Tuesday, 28 August 2007

Veal Heel on a C Class Cat.

Rohan's Blog has an interesting item about a foiling C Class Cat. It thing looks amazing but this picture clearly show a very basic design problem (in my opinion...)



With a cat like this one copying the Moth configuration will not work because the more windward heel you have the less righting moment. What they should do is try to turn off the windward foil. Then they can crank in the powerful solid sail they have. Maybe this is what they are doing but the speed data on Rohan's blog would not suggest this.

Veal Heel works great on a Moth because the more you heel them to windward the more righting moment you get. This has always been the case with moths since they got narrow with wings. (http://www.culnane.net/dc/sailing/moth/wshpaper/transver.htm). With hydro foils you can also use the lift of the main foil to help you get height to windward. Leeward heel on a foiling Moth is about as good a trawling a bucket upwind.



With the next generation of Moths we should also try to increase the instability of the system so that the more you heel the more unstable. This may not make sense but when you travel fast you have lots of dynamic stability so you can control the thing. Instability generates righting moment, which can equate to more power.

2 comments:

Rohan said...

they actually have a gearing mechanism on the rudder flaps that switches the amount of lift on each flap when you tack. you have to do it manually when you tack, but it is easy to do, just have to remember to do it (but i found it actually didn't make much difference).

i think they are planning to do something similar on the front foils too tho, as per what you mentioned. not sure how tho, but it will be a manual lever of some sort.

best mode for downwind is both flaps neutral and the boat dead flat.

-r

Doug Culnane said...

Thanks for the feedback Rohan. It sounds like they are going the way I guess that I would go. Maybe they just need time to get the system working well. We know from the Moth that sorted hydrofoil systems do 3 laps in the time others do 1, so refinement helps...

I was surprised that they are not going faster than a Moth considering the power and size they have. So either they have to get the system to work much better or power is not so important when flying. It will be interesting to see how this develops.

All the best,

Doug