Andy, at the risk of sounding dull, consider that a CB radio -- while maybe useless outside of America -- is a handy device. A good, solid model that'll work just fine on the salt should not cost you more than $100 US. If you pay more you'll be paying for knobs and levers and switches and dials -- that don't make the danged thing work any better for you.
Glen is very correct when he suggests a roof-mounted aerial/antenna. The short ones with magnet mounts - do work well. Longer is better, alas, and those with magnet mounts will work very well. Stay under $100 for the whole package - antenna and radio.
Whether you need one for BMST or not isn't part of my response, but rather one of our yearly comments about CB radios. I hope this helps someone.