Porthandbuoy
Well-Known Member
Not for reasons of drag reduction or fear of clutch damage, but to protect a cutless bearing that is cooled/lubricated via a feed from the seawater cooling circuit.
To lock the prop or not?
- Thread starter Porthandbuoy
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[70521]
Well-Known Member
What does your engine manufacturer say?
Personally, I don't lock the prop as is what Volvo Penta say in the manual. Before I switched to a folding prop we did a wee experiment 'locked and unlocked' - locked we lost 0.5 kt, or 12nm in 24 hours just over two hours drinking time in the pub.
Personally, I don't lock the prop as is what Volvo Penta say in the manual. Before I switched to a folding prop we did a wee experiment 'locked and unlocked' - locked we lost 0.5 kt, or 12nm in 24 hours just over two hours drinking time in the pub.
srm
Well-Known Member
Lots of ideas on this, try the search function as I seem to remember it being done to death a while back.
I lock my prop precisely for the reasons the OP gives, but on a previous boat also to protect a hydraulic drive. Others will come up with contrary views.
I lock my prop precisely for the reasons the OP gives, but on a previous boat also to protect a hydraulic drive. Others will come up with contrary views.
Praxinoscope
Well-Known Member
The gearbox manual for my current boat states categorically not to lock the prop, don’t know why, it doesn’t say, but on my previous boat with a Heurth gearbox I always locked the prop with no adverse effects over the 20 years I sailed near.
johnalison
Well-Known Member
It may depend on whether you have a folding prop or not. Our 2-blade prop doesn’t fold if allowed to spin, which would negate its advantages. With a fixed prop it is a matter of what the maker says.
Porthandbuoy
Well-Known Member
I have a fixed three blade prop. Just to clarify my query; I am only concerned about the cutless bearing which is not being force-fed water when the engine is not running, Under sail the shaft spins. Need I be concerned about the cutless bearing?
jwfrary
Well-Known Member
I assume this is a cutlass in the shaft log (forward or aft, two or just the one?) rather than a p bracket, in which case I think your fear may be well founded, then again the shaft speed will be lower when trailing than when operating the propulsion so perhaps there's sufficient water to cool the bearing at those speeds. Much depends on your configuration, a little more info would be good!
PlankWalker
Well-Known Member
I believe that with a fixed prop there is no difference in drag weather it is locked or not.
If that is true, there is certainly a difference in noise, wear on the cutlass, shaft and gearbox, if it is locked or not.
Plank
If that is true, there is certainly a difference in noise, wear on the cutlass, shaft and gearbox, if it is locked or not.
Plank
vyv_cox
Well-Known Member
That is not the case. There have been many studies, amongst others by Strathclyde University, Maine Sail and Yachting Monthly, all of which show that the drag of a spinning prop is considerably less than that of a fixed one
Stemar
Well-Known Member
I'm not an engineer, but some water will be getting in, and the bearing isn't under load the way it is when under power, so I wouldn't expect undue wear.
I expect someone will be along in a moment to tell me why I'm wrong.
R.Ems
Well-Known Member
The shaft will be turning far more slowly when you are under sail. In fact you could guesstimate it roughly, using prop pitch and boat speed.
Maybe you don't need water continually forced in there, compared to the approx 1000rpm shaft speed under power?
Fixed props give far more drag than freely turning ones, so not fixed will let you sail a bit faster.
But I would start by asking manufacturers first.
Maybe you don't need water continually forced in there, compared to the approx 1000rpm shaft speed under power?
Fixed props give far more drag than freely turning ones, so not fixed will let you sail a bit faster.
But I would start by asking manufacturers first.
Supertramp
Well-Known Member
My gearbox manual makes it clear that you can lock the shaft in reverse or let it spin. The gearbox will not mind. Not all gearboxes are the same as said previously. With regard to cutless wear, I let mine spin but it's only for short passages, a few hundred hours per year. I might lock it on an ocean crossing or if I sailed 1000's of miles.
Separately, letting the shaft spin gave me a big clue that my engine alignment had gone off as it no longer spun at 2 knts and vibration increased, not something I would have noticed under power.
I think the choice depends on the time spent spinning (and how easy you find replacing your cutless).
Separately, letting the shaft spin gave me a big clue that my engine alignment had gone off as it no longer spun at 2 knts and vibration increased, not something I would have noticed under power.
I think the choice depends on the time spent spinning (and how easy you find replacing your cutless).
Graham_Wright
Well-Known Member
Watching mine spin enthusiastically while under sail, I wondered yet again about extracting that wasted energy. The plotter is quite thirsty.
Moodysailor
Well-Known Member
It will suffer premature wear if left to spin, as you rightly say it is due to the lack of water lubrication that the engine would normally provide.
But as others also rightly point out, the shaft speed is so low under sailing rotation the extra wear is likely to be negligable.
Regards the cutlass bearing, in reality it won't make much difference unless you are sailing across oceans. I would definitely follow what the engine/gearbox manufacturer advises as this could have much more expensive and faster damage.
R.Ems
Well-Known Member
You aren't the first
Props are very poorly shaped for getting energy out of the water, unfortunately. Opinionated digression alert:
It the prop was a useful method of generating leccy, we would all use it.
A very expensive set-up, using the latest technology, may give some useful power on a long run; but the benefits are marginal, despite the illustrious St.Leo of Tally-Ho (or his financial backers) choosing such a system, presumably as a sop to the greenists.
Towed generators have very different blade designs; adjustable pitch while underway would certainly help a little bit. I have a towed generator, set up simply like a Walker's log but much heavier. They are very powerful, but a big faff unless you are on a long run in suitable conditions (probly trade winds).
Another philosophy entirely might be to compromise in the other direction, and optimise the 'propellor' design as a water-driven turbine, most efficient around the yacht's normal sailing speed. It would be very poor as a powered propellor, but if you could live with that, you would have propulsion for harbour manœvres, and a fair source of free electricty.
Another idea is a water-driven turbine entirely separate to the normal prop, perhaps retractable, I believe these are already in use on big expensive sailing yachts.
Anyway enough rabbiting.
Porthandbuoy
Well-Known Member
With regard to potential gearbox damage. Is it the act of engaging reverse while the prop is spinning that causes the problem? There is a definite ‘clunk’ that makes me kind of nervous. Perhaps the answer is to stop engine, let the boat slow until the prop stops spinning, then sheet in the sails.
Just looked at the price of feathering props. ?
Just looked at the price of feathering props. ?
vyv_cox
Well-Known Member
The 'clunk' is quite normal on a gearbox with some miles on it. The transfer gear moves from front to back between forward and reverse, the clearance is small, around .002 inch on my box, but it increases a little with wear. The sound is made by the gear moving from one thrust bearing to the other.
Moodysailor
Well-Known Member
The gearbox damage is done as the oil is often circulated around the gearbox by the input shaft (the engine end). On some it drives a hydraulic pump, on others the primary gear 'splashes' the oil around. If the engine isn't running, this shaft isn't turning, and no oil is getting to the bearings and bushes in the transmission, causing accelerated wear.
On some transmissions it isn't an issue, hence the need to consult the manufacturer - there is no point increasing the sailing drag if it isn't necessary.
As above, the 'clunk' is quite normal.
Scomber
Well-Known Member
Yep Vyv , half a knot on our 8.6m boat.
Poignard
Well-Known Member
Is a freewheeling prop more, or less, likely to become entangled with a rope or net than a locked one?
