Reversing engines.
       There are a lot of variations in engines and couplings to propellers with multiple engines and reduction gearboxes.
       The basic concept is solid drive from engine to propeller.   When docking or manoeuvring into port the engine is stopped and started numerous times.
      The engine room and bridge are connected by the Telegraph, you have seen them on the movies. The captain or pilot tells the engineers what he wants,  ie " Slow Ahead".  The engineer answers the call, by putting the ahead/astern lever in the ahead position., then he pushes the air start lever to air for a few seconds and then onto fuel. The engineer will maintain the engine rpm at about 30 rpm until another signal is received from the bridge.  One of the engineers will be permanently at the control platform recording the time and engine movements received and delivered. The next movement will invariably be a stop and the fuel lever will be pulled back to the stop position.
        If the bridge calls for "Astern" the astern lever is pushed to the astern position.  The engines have two sets of cams next to each other on each camshaft.  The reversing lever moves the camshaft to the other position where all the cams are in the position necessary to run astern. The engine is started normally.  Some engines have a  " lost motion" in the drive to the camshaft.  When reversing the air start  control reverses only  and the engine rotates in the reverse direction until it catches up with the camshaft.  The fuel cams are now in the position to run the other way.
       Ships have little or no steering until they are moving quickly.  But if they have a bit of momentum they will glide along for quite a way.  If there is wind they react accordingly.  A degree of steering can be achieved by turning the rudder and kicking the engine for just a few revs.  The adept captain or pilot can steer the ship close to the wharf using rudder position and short bursts of engine revs,  when they throw out lines and pull the ship up to the wharf.  There is a lot at stake with damage to wharfs and ships that tugs are always on hand.  Modern ships make use of directional pods, hence the less reliance on tugs.
         A lot of modern ships are diesel electric where the diesels run continuously and the control is all electric.
All for now,
Phil R.

Bloody hell thats fascinating I love explaining to someone that knows nothing about engines how they work and then telling them how many times that happens every second at certain RPMs you can see thei mind boggle. 
Just like my mind is boggling at how you maintain 30RPM at least you wouldn’t need a taco 2 seconds per rev wow lol at they speed you could nearly throw away the cans and manually run valves and a unit injector with a hammer Hahahaha 

Dave, how many CFM is that per revolution, your going to run into clearance problems putting that under the bonnet of the Patrol...

Phil, watching movies for years I thought the engines were controlled directly from the bridge. I didn't realise there was a person/persons running around and pulling levers down below!

So apart from the main engines what else were you guys responsible for, everything mechanical?
How many motors in total on a ship were there, generators, pumps and whatever?

Hey Tim 
At 3000rpm it is 3300CFM
AT 50% vacuum 15”hg on the  inlet side it’s still 3000cfm
If you try and run more vacuum than that it will cook itself very quickly so it will suck very quickly   But it won’t be able suck if I just dump the hose in to water it Will need a certain amount of air

Chappa wrote:
So is there a ratio of the size of the holding tank to the amount of air going through it?
Also how is the holding tank isolated from the suction?

Tim the tank size doesn’t really matter it’s the size of the tubes you use
so it depends on what you’re sucking all our work is wet vac so we only need a basic screen filter between the blower and tank the inlet side of the blower is ducted to the front top of the tank in front of the pusher plate for unloading inside the tank at this point is a cage with a floating ball that blocks that pipe off when the ball floats (truck full)
The inlet to the tank is our vac hose attached or a boom it comes in towards the front of the tank behind the pusher plate directed with a chute towards the back. 
The blower pumps the air out of the tank creating a low pressure zone in the tank and atmospheric pressure does the rest 
on the clean side of the screen filter there are 2 relief valves set at 15 inches of mercury so the blower never get dead headed

Now I've really got a head ache 

This lockdown is really stirring my imagination.
Try this one.

Not the best pics, but they will have to do!

Thanks for keeping them coming Phil.
Was there a reason why the ships were named after ports?