Suggest you go to FX sails site and fill out the estimate form for your boat.. I think you'll end up with sail dimensions from that.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)