Well, what can I say that hasn't been said many times before. "It is all in balance" and without truelly analysing this balance you might convince yourself that something will work when in reality it won't.
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<br>I will give you the best example I have (and than I will not comment on this anymore) :
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<br>Forgive me from ALSO using F16 in this example.
<br>(formula's used are explained on the F16 page)
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<br>Three boats.
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<br>iF20 Inter 20 weight 190 kg's length 6.1 mtr. width 2,6 mtr.
<br>Marstrom 20 weight 105 kg's length 6,1 ,tr. width 2,6 mtr.
<br>Formula 16 HP weight 100 kg's length 5 mtr. width 2.5 mtr.
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<br>all boats sailed with crew weights of 150 kg's
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<br>I would like to underline here that F16 is 2,5 mtr. INSTEADof 2,6 because we had to scale it down to full F18 equality and 2,6 mtr width would not produce that, 2,5 mtr did.
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<br>now lets approximately calculate wetted surface area's relative to F16
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<br>iF20 / F16 = sq. rt. (weight iF20/F16 * Length iF20/F16) = 190 sq. rt. ((190+150/100+150) * (6,1/5)) = sq rt. (1,36 * 1,22) = sq. rt. (1,66) = 129 %
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<br>M20 / F16 = sq. rt. (1,02 * 1,22) = sq. rt (1,244) = 112 %
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<br>F16 / F16 = 100 % ofcourse
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<br>Prismatic drag ratios :
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<br>iF20 / F16 = Weight / length = 55,7 / 50 = 111 %
<br>M20 / F16 = 84 %
<br>F16 / F16 = 100 %
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<br>High speed drag estimate (Combined wetted and prismatic drag) :
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<br>est iF20 / F16 = (129 % + 111%)/ 2 = 120 %
<br>est M20 / F16 = (112 % + 84%) / 2 = 98 %
<br>est F16 / F16 = 100 % by definition ofcourse
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<br>Lets calculate righting moments (leverage crew is width + 1 mtr. becuase ther is the centre of mass to be found, at the navel)
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<br>iF20 = 150 *(2,6 +1) + 190 * 0.5 * 2,6 = 540 + 247 = 787 kgm
<br>M20 = 150 *(2,6+1) +105 * 0,5 * 2,6 = 540 + 136,5 = 677 kgm
<br>F16 = 150 *(2,5+1) + 100 * 0,5 * 2,5 = 525 + 125 = 650 kgm
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<br>Now lets calculate rigjting ratios :
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<br>iF20 / F16 = 121 % , remember wetted surface ratio 129 %
<br>M20 / F16 = 104 % , remember wetted surface ratio 112 %
<br>F16 / F16 = 100 % , remember wetted surface ratio 100 %
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<br>Now is there any doubt which boat has a better wetted surface area to righting moment ratio ? Righting moment determines the maximum size of rig a platform can handle with respect to capsize. Obviously the F16 can carry the biggest rig relatively to it's drag. In absolute sense it will be smaller ofcourse. That is the twist.
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<br>This means one thing in order to keep up in the light air both the M20 and iF20 need to have more sailarea and probably higher masts. This can be done, no problem, but in medium air they will start to suffer as a result and in heavy air they suffer inmensely, F18 and all older boats will start passing these 20 footers and the iF20 will pass the M20.
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<br>Now lets compare sailarea's and see if both iF20 and M20 do add these amounts of sailarea.
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<br>iF20 18 sq mtr main, 4,85 jib 25 sq. mtr. genaker
<br>US I-20 19,4 sq. mtr. 4,85 jib 25 sq. mtr. gen.
<br>M20 19 sq. mtr. 0,00 jib 20 sq. mtr. gen.
<br>F16 14,75 sq. mtr. 3,5 jib 17,5 sq. mtr. gen.
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<br>I would like to remind people that both the jib and genaker were sized down the F16 group to slow down the F16 HP to the F18 performance and to allow single handed sailing with the same genaker. There are NO technical reasons why the F16 can't fly a 4,5 a sq. mtr. jib and a 21 sq. mtr genaker as both width and Texel / ISAF allow.
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<br>Mainsails
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<br>iF20 / F16 = 122 %, remember wetted surface ratio 129 %
<br>US I-20 / F16 = 131 %, remember wetted surface ratio 129 %
<br>M20 / F16 = 128 %, remember wetted surface ratio 112 %
<br>F16 / F16 = 100 %
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<br>Genakers ;
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<br>iF20 / F16 = 143 %, remember wetted surface ratio 129 %
<br>US I-20 / F16 = 143 %, remember wetted surface ratio 129 %
<br>(***iF20 / F16 big rig = 119 %***)
<br>M20 / F16 = 128 %, remember wetted surface ratio 112%
<br>F16 / F16 = 100 %
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<br>Jibs :
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<br>iF20 / F16 = 139 %
<br>US I-20 / F16 = 139 %
<br>(***iF20 / F16 big rig = 108 %***)
<br>M20 / F16 = 0 %
<br>F16 / F16 = 100 %
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<br>Now with respect to the mainsail area both the iF20 and US I-20 have just enough area to not be blown away by the F16. The US I-20 has only 2 % more which is hardly noticable on the course. With 2 % speed difference it will take an US I-20 about 2 minutes to overtake a F16 when sailing at 10 knots. That is creeping past.
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<br>It is the genaker area which will be factor that will put the Inter 20's / iF20 past the F16's, but any F16 sailor sailing any kite largere than 19 sq.mtr will regain the advantage. Same applies for the jibs of 3,75 sq. mtr or more . And coincidence has it that the both these measurements are proposed as the heavy crew sailsizes within the F16 rule.
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<br>Now, what more can we conclude from these numbers ?
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<br>But the real twist comes now. The pride of 20 foot designs !!! The M20 is even worse of than the iF20 is ! Only 4 % more righting moment but no less than 12 % more wetted surface drag ! the negatieve effect outweights the positive one by a factor of 3. iF20 does better, 21 % positive effect 29 % negative effect. The M20 high speed drag estimate is nearly equal to F16's drag ratio that DESPITE the fact that it has longer hulls !! And this is the real twist. The M20 platform is in drag relation harly distingiousable from the F16. The only reason that it is faster in light air is that it just has more sail area in the mainsail. Overall the difference is smaller. And ofcourse with only 104 % of righting moment and 128 % sail increasewith even more capszing moment increase due to a higher mast the M20 will be so heavily punished in NON-light windforces that it is not funny anymore.
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<br>Main point : the M20 is completely out of balance. It does have enough sailarea to overcome it;s wetted surface area of 112 % but at only a 104 % increase in righting moment it will be a BIG looser in anything than light air. In medium and heavy air it will be completely overpowered. And ofcourse it lack a jib alltogether and this will go a long way in correcting the actual performance of both the F20 and F16 classes upward with respectto the M20. So if any of you want to device a US F-20 that will develop into this than I say it is a BIG waste of money. Who wants a boat of USD 20.000 that is beaten in 50 % of the US regatta's and 75 % of the EU regatta's by a USD 9.000 boat.
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<br>Ohh I nearly forgot. the Worrell is a heavy air race right ? Anyone wants to sail the M20 against John on his F16 with 20 sq.mtr spi in this race ? No disrespect intended.
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<br>In all honesty even the US I-20 would do better in this race against the M20 And the IF20 would do better than the US I-20.
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<br>There are some other things that can be concluded from these numbers but the main point is that it is by no means easy to device a development rule that would really improve performance. Most of the time it would just give the impression of doing so.
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<br>No at the end of this I would like to underline that John P. on the old stealth (pre F16) has beaten many 20 footers on elapsed time during the season 2001 and even finished a mere 8 minutes behind a well sailed Tornado Sport in a 6,5 hour race. In NL geert beat 2/3 of a fleet of 57 F18's on a pre F-16 Taipan 4.9 (small spi)
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<br>No I appologie sfor using the F16 in this example, for it is really not about the F16 class but more about optimal designing and striking the right balance. And I offer these numbers as a counter argument against the impression that it is easy to optimize 20 ft. boats to even higher performances. And the comparison to the F16 was the best I had to show this and it is currently being confirmed in real life. A thing that can not be said about the CFR 20 and M20.
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<br>So please bear with me though this F16 crap and focus on the points that have been explained here.
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<br>And that is all will say about this now and in the future, It is up to you guys now.
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<br>Wouter<br><br>