A good small-power FM radio station option is available from the guys at www.mobileblackbox.com
. They have transmitters that will run on 12 volts, and the big one, the Orion-5000 has a 5-watt power output; enough to get in trouble with the FCC rather easily.
I use the Eclipse-4000, which in practice has a transmit range pushing a mile on good days. It has switchable mono-stereo output; stereo is a tiny bit noisy due to the multiplexed signal, but mono operation is very quiet; and seriously, who really can appreciate stereo in a raft-up anyway? Yes, you lose a little fidelity, it is not the audiophile solution that a hard wired link can be, but it is WAY better than those little cig-lighter plug-in FM things...
On our boat, I have created fake radio station ID tags, commercials, etc. You could also do commercials for bogus memorial day lakefront concerts, bogus lakefront restaurants, and even commercials with directions on how to get to your favorite party cove. It is a blast to have those sprinkled in on your playlist.
For FM, if you choose to go that route, remember a few guidelines that will keep the FCC away:
1. Never use a radio station call letter, ID, like KCOV, or WREK; that is a big no-no with the FCC; as it is basically fraudulant. Use a station name, like "DAX FM 105.5" or "107.3 The Duck", (my bogus ID).. no fake four-letter station ID's.
2. Never broadcast profanity, bad language, or explicit/graphic content, another no-no.
3. Never purposefully or knowingly step on another legal licensed transmission frequency. Here is a handy website that can give you a good recommendation for a clear channel near you: http://www.radio-locator.com
This cann be the big one, as a small local radio station can throw a fit, listen in, figure out where you are and then call you in. That is the most likely scenario that will cause you to get a visit. Be a good neighbor in the FM neighborhood.
4. Know that you are operating in a very gray area legally; there are lots of proper uses for this type of equipment, but as many that can land you in hot water. I personally believe that if you follow the guidelines above, in a transmit radius, (power) that is appropriate, (i.e. you probably do not want to buy the 5-watt transmitter) and you are not on and transmitting except for the times you are rafted up, you probably will not get harassed.
Oh, and p.s. I do not advocate or recommend this behavior, I only show you where and how so that you can get in trouble if you want to... that is totally YOUR decision!