To the best of my knowledge main stream Diesel Locomotives were Electric Traction for motive power.
No Idea about ships.
@boatgeek ?
But I found this:
https://www.brighthubengineering.co...re-the-main-types-of-ship-propulsion-systems/
So here's a primer on boat propulsion systems. This is likely long enough that I won't talk about propellers. If there's demand, I can come back with another whole set of nerdy facts. When I talk about efficiency below, I mean mechanical efficiency from the engine flywheel to the propeller. There's other factors in how efficiently an engine runs that I'll talk about in the text, plus more about propellers that I won't get to here. I'm also mainly talking about diesel engines. Gasoline is more or less nonexistent in the commercial world I work in, and gas turbines have a very small niche. The link above has some stuff that I think is off the mark, especially about electric drive systems.
From simplest to most complex, we have...
Direct drive or
Direct Reversing
This is the most common propulsion train on large cargo ships. It's pretty much what it says on the box. The engine is directly connected to the propeller shaft and propeller, with no gearbox, transmission, clutch, nothing. If you want to go in reverse, you stop the engine, let the propeller come to a stop, throw a literal or metaphorical lever on the camshaft to change valve and injection timing, and restart the engine in reverse. Needless to say, you don't want to have to do a lot of maneuvering with these engines, so tugs assist these ships in to the dock. These engines are extremely large, roughly the size of a double decker bus, run in the tens to low hundreds of thousands of horsepower, have cylinders you can sleep in, and run at low operating RPM, like 40-120 RPM. They also don't like to change speed very fast, so the process of ramping up to full RPM from idle and vice versa can take an hour or so. The upside is that the engines quite happily burn any kind of fuel (heavy fuel oil isn't too far from asphalt), and are very efficient if you're crossing oceans.
Efficiency: ~98%
Geared Drive
This is the drive system of choice for most of the boats I work on, which are small to medium (50'-400') commercial boats like fishing boats, tugboats, ferries, etc. The engine drives a reduction gear that drops the full throttle RPM from 900 RPM -2300 RPM at the engine to 150-1000 RPM at the propeller. As a rule of thumb, fast boats have small propellers turning fast and slow boats have large propellers turning slow for maximum efficiency. The reduction gear often has a reverse gear in it as well. Both forward and reverse are engaged or disengaged with clutches--the gears stay meshed all the time except for a few specialty gears. The reduction gear then drives the propeller.
You lose a little efficiency because of the gears, but you gain a lot of maneuverability and the engines are quite a bit smaller than the low-speed ones discussed above. Though that's relative. I'm working on a tug right now that has V12 engines that are 12' long and 6' wide. On the small end, you see engines that are more or less the same models as are in heavy duty pickup trucks.
Efficiency: ~95%
Electric Drive
This is the fancy stuff. In electric drive, you convert the power at least twice (mechanical off the engine to electricity, electricity to mechanical on the propeller) with the natural loss of efficiency that causes. It also is more expensive up front and takes a lot more space. So why would you do it? For specialized boats/ships where the overall system efficiency can be improved. First of all, if your electric load for the rest of the ship is roughly the same as the propulsion load, it almost always makes sense to go with electric drive. This is why cruise ships are electric drive--the hotel power is more than propulsion power. Another place is where you have a lot of different power needs that run at different times and/or where the propulsion engines often run at low power. Most diesels don't like running at less than 25%-40% power--you end up with carbon buildup and other maintenance issues. A classic example of this is a dredge. When it's running from place to place with a full hopper of sand, they want to go fast, so they have large main propulsion engines. But when they're dredging, they are tootling along at idle, which is hard on the engines. Add in the cost of major overhauls (usually set by hours of operation) and it starts to make a lot of sense to run everything on electric. On a large dredge, you can actually eliminate 2-3 large engines by going diesel electric, because when you're going fast, the large dredge pumps aren't working, and when the dredge pumps aren't going, the main engines don't need much power. The generators don't care which way the power is going.
Electric drive can also give you better reliability. On a geared drive boat, if you lose one of your main engines, you're SOL until you can get it fixed. With electric drive, you can bring another generator online (you'll typically have 3-5 generators) while you work on the generator that's out of commission.
Efficiency: ~85%-90%