Puzzling Drive Problem

[Dockhead]

I have the strangest problem with my propulsion system.

After sailing for 25 miles, I reached my destination, started the engine, and had virtually no drive. As if the transmission was in neutral. Absolutely without any vibration. I shifted in and out of gear, without any change. Got about 2 or 3 knots out of 2300 revs. After a few minutes, drive gradually returned. I motored into port and maneuvered successfully into a berth. Seemed like the prop was not biting quite as hard as it usually does, however.

Some background: This all took place after motoring and motorsailing 150 odd miles nonstop from the Solent to Dunkerque.

My first thought was that the transmission was slipping. I recently changed the oil in the gearbox and didn’t know how high to fill it up, since there is no upper mark on the dipstick. I filled it to an inch or inch and a half above the lower mark, which seemed about right. But maybe I overfilled it? There was some fresh oil on the outside of the gearbox, but not a big quantity. The oil itself is perfectly clean and smells fine, so no sign of clutches burning up inside. Besides that, a slipping clutch probably wouldn’t start slipping from cold, and then stop slipping after some time of running, would it?

My second thought is much more frightening. I had my propeller overhauled last year during my refit and put it on myself. It was hard torque the propeller nut because I didn’t have any good way to hold the shaft. But I thought I got it torqued down reasonably well and locked the propeller nut with the set screw in the Brunton propeller. But when I hauled the boat out again a few months later, the prop was – to my horror – a little loose on the shaft. I torqued it down again and locked the prop nut with the set screw (breaking the allen wrench off in the set screw in the process, which was the subject of a different thread). When I hauled out again on 1 April, the prop was tight on the shaft.

However, I had the wrong anode, and had to temporarily adapt a MaxProp anode. Before leaving on this trip, last week, a friend of mine and member of this Forum came over with his diving gear, to put on the correct anode. We had to move the boat to another berth to get out of the tidal stream for him to dive, and when changing gears from reverse to forward (or the other way around – unfortunately I can’t remember), there was a fairly loud graunch from the drive shaft which sounded exactly like what happens when my ropecutter is chopping up a rope wrapped around the shaft. My friend dived and changed my anode and didn’t see anything wrong with the prop – no rope, and it seemed tight on the shaft to him. Going back to the other berth, I noticed that the prop was not “biting” as hard as usual.
Then I motored 150 miles without incident, and then yesterday, again the loss of drive. I was, until today, with a very experienced sailor who even owned a boatyard, and we couldn’t figure anything out. We looked at the shaft while tied up to the dock and it rotated normally in forward and reverse. But then the propeller had bite again, too, so the problem was not going on. My friend didn’t think it could be slipping clutches – the oil smelled too fresh and behavior not consistent with it. He didn’t think that the prop could be falling off – why would it come off partially and not fall off entirely? So his theory was that it ought to be some kind of plastic bag on the prop or something like that.

So now I have another, frightening theory – what if the prop really has come loose again, and the horrible graunching noise was the keyway getting ripped up? In forward, the propeller is pressing forward onto the shaft, setting itself onto the tapered face of the shaft, so that it more or less works. But while sailing, I have the Brunton prop feathered with the transmission in gear, and the pressure of the water tends to twist it off again, so that it is not engaging at first when I start motoring again. Going in reverse likewise twists it off of the shaft taper.
There is one problem with this theory - the prop nut is held with a set screw in the prop. If the prop were to start spinning on the shaft, the nut would spin with the prop, not with the shaft. So in reverse, if the prop were really spinning on the shaft, it would seem that it would instantly spin off the nut and the prop would fly off the shaft and onto the bottom.

The problem with the bag theory is that there is no way that I would have the same bag on the prop at home and then 150 miles later.

The problem with the transmission theory is that the oil doesn’t stink and the behavior doesn’t seem to be consistent with slipping clutches – slipping less, rather than more, after warming up.

A fourth theory could be that the Brunton prop blades are not opening up for some reason, but that seems impossible – the prop is newly overhauled and blades were rotating freely at every haul out and as checked by the diver just before departure on this trip.

The consequences of the prop-falling-off theory are so horrifying, that I’m of half a mind to find a travel lift tomorrow and haul the boat out, but that will cost a fortune, and will only eliminate one possibility. I would dive on the prop myself with a snorkel, but this is the North Sea and the water is really cold. My friend who dived in the Hamble was using a dry suit, which I don’t have and don’t know how to use. I could hire a diver, but that is likely to cost nearly as much as a haulout, and if a problem is found, I’ll have to haul out anyway. Bleh! As usual, the wise thoughts of the CF community will be much appreciated!

[LeaseOnLife]

I would run it tied to the dock, have someone observing the prop-shaft while shifting between idle, reverse, forward.

• If shaft spins, but no thrust => check prop/keyway etc (haulout)
• If shaft doesn't spin => transmission. You could go so far and block rotation of the shaft/propeller, then engaging the trans should stall the engine.

[Dockhead]

Originally Posted by LeaseOnLife

I would run it tied to the dock, have someone observing the prop-shaft while shifting between idle, reverse, forward.

• If shaft spins, but no thrust => check prop/keyway etc (haulout)
• If shaft doesn't spin => transmission. You could go so far and block rotation of the shaft/propeller, then engaging the trans should stall the engine.

Thanks! We actually did that -- shaft rotated BUT there WAS thrust. The problem comes and goes.
.
I guess one thing I could do it run it up in reverse at the dock and let it run for a long time and see if the prop falls off or if the problem reappears from going in reverse for a long time. I guess that wouldn't be such a disaster as the prop could be recovered and the boat towed to haul out.

But what do you think? Does any of these theories sound at all plausible? My problem is that every one of them seems to have a fatal flaw.

[LeaseOnLife]

I would run the heck out of it, at dock, and hope for some repeatable scenario. Anything that comes and goes is hard to debug....

One thought: While the blades move freely when moved by hand, can load cause some binding and stop them from rotating in the proper position?

[Cheechako]

If it comes and goes it sounds lie the transmission... clutches? Did you put the right oil in it? is it ATF?

[Dockhead]

Originally Posted by Cheechako

If it comes and goes it sounds lie the transmission... clutches? Did you put the right oil in it? is it ATF?

it's a Kanzaki which takes straight 30 weight motor oil, not ATF. I used 15W-40 regular motor oil like I use in the main engine. Do you think it could be not viscous enough? I think other people are making the same substitution.

[Lancerbye]

Last year I found myself in a similar situation. I checked everything as you have and after some tests at the dock it totally quit working. I could see that the shaft was not turning. I pulled the transmission to find a damper plate with a bunch of broken bolts still having some bite when it was tight up against the flywheel if it hit the bolt ends right. Having twin engines and sail I was able to get back to port without any problems, however after this scary discovery I replaced both damper plates with heavy duty ones. The starboard drive which had been the one still working had all the 12 bolts nice and tight, but the plate springs and internal pieces were breaking down. Damper plates are one of the out of sight, out of mind parts that can bite you in the rear. These were probably the originals on a 33 year old motor sailer.

[weavis]

Originally Posted by Dockhead

it's a Kanzaki which takes straight 30 weight motor oil, not ATF. I used 15W-40 regular motor oil like I use in the main engine. Do you think it could be not viscous enough? I think other people are making the same substitution.

Should be fine on the oil 15W-40

If its the transmission, only 3 things I think it can be.

Too much/too little oil
Broken oil pump
worn clutch plate.

If you have a trawling lever.. try moving it to another position.

[bornyesterday]

First find out the correct oil type and level for your transmission type and put that to rest.

Handheld non-contact tachometers are cheap now - you could use one to monitor shaft revolutions and compare with your engine tacho. If the two readings differ by more than the reduction ratio - and variably - then obviously your transmission is at fault.

Is it possible that you didn't tighten your prop correctly when you replaced it previously?
If so then every time the prop reversed the taper could let go - then the loose key could hammer side-to-side in the keyway and might eventually shear, leaving only the shaft taper and locking nut to drive the prop intermittently.
The noise from this would have been noticeable but if the key had simply been forgotten there might not be any noise.

[cal40john]

This manual on page 21 says the bottom of the dipstick is low and the mark is the high level. Is this anything like yours?

I'm not that familiar with wet clutch trannys, but if you had way too much oil could the plates slip until the oil worked out of between the plates?

http://yanmar.com/product/marineplea...Manual-ENG.pdf

[weavis]

Originally Posted by cal40john

This manual on page 21 says the bottom of the dipstick is low and the mark is the high level. Is this anything like yours?

I'm not that familiar with wet clutch trannys, but if you had way too much oil could the plates slip until the oil worked out of between the plates?

http://yanmar.com/product/marineplea...Manual-ENG.pdf

Id be tempted to drop the oil level first. Its the quickest and cheapest elimiination test to do.

[Dockhead]

Originally Posted by weavis

Id be tempted to drop the oil level first. Its the quickest and cheapest elimiination test to do.

I think that's good advice. I will start with that.


I have thought long and hard and it now seems to me that it must be the transmission. I've had a couple of ropes in the rope cutter (pot buoy off Sark; stray pile line) and perhaps I damaged the transmission with those incidents. Maybe last week leaving the berth I picked up some kind of floating junk in the prop, and that was the last straw foe the poor gearbox.

I wish I better understood how these gearboxes work, so I could visualize it. I've never seen one apart.

[Dockhead]

Originally Posted by cal40john

This manual on page 21 says the bottom of the dipstick is low and the mark is the high level. Is this anything like yours?

I'm not that familiar with wet clutch trannys, but if you had way too much oil could the plates slip until the oil worked out of between the plates?

http://yanmar.com/product/marineplea...Manual-ENG.pdf

Thanks! Now I finally understand the dipstick marks. Indeed, my gearbox is overfilled by an inch or so. First thing I will do is to lower the level.

I am also wondering whether too much oil can cause the disks (or cones) to slip. I really don't know anything about this type of gearbox, I'm afraid. I had wet clutches in motorcycles years ago, but that is the extent of my experience.

[Neptune's Gear]

Almost certainly overfilled IMO. In my trans, overfilling causes intermittent inability to select fwd gear. Strange, but true!
If it was your prop, once moving, the keyway would be destroyed pretty fast...
Good luck!!

[atoll]

had this problem before when the gearbox oil has many hours on it.

the first thing i would do is to drain out the suspect oil and replace with a know brand of the correct oil as specified by mfg.

could be you have been sold "fake" oil,that is infact a chinese or indian counterfeit product,made from old filtered oil.