Racing Cat: Shared Lift/Curved foils

[Doug Lord]

A long time ago Bill Roberts came up with a concept he calls shared lift for the Arc 21( http://www.aquarius-sail.com/catamarans/arc21/index.htm ). In short ,it allows the daggerboard to be ahead of the forward beam and maintains balance because the board is a bit smaller and the rudder a bit bigger than normal. It also improves windward ability and tacking speed as compared to boats with a sort turning arm.
It occured to me today, after thinking about the A class rig positions shown in the document below( under pictures), that this system coupled with curved foils on the daggerboard and rudder might provide the ideal catamaran "foil assist" setup.
The advantage of shared lift would allow the daggerboard to be much further forward while not affecting balance. And by using a curved daggerboard the vertical lift generated would have a much more controllable, positive effect on preventing the bow from buying while helping to lift the boat,reducing wetted surface and drag. I think this system would allow a tighter curve than is currently being used with a greater portion of the daggerboard area used for lift.
As an additional aid(while underway) in helping to reduce wetted surface AND reduce pitching I'm proposing curved lifting rudders as well. The rudders would be shaped more like the Hobie Trifoiler main foil(pointed inward) and would retract in a cassete vertically.
Any thoughts or comments are welcome....

see this thread: Foiling/Foil Assist: Martin Fischer A Class Cat


Pictures,L to R:-1) Arc 21 with daggerboard forward of main beam, 2) Nacra curved foils-the proposed boats foils would have a tighter curve and draw less water,3) & 4) the Trifoiler foil which would be used on the rudder of the proposed boat albeit with less horizontal foil area, 5) Picture of Martin Fischers semifoing A class Cat-notice how far forward the boards are compared to the boards on current A Class cats in the pdf below- CLICK ON IMAGE :

[Doug Lord]

This is a rough sketch showing the daggerboard position using the system described in the first post. This allows substantial vertical lift forward which could allow the boat to be driven hard. The curved foils have a much tighter curve than normal(rule induced in the A class) and the boat, as sketched, would not be A class legal. Also keeps the max board down draft to about 2.2' for an 18 footer.

click on image: (mast position same as the ASG3/XJ A Class cat in the previous post pdf)

[Doug Lord]

More information on curved lifting foils is available here: Advantages/ Disadvantages of Curved Lifting Foils on Monohulls/Multihulls

Also check out the new Sailracing magazine-subscription here(free): http://www.sailracingmagazine.com/back_issues.html