Morning Memart. I'd go with a base unit. Some portables are spotty enough that you can just barely communicate with vessels that are within visual range. Portable units are great when connected to long, good quality antenas but in my opinion, that just defeats the purpose of portability. As it IS a security item you also don't risk forgetting the portable "in another coat" when you really need it out on the water. If you're still hell bent on getting a handheld, you might want to PM Wayne (Irishfield). He has experience in maximizing a handheld unit's range.
Good luck, hope it works out for you.