Hi John
A long skeg may well be the answer.
However, I have stopped developing my cat as I am in the process of building my next contraption....I reckon I have found quite a fast hull shape so am making a much lighter monohull using the same hull shape but with hiking racks. I'll be experimenting with amas on each side to add a bit of stability. All up weight is on target for 35Kg using an 8 - 9 metre windsurfer rig and 16 guage alloy tubing for the racks.
Apologies for mentioning the word monohull on this great forum.
Andy