If you are thinking of the KiteShip type setup, then they can be attached anywhere you think is strong enough. On a beach cat, a good place would be on the main beam at the inner gunwales. Perhaps with a turning block at the bridle tangs. You don't want to attach to the mast, as the point is to eliminate the heel moment. When we set this up on Afterburner (a 52ft beachcat) we used a halyard line on the mast to control kite height when launching/recovering. Everything else was at deck level.

See www.KiteShip.com for details on their systems.

Mike.