Curved Lifting Foils on Cruising Cats??

IMHO the only gain will be the boat looks faster (only looks !) and cost more

 

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Just for comparison, on a racing tri like Gitana or Banque Pop weighing about 15.5 tons, the maximum total lift and/or downforce on the mainfoil is around 2.5-3 tons.

 

Their higher speed capacities give them of course also higher lifting forces, I would be surprised if it was otherwise.

 

Given the curve of the board, if the lift is resolved into vertical and horizontal components, it seems to me that about 75% of the lift is horizontal (pure guess). So a C board is pretty inefficient if your goal is to reduce drag by lifting the hull to reduce wetted surface. I think their main benefit is to prevent the lee bow from burying (effectively increasing RM) so the boat can be pressed harder, or just be better behaved if sailed more conservatively.

It would be interesting to measure the effect vs a small canard foil mounted closer to the bow—but that might raise questions as to why it's needed (when C boards are somehow excused from that discussion).

But like others, I suspect that the curve in the Catana boards is more for reducing the intrusion of the boards into interior space, a happy payback is a bit of lift, modern looks and ability to make rapturous marketing claims. It's undoubtably more expensive, but probably insignificant in the cost of a 20m luxury cruising cat. Value for money? You'd have to ask the owners who can feel smugly superior to owners of straight–boarded cats without ever putting it to the test.

 

That's in accordance to what Catana claims... (the link needs for me a few seconds to open up at the quoted piece)

‘‘ . . . . curved foil-type daggerboards to help avoid the risk of "tripping up" . . . . ’’

According to the vids and pic in post #129 in the other thread they sail a lot with both boards up, a simple test for speed gain would be to drop them, and ‘‘ . . . to optimise the pointing angle . . . ’’ from the first above link would also work better with the lee board down when they're not straight down wind sailing.