I found the paragraqph about catamarans in Frank Bethwaites book :
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<br>Advatages :
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<br>- ratios power to weight can be very high
<br>- slender hull shape escapes the force mode drag which is very important at medium speeds say around 10 knots
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<br>concludes : moderate wind performance should be superiour when properly designed.
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<br>Disadvantages :
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<br>- Total wetted surface of the twin hulls is always more than a single monohull
<br>- They can not heel to use gravity to twist of their sails in light air with he experimentally shows to be VERY important.
<br>- Their slender hulls can not plane and therefor they can not go really fast as the 18 ft skiffs.
<br>- Very litted volume in the bow so you can drive them as hard on a crosswinder or broach reaching.
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<br>concludes : Light air performance is disappointing and heavy air performance is okay but not great.
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<br>Assume Frank is right. How do we attack all these points ?
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<br>First we thank him for the advantages !
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<br>Than we conclude that the wildthing manourvre must be considered to be the first thing to be mastered on a cat in light air in combination with light weight and a big twist in the mainsail c.q. squaretops mains. This will be the reason why all F16HP's will have boards and squaretops, otherwise wilthinging will become very dificult.
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<br>So the first two points will more or less succesfully attack the first two named drawbacks.
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<br>The third point : this is a tough one ! I don't think we will ever overcome this without inclining daggerboard so that they act as foils or to incorporate lifting spis. He calculates huge speed increases for planing boats but I feel that increase should be less due to trying to run over hilly country without shock breakers. The smoother ride of the cat could go some way in closing the cap. And the greater stabiliy of the cats should help in outrunning all but the true professional skiffers
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<br>Forth point : diving. Well, I have a video of the 18's at home and I don't see any of them with their bow section touching the water at all. So if they stay up by putting weight aft and lifting their bows out than why should a cat be limited in speed by their small bow volumes ???
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<br>Must be a small oversight by Frank.
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<br>This is to all would be designers and homebuilders. Bear these points in mind and go get those 49-ers on elapsed time.
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<br>Wouter<br><br>

brings up.. are racks allowed behind the hulls?<br><br>

Not yet, Was looked but chosen too not to incorporate in order to garantee that foundation boats are competitive as well as heavier crews are compedtitive in the start-up fase. And the limited sailarea does not really warrant these wings yet.
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<br>Having said this, I'm sure it will be incorporate over time when the class picks up and a need to use these wings has arrisen.
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<br>Good point however Stewart.
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<br>Wouter<br><br>

Wouter
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<br>Glad to see you have managed to either purchase a copy of Franks book or borrowed it from someone. I had a big problem getting hold of a copy.
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<br>mark<br><br>

I found quite a few observations being confirmed by Frank Bethwaite, so I feel we are on the right track with the F16HP.
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<br>I kept an eye on amazone for a while and two weeks ago they indicated they had a few book in stock so everyone who wants to get a copy go to amazone and order one now. It cost me only 36,33 US$ including shipping to the NL. The book is full of info and experimental data and worth the 36 dollars.
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<br>Wouter<br><br>

By the way you can find some interesting info from Frank on the last two "Seahorse magasine" it is based on the development of the 29er but he as always something interesting to say and pick up.
<br>"Seahorse mag." is a must have if you are interested in all form of yacht racing with pro writing article ,no bul. just real info& opinion not like most other mag. you find around !!!!<br><br>

Don't get me wrong here, I like Frank and think he has done a lot for sailing around the world. But when it comes to his ideas about Cats and 18ft skiffs he has lost the plot. Here in Sydney we often have the oppourtunity to run against the skiffs. I have never been beaten upwind and when we were not using kites it was close downwind. Now that we have kites on the T we are in another world as far as performance. During the 18ft skiff worlds held here earlier in the year we matched up against the fleet on several occasions, We had just fitted the new rig to the Tornado, We were much faster up wind and much to the surprise of the skiffs were faster by an even larger margin downwind. This was in light winds (about 10 kts) since then we have had many runs with the skiff in up to 25kts and each time we are substantially quicker. Recently I have been sailing a Taipan 4.9 sloop with a kite, again the little cat is much faster on all points of sail compared to the skiffs, In all conditions. <br><br>

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>

A lot of things in sport mess with the laws of physics once the sport becomes well developed. For example a Top Fuel drag car should not be able to cover the 1/4 mile in the times they are doing currently, when you work out the Hp and grip they should be about 1.5 seconds slower than the are!
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<br>As for my steering abilities I think I am OK, better ask Bundy and My special friend Mitch....<br><br>

Indeed, physics put you in the ball park the rest is left to fate.
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<br>Well Mitch became a Dutchy just recently so I may get a change to ask him. I just wanted to know if you're a sailing God that can even win cat races sailing an optimist. Your experiences now show that beating 18teens is alos possible for us mortals.
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<br>BTW, have they counted the (downward or backward) thrust from the exhaust pipes ? Those engines pump quite a volume of air while racing. Good point by the way.
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<br>Do you have objections to me using your comments on the F16HP webpage ?
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<br>Wouter<br><br>

wouter<br><br>

Hi Wouter,
<br>It can be pretty hard to find it.I know that in W.A. it was hard to find it but in Sydney easy,execpt that it come by container on ships and was 3 month late every time .
<br>Only one solution left,i had to suscribe and dont regret it!
<br>For more info:www.seahorsemagazine.com
<br>Maybe to make sure it is what you are looking for keep hunting for ita little bit more!
<br>After a season and half on 16ft. skiffs i have to say they are great fun but they are a real pain to try to get go in .
<br>The fleet here in w.a. is realy sad but in Sydney it is actually big business with a lot of help from clubs to get you started . But to get any where it is not easy so many guys have been doing it for so long it is hard to catch up and of course you have to find 2 crew all the time !Not always easy.
<br>So if you have a fast class, easy to learn on and fun you can bet it is a winner with everyone!
<br>Fabrice.<br><br>

macca, if one looks at the records of the 18teens.. its interesting to note that the last few seasons the class as a whole has slowed .. Not sure why..
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Stewart,
<br>I read that the recent skiff hulls have a higher planing speed (threshold)in order to improve light air performance. Moderate wind performance is sacrificed a bit. Could this be what you have noticed?
<br>To you and Macca. Have either of you raced the 49ers on your cats? I have heard that in short courses the 49ers are pretty quick compared to the 18ft skiffs due to their quicker handling, kite launchers etc, so I was wondering how these fair compared to the Taipans and Tornados.
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<br>Cheers
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<br>Simon<br><br>

The 49er V's either a 4.9 or a Tornado without a kite see's the cats winning by a massive margin, with the kites it is a joke. The Skiffs are painfully slow up wind, Not something that you notice when watching the skiffs in isolation but when on the same course the speed difference is staggering. At the Sail Auckland Olympic regatta in 1999 the Tornado's and 49ers were on the same course. The T's started 10 mins after the 49ers and on a 1.2nm course we had passed them all before the first bottom mark. This was in in extreme conditions 25kts plus. After that race we were given our own course, whether for safety reasons ( the closing speeds and angles were awesome) or so save further embarrasment I am not sure!
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<br>The 18's have been slowed in the last few years, It was very complex for a while with divisive fleets sailing under different rules... But the basics are that the wings have been "clipped" and now the max beam is about 14ft. The boats are getting back to the speed they once had through good development. My contacts in the skiff community are on a few paths that are quite interesting, including building a foil bourne skiff and rotating wing masts! (about time) But the basic rule for the skiffies is that unless it's a Hobie 16 don't even try to race it!!<br><br>

I will look in more places for the magazine !
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<br>>>So if you have a fast class, easy to learn on and fun you
<br>>>can bet it is a winner with everyone!
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<br>I'm quite certain the new class can supply all of these things. I'm also very hopefull that this F16 class will stay around and below US$10.000 per complete boat as it is right now. Money will determine alot.
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<br>Fabrice, what do your friends at your sailing club think of the F16HP. I see that the 16ft. class is looking for a youth baot leading up to the 16ft. skiff class because getting in to the class is hard. Maybe the (inherently more stabil catamaran) F16 HP class is a good training platform with the potential to give an immediate speed satisfaction that teenagers need to be kept interested ? The most be some 2nd hand Taipans lying around where you sail. Alot of aspects of catsailing are very comparable to skiffsailing ; for example getting to grips with apparent wind angles !
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<br>WOuter
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<br>Wouter
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