Aircraft engines are designed to be light, and sacrifice low cost and the ability to burn cheap diesel fuel for that.

Ship engines are the way round: their weight doesn't matter much, but it matters that they use the cheapest fuel possible.

Exactly. In fact, for some applications GE are using modified aircraft turbines on ships: https://fas.org/man/dod-101/sys/ship/eng/lm2500.htm

Those are for military use, where speed matters but money is basically unlimited.

Money is unlimited, but fuel efficiency isn't just about money for the military. More fuel usage means more supply lines. That's less of an issue for navies than armies but still important.

I see your point but aircraft engines can burn diesel, and many small power plants and backup power stations use aircraft engines in stationary services with diesel fuel.

> Aircraft engines are designed to be light, and sacrifice low cost and the ability to burn cheap diesel fuel for that.

Small correction: aircraft engines generally use kerosene-based fuels (Jet A-1, Jet B). Also cost-wise, aircraft-grade kerosene costs more relative to other uses of kerosene since those applications can tolerate kerosene of lower quality than aircraft-grade kero.

https://en.wikipedia.org/wiki/Aviation_fuel

That's what I meant by "sacrifice ... the ability to burn cheap diesel fuel". Probably worded ambiguously :(

Your sentence was fine, and I don't know if anyone thinks jet engines burn cheap diesel fuel, do they?

The entirety of the drive train is huge. You have to turn two propellers which have to propel a ship weighing thousands of tonnes. To produce the necessary torque you need to have some big components. The supporting infrastructure you need to heat and circulate the fuel, then to supply it to the engines is another thing too. Gas turbines are much smaller but would be unsuitable for this particular application as they have good efficiency only at high loads. The range of loads this is used for would mean they are unsuitable.

A number of very large cruise ships now have the drive entirely decoupled from the fuel burning engines. Same idea as a diesel electric locomotive. Big engine burns heavy fuel oil, turns generator, power goes to electric azipods.

Smaller new vessels do this too.