Fedor,
Have you looked at the comparison of the Atlantic, Pacific, Harry,
and Equal-L (hulls the same length) proa forms at:
http://users.kymp.net/~kcad/proares/Cruising_proa_consepts.htm
(I believe this is the original version)
http://www.boatdesign.net/forums/attachments/multihulls/25353d1221426812-proa-design-cruising-20proa-20concepts.pdf
(different version with a wetted surface area graph)
The Equal-L proa has about the same overall resistance as the
Harry for a one-ton proa, and slightly lower resistance at four
tons. If all hulls were then optimized,
I'm generally sold on the shorter ww hull, largely for the
elimination of corkscrewing when beating to windward. I had a
miserable 30-degree day this past November beating into steep chop
when taking my catamaran back to the boatyard, and spent about two
hours dreaming about both my hulls meeting the waves at the same
time. Right now that's high on my list, though in the summer I
might not care as much.
In any case, I liked how the harryproa rated in terms sail area
and wetted surface area, where the Harry has the second lowest
wetted surface area and the second highest sail area (righting
moment). The sail area / wetted surface area graph was the most
interesting to me.
While the Atlantic edged out the Harry at some points, both were
very close, and both were at the top of the chart. Combine this
with the Atlantic's problem of putting the mast in the
accommodations section, and the mast going higher into the wind as
the boat heels, the Harry looks even better.
It might not be enough to sway someone who's a religious follower
of Pacific proas, but it was certainly enough for me to continue to
justify my personal preference.
- Mike
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