system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it more efficient for large ships to be powered by Diesel-Electric or similar two stage powerplants? I thought changing energy types and systems always involved losses.

For example, aren't you losing a small % of energy converting the diesel in your car into power to move your car?   
So then, wouldn't you lose more % if you used diesel to then make electricity and THEN power a ship?  
IE: The longer the chain of conversions, the less efficient your energy transfer will have. But I know large ships use an extra step compared to cars or a regular engine, why is that better for large ships?
gpt
Because the alternative would be hooking the diesel engine directly to the motor of the ship which is less efficient and leaves you without a source of power for anything electric on the ship. 

ICEs and diesel engines have an optimal performance window for RPMs. You can make a diesel engine really efficient by running it at one set rpm and powering a generator and using the electricity to actually do the work you need done.

This is the reasoning behind diesel electric locomotives as well.