Thank you for your comments Macca, it is just what I want to hear ! That will probably make it dangerous, but nevertheless .. !
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<br>I agree that Frank has overlooked one or two things on cats. Example he makes a mathematical mistake in the way he estimates performance increase when looking at drag. differences. A displacement cat with twice the sailpower will go about 1,4 times faster when it's drag graph is given by velocity squared. This is more or less true on simple assumption and more importantly it is mathematically correct. However he also claims that a planing 18 footer which starts to plane after 5 knots and behaves as a displacement craft at lower speeds, accellerates to TWICE the speed when it's sailpower is doubled. This is mathematically wrong. For the math kids out here. He assumes the drag graph for planing to be a true linieairy function (must go through the origin of plot) when it actually is a lineairy variation (same as a lineairy function but without the need to pass through the origin of the axis) . When doing the correct math the skiff speed increase estimate becomes :
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<br>assumptions :
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<br>Drag cat and skiff same when both in displacement mode. According to Frank this ends at speed 5 knots for the skiff.
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<br>Drag of planing skiff increases with a constant ratio (straight line) after this speed of 5 knots.
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<br>Speed increase skiff when double the windforce when starting at 5 knots = 1,5 time the speed or 7,5 knots. Cat increased to : 1,41 (=sq.root (2)) times or speed of 7,1 knots
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<br>Now when windforced increases again by two :
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<br>Skiff speed = 12,5 knots
<br>cat speed = 10 knots
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<br>Another 2 times (8 times total):
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<br>Skiff speed = 22,5 knots
<br>Cat speed = 14.1 knots
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<br>Ofcourse all the speeds below 5 knots are equal.
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<br>So based on Franks own data and assumptions, the skiff is faster when planing WHEN all other things like weight and sailarea are equal but very much less than he predicts.
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<br>Anyways, I'm rambling and probably lost several of you guys already. ANd Frank called the cat superior in medium windstrengths which would agree with your 10 knot experiences.
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<br>I am however very happy to hear that you beat 18 footers in the heavier airs too where planing might well give them an edge when They don't park it or flip it or snake too much.
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<br>And it is even more great to hear that the Taipan 4.9 with kite is holding up to them too. Would you consider yourself a very good sailor a la mr. Booth or mr. Bundock or do you think that a capable crew can obtain the same results ?
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<br>Btw ; I'm not a Frank worthshipper (zealot) despite the fact that I regrad his book as exceptional when compared to many others book and respect his experiences.
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<br>Gee man F16 HP capable of beating 18teens ! Ain't this little thing class fast.
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<br>Thanks for the comments
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<br>Wouter<br><br>