I concur. Marine VHF radios need to have Part 80 acceptance from the FCC. There are VHF LMR radios out there that have Part 80 certifications, some of the newer Kenwood's do.
But, the 3dB difference between 25 and 50 watts won't mean much.
Instead, get a good Marine 25 watt radio, as it will have the functions that you want. Get a power supply suitable for 12 to 15 amps or so. If you really want to make a difference in your set up, put your money into the antenna. Skip the cheap fiberglass antennas designed for boats. Instead, put the money into a decent base antenna designed to cover 156-160MHz. Use good coaxial cable, nothing less than 1/2 inch heliax or LMR-600, better if you can afford it. Get the antenna up as HIGH as you can. Since there isn't much in the way of topographical shielding on the ocean, your distance is limited by antenna height. The higher you get your antenna up, the farther away your horizon is going to be.
It's been a long time, but back when I was in the Coast Guard, I seem to remember MSF-5000's Motorolas being used in some remote base set ups. Not sure what they use now for remote bases, but remember, they fall under the NTIA, not the FCC.