In addition to the good doctor's advice, if the boat has not been kept pristine you may see some significant rust on the keel (cast iron IIRC). External rust is mostly cosmetic and can be blasted/faired with a bit of work.
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)