Just a spray rail. Look where it fairs back into the hull. The Mk1 hawk had a problem with the spray from this area flowing over the rounded deck and hitting the main beam making the leeward hull a very wet area for the crew.

Cheshirecatman

OK, I can see that. I can really feel that water washing over the deck and hitting the front beam on the I20 and it drives me nuts. Nacra solved that on the Infusion by making the top forward deck relatively flush with the main beam. They wouldn't stop a pitchpole but maybe you can get a little lift out of it with those chines (or whatever you would call them).

It's not like this is a new concept, although the implementation is different.

Shark Catamaran (check out the spray deflector on the bow):


If you look closely at these Cougar catamarans, you can see the same spray deflector (this is from 1965):

It could also be to add stiffness locally, or just styling.

Gareth