Running on one engine – possible damage to gearbox?

MYStargazer

MYStargazer

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My boat’s got two engines, on shafts. The gearboxes are Borg Warner 72C 1.52:1.

If the boat’s being run on only one engine (at slow speed in a speed-controlled river, for example) is the unpowered gearbox at risk of damage when being turned by the unpowered prop?
 
I'm not familiar with borg warner boxes, but I have done this a lot in the past on various boats. as long as you alternate engines every hour or so I don't think you will do any harm. Going slowly on a river, say 4kns, the shaft probably wont turn much at all.
 
Have got those boxes on my boat,they are supposed to be fairly robust bits of kit.One gearbox may be counter rotating ?
Have looked my W/S manuals and it does not mention anything about locking any freewheeling shaft.
Would not have thought on canal/river that sufficent speed would be reached to rotate prop hence shaft fast enough to cause damage in gearbox?
Frequently run on one engine at 4knts or so merely to keep exhaust noise down.
 
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hwmbo said:
My boat’s got two engines, on shafts. The gearboxes are Borg Warner 72C 1.52:1.

If the boat’s being run on only one engine (at slow speed in a speed-controlled river, for example) is the unpowered gearbox at risk of damage when being turned by the unpowered prop?
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You actually have BW 72CR. Provided you stick to trolling speeds you can safely allow one transmission to idle and still maintain adequate cooling and lubrication. Direct lift from BW owners manual, page 13 titled Freewheeling.
 
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Afaik you must have cross over cooling system for the shafts, thus sea water circulates the unpowered shaft/gearbox via running engine and you won't harm the shaft seals etc.
 
Melida said:
Afaik you must have cross over cooling system for the shafts, thus sea water circulates the unpowered shaft/gearbox via running engine and you won't harm the shaft seals etc.
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wouldn't do any good as the oil flow through cooler is driven by the input shaft.

Shafts are likely to turn from less than 1 kn. Late starter has given the answer, but dont over heat the box, as many are fitted with paper faced clutch plates, (which burn if the oil is too hot) similar to automotive boxes. Bronze plates are available as a replacement.
 
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If it is hydraulic oil pressure type then it isnt too far apart from my Hurth ZF 63A (same as Volvo Penta HF63)

I lost cooling off alderney.
shut one engine off and went to Guernsey say 20nm ish

My manual said ok for slow speeds.

The prop shaft turns at the same speed as the other one, its in neutral but the prop will spin it at the same speed.

My boat does about 12-14knts on one engine depending on conditions and that day I cruised @ a reduced 10 knots.
the redundant gearbox got hot.

Following that Col has just rebuilt it for me.

Total rebuild including Clutch plates, seals etc


To be fair the gearbox didnt pack up as such, I managed 500-600 nm on it following the cooking and finished the season but it was reluctant to change gear without stalling.

As a get you home , fine.

It would be my last resort and I should have popped into alderney instead of pushing it to our preferred marina.

DO not carry on for far on one engine unless you have to.
 
Dear me.............

Freewheeling was direct lift from manual, watch my lips, the clue was 'trolling' bowling along at 10 knots certainly ain't trolling!

I first got to know the BW Velvet Drive in 1963 and pretty confidant about it's capabilites, clutch plates are disengaged when no pressure from lube pump on input shaft. I would have zero issues with OP's original question.

Stern gland water supply at slow speed, all depends on type of stern gland, a PSS would be perfectly happy, lip seal device such as Alan Burnard design may not, all depends.

As to Oldgit running 72CR's with no lube oil coolers, simply nuts! No wonder I gave up surveying engine installations, the things people do or maybe not do, beggars belief another case of RTFM.............
 
Latestarter1 said:
Dear me.............

Freewheeling was direct lift from manual, watch my lips, the clue was 'trolling' bowling along at 10 knots certainly ain't trolling!
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Well I know that now !

To be fair the Zf instructions in my manual DO NOT SAY TROLLING SPEED ONLY.

Just reduced speed.

I had reduced from 32knots to 10 knots which I thought was a reasonable reduction , accepted it wasnt in retrospect .

Im not entirely sure what trolling speed is but in a heavy sea 10 is about right, 6 is alright if it is calm.

Are you talking about speeds lower than 8, 6, 4 knots ?

Im starting to think twin engine isnt really much more reliable than single.
 
hwmbo said:
My boat’s got two engines, on shafts. The gearboxes are Borg Warner 72C 1.52:1.

If the boat’s being run on only one engine (at slow speed in a speed-controlled river, for example) is the unpowered gearbox at risk of damage when being turned by the unpowered prop?
Click to expand...

Depends on the gearbox so the manufacturer will advise. On Play d'eau, the following is what Twin Disc says,

- do not exceed normal propulsion speed of the vessel, and run the engine with the transmission in neutral at normal fluid pressures for 5 minutes, every 8 hours.

- maintain the oil level at the full mark on the dipstick, or lock the propeller shaft

The other consideration is the shaft seals and if they have pressurised water fed to them. By allowing the shaft to turn, is damage kikely to occur?

One last comment - I suspect you've seen many times before, it's been shown that a free-wheeling prop creates less drag than a locked prop.
 
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