Volvo MD11C - In Neutral When Sailing?

CaptainBob

CaptainBob

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Went on a sail around the Eddystone yesterday - was a brilliant day out - but noticed a whirring sound from my prop which was obviously spinning in neutral due to our forward motion.

A friend suggested it would be better to put the engine in reverse to stop this.

I think the engine manual says to put it in neutral when sailing - but has general opinion changed since that was printed?
 
I have same and cofused by manual advising leave in neutral I contacted boat manufacter he advised leave it in reverse , you can still apparently start engine in gear if you cannot get gear back into neutral, but I not tried that.
 
Somewhat counter intuitive, but letting the prop free wheel adds more drag than when it is prevented from freely turning.
 
[ QUOTE ]
A friend suggested it would be better to put the engine in reverse to stop this

[/ QUOTE ] That is what we alwys did.
 
[ QUOTE ]
you can still apparently start engine in gear if you cannot get gear back into neutral, but I not tried that.

[/ QUOTE ]

Done that a few times. Seems to work fine.
 
We always put our engine into reverse, but if you talk to Volvo they recommend leaving in neutral - they say that putting it into reverse is like putting a car into gear and then constantly rocking it back and forwards. In other words it adds wear to the gearbox.
 
I found with my Volvo 2003 that if I put it in reverse when sailing then it would not go back into neutral i.e. it was stuck(& yes the splines on the Volvo gearbox have been done)The engineer said that Volvo gearboxes should be left in neutral which bears out the above advice.I now have a Kiwiprop which feathers in neutral anyway.
 
I spoke to Volvo at the boatshow a few years ago and they told me that my engine should be put in reverse under sail.

They checked it out based on the gearbox/ engine combination.

It took them a while to sort out as some are best in neutral.

I asked did it really matter and they were insistent that there was a correct thing to do for every combination if wear was to be avoided.

Mine is a md21b ( not sure about gearbox)

Tony.
 
Hi Bob, I leave mine in neutral, always have done, in the apparently mistaken belief that it would reduce drag. Confused now !
 
It all depends upon exactly which engine and gearbox model that you have installed. Volvo manuals usually say what is best for each gearbox but if not available then I suggest that you ask the Volvo Europe technical dept - they are usually very willing to answer such questions.
 
Least resistance is a stopped/locked prop when sailing.

For some gearboxes (one attached to my Yanmar is one!) manufacturers insist that the gearbox may be damaged if reverse is used to lock the prop! Certainly mine stuck in reverse and had to start engine to disengage it.

I really hated the sound of a wirling prop so bought feathering prop and now can use reverse to lock prop and it doesn't get jammed in reverse any more.
 
Probably true for an inboard installation with the friction of the bearings, seals and gearbox requiring quite a torque to get it spinning. I'm not sure how you'd measure the drag with an inboard though. With an outboard in a well as I have, the drag quite easily measured and is much less with prop spinning. I put that down to the fact that the measured torque to turn a prop in neutral is about 10x less with an outboard.
 
Regardless whether the prop is conventional shaft powered or outboard it does not change the principle that a non rotating prop drags less than a rotating prop.
 
It is counter intuitive, and I believed it until a couple of years ago when sailing over '000s of miles in one season. The data for me showed that locking the shaft took 1/2 knot off my speed.

The plan now is to fit a feathering prop...
 
Agree with phlim on basis of data published in a similar debate on the MOA website:

Hope this works!:
[image]http://s58.photobucket.com/albums/g265/rlindsaybrown/?action=view&current=image002.jpg[/image]

Obviously not!
 
That graph is certainly contrary to my understanding.

It would be helpful to understand what the test parameters were.

Here is an extract from Kiwi Props: Quote:
"................The best example one can use is a helicopter gliding down without power in auto rotate mode. For maximum lift – you want the blades rotating as fast as possible. This equates to maximum drag on a rotating prop.

It’s all about the rotating energy left in the wake.

So often contrary to initial thoughts a locked prop will usually have less drag than a rotating prop." end quote.

The full context can be seen here: http://www.kiwiprops.co.nz/auto_rotation.html
 
"I think the engine manual says to put it in neutral when sailing - but has general opinion changed since that was printed?"

With Volvo engines, or more correctly with Volvo reduction gears, the manufacturer requirement of a freewheeling propeller has nothing to see with increased/decreased drag (which as a contoversial debate is second only to Which anchor is best /forums/images/graemlins/grin.gif), instead it is required by Volvo reduction gear conception.
In these gears, with a running engine, the command lever causes a slight movement of the secondary shaft (the one bearing the propeller), the slight friction causes the propeller to begin producing thrust, this moves back the secondary shaft and the transmission of movement is then obtained thanks to the propeller pushing against the friction area.
Should one just move the small actuating lever with a stopped engine, the propelles would not produce any sufficient thrust to activate the transmission and the friction areas might be damaged.

Reverse gear works in the same way.
BTW, this also explains why the actuating lever in reverse might be hard to move with engine stopped and boat under sail: with the command lever in reverse, the secondary shaft is brought near the friction area, as the propeller is turned by the flowing water it will block the transmission and the small command lever may be unable to separate them, at least until boat speed is lowered.
 
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