Using one engine on a twin engined boat

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Is it more economical to use only one engine when you can? Will the boat drift to one side? Is this dependant upon shaft or outdrives ?

Or should I just buy a twin engined boat with smaller engines ?
 

eddieperkins

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Jason,
Yes it is more economical. However it is very dependant on the particular boat as to how easy it is to control on one engine, some steer fine others do not. I think you should be looking at overall suitability of the boat for your intended use. There are many boats that are desigend for planing performance (20+knots) that spend their time on rivers pottering around at 5 knots. This seems to me to be a waste of an expensive engineering and is not good for the engines to be used in that manner. It would be better to get a boat that suits the envisaged use.
Regards,
Eddie
 

byron

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A twin engined boat is designed to perform with two engines and will be difficult to manouvre with one engine. Apart from that it is bad for the engine & gearbox of the engine not being used to be dragged along which is why our sailing chums have a feathering prop or a means to stop the shaft rotating whilst under sail. I would suspect too that if you had an accident whilst working only one engine you could be accused of not maintaining full control of your vessel. Certainly a collision of any type would leave you wholly responsible.


©2001
 

trev

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I would frequently use only one engine on a petrol engined Fairline I once owned, especially when pottering up and down the river. She had outdrives and therefore steered with no problem at low speeds. I used to bring in the other engine for locks and the like, and alternate the engine being used. This caused no problems at all and was much more economical than running both all the time.
I then owned a petrol driven Carver for a while and she would not steer at all on just one shaft (small rudders and shaft drive).
Since then I have owned only diesel boats so economy is no longer a factor - Full Ahead Both !!

Trev
 

ArthurWood

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As others have stated, decide what you want to do with the boat you are considering, but note that
-it is more economical to run on one engine
-some transmissions can be damaged by "freewheeling"
-a shaft drive is almost impossible to steer at idle speed on one engine and the rudder will probably be hard over at, say 8kt
-only do it in calm, open water with minimal traffic
-on a recent cruise, I ran for several hours at about 8kt on one engine, using the other only for docking because I was waiting for a part to fix a fault. It was quite a pleasant change from 20+kt, especially as we were in the Bahamas. I even began to think about changing to sail, but the thought of all that string and cloth...........:).
 
G

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My Birchwood has twin turbo diesels on shafts and this type of engine does not like to run for long periods at less than the speed at which the turbo cuts in (in my engines about 2600rpm). Secondly, the gearbox does not like being freewheeled so the answer is to put the "dead" engine in gear and not try to exceed say 5knts.

I have used one engine to go through the Crinan canal whilst on passage to the western isles, but started the other engine when maneuvering in locks. The canal has a 4 knot speed limit and I could do that at tickover with both engines. Running one engine at about 1100 revs felt more comfortable. Steering on one engine even in the confines of the canal was no problem.

Generally though, you should buy a boat which is designed for the sort of use you will give her most often. A twin engine fast boat this means cruising on both engines at say 75% of full speed.

Nick
 

adrianm

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At the weekend I lost an engine and had to go from the Isle of Wight to Brighton on the port engine only. To make progress without excessive rolling I had to keep the engine almost flat out the whole time.

What shocked me most though was how hard it was to steer. Obviously the boat was very happy to got to starboard but the amount of pressure I had to apply to the wheel to go straight was incredible.

Not something I'd want to repeat again!
 

colinroybarrett

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Depends:-

On all the things others have said here already.

Our boat handles reasonably well on one out of two 108hp engines on conventional shafts, with twin rudders. One full turn of the wheel and away you go. On the river she tends to crab a little and will slowly drift to the opposite side that the engine is running on, which makes lining up for narrow bridge-holes fun!

We always fire up the second engine for close-quarters manoeuvring. We have had no trouble with our Borg-Warner hydraulic gearboxes, which quote that the un-used gearbox will free wheel happily for hours at “trolling speed” without any damage.

Our consumption drops from 2.2 down to ¾ gallons per hour at River Thames speed, which is a considerable saving, even with red diesel.

Count up what, in reality 99% of your boating will be, and buy the appropriate boat? Two engines, not quite in synch and running hard, can be VERY wearing on the ears.

You’ve twice the annual maintenance fees and not always twice the reliability, unless everything, including fuel tanks batteries etc. are duplicated.

Cheers,
CRB
 
G

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I occasionally run on one engine - particularly when I'm on the Hanble or Beaulieu River because they are so long and having outdrives I just have to offset the steering and she's fine. I have Volvo 290's and I'm pretty sure they are OK freewheeling as the propshaft drives the oil pump [well, thrower] and so the drive will be lubricated thoroughly?

To be safe, contact the makers of your gearbox and ask! It will always be mre economical and actually better [as several have stated] to have one engine working at higher rpm than two at a low rpm [especially diesels] ...

If however, the boat control is degraded then you may find it very stressful trying to hold course? Although I have not tried it in this scenario - adjusting trim tabs may cancel out the effects of running on one engine?
 
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