curve of areas

[ibi]

Hello

I am interested in yacht designing. But this is more like my hobby. I have one question conected with the canoe body designing.
Many sources suggest optimal geometric factors of yacht hull to minimize the wave resistance. These are Cp, LCB and so on. But what about the shape of the Curve of Areas? Setting of the geometric factors is possible for different shapes of that curve. So - what is the best shape? I have read about trochoid theory of the curve of areas, but it comes from the 19th century. Is there any new approach to that problem?

[Stephen Ditmore]

Please see
http://boatdesign.net/forums/showthr...p?threadid=319
esp. my postings of 1/25 - 1/29. If you find a more up-to-date source than the 1987 Stars & Stripes article I cite I'd be interested in learning more, too.

[Stephen Ditmore]

You might also want to check out
http://www.zwakenberg.de/hulldrag/

[ibi]

Unfortunately, I have no access to the SNAME papers on this. The only one I've got is on the optimizing the SAC by OPTIMIZE program from SAIC by the Stars&Stripes syndicate 1987. But there's nothing about the "correct" shape of SAC.
I have yet another question. What about the keel volume? Should it be included in SAC? If so - the canoe body should be "cut" a bit to maintain smooth shape of SAC. In the book "Sailing Yacht Design" it is written, that the keel volume inclusion comes from the designers' expirience. Any comments on this?
I'll be very greatful!

[Stephen Ditmore]

There've been attempts to do things like that, but I've never seen it on a winning raceboat. The more accepted approach now seems to be to make the keel as thin as strength considerations will allow at the hull/keel juncture, and in general to keep the foil thickness at 10% of chord length or below. Interestingly a 10:1 or higher length-to-beam ratio is also about what is necessary for the wavemaking of a multihull to substancially diminish. Keels contribute to wavemaking, but when the vessel is making leeway much of that contribution is on the windward side owing to the same pressure differencial that is allowing it to produce lift.

The exception may be older style vessels for which the hull and keel are more integral. In pre-1983 12 meters the long, swept leading edge in combination with a reletively thick keel section was quite successful, and Larrson seems to suggest in his book that the lift profile of the entire hull/keel combination on a boat such as this should be made as nearly elliptical as possible for optimum performance. Apparently it's one of those things where you either go one way (treating them as integral) or the other (treating them as seperate) and design the boat accordingly.