So you want a regular marine radio, which you are going to have to wire and install to your boat. I guess at this point I don't understand why not then go through the extra hour of trouble dropping some line and holes for passive speakers if you're going to go THAT route. If you're going to install a system install it the way it's intended. That's too many connections that can go wrong in my mind. Passive speakers attached to the radio will use much less power and be much less frustrating to fail than a mounted radio trying to independently connect to a bluetooth speaker.
Bluetooth, Radio, can buy more than one and link them (wirelessly? Can't tell, looks like you need a wire).
There are many examples of free standing single-unit bluetooth speakers with a radio including from Bose that have an FM/AM receiver.
Use duct tape or rope you don't want to make holes.
It would be interesting to see a hard radio wired to a jack to connect to a free-standing bluetooth TRANSMITTER so that you could randomly connect other speaker devices around. But again as earlier that is getting a little complex of a system for my tastes, and an extra bob that needs it's own power, settings, button presses, and connection.
The whole thing is FAR too much trouble in my mind considering the ability of smartphones to stream and download massive amounts of data, even with small amounts of signal. Obviously that's not always a perfect solution, but nothing is.
There are cellphones that still come with FM/AM recievers installed on them and there is a movement to make sure this continues or becomes available;
Free Radio on My Phone
For what it's worth I am a musician and teacher, I've played in some major halls and done quite a few recordings of varying qualities. I'm of the opinion that all recordings are facsimiles and they need to be taken as that. It will never sound like Carnegie, so I just enjoy it for what it is. There are low quality recordings that I enjoy more than the artist live.
I use a Philips Shoqbox that I found on slickdeals.net one day. It gets plenty loud. My sound system is my phone and that. The shoqbox at full volume lasts a ridiculous amount of hours.