Jack, are you sure that is an Hobie Bob? It looks like a Prindle Pete.
I read somewhere that a raindrop is the most perfect aerodynamic shape. And then in an article about raindrops, I found the attached, computer-generated drawing of a virtual raindrop.
It will look very familiar to anybody who has a Hobie bob.
So, IF a raindrop is indeed the most perfect aerodynamic shape, even if a Hobie bob doesn't provide any lift, at least it seems that it would present the least possible amount of drag.
if the volume of the float has to be aerodymnamic only, maybe so.
However it could serve a second purpose (lift shape) It would seem best to make it a flexible wedge of foam integrated into the top of the sail to give it thickness, like padded sails were. Then it would contribute no additional drag.
I think that David's idea is near perfect in design. Implimentation may be tricky, but if you could make the sail take a perfect shape on either tack, this would be a favorable way to carry an anti-turtle float.
Perhaps inflated battens as on a traction (kite-boarding) kite?
GARY
I don't get that. If you make the top of your sail fat and symmetrical, wouldn't you lose some drive out of it and also cause some drag?
I'm not sure I understand the "wedge" thing and which-a-way it is pointed or placed in relation to the sail.
I am just interested in all this stuff because I would like to see something invented that would be practical for people to use for safety reasons and at the same time be acceptable to the serious racers -- the bob snobs.
Not symetrical. Asymetic as a windwurfer sail or a traction kite. It would have to be able to invert for each tack, providing a convex cuve on the lee side and a concave shape on the windward side.
GARY
Okay, I thought you were talking about a wedge-shaped wedge, but I guess you're not. Some sails are made with a pocket at the top for a piece of flat flotation. Is that what you are talking about? Or something else?
That is it. The padded sail was not for flotation but to give thickness, like the semi- soft sails on faSter ultralights etc. This is a preferable sail profile, but of course has its complications, but when combined with the need for flotation, could justify itself and lead to a technological leap through the back door, so to speak. Wing sails are the future. Spin's are not. When the lift of slotted rigs is realized (very high lift to area ratios off the wind, because the wind can be "bent" around the slats a lot, and drag is not an issue), there will be no need for spin's.
I gues the comparison is that airplanes land at comparitively low speed with all kinds of slots, flaps and slats deployed, because drag does not matter.(you are trying to put the brakes on, and burn up altitude, so you have energy to spare) You need lift at low speed. You could achieve it with a new type parachute foil too perhaps.
A sailboat meets this technology from the other end by not caring about drag when off the wind because the wind (drag)is about in the same direction as he wants to go. He too could (and does) use a parachute/kite type device to this end. They are a pain to deploy, but apparently easier for boats to use than planes....
Would a sail be more efficient if it were flat on the windward side instead of concave? In other words, more like an airplane wing? (For the sake of the question, assume that the boat will only sail on one tack.)
This has been tried on the 12 meter AC boats. Stars and Stripes tried a two sided, hollow sail. The idea was to be able to control the shape of the sail by varying the tension on either panel. I don't believe they raced with it.
Sort of. A low speed wing needs some thickness but actualy still needs to be concave on the "underside". This varies with the lift/drag required as well. (windward or leeward again)Some thickness is always required, and better than none.
If Hobie Bob was symetrical and stretched for the length of the square head, this would be an improvment, because it would also help out the end plate effect (See other thread). However I dont think it would be that hard to make an articulated one. Say a alligator (kids toy) looking bunch of foam segments that radiused into each other with a batten looking thing spine. The fit need not be perfect (actually a gap is prefered) just so long as the flow can stay attached.
Reading back over: If you follow that, you get a prize..
Depends on what the prize is. 