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Make it a hovercraft!
If the rules allow it, and it's downwind, you're theoretically better off with a propeller and a windmill- these devices can outrun the wind.
You stick a windmill on the boat and use that to turn the propeller. If the gearing is right, it's very, very counterintuitive, but it can in principle outrun the wind.I must admit though I've never heard of people doing it with a boat, but it definitely has been done with land yachts type things. Normal land yachts don't do that though, they just go at an angle to the wind and can outrun the wind that way with only a relatively simple sail; but the sail type land yachts can't do that directly downwind, whereas the windmill version can.
I just lost my post before I could post it. Anyhow, much shorter now:I am not sure I understand the the hull shape details you describe, especially the "flaring out" part. I have seen some concave designs in racing canoes, but maybe you can look at the pictures I linked and tell me what you think comes the closest:1) http://www.kayakcentre.co.za/images/mustang.jpg2) http://blog.mlive.com/lcn/2008/07/CANOE3.jpg3) http://img.nauticexpo.com/images_ne/photo-g/rowing-shell-touring-single-scull-130942.jpgAnd what do you think about this rowing catamaran I just found:4) http://www.fotothing.com/photos/0b4/0b48d42c02c342c69bbbdca51e9919d2_adc.jpgLee, I love all this information you post. This will be a great boat!I will wait for Sophiecentaur to talk about sail design for downwind only.
Quote from: wolfekeeper on 28/06/2009 22:31:21If the rules allow it, and it's downwind, you're theoretically better off with a propeller and a windmill- these devices can outrun the wind.This cannot work. As the boat starts to move, the wind speed over the boat decreases; wind speed over the boat, and therefore its 'windmill' will be absolute wind speed - boat speed. If the boat's speed is equal to the wind speed there is zero wind over the boat, meaning there's nothing to drive the windmill. If the boat travels faster than the wind then the wind speed over the boat will be negative, effectively slowing the boat down.
If your sail surface must not exceed 256 sq cms, and you will have a permanent tail wind, I wonder if your sail should be 13cms high by 20cms wide giving a total of 260 sq cms. then cut 5 x 1cm sq holes in the centre keeping you within the allowed surface area and creating the same effect as a parachute.[diagram=478_0]
Is it cheating to freeze the water and mount the "boat" on skates?
...and oh yes, you might want to consider using a bulbous bow. These are normally only found on quite large vessels but they can also be effective with very long narrow hulls running near their max speed, so they might work. The convex hull requirement for many racing boats normally precludes their use.http://en.wikipedia.org/wiki/Bulbous_bow
Hmm... not really. That just has a reverse raked bow and I'm not sure that it offers any advantages over a non-raked vertical bow. The idea behind bulbous bows is that they protrude ahead of the vertical bow, below the waterline, so that the bow wave they produce is out of phase with the bow wave produced by the vertical bow at the waterline and so tend to cancel or reduce it.To be honest, I probably wouldn't bother about trying to incorporate bulbous bows unless I had an excess of free time, both for the designing and making them, and the subsequent testing of them.
Yup, that looks good to me. You won't be able to use a circular cross section throughout the hull, of course, without also making the hull very curved along its length i.e. when you look at it from the side it would have a very curved bottom. You don't want this; you actually want the hull to be very flat along the hull center line, from bow to stern, so the cross section will have to become more (vertically) elliptical as the hull becomes narrower.So when you look at your hulls from the top they'll look just like your picture but from the side they should look like a low but wide rectangle. This curvature along the center line of the hull is called 'rocker' and the degree of rocker affects how easily the boat can turn; you want it to run straight though, so zero rocker. Some sea kayaks have been designed with negative rocker i.e. the bow and stern are deeper in the water than the middle of the hull, to help prevent the kayak turning when paddling obliquely across waves/swell, but you don't need or want this either.
How are you planning to build your hulls? As weight is of paramount importance, because it dictates the buoyancy required, which then dictates the hull cross section etc, they need to be as light as possible.
I would just add to LeeE's post, make your hull/rigging as light as possible, regardless of stability, remember, you can always add ballast, but taking it away would not prove easy! Also make sure your hull has a good, well hardened coat of beeswax to reduce friction.