Pete,
When considering a A cat, the thing that might be a consideration is what is the core material is in the hulls.

I would want to know what fabric (carbon, kevlar or glass), what glue (epoxy, poly) and what is the core material.

As far as core material.

You can get nomex, foam, end grain balsa cores. The carbon is the skin on the outside and inside is made stronger by being held paralell by the core. Think about an I beam truss, the web (middle part) is like the core, and the caps are like the carbon skin. the whole is stronger than the parts. The American cup teams are now using honeycombed aluminum over carbon skins. The core holds the skin in suspension and it makes it stronger as a whole system.

The A2 was balsa, and I believe they have switched to nomex. (someone correct me please if I'm wrong here)
Vectorworks marine is using corecell foam as a core.

http://www.spsystems.com/solutions/...cell_A_Foam.pdf#search='corecell%20foam'

All of these core materials have advantages and disadvantages. Nomex is the lightest of the cores, is hard to get, and it is widely used in the construction of airplanes. It lays in the molds very easily, especially the OX (overexpanded) stuff, so its a very easy choice for the homebuilder. But its a open honeycomb, so any pinholes in the skin will absorb at least a little water. Nomex is kevlar paper honeycomb, so I'm not sure if the water will pass between the cells in the honeycomb. In order to get a good bond to the nomex, you need to be very careful when you are laying up the skins.

Balsa endgrain is wood, so it will absorb water if the skin has any pin holes. But balsa is the least expensive core material and some research shows that wood holds up better to long term cyclical loading.

I went with foam, and you have different types of foam on the market, Corecell, Divinycell, Kegecell and Airex all have different properties.

The Vectorworks XJ uses Corecell, which is very stiff and will not absorb water. I think foam over carbon gives you the lightest, stiffest, and most water resistant hulls.
Foam retains its shape, so it doesnt want to lay in the hull molds, you need to either heat it or coax it in or both. Supposedly Vectorworks has this figured out and uses some combination of heat and pressure to get the foam to behave. I used a heat gun and weights. Not exactly scientific and it took forever.

Bill