Propane is heavier than air, would sink into the bilges. The tanks themselves are a risk. All propane tanks have a pressure relief valve for venting if they become over pressurized. If there were a vessel fire, the tanks would become bombs. Storage of tanks on the vessel would also be an issue. Electric cooking appliances are safer. Unlike home construction, vessels are required to use stranded wire instead of solid core, like Romex. Stranded wire prevents vibrational failure of the whole conductor.
For private boats most of them already have an issue, since they are gasoline powered.
For the tow boat industry, their standard used to be diesel fired cooking.
Gunner
When my Dad owned a cabin cruiser, CNG was the cooking gas recommended by UL.
Not as hot as propane but lighter than air. And always run the bilge blower before lighting the stove or starting the engine, especially if gasoline powered.
Prayers for those poor souls.