circa 1975 18' starfire tri-hull help!

ok guys, this boat was acquired by my grandfather form Francis Ford Coppola when he was filming Apocalypse Now in the Philippines. In the early 90s a strong typhoon hit us and the boat was left out for a couple of years. I have never owned a boat so I dont know much about it. All i know is this boat is a 18' starfire but i cant seem to find any information on the net. The engine has seized so if ever i will have to replace it. Was thinking of converting it to an outboard. Hopefully you guys can shed some light on it. I am thinking of restoring it so any of your inputs will be highly appreciated. Since I am from the Philippines the boat will be used in the ocean. I read that tri-hulls dont really perform well in the sea so thats one issue that makes me think twice about the restoration project. Would it be worth restoring it?
Here's a link for more pictures http://gallery.me.com/mikecancio#100073&bgcolor=black&view=grid