Sigi,

This was the first question the oldest and most experienced multihull sailor in Brazil asked when I first showed him my dream boat. All fins are potential kelp-catchers and more fins = more kelp to get read of...

To date, none of the Catri owners I am in touch with complained about kelp or debris catched by the ama's foils. I guess the problem is minimized because the foils are swept-back and/or because the ama's foils are designed to go in and out of the water in higher speeds.

Anyway, I think the cross of the rudder blade with its foils is a stronger candidate to catch kelp - but the rudder is also easier to clean.

There is another risk as well - solid debris in high speed. I was informed that the guys in San Francisco exceeded 30 knots, so I started worrying and asked the builder in Brazil his opinion.

He told me not to worry at all and that a worker once fell very heavily over one ama transom, the foil geting all the load. The worker broke his leg, but both the foil and the foil/ama seam remained unscratched.

Cheers,
Luiz