Feathering prop question

[steffan]

We have a 34 ft monohull, Yanmar 3GM30F, Kanzaki transmission, and a Kiwiprop. Last week we were on a broad reach, 15-17 kts, slight to moderate open Lake Superior swell, doing hull speed with occasional departures above as, I assume, we surfed a couple of times. Faster than we normally get to sail. We are not experienced passagemakers, bear with me.

Boat developed an unfamiliar hum, eventually diagnosed to be the prop shaft spinning. Since this has not happened to us before my solution was to start the engine, throttle up for a minute, then shut down as usual in neutral. The prop stayed feathered for a couple of mins, then the shaft turning came back.

I ran the engine again, this time shutting it down at reverse idle and leaving it in gear. That solved the problem, but I wonder if it was the right thing to do?

We still leave it in neutral normally and we haven't sailed fast enough since to see the problem again.

[Dr. D]

My boat also has a feathering prop. When we bought the boat we were told to put the transmission in reverse while sailing. A few months ago I noted in the sail drive manual and the Yanmar engine manual state that the transmission should be left in neutral while sailing. I called the dealership and asked about the apparent discrepancy. The service manager stated with a fixed prop the transmission must be in neutral to avoid torque acting on the transmission. With a feathering prop, the transmission should be in reverse to fold the prop. With it folded there is no torque produced.

[noelex 77]

Yanmar strongly recommends /insists that when the motor is not running the box must be in neutral at least for all small/medium sailboat engines and with most (all ?) gearboxes and saildrives.This applies to all props fixed, feathering and folding.

The need for the gear box to be kept in neutral with feathering or folding props seems a strange requirement and some do not follow this directive, nevertheless that is what they advise. There is service bulletin to this effect that should be found with a Google search.

With all (or nearly all?) folding props, very briefly putting the gearbox into forward or reverse (this depends on the gear box) will fold the prop and it can then be switched back to neutral and left in this state while sailing. This also applies to most feathering props, but some models at least in some installations can spontaneously unfeather in some conditions and of course they tend to remain this way.

[MicHughV]

I think a lot depends on your transmission.
I had a max prop on a Westerbeke, which had a hydraulic borg-warner gearbox, once the engine was off, the prop shaft would continue to spin as the blades would not feather properly. I had to slow the boat down, as I had to physically get into the engine compartment to stop the spinning shaft, usually with a set of vice-grips around the shaft.
My max-prop was a two blade, while I was down in the engine compartment, I could rotate the shaft so the blades would align behind the keel. I had marked a spot on the flange for this purpose.
But it was a pain in the butt. Once in a while, I would run the engine to charge the batteries and the whole process started over.
Despite this, I love the feathering prop.

I know some people with a feathering prop that will stop the engine, while it is still in gear, this also seems to do the trick, I'm told.

[noelex 77]

I should have mentioned that with a hydraulic gear box a shaft brake is normally required. Putting the gearbox in gear with the engine off does not lock the shaft. Stopping the engine in gear can sometimes work, but not in many installations.

When racing we would align our fixed two blade prop behind the deadwood. I have never heard of this being used to remove the need for a shaft break when using a hydraulic gear box with a feathering/folding prop. It is always nice to learn new tricks, so thanks for tip, although once again this would probably only work on a few boats.

[kenbo]

My first thought is that your Kiwiprop may need servicing i.e. cleaning and greasing of the blades. It should feather very easily and with the ungeared blades it should provide little or no torque to the shaft.

Cone clutches like the Kanzaki are very different from the multi-disc wet clutches found in a Hurth or ZF. A cone clutch is designed to transfer torque to two rotating shafts. It is not designed to stop a rotating shaft. The reason being is has a small frictional surface area and the bronze friction surface is not that thick. If the surface gets glazed you dont have much to work with.

In my opinion I'd leave it in neutral and dive on the prop to see if it needs servicing.

[steffan]

Originally Posted by kenbo

My first thought is that your Kiwiprop may need servicing i.e. cleaning and greasing of the blades. It should feather very easily and with the ungeared blades it should provide little or no torque to the shaft.

Cone clutches like the Kanzaki are very different from the multi-disc wet clutches found in a Hurth or ZF. A cone clutch is designed to transfer torque to two rotating shafts. It is not designed to stop a rotating shaft. The reason being is has a small frictional surface area and the bronze friction surface is not that thick. If the surface gets glazed you dont have much to work with.

In my opinion I'd leave it in neutral and dive on the prop to see if it needs servicing.

Thanks, I'll have her on the hard within a month up here and the prop will get attention for sure.

[MicHughV]

I don't know about other feathering props....but the max prop, unless perfectly feathered, will have an angle to the water, and even a slight angle is enough to cause the prop to rotate.
I would stop the engine, while still in gear, to stop the prop from spinning, but the minute the engine stops so does the hydraulic fluid for the borg-warner hydraulic transmission and the prop would never fully feather, necessitating a trip to the engine compartment. As I always wanted to align the prop behind the keel, this little extra effort was not a problem. A pain in the arse sometimes, but not a problem.

On my first boat, I had a Volvo engine with a fixed two blade prop and would lock the shaft in reverse. Never had a problem and as above, I would make a trip to the engine compartment to align the blades behind the keel and maybe having the smaller blades did not exert enough torque on the transmission to be a problem.

My Beneteau has the Yanmar, with a 3 blade. Strangely enough, even at speed, the prop does not rotate. The only thing I can think of is the Beneteau has a relatively thick shaft log underwater and the prop does not get enough clean water to rotate, but this is a guess on my part.

Three different boats, three different engines, three different props...and I'm still none the wiser.

This topic has been beat to death on other threads, regarding prop drag while under sail, and whether to lock or not.

I don't think there is a consensus, despite a plethora of first hand experience, studies, etc..etc....a feathering prop gives one the best possible least drag feature, but even so, it requires a number of other circumstances to alignas well.