Twin Engine Running On Single

[wooster]

Hi all,

I have a twin engine boat and I am wondering about the benefits/disadvantages of running it on a single alternating between each engine for long stretches of river on the Broads as each engine on it's own has plenty of power. I've asked a few folk with different replies.

I've been told:

1. it would save fuel

2. make less noise

3. cause reduced engine wear

4. It is healthier for diesels to be run at higher revs than I need to with both running  - which is barely more than tickover.

 I realise the handling would be different and I'd need to steer a bit more in one direction and for mooring I'd revert to twins. So far the only argument I've heard against was from someone on the internet who said as my idle prop was in the water while the boat was cruising it could force it to go against the direction it should go and could strip something or other ( can't remember what ) 

Is the concern valid or not? Are there any other arguments against this idea?

Thanks 

 

 

 

[wooster]

Meant to say that my props are on shafts

[grendel]

I would imagine such a scenario might be possible if travelling at high speed on one engine, but at broads speeds? apart from the drag. but thats just my thoughts, if anyone has any hard information on this I am interested in being educated.

[Vaughan]

I agree with all four of the points in your post.

A stationary prop on a shaft drive will certainly cause drag against the steering but will not do any actual damage.

If your boat has out-drives, the handling problem becomes more complex but with a bit of practice you can moor a shaft drive cruiser on one engine with no particular problem.

[Vaughan]

14 minutes ago, Vaughan said:

 

A stationary prop on a shaft drive will certainly cause drag against the steering but will not do any actual damage.

 

Actually, I had better qualify that remark!

If you have a hydro-mechanical gearbox such as PRM, this will spin freely when in neutral.  Problem with that, is that the oil pump in the box is driven by the input shaft from the engine.  So if the engine is not running, no lubrication!

I really shouldn't have made my last post without thinking, as when we are towing a boat alongside, we always block the prop shaft with Stillsons, to stop it turning.

If you have a splash fed gearbox such as Hurth, then you could happily run on one engine.

[annv]

Hi Wooster On problems except as Vaughan said i did this on my last boat for twelve years didn't make much difference to steering,  when turning round i would use both as i didn't have a bow thruster, i tended to use the starboard engine as this had the larger alternator to charge domestics, other one just starting, i did however have Borg Warner Velvet gearboxes John

[WherryNice]

Parents did this on their Ocean, only real issues came if you had to unexpectedly stop quickly and did so on just one engine, this resulted in going very sideways! 

[wooster]

I'm honestly not sure about gearboxes. I believe mine are Hurth or TCM but I perhaps should make sure

[Bikertov]

For Broads / river boats, it there any reason to actually have 2 engines ? I am guessing most engines are running at a fraction of their potential performance.

It's not as if you can go any faster, due to the max 6mph limit. I believe a lot of other river systems are similar.

So unless you are sea going, and presumably most Broads / Broads-based boats aren't, then surely 1 is enough however big the boat is ?

[wooster]

Thank you all for your help. As you can tell, I'm no expert on this stuff and need all the advice I can get.

I just made sure and, yes, the gearboxes are Hurth,. Does this mean I should be all right cruising with just one engine?

[CambridgeCabby]

We always used to run on both engines on Cerise Lady , but they were only 42hp each , our fuel consumption was very frugal and the increased manoeuvrability when mooring can be useful 

[Vaughan]

12 minutes ago, wooster said:

Does this mean I should be all right cruising with just one engine?

Yes.

When on one engine, you are always going slightly sideways, so keep your eyes right up the river ahead of you and don't look too much at the bank.  This will soon tell you if you are drifting sideways.

When mooring alongside, always try to moor with the running engine away from the bank and come in at a slightly sharper angle than usual.

Edited to add :

Mooring stern on is still possible but needs a lot more practice!

Edited September 24, 2021 by Vaughan
line added

[wooster]

Thank you very much. I'm at Rockland Dykecat the moment and about to set up river to Brundall.

I'm going to give out a go 

[CambridgeCabby]

I’ll look out for a boat going round in circles 

[Vaughan]

2 hours ago, Vaughan said:

and come in at a slightly sharper angle than usual.

Again, I may not have put that in the way I meant!

What I meant was,  rather than approach at a fine angle, come in slowly at about 35 degrees from the bank.  As you go astern, the bow will stop and the stern will come round, in line with the bank.  If this needs adjustment then every time you go ahead or astern will bring you closer to the bank.  If the running engine is the one close to the bank, then each time you come ahead or astern will push you back out into the middle of the river.

 

[wooster]

Thank you. I managed it without incident. I did change back to twin to moor in our marina as it's a bit of a tight stern-on mooring.

It might not become a habit but it's nice to know the option is there on a pleasant day when idling down the river can be peaceful and quiet