I believe diesel may be somewhat safer than propane on board and, in the winter when I wasn't doing much sailing, I had a tank full of fuel to keep me warm.

Now that I am in south Florida and don't do much sailing in the hurricane season, I have a tank full of fuel for the generator should the electricity be knocked out.

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It seems to work well. It is a cp12 platinum cat heater installed by the original owner I think. It still works all these years later.  Here is the website http://ventedcatheater.com/

Ours is a 70's brown color but looks identical to this. When if first lights up it will have a tinge of red glow to it but soon it is just black and radiates heat. It is thermostatically controled. It will turn itself on and off on it's own if via thermostat if the power to it is on at the DC panel. All exhaust products are vented outside the boat so it is a dry heat. We don't get moisture buildup in the boat like most propane heaters create, nor do we have to worry about carbon monoxide. Though it is pretty voltage sensitive for starting.. It pulls a very short burst of energy to heat a glow plug that starts the combustion process. On that circuit we have a voltage drop that sometimes causes it to not ignite. The current battery project will be fixing that issue as we are checking and replacing wires or cleaning ends of connections to fix high resistance in some circuits. It has an automatic failsafe that turns the propane off if it doesn't ignite.

Thanks,
Sophi