<br>This however does not mean that I dont share your and Stewards wish for a maximized HP class'. Personally I would love to have my modified Taipan smoke the hulls of F18's next season but I really do think that it is standing in the way of getting this class of the of the ground. And we can only go truelly F16 HP (max. gen size, even less restrictions, wider) when we have a broad basis of participating sailors . Till that time we have we can have one or two open features and to my opinion gen. size is not one of them.
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<br>summary
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<br>- Mast and sailarea are limited flexibally by the rated sail formula
<br>- Length is permanently fixed to 5 mtr
<br>- Gen. draw height wiil be fixed leaving flexibel luff to heavily raked boats.
<br>- weight is limited to 100 kg's or less and overweight is corrected out by the Texel performance prediction formula giving jib size. This implies that overweight can be counteracted by sailing with a light crew.
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<br>- width is still unregulated by being analysed wether it needs to be regualed. Point named above (sailing light) is taken up in the analysis.
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<br>Wouter
<br><br><br>

If you decide you wish to go 7.550 meters draw.. Then you will need to increase the prod length. 1.4-18 meters from stem rather than the 0.8 meters your now setting in concrete..
<br>There are some advantages in increasing prod.. The "wing" becomes low aspect and is less inclind to collapse due to changes in angle of attack..
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<br>As for breaking expensive masts.. If I can hold up a 24 sq meter mast on the tip of my skiff (dia 2.5 mm) I14 hold 27 sq meters on smaller tips we just use uppers to handle the downhill forces... Im sure the mast makers can design a layup for the 16 mp.. Older rigs just add a second diamond above the hounds to take the kite..
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<br>Finally If Wouter one sets the kite with its sail area not behind the rotation point you will be surprised how light the sheeting forces are.. I have sailed solo on a skiff with 24 sq meters.. With a lot less righting moment and stability than this new class.. So 18 and 21 sq meters shouldnt be a problem..<br><br>

Wouter,
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<br>Can you send me an example how you calculate the allowed jibsize?
<br>I assume you take the complete set of formula’s from Texel or Isaf, change the value for “rated weight” for boat weight+real crew weight.
<br>Than , of course, at a fixed (103 for Texel) rating a jib can be calculated.
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<br>For the Spi area, it’s not that big deal to me if You want to limit it 17^m, for the minimum weight I have more concerns:
<br>Even though it seems to be achievable when building new boats, it’s still bad news for the existing classes:
<br>In case of taipan/stealth/isotope one should buy a lot of stuff (mast/beams/rudders/daggers all carbon) . That’s hardly an option.
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<br>This is also the reason that I’d like to see your calculations; if it is possible to compensate a slightly heavier boat with a larger jib, well than the problem is solved.
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<br>Geert
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Geert,
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<br>>>Can you send me an example how you calculate the allowed jibsize?
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<br>Yes, I will use something like the Texel calculator that is already available on my personal webpage www.geocities.com/kustzeilen/
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<br>This is example however because I'm still looking at the ISAF system and working on some independed calculation methodes (like wetted surface area) to validate the use of a rating system like ISAF (Texel)
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<br>The form, and I think that you were asking that, will be something like the Texel system were one parameter is left unregulated so that final speed potential can be equalized by changing this parameter. In practice, fill in all measurements in the calculator and start changing jibsize (jib luff) till the final rating equals 103,0 uder texel or 1,009 under ISAF.
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<br>>>I assume you take the complete set of formula’s from Texel or Isaf, change the value for “rated weight” for boat weight+real crew weight.
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<br>Right !
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<br>>>>Than , of course, at a fixed (103 for Texel) rating a jib can be calculated.
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<br>Indeed, and I've there is any truth in both systems we will have a fair equalizing system.
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<br>>>For the Spi area, it’s not that big deal to me if You want to limit it 17^m,
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<br>Actually I'm proposing to make it 17,5 sq.mtr. now becuase of teh 83% rule (also 91 % RULE). This is partly caused by the fact that a aluminium standard taipan 4.9 at 108 kg is equal to F18 with this is size. But I will present a better and fully worked out case to you all, but I'm being delayed a bit by extra work caused by name change etc.
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<br>>>for the minimum weight I have more concerns:
<br>Even though it seems to be achievable when building new boats, it’s still bad news for the existing classes:
<br>In case of taipan/stealth/isotope one should buy a lot of stuff (mast/beams/rudders/daggers all carbon) . That’s hardly an option.
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<br>Indeed, well I working out a math. model right now and apart from giving my point of view I can't anything to this discussion than that you have a good point and that it needs a closer look. And I'm giving it just that.
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<br>>>is is also the reason that I’d like to see your calculations; if it is possible to compensate a slightly heavier boat with a larger jib, well than the problem is solved.
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<br>Well, I asked a befriended cat designer for help on the high speed spectrum of the cats. In the low speeds I say make effective sailarea equal to actual wettedsurface ratio. And of course at low speeds, cat width is not an issue so the smaller Isotope would not be treated unfairly in that respect. this I working on a acceptable but simple model and that will take some more time. Part of results are already presented online in the equalisation to F18 webpage. Have you seen that already ?
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<br>Regards,
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<br>Wouter
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