James Hleba wrote:

All this info is fantastic thanks! I think I will just play with foil only on the dinghy.

Something like this?  https://www.youtube.com/watch?v=yh3tnu1EPeQ

John Bull, the founder of Solway Dory had a dory converted into a double Bruce foiler like the Foiler 21 by fitting a set of cross beams and two flat plywood plates.  Even something as simple as that worked.  I actually have a set of foils that should be suitable, left over from a different project.  They are light for their size, but would still make a largish parcel.  I don't know how much it would cost to send them from Trondheim to Washington state.  If you want them, you can have them for the cost of postage.  Contact me if you want pictures of the foils.

James Hleba wrote:

I am just musing here and think it is a really cool concept. Any folks have experience with this?

From what I have read, people that have built foil stabilized boats seemed to like them and they have been proven to be fast.  I have never seen such a boat, let alone sailed one. Have any of you folks worked on foil stabilized boats or is it one of those things best left in the 70's?

Paul Ashford reported on his Bruce foiler experience in an AYRS publication, saying it worked just fine on a lake, but when he took it out on the North Sea, the foil tended to pop out of the water when it was to weather.  The problem is that, with a fixed foil, there are conflicting requirements for dynamic stability when the foil needs to lift or pull down.  

When the foil must pull down, you want the downwards pull to become stronger as the foil lifts.  That can be achieved by the upper part of the foil having a steep angle to the surface, and the lower part a shallower angle.  Then as the foil lifts, the force vector becomes more vertical.

When the foil must push up, you want the force vector to become more vertical, provide more lift, when the foil goes down.  You get that from the upper part of the foil having a shallower angle, and the lower part a steeper angle.  The compromise between the two is the straight foil, and that is still vulnerable to popping out in a seaway.

A proa leaves the foil on one side, and it can be designed accordingly.  Fritz Roth is extremely enthusiastic about what he calls the vector foil proa (he developed the idea independently of earlier AYRS publications).  He says a 7 metre long boat worked wonderfully.  You can find videos of models on youtube: https://www.youtube.com/user/vectorfoilproa  

Once you make the foil movable, you can get around these problems.  I wrote an article on hinged foils in AYRS Catalyst #23: http://www.ayrs.org/catalyst.htm.  (That issue also includes a description of a very interesting wind-vane self steering system that won the AYRS John Hogg prize.)  I followed up in Catalyst #45, describing my tests of a hinged foil system on a radio-controlled model.  It did have more stability than its counterpart with a keel, but seemed slower.  I attribute that to more bits breaking the water surface and creating wave drag.  At the time, I thought this was reason enough to give up on the idea.  Since then I thought of another design, and will have to see when I find the time to build a model to test that.

Then there are John Slattebo's designs, Bruce foilers whose foils you control by hand: https://www.youtube.com/watch?v=tzPYbzbdOTg and http://www.raptor-uk.net/.  I had a Raptor for a while.  I found that a very high aspect ratio foil and very light weight outrigger hull to windward are not enough to keep you upright when you stop.  If you don't want to control the foil by hand, you could use a forward feeler like the Trifoiler: https://www.youtube.com/watch?v=zXSgZCDVWOM  It looks like you could use that system on one side only to make a Bruce foiler, but Ketterman used it not only for stabilisation, but also to make the boat fly. 

David Thatcher wrote:

There seems to be a lot of current work going on with foils. Obviously the Americas Cup catamarans, and I now see quite a few smaller foiling catamarans sailing around our local Auckland Harbour. I am sure I have seen some articles about foil stabilized larger monohulls yachts in Yachting World and there is talk about use of foils on Mini-Transat yachts.

As I see it, hydrofoils on sailing boats have up to four functions:

1) Steer

2) Control leeway

3) Increase stability

4) Lift the boat out of the water.

Plain Bruce foilers do 1 - 3 with a simple design, but have the problem of the Bruce foil popping out when to windward in a seaway.  You can get round that with a little more complication, but if the boat is light enough, you might as well also fly.  The foils of a Trifoilers perform all four functions.  If you want simplicity and sail in rougher water, just put a Bruce foil on each side: https://www.youtube.com/watch?v=AAkeWQi8r-s

The foils of America's Cup catamarans don't offer more righting moment than the hulls they lift.  By increasing the lever arm between sails and what remains in the water, they actually increase heeling moment a little.

A nice explanation of the Dali moustache foils on monohulls is at https://www.youtube.com/watch?v=YHtp6FMUzDc

Hello all,

I have been doing a bit of reading (dangerous!!) and came across an awesome book called Design For Speed Sailing I think it was AYRS 82 and came out in 1976.

If you are not familiar with the Bruce foil system, it uses a single board with a low aspect ratio foil at a critical distance from the main hull like an out rigger proa. The foil grabs in and pulls to windward while lifting on leeway side.

In AYRS Hydrofoil options, a nice illustration with a reduced sized float that also keeps the boat stable and balance at rest. This design has the foil split in 2 with part in the front and part in the back of the float as 2 foils are less likely to loose grip or be pulled from the water at the same time.

I am just musing here and think it is a really cool concept. Any folks have experience with this?

From what I have read, people that have built foil stabilized boats seemed to like them and they have been proven to be fast.  I have never seen such a boat, let alone sailed one. Have any of you folks worked on foil stabilized boats or is it one of those things best left in the 70's? The foiler seemed to be in a great state of development leading up to the untimely death of Edmond Bruce. From my readings and the scraps of info I can find, research seems to have stalled on the matter since then.   

I would love to here from anyone that has tried this! If I can be convinced that it is a seaworthy design (rigorous dingy testing in bad weather) it sure would be neat to drop 4400 lbs as far as power to weight ratio goes. Mr. Bruce also claims through all of his research to have created a non heeling boat. This is cool.  

Was it a great idea with unenthusiastic development, or just a proven flop? Any first hand info on the subject would be the best. If folks are interested and it is ok I may be able to take a few snap shots of the illustrations from the book.