I'm experimenting with these German wall mount small space heaters in my home. I have several extraneous bedrooms and bathrooms which are used sporadically or only in summer season. I installed one of the 2000 watt 240 volt models and very pleased with the air flow and heat output.

That got me thinking these are adaptable to living aboard. Electric makes sense for dock boats. No flues, no fuels, no tanks, no lines. And it's quiet, only the whoosh of the squirrel fan. Plus simple installation and very affordable. $150 for the 1500 watt.

Unlike cube or other portable electric heaters, these direct a substantial amount of heated air toward the floor(sole) and pull cold air at floor height into the back of the unit. Sets up a nice flow that evenly heats a large bathroom(which is not directly heated otherwise), nicely. Accurate thermostat works well and I'm using the timer-ed version that you can set for full heat which then reverts to thermostat setting after it times out. Plus, they have a frost prevention that comes on at 45 degrees, even if thermostat is turned to lowest(off) setting.

You can get models that run on 1-15 amp 120v circuit and put out 1500 watts. Probably enough for most liveaboard boats and areas. But the 2000 watt is 25% more heat, if you have 240 volt at the dock. That's more than 6,000 btu output, about the same as 10 lineal feet of radiant baseboard.

About 12 x 14" or so and sticks out about 4" from the wall. Designed to hard wire only, I'd wire it to remove easily and stow when you're not on a dock.