Information

[kreg]

These are test render;
Could you advice if there are some mistakes?
I noted that in the last america's cup , the designers have given particular attention to the shape of prow, but i didn't understand how the prow can increase the speed.
Could you give me some advice to make my prow better and speeder?
Thanks for your time.

[kreg]

ps:
Lbg=20,204 m
Girth Component (G)= 1,912
Freeboard at FGS= 1,501
Freeboard at Amidships=1,293
Freeboard at AGS= 1,232
Weight of Yacht (W)=23974,937
Draft=4,1
Lwl=18,168
Beam wl=3,613
WSA=67,905
Max cross sect area=2,665
Waterplane area=47,472
Cp=0,482

[Andrew Mason]

Kreg

Nice job.

My undertanding is that the bow shape on AC boats is an attempt to get a long static waterline and a reasonable overhang to increase the waterline length when sailing, while maintaining a low LBG.

The long spoon bow gives up too much static waterline length for a given LBG, while a plumb stem does not increase its waterline length when sailing upwind at speed. The currrent AC bow shape is a compromise between those two extremes.

It may also be easier to have a high prismatic coefficient with the current bow shape, I think it is difficult to get adequate volume forward with the older style spoon bow.

[sorenfdk]

I agree with Andrew. It seems that the designers have placed the second "knuckle" in a way so that the waterline length is increased when the yachts heel.

Regarding the prismatic coefficient, I think that yours is a bit on the low side. I don't know the CP of the ACC yachts, but I would probably increase it to about 0.53-0.54. As a starting point, you could use Gerritsma's formulas for resistance and calculate the optimum CP for your expected speed.

[Andrew Mason]

My guess is that he has calculated the Cp with the appendages attatched, rather than just the canoe body.

Andrew

[kreg]

yes, in fact, the cp for canoe body is 0.55; Can you tell me where i can find the Gerritsma's formulas?
thanks.

[sorenfdk]

It is common practice to use the cp of the canoe body - 0.55 sounds about right to me.

Gerritsma's formulas can be found in "The Bare Hull Resistance of the Delft Systematic Yacht Hull Series" by J.A. Keuning et al. You can download this paper (and a lot of other interesting stuff!) at http://www.sailboat-technology.com - go to "Online Articles"

[kreg]

ok, thank you very mutch sorenfdk