Locking the prop

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At present I have a three bladed fixed prop driven by a 50hp Yanmar. Once under sail at 6kts I have an irritating hum from the turning shaft. It's barely audible but it's enough to irritate!

The Nauticat manual says put the engine astern (when stopped) to stop the shaft turning. The Yanmar advice on the web is not to engage astern but to leave turning otherwise the gearbox will lock in astern and the engine will have to be started in reverse gear engaged (which is the case on my boat).

So; what to do? What do you all do? I just sit in the cockpit worrying about all the unnecessary wear on the gearbox and shaft seal if I leave turning but worry about locking the gearbox up if I do put it astern. I think I'm gonna have to get a folding prop this winter! I've seen it suggested that one can apply molegrips to the shaft to stop it turning - but I can imagine the damage that would be done by forgetting to undo the grips before starting the engine!



rob
 
I always put the engine in gear astern when sailing and have never had a problem. I've heard arguements for and against but as you say, the "hum" is annoying. I have a Yanmar 2GM20 with a Hurth type gearbox.

Interesting idea with the mole grips but like you I know I would forget one day. Also means you can't start the engine quickly in an emergency.
 
Hi

Restaring the engine running astern is not going to damage it, as soon as it fires up move the control to neutral.

However the drag upset me, sailing in company last year convinced me that the prop was costing a lot of speed under sail, spinning or fixed.

I have just fitted a volvo three blade folding prop to a yan 56 and I think I get about another knot and a bit under sail and 1.5 knots under engine - in other words the standard prop was too small the drive boat efficently and too big to sail with.

Worth a consideration
 
Nothing wrong with the mole grips, as long as you tie the starter key to them! But I would only use them if I was going on a longish passage and wouldnt need the engine in an emergency. Plus the engine would probaly break the moles if put in gear. Have you considered a few turns of rope, wrapped around the shaft as in a spanish windlass, must less danger of damage if the engine is started and put in gear, but tie the keys there again, or put them in your pocket, gives you time to think why they are there?!?
 
We have a Volvo whose manual also says not to engage astern. But we do, the local agents for the engine said to, and is what most seem to do. It often jams in astern and we release it with a brief kick on the starter with the mechanical fuel shut off on the engine panel pulled (which not all boats have) so as it doesn't start.

Much better than the endless rumbling if left rotating. I have never been much interested in locking the shaft, both from the danger point of view and the fiddling around in the bilge point of view unless it is interlocked with the engine so as it releases automatically - which seems an expensive and prone to maintenance item given that the gearbox seems to do the trick for us.

John
 
We put our 1GM into "astern" when sailing in order to lock the prop. I wasn't aware that this was a problem, and if you take it out of gear while still sailing the prop will start to spin again. The engine hasn't failed to start up in neutral when required. Yet. (Touch wood, etc.) Mole grips are far too dangerous with a memory like mine.
 
I did read in one sailing mag about someone who put a disk brake mech on the propshaft and used that to stop the shaft ....
 
I did the same 2 seasons ago and the improvement has been dramatic. I still put the gear in astern when sailing and prop folds and my speed increases.

Regards.

Peter.
 
[ QUOTE ]
does your gearbox "lock up" so that you have to start in gear?

[/ QUOTE ]

Nope, I return the throttle to the idle position, push the tab in to deselect the drive, push throttle forward a bit and hit start. Starts in neutral as usual.
 
I've never had any problem with parking the gear in astern when sailing on current (Beta) or previous (Volvo and Yanmar) engines, whether with conventional or Hurth gearboxes. The prop in my current boat is a 3-blade Brunton Autoprop which gives outstanding efficiency and low drag but may need either forward or reverse gear to silence it depending on sailing speed.
 
I usually put my 3GM (saildrive) in forward. Once in a while it won't engage with the engine stopped so I use reverse instead. It doesn't lock up.
 
I use fishing line, simple and cheap and if I forget it then the worst that happens is the line breaks and Ihave to replace it.
Works a treat.
 
No, I don't think the cutlass bearing has had it; in fact the noise that I can hear is simply what I would expect to hear with a shaft freewheeling through a seal. I suppose I'm more concerned about the contunual turning of the prop for no reason - but I suppose that it's a lot less wearing than being driven by the engine at 7kts. So maybe I should just forget it and not worry about it.

rob
 
Unfortunately, this is an eternal dilema. I talked to the Yanmar dealer in my location about this. They disadvise engaging a gear and suggest to just leave in neutral and shorten the maintenance schedule in 25% for gearbox lubrication, etc.
With the previous motor (Diter), I would engage a gear and never had a problem.
I'm doing what yanmar suggests and have to cope with the spinning noise...not to much since everything is new, I guess; but would like to have that extra knot in performance. What I can't understand is why a folding or feathering prop is about half or more the price of a new engine.
Wish somebody could explain this to me. /forums/images/graemlins/shocked.gif /forums/images/graemlins/confused.gif
 
I asked this a few months ago and finally got the official answer that modern gearboxes lock up in gear due to the cone clutches. The Yanmar dealer said I could "stress" the gearbox. Having lived with a spinning prop for a while I will change to a folding prop asap
 
Don't even think about the mole-grip plan unless you are just about stopped in the water and/or the shaft isn't turning - the torque will tear them out of your hands and fling them who knows where. Tried that & got the scars!

Good idea about the keys but I'd suggest a large red streamer on the key/grips so you can recover it from the bilge!
 
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