I have the strangest problem with my propulsion
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!