Hi FF, what's a baseboard radiator?
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These are a piece of copper tubing that has aluminum fins pressed on that simply radiates heat by convection.No internal fan is required.
Probably the "best" US heating system made was the old Way Wolff.
These are home style gun systems that were built to pass USCG requirements for inspected boats.
They were bulky and quite expensive , but as reliable as house units , a claim the truck take outs can never make.
One problem with HW heat is the problem of mental masturbation in it is difficult to STOP , adding features and complexity .
The furnace can heat domestic hot water , towel racks , pre heat the main engine & tranny and noisemaker.
With a bunch of thermostats individual compartment heat (zone control), cool in the sleeping area , normal in common spaces and warmer in shower area , EZ.
With a few valves the main engine or noisemaker can serve as heat source .
Keep a good schematic if you go wild.
Your boat photo shows a larger boat , 2 truck units might be not much more than a single big unit and would allow redundancy or parts scavenging .
Frankly I , with a boat that is large quite , would consider a home style furnace .