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Marine engine transmissions

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NutmegCT

NutmegCT

Great Pumpkin
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When I come to a stop sign, I (or the transmission) disengage the clutch so the engine doesn't stall when the drive wheels stop turning. You can see a small marine engine and gearbox here:


Does a massive diesel engine ocean liner have something similar? Somehow I can't see a "gearbox" on something like today's QE2 or Queen Mary, or even the run of the mill cruise ships.

I can visualize an old steam ship coming slowly to a stop, because you just shut off the steam flow to the cylinders; the "fires" keep burning. But diesel engines? Shutting off the fuel would actually stop the engine.

Just realized I don't have a clue how ocean liners and cargo vessels actually "turn on and off" the propulsion system. Or does reducing the engine to a very slow rpm let the ship remain relatively stable, because the props/screws are turning *very* slowly? Same for "Full Reverse!" - do marine diesel propulsion systems on massive ocean going vessels actually change gears?

OK - back to my cave.

Thanks.
Tom
 
Varies. Steam, reverse throttle jet to forward turbine, increase to aft. Been places where they set a record going from all back full to all ahead flank, cavitate.....emergency situation, stern exceeded test depth.
Some diesels....like some ferries used to be around here....stop the diesel and start it in reverse (or so I've been told by folks who used to work on them). All stop, there is a massive clutch on some...hydraulically operated. The new ferries are diseasemal-electric...like our old submarines....makes it easy to stick it from maneuvering. Most of the direct-drive units I am somewhat familiar with were diseasemal-electric or steam turbine off a boiler...either fuel oil (Bunker "C") or hot rock.
 
Typical diesel-powered cargo ships are direct drive. Engines rev up to 120 rpm. I'm talking big freighter types.
 
The old tugs up to and after WW II used massive reversible engines, no transmissions. You stopped the engine and restarted in forward or reverse by throwing the rack over. Quite a few were air cylinder start. PJ
 
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