engine in gear when sailing

[blackbeard]

I'm sure this has been discussed before but I don't remember any definite conclusion.
When sailing at a reasonably brisk speed under sail alone, the propeller on my boat turns. It's a two bladed prop driven by a Yanmar 1GM, shaft drive, usual gearbox.
This can be prevented by putting the engine into reverse gear when the engine compression stops the prop turning. (Oddly, this doesn't seem to work in forward gear).
I've heard it said that allowing the prop to turn will lead to excessive wear on the gearbox (although it does seem unlikely that this will amount to much).
(I've also heard it said that with a saildrive, excessive wear will occur if the gearbox isn't in neutral!)
The effect on boat speed of selecting reverse gear seems to be negligible although I have been told the boat will be marginally faster with the prop not rotating.
Does anyone actually know if I should engage reverse gear when sailing? Or should the gearbox be left in neutral? Or does it make no difference?


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[tony_brighton]

In theory a rotating prop will cavitate and create more turbulent drag than a stationary prop. The wearing of the gearbox is a valid concern; I believe Volvo advocate stopping the prop for their Saildrives.

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[ParaHandy]

yanmar gearboxes are cone drives so, when you put her in reverse, the male cone moves towards the female reverse cone. However, the shaft supporting the male cone is on a helix thread and the rotation of the main drive (thro' the layshaft supporting the male cone) screws the male cone into engagement with the female cone and locks it thus, if the engine is not rotating, the whole lot does not rotate. If you put it in forward, the male moves toward the female forward cone but the helix is trying to screw the male away from the female cone.

if your male cone is set correctly and the gear change linkage is not sufficiently worn that either the forward or reverse cones do not engage, then leaving it in neutral ought not to do any damage.

I have found that fresh oil allows the prop to rotate for a few months - over 6 months old or so it becomes gooey enough to stop the prop rotating.

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[Evadne]

I've also found that no oil allows the prop to rotate at much lower speeds than a correctly filled gearbox. Sort of an audible dipstick. I stop the prop because it increases the intervals between lifting up the cockpit floor hatch and remembering to give the stern greaser a turn, and reduces oil loss from my slow leak from the gear box.

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[Mike_02]

Think yourself lucky that you can do this. I have a dolphin engine with no gearbox. I have to jam a screwdriver into the shaft to stop it turning.

But i have about 4 or 5 screwdrivers in the bilge now as they fall out.

Any ideas for making a better soloution.

M

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[Dominic]

I lock the gearbox in reverse - as you describe - while sailing.

Cuts down on gearbox wear and cutlass bearing wear. Also stops the engine vibrating on its mounts.

If you keep your boat on a swinging tidal mooring then it would make sense to leave the prop in gear - to avoid wear as described.

The theorists also tell me a locked prop has less drag than a freewheeling one.

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[vanman]

I used to have a Yanmar 2GM and put it in reverse when sailing. sometimes it got 'jammed' in reverse. I never forced it back to neutral to start the engine, just started it in gear and then selected neutral.

Ian

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[Tim_Stokes]

I have a Volvo engine and the instruction manual is very clear that it should not be left in gear when sailing. If I put it in reverse it then locks and I have to start it in gear to release. The manual says that it should not be left free running for more than 10 hours without running the engine in gear to relubricate the gearbox. When I asked the Volvo agents they said it should not be put into gear when sailing. However others have told me to ignore that.

I would like to put it into gear to stop the rotation as I feel it must be causing some wear. However I am loath to go against the manual. The only option is to have a brake put on it.

Am I worrying unnecessarily? I would welcome any advice.

Tim

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[dickh]

I have a Perkins Perama with a Hurth G/box - same as the VP2020. As the gearbox is filled with oil I fail to see that allowing it to freewheel damages the box, or if you leave it in gear - the Hurth manual says to put it in reverse if you don't want the prop to rotate. Mine certainly doesn't lock after keeping it in reverse.

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[charles_reed]

What an interesting set of questions:-

1. With a fixed prop reverse prevents it from turning, with a feathering prop such as the Autoprop you have to use forward.

2. The research that has been done on the slowing effect of a prop has resulted in a pretty murky picture - dependent on the boat - leaving the prop turning has negligible effects at very low speeds and at the limit of displacement speeds - at intermediate speeds the drag can be quite considerable. Effectively it's the ball of water round the turning prop which slows a boat down, how large this might be is also a function of the prop pitch and the position of the prop in relation to the turbulence caused by the boat's keel and underwater configuration.

3. On many boats with conventional stuffing glands the friction is sufficient to prevent appreciable shaft rotation, with low friction glands the wear on the cutlass and the waterseal can be appreciable.

Generally speaking it is only safe to engage gear on the dog or cone-clutch boxes - on some hydraulic boxes, there is a real risk of the box seizing if left in gear.

Whether or not to brake ones' prop is not a simple black and white question, despite the simplistic answers on frequently gets.

As it so happens I do need to lock my prop, it's a 3-blader on a wide-transom, low-resistance boat, midway between keel and spade rudder.
On a long-keeler with a cutaway for a 2-bladed prop I'd be wasting my time.

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[charles_reed]

Dolphin prop brake

Solenoid-operated to off position when ignition turned on.
The only one I've seen was made by the owner who had bolted the disc into the flexible coupling.

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[vyv_cox]

Charles,

Your No.1 is gearbox dependent. With my previous Bukh engine (ZF gearbox?) I could lock the prop in either forward or reverse. My current Yanmar, as someone else has said, will not lock in forward but only reverse. Even with the Autoprop, it continues to rotate if left in forward. I engage reverse as soon as the engine is stopped, then restart the engine in reverse and move it to forward.

Vyv

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[oldharry]

I have ususally found that leaving the prop free wheeling creates marginally less drag on a light hull - but most boats I have owned or sailed it doesnt make any noticeable difference.

Locking it with the gearbox is OK with mechanical gearboxes, but many newer ones are hydraulic, and not only may not lock the shaft, but could possibly be damaged - a bit like towing an automatic gearbox car, hence the advice to lock off in reverse on some makes, where presumably the reverse gearing is acheived mechanically.

If the shaft is easily accessible, Molegrips will lock the shaft quite happily - as long as you remember to remove them before starting the engine!

As most shafts are not easily accessible, fitting a remotely controlled mechanical shaft brake is the only solution, and although I have heard of them I do not know if they are still made or by whom.

Otherwise a winter project for the home bodger?

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[NigeCh]

I think that it's a question of suck it and see. What you ought to do is do a set of tests over a period in different wind speeds with the prop freely rotating and with the prop locked to see whether there is any difference in speed and more particularly, whether the steering is affected. You have a Hunter 245. It is fin keel with an exposed prop just forward of the rudder.

Charles Reed in his response has highlighted a number of points that should be considered. IMO, you should also be looking at the following: 1) that a freely rotating prop when sailing might wind itself up on some underwater debris ie ropes or nets; 2) that you will always feel the vibration of the prop through your feet; 3) that you will get extraneous noise as a rumble; 4) that the prop creates a drag ball that may cause your rudder to be less responsive.

A freely rotating prop works for some boats with no effect on steering. But on others it causes the steering to become more than soggy. As others have said below, there is no one easy answer to this. Personally, because you have an exposed prop close to the rudder, I would lock it off - On a Yanmar 1GM10 if the propshaft has its Woodruff keys set properly a two bladed prop will lock in the vertical position.

Do some tests - especially to see whether the steering is affected in all airs and let us know - It's an ongoing subject that's been controversial for yonks and it's good to see the question being raised again.

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