Using just one engine

[Doghousekeeper]

Advice for a confused newbie, please ...

In talking to pals about cruising economy (I don't plan to dash about, 6 or 8 knots is plenty for me), one pal has suggested that I should run on just one engine as that will save fuel and will also allow the engine in use to operate at higher revs and under more load - which he says is good for it - and another pal says I should run both engines as that is better for the boat and running well below their capacity will avoid any strain on them.

I'm confused. Can anyone help?

(The engines are Perkins Sabres, 225 hp on a 40' boat)

 

[Mr Googler]

Never done this myself and cant see how more load is a good thing especially on bearings and gearboxes etc.

On my boat only one engine runs the steering pump so if its the same on yours and you turn off the wrong engine...no steering or very difficult to steer at least!

If you have engine hour meters and do this alot then you could end up with an imbalance in hours. As a prospective buyer in the future I would want to know why. Has one engine been loads of trouble etc.....

Charging of batteries may also be a problem depending on how yours is set up.

I know Trans At boats have wing engines (ie Nordhaven) and you just use the one main on long passages but they are designed for this.

I would think with such big lumps using both is the way forward and after all thats how they were designed to work. /forums/images/graemlins/grin.gif

 

[Sultans_Kapitein]

Many thoughts on this subject, but all 'based' on sound advice! For example operating engine under more load is good for diesel engines, they do not like to 'putter' better to work them and all that, but then you are 'haring' around. Don't want to 'strain' the engine, also good advice, but in a boat it is hardly likely to happen. A method often used is to have both engines running, but to only have one in drive at any one moment. A couple of advantages in this, firstly you are only burning significant fuel on one engine so that is more economical, but the other engine is running and so IF the drive engine should develop a problem whilst underweigh you do not have to 'struggle' to start the second engine in a bobbing craft. Also this method makes it easy to use bith engines for manoeuvuring. The one that is best is the one that suites you and your setup, e,g, our friend who has take off from one engine for his steering.

Mal

 

[stefan_r]

Other problems I am aware of are around gearboxes.

My TwinDisc gearboxes are very specific. If I am running on only one engine I must lock the prop shaft to prevent it "feathering" i.e. turning slowly due to the water pushing past it as this means that the gears conncted to the shaft are also turning...however because the engine is not on the oil pumps are not on and therefore the gearbox is not being lubricated.

In the event the shaft cannot be locked in place the procedure is to blank off the dipstick and fill the gearbox with oil to overflowing to provide enough cooiling oil over the gear faces as possible.

This is all too much hassle...so I always run with both engines on and in gear.

Makes steering in a straight line easier too!!!!!!

 

[Sultans_Kapitein]

[ QUOTE ]

This is all too much hassle...so I always run with both engines on and in gear.

Makes steering in a straight line easier too!!!!!!

[/ QUOTE ]
I can see your point, but I suppose you could just leave one on 'tick-over' but in gear, that would effectivly 'lock' the prop. But as for helping to steer straight, maybe you should take more water with your Whisky /forums/images/graemlins/grin.gif

Mal

 

[Bandit]

Running on one engine is unlikely to save you fuel as you have the drag of the other prop and basically X hp requires Y litres of diesel whether x hp is gained from one or two engines.

Steering on one engine is a pig in any sea.

Before you do run intentionally on one engine make sure that if the other prop turns that the gear box will lubricated some require input power to pressurise the gearbox oil and you could damage the gear box.

Backing off say 500rpm is going to make a big difference to your fuel economy on two engines.

Running an engine like yours at half power should not be a problem, what is not good for an engine is to run it at idle all the time.

If you get your enjoyment from going from point A to point B rather than going for a "run" the important thing is miles per gallon rather than litres per hour.

I am looking at getting Floscan meters for this very reason.

 

[stefan_r]

[ QUOTE ]

I can see your point, but I suppose you could just leave one on 'tick-over' but in gear, that would effectivly 'lock' the prop.
Mal

[/ QUOTE ]

Hmmmmm....not so sure it would.

Engine on, gear in neutral - prop still feathers; and I suspect gearbox in neutral may not fully engage oil pumps...
OR
Engine on, gear in forward on idle - prop turns slowly...more slowly than the other. But probably being pushed quicker...stressing bits?


Leaving an engine in tickover, under little/no load will lead to bore glazing too...very unpleasant.


Still two engines, in gear, equal throttle=confident I am not building another issue.

 

[Sultans_Kapitein]

Cannot disagree with anything you say, both you and the OP have relatively modern boats, therefore all the bull I am preaching probably does not count. The engines in my boat were probably not new when installed and when that was is unknown, but is probably 1971. So the engines are Leyland 6 cyclinder normally aspirated diesels, putting out about 110Hp, nothing fancy about the props. So I shall retire from this post and leave it to people with more suitable experience of more modern boats.

Mal

 

[MapisM]

Wow

Apologies for going o/t, but I for one would be interested to hear more about your vessel.

 

[Sultans_Kapitein]

Re: Wow

I think you have perhaps forgotten the we have already had a similar discussion before, when I commented on the size of your aft deck, and also the design and build of your radar arch? I did provide you with links to Photbucket. But if you had not forgotten, please do not think I am being rude. I will be more than happy to talk about my pride, even though I have not yet had much joy. Please send me an email, providing you won't mind to much if I go into 'doting parent' mode.

Mal

 

[MapisM]

Re: Wow

Doh! Sorry Mal, your Titanic! Now I remember....
Will pm you my email anyway, I'm more than happy to look at any progress she made in the meantime!

 

[alruss]

Re: Wow

So am I, interested, will PM my e-mail for pictures and progress reports.I have old boat to refit so always looking for tips and ideas.

 

[blueglass]

I also have perkins sabre 225 Ti's in a similar size boat and yes i do run on one engine at times if on a slow run. I spoke to a perkins engineer about this and the issue involving feathering and lack of lubrication in the power train which is just trailing, is a real one. I was told however that if i was to alternate the engines on an hourly basis all would be fine. I also understand any fuel savings would only be gained at quite slow speeds, say 6 or 7 knots. at anything much above this the drag of the trailing prop counteracts any fuel saved. you also need to investigate what equipment on your baots electrics are tied into each circuit. for example on mine, with only port engine running - no fuel guage. with starboard only - no rudder indicator.
all in all I am doing it less and less because it is all a bit of a hassle, but on a long run at very slow speeds e.g on inland waterway runs with speed limits, it is very useful, as 2 lumps labouring slowly at 4 knots all day is very bad news for a big diesel

 

[Doghousekeeper]

Thanks everyone for the very useful comments. I can see how a trailing prop could cause real problems for the engine ... but how is that not a problem when the boat is moored in a tidal stream? Is there a critical speed of the water flow where it becomes a problem?
/forums/images/graemlins/confused.gif