Running On One Engine

[lhuff35204]

My 38 ft powercat has twin Yanmar engines and I have from time to time lost an engine due to overheating or fuel problems and been forced to run some distance on a single engine. During these times I've allowed the idle propeller to "free wheel". I've since learned that this could lead to transmission and prop shaft overheating since no cooling water is flowing. What steps should be taken? Is this a serious concern? Note that many of these PCs crossed the Atlantic (from South Africa) on one engine to conserve fuel but I do not know what steps the delivery personnel took. Also, I do not have transmission gauges.

[SwellGuy]

Originally Posted by lhuff35204

My 38 ft powercat has twin Yanmar engines and I have from time to time lost an engine due to overheating or fuel problems and been forced to run some distance on a single engine. During these times I've allowed the idle propeller to "free wheel". I've since learned that this could lead to transmission and prop shaft overheating since no cooling water is flowing. What steps should be taken? Is this a serious concern? Note that many of these PCs crossed the Atlantic (from South Africa) on one engine to conserve fuel but I do not know what steps the delivery personnel took. Also, I do not have transmission gauges.

This depends entirely on the make and model of your transmission. Some transmissions are best left freewheeling. Some transmissions are best left in reverse. Some posters will claim to have an answer for you without even knowing your transmission. Don't listen to them. Read your manual!

[a64pilot]

An automobile automatic transmission will certainly be ruined if the car is towed for very far or fast.
I have not heard of that possibility with a Yanmar transmission, but my limited experience is with little sailboat trannies too.
If it’s not addressed in the manual, I’d call a good, reputable Yanmar dealer and ask what is the procedure for motoring with one engine off. I wouldn’t ask directly if it will hurt the transmission, there may be other procedures, like I believe for instance that many power boats have forward facing water scoops for their engine water intakes, and you may need to close the seacock also if yours does.
Soprtfisherman we had years ago we needed to close the seacock, or were told to anyway.

[Simi 60]

Originally Posted by SwellGuy

. Read your manual!

Smart advice from Captain Sensible.

The other thing that may be an issue is water injected stuffing box and cutlass bearings not getting enough lubrication.

[Simi 60]

Originally Posted by lhuff35204

My 38 ft powercat has twin Yanmar engines and I have from time to time lost an engine due to overheating or fuel problems .

Here's a word you may not have heard of.........Maintenance.

. been forced to run some distance on a single engine

Maintain your engine, sort out your fuel system, run multiple filters and learn how to change filters on the fly like us single engine guys do and you should never be "forced" to run a single engine again.

[mcarthur]

We will be (not yet!) doing the same on our powercat. The manual for our gearbox says it's ok to freewheel, so check your gearbox (not engine) manual. Ours is a Hurth 450A2/ZF45A.

Regarding the Leopard's that get delivered on their own hulls, I doubt that the crews did anything special during delivery. Of course they could have removed one prop for the trip and just run on the other, but that would have massively increased the hours on one engine only (IIRC it was about 6000nm via St Helena and Brazil to the Caribbean) and they averaged about 7kn, meaning 850 hours or so on the motor. MUCH better to use both, one at a time, and only put 420 on each engine. Since I can't see them going down during the trip to swap props , I'd guess the Leopard's (if that's what you have) are ok...but read the gearbox manual, or find the model and look online for one.

The other thing to watch is your shaft seal. Some, like the PSS we use, have an pumped water-hose to feed the seal. If you're freewheeling, this won't give you the water needed and you need a cross-feed from the engine that is working. However, it's pretty unlikely you'll hit the 12 knots (IIRC) which needs the water feed, and any less speed won't need it. Check your shaft seal manufacturers advice...

[RaymondR]

If you are worried about it overheating you just need to feel it occasionally with your hand. If it gets too hot to touch for a few seconds it's probably too hot.

[Bruce K]

My powercat is fitted with ZF transmissions, according to the manual it is ok to freewheel, which I do occasionally, it only requires 2 to 4 degrees of rudder to compensate, which I find amazing, since the props are almost 6 meters apart. My PSS shaft seals have a crossover so both seals receive water if one engine is running.

[mcarthur]

Hey Bruce, can I ask why you run on one only sometimes?

We're thinking of it mostly for ultra long range trips, not the usual stuff, but I've heard others say it's their standard way of running at "hull speed" or less as it halves the maintenance (well towards 50%) and runs the single engine on a powercat (not necessarily on other boats!) at a more efficient point for the speed.

[Bruce K]

Originally Posted by mcarthur

Hey Bruce, can I ask why you run on one only sometimes?

We're thinking of it mostly for ultra long range trips, not the usual stuff, but I've heard others say it's their standard way of running at "hull speed" or less as it halves the maintenance (well towards 50%) and runs the single engine on a powercat (not necessarily on other boats!) at a more efficient point for the speed.

My cat is a" Displaneing" type ie displacement foward with planing flats aft, it use a bit less fuel running on one motor, does "feel" a bit strange though, I have not yet done any long distances yet, intend to go to Tassie this summer, but family committments may prevail!

[Simi 60]

Originally Posted by Bruce K

My cat is a" Displaneing" type

Stealing the words from Peter Bradys mouth

[Bruce K]

Originally Posted by Simi 60

Stealing the words from Peter Bradys mouth

My Cat is not a Brady, designed by John King, who was Ben Lexcen's partner, I think Ben was using a similar hull shape long ago, possibly before Brady.