[nradov]

Fusion fuel isn't going to be free. Fusion reactors aren't magic: in a sense they're very traditional in that they will be used to turn water into superheated steam that spins a steam turbine to drive the propeller. Just like in 1897. Even if the fusion reactor could somehow magically be made maintenance free, the steam plant will be maintenance intensive. Ask any engineering officer who worked on a steam plant, regardless of whether the heat source was fossil fuel or fission. This is part of the reason why merchant ships switched from steam turbines to diesel engines decades ago: lower maintenance costs and lower crew training requirements.

Maritime fusion power could be a good idea but you have to evaluate complete system lifecycle cost instead of looking at just one component.

[DennisP]

Fusion fuel will be close enough to free. Deuterium is less than a thousandth of the hydrogen in water, and there's enough in your morning shower to provide all your energy needs for a year. A liter of heavy water costs about a thousand bucks.

For DT reactors, lithium is the other side of the fuel equation, and at the scale we need that's really cheap as well.