Twin Rotating Foils on Multihulls/No Daggerboard

Why wouldn't twin foils similar to the foils used on CBTF be adaptable to multihulls -probably in combination with a system like VARA so the foils can be retracted? Or VARA on the front foil with a standard kick up rudder? Leeway elimination, vastly improved manouverability, adjustable balance with different sail combo's would seem to be some of the benefits...

[usa2]

probably because there are asymmetrical foils (banana boards or whatever they are called) available for multi hulls and they are more efficicient than a symmetric board. And you can change the balance of the boat just by raising the board. No need to make it all complicated.

Banana boards are daggerboards that are curved so as to form a vertical lifting surface towards the bottom of the foil-not necessarily relevant to twin foils; they're used to partialy lift the boat. However, nothing says that the twin rotating foils couldn't be "l" shaped(and partially retractable) or have small t-foils on the bottom for partial vertical lift just like banana boards along with the possible advantages of the twin foils.Nothing says the twin foils couldn't be asymetric for that matter...
Bill Robert's "shared lift" concept for the ARC 21 is halfway there with the daggerboard forward of the forward cross beam and smaller than the rudder.
If tacking was dramatically improved; if collective worked well enough(both normally and tactically) and if the advantage for adjusting the boats balance was significant enough it might be a good idea-maybe somebody out there has experimented with it?

[Steve Clark]

Doug:
In something like 1965 Van Alan Clark's Beverly ll had daggerboards that could be steered and operated very similarly to the VARA system.
You could steer with either the rudders or the daggerboards, but he mosly envisioned being able to gybe set a positive angle of attack on the daggerboards, there were tillers and a cross arm with a comb. Increments were 1degree as I recall.
The daggerboards and rudders dropped through cylindrical cassettes, the only difference being that the cassettes were smaller than the 100% chord of the foil. There was a slot in the bottom of the hull to let the foil pass. The top of the board turned into a keyed shaft.
Pretty clever but failed because you just can't build stuff like that out of polyester and glass. Done out of carbon....
This and other examples really call into question the enforcability of the VARA patent.
SHC

[Daniel Charles]

This is not precisely an answer to the question, but I used in 1982 twin NON-rotating foils for steering. Each foil was warped, in such a way that the deeper it was lowered, the largest its angle of incidence. There were twin foils, interconnected to the tiller, which lifted one foil and lowere the other. I tested it on a 5.5m sailboat with kite rig. It worked pretty well, like a normal rudder but with only a third of the wetted area. It was a canard arrangement.

[rob denney]

G'day,

No reason at all why it wouldn't work. This is exactly the system we have on Harryproas (we call it the TFFB system Twin Foil _Floating_ Ballast ) and it works a treat in terms of negative leeway , as I discovered on the weekend on my 25 footer, which has the rudders mounted on the sides of the hull.

Unfortunately no one else was out sailing so I did not get a chance to see if the gain in height was balanced by a loss in speed.

What was far more noticable is the gain in speed when the front foil is lifted on any course other than hard on the wind. in my opinion, if I was limited to a single movement on a foil, it would be raising and lowering it, not turning it.

Steve Clarke, if you read this, could you drop me a line, please (proa@iinet.net.au). I would like to run some ideas past you for the next LAC, if you are interested.

regards,

Rob
www.harryproa