I know about the Atlantic Star; are there any others? By “big” I mean say 300’ long or more. What’s the biggest steam cargo ship afloat?
Just a wee nitpick. She has steam turbines giving power to generators producing the electricity that powers the electrical motors that make her move. In my book to be called a steam ship it should have a steam engine.
That’s what I was thinking. I’m only aware of one currently operating steamship larger than tugboats or medium-sized lake steamers like the TSS Earnslaw and river-based paddle-wheelers, and that’s the PS Waverly, an ocean-going steam powered paddle-wheeler that’s 239ft long and based in Glasgow.
We have a couple of steamers in Stockholm, like the SS Mariefred and the SS Blidösund, which are both coke fuelled, plus a couple of diesel fuelled ones. They are a bit smaller than the TSS Earnslaw but they are used in every day traffic.
PS It’s the PS Waverley.
It says steam turbines in the wiki site. How do you know there are also electric motors?
I think the point we’re making is that, really, for something to be called a “steam ship” it should be powered by a steam engine, preferably one which involves people in overalls shovelling coal, wood, or dogs into the furnace to keep it going.
OK, I thought you were narrowing it to turbine ships since nobody would build a piston steam engine for a large ship in 1984. I didn’t realize after poking around the net that there were actually steam turbine locomotives built. Interesting topic either way.
Because in modern ships it’s electrical motors that move the propellers. The diesel engines, or in this case steam turbines, just give power to the generators. All according to a friend of mine who happens to be a naval engineer. It’s the same technology in diesel fuelled trains.
I see your 46,087 grt and raise you to 51035 grt and there are four of them, the SS Endeavour River, the SS Fitzroy River, the SS River Boyne, and the SS River Embley. Sadly, they are due to go out of service this year I believe and at least one of them may already have gone.
We’ll have none of this candy ass fuel oil burning steam turbine driving electric motors nonsense, neither.
These girls are coal fired, and the steam drives the prop direct. Yes they involve guys in overalls, yes they involve coal, and well, they kind of involve shovels as long as we are talking mechanical shovels 
And you could drop all of those little lake steamers into one of the (four) holds of the Embley and not even cover the tanktops with the wreckage.
There were actually steam turbine ships for a number of years in both the direct drive and reduction gear set-up. And modern train engines use piston diesel engines/electrical motors.
I think our OP has his answer, in that case. 
The thread on really big engines seemed to indicate otherwise.
Note that essentially all nuclear-powered vessels use steam turbines. This would include a bunch of submarines over 300’ (e.g. the Los Angeles class) and of course aircraft carriers (e.g. Nimitz class).
There certainly are steam plants in large civilian ships, too. Here’s a link (warning: PDF) that describes a simulator for training would-be operators of the steam powerplant of a large crude-oil carrier.
And how are those turbines running by steam.
Her name is really the S.S. Alantic Star. The S. S. stands for steam ship.
In some modern ships it’s electrical motors not all. There are a lot of drict drive diesel ships being built.
You must have misunderstood your friend. This is one method of getting power to the propellers, but not by any measure the rule or even the most common method. In *some * applications, though it is the rule. For example, azimuth thrusters are often electric-powered, and a subclass of those, azipods, always are. These methods of propulation are becoming very, very popular with cruise ships, and perhaps that’s the context in which your friend was speaking.
As has been mentioned, there are many steam-driven vessels in the Navy.
A typical arrangement, dating to before WWII, is a pair of turbines, one high pressure and the other low pressure, that drive a set of gigantic reduction gears that, in turn, drive the shaft. The steam goes in the HP turbine; the exhaust goes to the LP turbine, and the exhaust from that turbine goes to the condenser.
There are several gear configurations, but a common one is to have two reductions: the turbines end in pinions; those mesh with mid-sized gears; those drive another set of pinions; those mesh with the bull gear. The bull gear is connected directly to the shaft.
I really enjoyed the concept of being in an steam engine room while in the Navy. Though my own line of work did not normally involve handling the throttles, there was one particular drill where I controlled the ship’s engines from an upstream valve—a monster ball valve that was bigger than I was. I had a smile the whole while as I turned that hand-wheel 
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You forgot one of the most common sources of steam engine fuel, mummies.
Just to update and revive the “steam ships in service” posts, the 410-foot S.S. Badger is a coal-fired steamship built in 1952 that’s homeported in Ludington, Michigan, and still operates as a car ferry across Lake Michigan. It’s said to be the largest coal-fired passenger steamship still operating in the U.S. in 2015.
There’s the Minne Ha Ha in Lake George N.Y.