Wow, Mike, I really tickled your fingers with that question!
<grin>. Thanks. I love all the feedback.
I have been taking the approach you suggest, which is to just
put up as much sail as I can. For the 38' Contrarry, it would have to
have a 2 part mast to get any useful amount of sail, so I might as well
make it tall. I am restricting myself to 62' off the water because of
the Intracoastal. Of course, in NJ, even 40' won't work, so you really
can't use that section.
But, back to my basic question... according to the SA/D and
Bruce calculations, Rare Bird should be nowhere as fast as she is. I
think this demonstrates a fault int the SA/D particularly, since she is
fast at speed. The Bruce number might be a better predictor of light
wind performance, since Ono's harryproa suffered there. (I need to get
the spec's of Ono to add it to my chart).
What I am getting at, is that increasing the sail area has more
effect than just raising the mast. It also makes the boat beamier,
since I don't want to get hit in the head with the boom if I am caught
aback. The other option, raising the boom, makes it hard to reach. So,
I would really like to be able to predict proa performance based on
sail area, displacement, hull length and hull beam. If anyone has any
formulas that add the hull shape to the sail area/displacement values
to calculate performance, I would love to hear about it.
There must be a calculation based on wetted surface area and
some adjustment for the hull fineness ratio. If that force could be
estimated, I would think you could calculate the potential force from
the sail and come up with a number that way. It would be valid up to
the point where the righting moment is approached.
In terms of the wing sail, I think I will give it a pass. It
looks interesting, but I have a few problems with it.
1) as you say, it would require a bit of experimentation
2) I dont' want to have to build all those internal shapes
3) too many control lines (like a junk rig)
4) sail doesn't hold shape between teh ribs, so I am not sure
how much benefit you actually get
5) more things to break
I think I am going to go with a wing mast and as big a sail as I
can deal with, but I do wish I could quantify it.
You brought up one question I had not considered: the windage of
the bare mast. What should I be doing about that? While I hope to never
have to sail under bare poles, I certainly can't rule out be anchored
in a hurricane. What should I be looking at in terms of wingmasts and
safety?
Thanks again for your thorough reply. I keep losing track of
much of this information, so I am goign to file this thread away, and I
am going back to look up some of your other posts, because they often
have really great info I should keep track of.
- Gardner
P.S. the plan is to build the camper; the contrarry is probably
twice the boat (cost, time) and I have to view harryproas as
experimental until I can charter one for a week.