On Fri, May 29, 2015 at 3:33 AM, taladorwood@yahoo.com.au [harryproa] <harryproa@yahoogroups.com.au> wrote:
Your last post got me thinking. You basically canted an asymmetrical foil to provide lift for the windward hull.
Correct. Tried it with a 6 hp motor yesterday and a single foil amidships on each hull. Some fascinating results, although 10-11 knots is not really fast enough to draw conclusions. At this speed, the foil does not stall at very high angles of attack (bows over a metre out of the water, stern about 150mm immersed, rob hanging on tight) and moving weight forward to level the boat out brings it back to level but without enough power to fly.
Outwards pointing foils / \ are inherently unstable, unlike \ / foils. It was still possible to get it flying on just the 2 foils, but the added height caused the prop to ventilate.
It was interesting how forgiving everything was. Much slower movements required than for say a foiling kite board. I will put some movies up on the blog soon.
It occurs to me that canting the rudders on the leeward hull could do the same thing and the canting could control the turning and leeway of the boat at the same time.The foils would work better on the outside of the hull rather than between the hulls. Basically the leading foil turns the boat to the windward hull, vertical has the most turning moment and the more horizontal the foil the more lift and less turning moment and less resistant to leeway.
Works better, but much harder to support. Plus, a kite is non heeling (supposedly. I managed to flip the kite powered Laser last week) so the extra width is not needed.
There are two downsides, that I can see though. The first is that the turning momentum would be similar to a rudder restricted to less than 5 degrees or so. and the second is that the trailing foil would be exerting more upward force than the forward foil, aggravating the bow down attitude.If you went with two axis control of the rudders then there would be no downside (drag penalty) other than the additional hydraulic ram.
It is a big ask to steer with the foils that are flying the boat, unless they have vertical ends which would be very good, but hard to steer.
Or perhaps more interestingly, you could go with an asymmetrical lee hull to compensate for the leeway, add two canting rudders to the outside of the windward hull and have a fully foiling hydrofoil.
Assymetric hulls are very low aspect ratio foils, so don't work very well at leeway reduction. They also don't work very well if the hull is flying!
Your current rudder configuration is already close, and you are currently paying the drag penalty for surface piercing foils anyway. I am thinking J or C shaped foils : )
J and C are much harder to build. The ones I have cost a couple of hundred bucks, were made on a sheet of mdf and are mounted with galvanised bolts and a ratchet strap. J and C foils kicking up in a collision is also a big problem. The straight ones are not.
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Posted by: Rob Denney <harryproa@gmail.com>
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