Running single engine

T

timjet

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I'm participating in a topic in another forum that discusses the wisdom of operating single engine to conserve fuel. Having recently bought a used Carver 35 ACMY and having little experience with it, I'm wondering if fuel savings can be had operating in such a manner.
Opinions please??

Tim
 
In an emergency situation, then OK. Otherwise, I don't think it's a good idea. In my opinion, if you're that concerned you shouldn't have a twin - if you have a twin then use 'em!
 
no reason not to if you keep the speed down to 6-7 knots
 
Yup! trolling for albacore(or anything at slow speed as Brucie said) with twins, it saves gas by running on one.
 
This is one of those things that you will get a plethora of opinions on.

Personally, I've done it and continue to do it. The only thing I do is put the unused engine in gear do the prop doesn't spin.

Bob
 
quote:
This is one of those things that you will get a plethora of opinions on.
Click to expand...


If you think that is a big discussion topic wait untill the locked shaft vs spinning prop discussion starts.
 
there is no need to discuss locking vs spinning, you dont' have a choice in the matter and should follow the transmission manufacturer instructions. In most cases, they recommend you lock the shaft and obviously you also need to follow the instructions of the dripless seals manufacturer, if equipped.

Putting the engine in gear usually doens't not work since most inboard trannies are hydraulic and with the engine off there is no pressure for the clutch to engage. check that before assuming that you are locked!

these issues aside, i'm still not sure that you really gain a lot by running on one engine jsut to save fuel... if it takes X hp to push the boat at Y speed, whether or not the hp comes from one or two engine makes little difference and whatever you win by eliminating losses due to friction, heat, etc... you probably loose it by the locked or spinning prop.

Not worth it. if you're concerned about fuel, then slow down half a knot.

also, twin engine boats are propped for twin operation. if you try to run a little too fast on one engine, maybe just by 1kt, that engine could be slightly overloaded increasing wear...

now, just like any multi engine pilot trains for operation with an engine out, boat owners with twin should practice running on one engine once in a while (docking, turning, etc...) instead of relying on that red or yellow card they carry! :)
 
I once talked to guy that had the same boat as mine and he did the whole loop on 1 engine. A month ago we had a vistor at our club with a 34' Wellcraft express and they were out on a 7 week cruise and he was running on one engine and he told me they have doing it for years. Can't tell you what they were doing with there trannyshafts.

Niles
 
actually my ZF trannys are aren allowed to frewheel as are many others. And a lot of study has been done on locked vs frewheeling props by the sailing community.
 
quote:
Originally posted by pdecat

actually my ZF trannys aren allowed to frewheel as are many others. And a lot of study has been done on locked vs frewheeling props by the sailing community.

Click to expand...


ok Bruce, make up your mind!

is it "aren't" or "are" allowed :)
 
Bob, you should check because I don't think your prop will stop freewheeling if you put that transmission in gear. The only way to stop it is to dog the shaft down. My Borg Warner trans manuals state that freewheeling won't hurt them. Check your manual.
 
quote:
Originally posted by Gregory S

Bob, you should check because I don't think your prop will stop freewheeling if you put that transmission in gear. The only way to stop it is to dog the shaft down. My Borg Warner trans manuals state that freewheeling won't hurt them. Check your manual.

Click to expand...


Greg, you are correct. Mine also says it doesn't hurt them at all. So, I guess there's no need to keep putting it in gear.

Just an old habit and old habits die hard. :)

Bob
 
I'm not a fan of running a boat on one engine unless the other engine is busted. I do agree wholeheartedly with Pascal's point, that you should indeed practice what to do if an engine fails...

I come home on one engine so damn often people tease me that I wouldnt know what to do if I ever docked with the two of them running!!!
 
Since each boat is different, one answer doesn't apply to all. For some boats however there is a speed below which it may be more economical to operate on one engine. Since any engine and especially diesel's take a certain amount of power just to run the accessories, (2 water pumps, alternator, and swing that heavy crank shaft and fly wheel), the trick is to find at what rpm more more power is applied to the prop than is used to run the accessories. That has to be balanced with the increased drag of the rudder correcting for the assymetrical thrust along with the freewheeling or stopped propeller. I think that speed and rpm combination can only be achieved by trial and error. Flowscans would be a big help.
 
Have you tried unfurling the sails?

RWS
 
Consider that most of our boats will run at max bow down speed with very little power, probably less that 100 HP. That power can come from one engine or five engines and each additional engine contributes identical overhead losses but a smaller share of load power than the one engine alone.

Try running at slow speed then shifting one engine to neutral and you will note the small contribution to speed of the second engine and how easily the single can pick up the extra load to get back to speed. The second engine is contributing only the small share of power needed to gain the incremental speed. In actuality they share the load depending on throttle settings but it helps to think of it that way. This demonstrates that the second engine uses an equal amount of overhead fuel but contributes a smaller amount of power
n.b. This will only work at bow down speeds and below.
 
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