The original thhinking behind the short ww hull was based on the absolute guaranteed fact (according to all the experts at the time) that a weight to windward proa would luff up into 'the irons of death' after a shunt. I could not see how, but hedged the bet by making the hulll short and wide(ish) to minimise drag from wetted surface at low speed. The boats worked so well that the shape was kept. It is also noticably more comfortable than a catamaran when sailing upwind in waves. The hulls rise together rather than the corkscrew motion on a cat.
Rob started teh question to understand if a 8M fatter WW hull is better or worse than a 9M slimmer (given that I think difference in weight/costs could be managed). But it resulted in thinking about the turning momentum the differences generate.
So this may be hard without a drawing but my thoughts are as follows
1) sailing at 16kts there is about 50N difference between the optimal hull and the not-optimal LW hull (per Rick's model). So if the WW hull is fatter and shorter wouldn't it have even more drag. for argument sake it doubles compared to the difference between the optimal and non optimal shapes (so 615 +2*50= 715). So total forward force is 615 +715 = 1330 in the lw hull. Drag is 615 in the LW hull (excluding rudders etc) and 715 on the WW. So we have a momentum of 715*6m (width) = 4290NM. (The drag difference component is about 6*100=600 so about 1/7th)
2) the the sail point is about 1M aft of the center of the boat. If sideways force is 3:1 versus propulsion than sideways force is about 3*1330=3990. 3990*1M = 3990
So total rotating momentum seems to be 3990 + 4290 = 8280NM. Countering that will create additional drag.
Baring stupid calculation mistakes and wrong assumptions it seems that optimizing WW hull shape could change around 10% of total drag and 10% of rotating momentum challenge?
Rick would it be a lot of work to guess/analyze what say the drag curve of the WW hull of Harry is?
--- In harryproa@yahoogroups.com.au, Rob Denney wrote:
>
> Definitely one of the factors that should be considered, along with
> capacity, maneuverability, comfort, increased loads and costs from a longer
> hull, etc. I have not done such an evaluation and afaik, nor has anyone
> else.
>
> If performance was high on the list, then it would be worth it. Although,
> if performance was required, you would probably be flying the hull more
> often anyway.
>
> rob
>
> On Wed, Feb 20, 2013 at 12:09 AM, fvonballuseck wrote:
>
> > **
> >
> >
> > Hi
> >
> > looking back at the files posted by Rick/Rob for the optimized LW hull for
> > the Solitarry I see that there is about a 10-20% difference in the
> > 5-15knots range for drag for differently optimized hull types (but same
> > length).
> >
> > Did anybody by chance calculate the difference in drag for the WW vs the
> > LW hull? and the resulting momentum.
> > Given that 99% of all sailing will be done with the WW hull in the water I
> > was wondering if this should be a factor in considering WW hull length (or
> > even general WW hull design)?
> >
> > Fedor
> >
> >
> >
>