Foiling on a canting keel ...

… is possible on a 155cm model yacht:
We added to the canting keel an angel of 5 degrees, viewing from bow to stern. The keel lifts the bow out of the water. Now we try to add foils to the daggerboard and rudder.


Maybe a lifting foil on the leeward side of the hull, but not on the windward side. Adding angle of attack to the canting keel will negate the righting moment and increase the drag at the same time.

Better photo of the new Vendee boat design. Reaching and downwind performance is improved.


I’d like to shed a little light on KPI… Keel Pin Inclination.

It really started with Juan K and the ABN Amro Volvo boats, He also added a recess which reduced the high pressure zone at the keel/hull interface which reduced drag from the water flowing over the upper surface of the keel and added yet more speed. An additional technique that is still employed today.
KPI was 3 Degrees, and did supply lift, but there is a “but”
It is all about roll centres. With wide powerful sterns, as the yacht heels it also pitches bow down. The wider the transom, the more exaggerated the effect.
When you remove the pitching down angle from the KPI of 5 degrees you are left with 2-3 degrees of lift angle from the keel fin- which helps counteract the weight of the Bulb.
This is also removing righting moment, so designers added yet more beam, for more leeward lift and moved the daggerboards inboard and more vertical. so the Volvo’s in 08/09 were bang on max beam, and gained lift from the boards too.

Fast forward to 2015 and we are building ocean going monohulls that can sail at nearly twice the wind speed and are nigh on fully foiling. If we could have T foil rudders, we would…!

If I had on concern with the design of the M155, it would be that it is too narrow. You need some additional beam to carry the sail area it has and I feel that foils are not going to help as much as you might think.
Foils need forward speed to generate lift. They are also a source of a fair amount of drag. If you add a foil to a narrow & overpowered yacht, it will not be a magic solution. Without the beam, its not going to power up enough to get you into the speed range where board will generate the lift you need to to right the boat and lift it clear to start reducing the wetted surface. If it does, then the foil shape is not going to be optimised for the upper speed range you are targeting…More likely, its slowing you down for a greater percentage than assisting. I.E - it will have a very narrow operating range.
There is a huge amount of study both practically and in theory before the beam is decided upon. This foil assistance is another dimension which we are only really beginning to explore.
If you can get the ratio of beam and foil correct, the rewards are amazing.

I have done a similar thing scaled down, with Big asymmetric sails and foils. My goal was to be as light as possible and the solution was a canting canard which had a T foil. Simpler = lighter - I needed just one additional channel for the keel control and the canard canted proportionally to the keel on the same Mech. A 1000mm boat weighed just over 2 kg all up. If anything, it was too light as it slowed too much tacking!
Just can’t win!