One engine get-home.

Karearea

Karearea

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Looking at buying a boat with twin diesel power mostly for the get home ability if one engine breaks down.
A concern I have developed when reading about deliberate single engine use (for economy) is:
1) Is it possible to lock the shaft of the non-operable engine on most/all boats?
2) How do you know whether it is safe to let the redundant shaft rotate (lubrication)?
I'm asking as I wouldn't want to cause any damage while in "get home" mode.
Thanks for any info. ... G
 
Nice can of worms here .. :) ...
1) Depends on engine/gearbox and drive configuration ... so impossible to answer without more detail.. in most cases with normal shafts... yes, you can lock the shaft somehow, the questions are why would you and would it be OK not to ?
2) Your engine and gearbox manufacturer can advise you about that ... in my case the manufacturer say no harm if running slow up to two hours.

the key here is if in true "get me home" mode ... ie failure and possible risk to crew, then why worry about damage... surely life & health is more important than damage to material things... and BTW, there is no difference between running on one engine and other shaft rotating, or being towed and having shaft rotate... would you consider locking the shaft, if RNLI started towing you in ?
 
There is no gain in running just one of the two, the one that's doing the work will get rid of more fuel, so use the pair, and if one breaks down then start worrying about your concerns, but I reckon you will suffer NO ill effects.
 
Last edited:
Divemaster1 said:
Nice can of worms here .. :) ...
1) Depends on engine/gearbox and drive configuration ... so impossible to answer without more detail.. in most cases with normal shafts... yes, you can lock the shaft somehow, the questions are why would you and would it be OK not to ?
2) Your engine and gearbox manufacturer can advise you about that ... in my case the manufacturer say no harm if running slow up to two hours.

the key here is if in true "get me home" mode ... ie failure and possible risk to crew, then why worry about damage... surely life & health is more important than damage to material things... and BTW, there is no difference between running on one engine and other shaft rotating, or being towed and having shaft rotate... would you consider locking the shaft, if RNLI started towing you in ?
Click to expand...

+1
 
Avoiding the question, I would wonder where you are boating and why you think you need two engines if the only reason is a breakdown? By the way, how many fuel tanks would that be?
Two engines because of the size or power needed for that type of craft, yes, but it seems a UK paranoia that two engines are needed where one (ok,I assume reasonably modern and maintained) engine is perfectly adequate.
 
gigm: Could be on the remote NZ coast between (say) Napier and Wellington and potentially 100nm from any shelter or NZ Coastguard (of which I am a member) base. You could probably say we in NZ are also paranoid as most boats above about 11 metres would have twins. Probably just the one tank but wouldn't diesel be just one of several potential issues? Would assume both engines well maintained. .... K
 
omega2: I would not intend to deliberately run on one engine as intensive online research has shown me that most would agree with you.
Just thought "knowledge is power" and it would be good to know of any relatively simple measures (other than top maintenance) could be taken in preparation should the worst ever happen. ... K
 
Alf: Unfortunately I'm not sure of the gearbox/drive as was hoping there may be some conventional wisdom out there that could be applied generally. Hoped there may be an easily applied and accepted method/mechanism for locking the "dead" shaft to prevent potential damage in the event of needing up to 12 hours of single engine travel. I guess not.
By the way I am usually an optimist! ... K
 
If your prop shafts are water lubed (ie. are fed water from the sea water circuit leaving the heat exchanger), then a hose connecting the two shafts's feed lines would ensure lube to both even if one engine is stopped.
 
Karearea said:
gigm: Could be on the remote NZ coast between (say) Napier and Wellington and potentially 100nm from any shelter or NZ Coastguard (of which I am a member) base. You could probably say we in NZ are also paranoid as most boats above about 11 metres would have twins. Probably just the one tank but wouldn't diesel be just one of several potential issues? Would assume both engines well maintained. .... K
Click to expand...
Thanks; noted, some places are more remote than others !
 
I read on an aviation site that there are more serious/fatal accidents involving twin engined planes and single engined planes.

There was also a comment, that the only use for the second engine when there is a failure on the first, was to get you to the crash site!
 
michaelchapman said:
I read on an aviation site that there are more serious/fatal accidents involving twin engined planes and single engined planes.

There was also a comment, that the only use for the second engine when there is a failure on the first, was to get you to the crash site!
Click to expand...

That might be more relevant if the OP wanted to stay on the "plane" :p
 
I've never understood the total insistence some people have on having two engines for the unlikely event of a breakdown. Aside from saving a little inconvenience, what can two engines do that an anchor an 'm' flag and a seastart membership can't?
 
PotatoNavigator said:
I've never understood the total insistence some people have on having two engines for the unlikely event of a breakdown. Aside from saving a little inconvenience, what can two engines do that an anchor an 'm' flag and a seastart membership can't?
Click to expand...

Provided you are within anchoring depth and no more than a few miles from shore then nothing, but try that outside 100 nm, in the middle of a channel, or as in the OP's situation, then loads. When I started out boating in a small cuddy speed boat I had three failures at sea. Neither was engine specifically. A broken starter bolt, a stripped grub screw in the throttle lever, a stripped tooth in a gearbox. If I didn't have an auxilliary I probably wouldn't be boating right now. It's scary when there's a failure and the sea becomes mighty menacing when it happens. I can absorb the cost on the comfort factor alone.
 
Karearea said:
Looking at buying a boat with twin diesel power mostly for the get home ability if one engine breaks down.
A concern I have developed when reading about deliberate single engine use (for economy) is:
1) Is it possible to lock the shaft of the non-operable engine on most/all boats?
2) How do you know whether it is safe to let the redundant shaft rotate (lubrication)?
I'm asking as I wouldn't want to cause any damage while in "get home" mode.
Thanks for any info. ... G
Click to expand...

Hi Karearea. The only real benefit of running on one rather than two, is the reduction in hours and therefore servicing costs. Note that a windmilling props creates less drag thank a locked prop, so it's better fuel-wise and drag-wise to let it spin.

It's wise to check with you geabox manufacturer that it's OK to let the shaft spin. For example, our Fleming's TwnDisc gearboxe manuals state when running with a windmilling prop, "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."

When running on one you'll have an element of assymetric thrust making the boat want to turn. To stop this, rudder needs to be applied creating more drag but more to the point, continuous strain on the rudder stock.

So, as far as I'm cncerned, the only real benefit is reduced hours on the stopped engine and hence servicing costs.
 
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