That looks like a unique piece of history...nicely restored too! I don't have any idea what that is either.
However, the design of the boat looks like it will just be prone to submerging the bow. The stern of the boat (with what appears to be the gudgeons where the rudders attach) seems to extend very far aft while the bows are very short in relation to the ****. The bow submarining appears to be largely due to the nature of the design. Ideally the amount of bow out front should look like the sterns do now...if only you could move the **** and mast back closer to the rudders!
Everything that Carl said above is certainly true. Try raking the mast back as much as possible and keep your crew weight as far toward the back as you can in order to minimize this tendancy.
Do you know what kind of catamaran it is?
