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Author Topic: Diesel tug, reverse?  (Read 3184 times)

Martin [Admin]

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Diesel tug, reverse?
« on: March 09, 2010, 01:17:07 PM »

On early, and perhaps modern fixed prop or non diesel-electric / hydraulic  tugs, how is instant reverse achieved?
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tugmad

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Re: Diesel tug, reverse?
« Reply #1 on: March 09, 2010, 04:36:14 PM »

There are two ways,
one   with a gearbox .   single direction engine and a reverse,sometimes reverse reduction gearbox.

Two       A direct reversing engine ie, the engine will run both ways , this is achieved either by altering the fuel pump timing with a moveable cam shaft this applies to mainly two stroke engines,or altering the main camshaft timing to allow the valves to open at a different phase, 4 stroke.
hope this helps  Geo. ;D
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Martin [Admin]

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Re: Diesel tug, reverse?
« Reply #2 on: March 09, 2010, 05:30:09 PM »

Thanks Geo,   :-))

 I looked that up and found this:  http://www.tugboatenthusiastsociety.org/Pages/tugmach-diesel-01.htm
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portside II

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Re: Diesel tug, reverse?
« Reply #3 on: March 10, 2010, 09:18:15 AM »

And don't forget about the tug's that had two engines running at the same time and the drive switched between the two.
instant reverse  :-)) .
daz
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Netleyned

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Re: Diesel tug, reverse?
« Reply #4 on: March 10, 2010, 05:17:08 PM »

Was that the system used on Zwarte Zee?


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portside II

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Re: Diesel tug, reverse?
« Reply #5 on: March 10, 2010, 09:03:37 PM »

i think that was the system they used .
daz
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farrow

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Re: Diesel tug, reverse?
« Reply #6 on: March 11, 2010, 10:44:40 PM »

On all the conventional powered diesel tugs that i have been on including CP systems, there is no instantaneous reverse, as you have to wait for the engine revs to slow down to enable the gearbox cogs to mesh and then there is always a built in delay of 15 to 20 seconds, before the change of gear actually happens. For emergency crash stops there is a system which crashes the gearbox astern, but that is for emergencies only the high engine revs could probably damage the gearbox, the system is usually tested at specified periods by an engineer and the engine is usually at low revs. Though on small and medium tugs I have been on it does not exist.
Voiths and aqua-master systems you can go immediately ether way as the engine revs are always constant. Also steam recip can go astern immediately.
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farrow

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Re: Diesel tug, reverse?
« Reply #7 on: March 11, 2010, 10:54:35 PM »

I am sure Shipmate60 can explain better than me he was a chief engineer on several types of tugs and is well versed in this subject.
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tugmad

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Re: Diesel tug, reverse?
« Reply #8 on: March 12, 2010, 07:47:45 AM »

On a couple of tugs that I was engineer on fitted with British Polar engines we had a quick reversing system which was connected to the Camshaft and air start aystem so that when used (not often as it was very heavy on air) it used starting air blown in the cylinders to slow the engine and also moved the camshaft at the same time. and she would restart Astern on the bounce.
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catengineman

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Re: Diesel tug, reverse?
« Reply #9 on: March 12, 2010, 02:44:23 PM »

Ah the great British Polar with a ring piston blower and if oil got onto the RPB valve and it did not change then the inlet became the exhaust and the exhaust became the inlet and the engine room filled with smoke very quickly.

I know those engines very well
One of the oldest working tugs on the river Thames had a Polar and was engine room controlled as the Westinghouse system was in need of repair and a lot of money.

tug name RANA (owner skipper but worked for a company A C Bennett & Sons)
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tugmad

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Re: Diesel tug, reverse?
« Reply #10 on: March 12, 2010, 02:57:40 PM »

Yes I know her well, The Kent has this type of starting gear M45M polar. %%
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catengineman

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Re: Diesel tug, reverse?
« Reply #11 on: March 12, 2010, 03:03:47 PM »

The Linda Bennett also had a Polar
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farrow

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Re: Diesel tug, reverse?
« Reply #12 on: March 20, 2010, 12:25:33 PM »

Well I can only speak from experience with MoD vessels which never used polars, but the Sun 21 was engine room controlled and my father was her chief engineer for some time. I remember my father telling me of the arguments he had with masters who wanted to use the engines like a steam boat,  he would never reverse the engine until it reduced to the correct idling revs, then you had a 15 sec delay befor it changed gear.
Most screw diesel tugs had a geabox attached to the end of the engine and would only change direction of drive when the engine revs were at the correct revs. A damaged gearbox is very expensive to repair especially if it shatters across the engine plates and I have heard of marine gearboxs going bang, followed by a UB40 for someone.
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farrow

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Re: Diesel tug, reverse?
« Reply #13 on: March 21, 2010, 10:42:25 PM »

I forgot to mention, that before the gearbox can change direction of thrust, the shaft brake must engage to stop the shaft rotating, otherwise the engine can be made to run in reverse direction, caused by the momentum of the prop.
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tassie48

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Re: Diesel tug, reverse?
« Reply #14 on: March 26, 2010, 03:03:43 AM »

Martin on one tug I worked on we had a British Polar Two stroke Diesel I use to use the telegraph to ring down stairs to stop engine then go astern.The catch was its a fix drive the engine went in reverse to turn the prop backwards hence the need to stop and restart, the engineer had to air start the engine each time  and if you were having a bad day coming along side and need to stop start old bryson would get cranky with you.To go faster he use to pour on the coal (open up the throttle which feed more diesel to the engine)great tug tons of grunt push any thing any were ,went from her to a old Empire tug Wellington NZ to a shifter tug small tug with huge bulges underneath twin vee16 two strokes 80 feet of grunt got the sack from her for pushing a sub too much the Yank skipper told me to P.O so I told the crew to dog down the aft hatches and come up  stairs reved the old girl up and push this sub into its berth breaking a pile when we hit the wharf 850 hp per side.
Went to a old yank tug and dragged a dredge to Japan back wards across the Pacific again old two stroke diesels tassie48.
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farrow

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Re: Diesel tug, reverse?
« Reply #15 on: April 25, 2010, 04:31:17 PM »

The old MoD tug Expellor was the same used air to change the engines direction for ahead and astern. She could do 9 changes before the need to recharge the bottle and the airpump could not keep up with supply when too many moves came too quickly. Not only that she had no steering wheel just three buttons, they where port, amidships and starboard, pressing the button in the direction you wanted the wheel, then a quick touch on amidships to stop at the angle you wanted. She was a war reparation vessel from Germany.
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