Spinning prop

[Neeves]

A few props have a rubber bush inside them as an electrolytic cut off. It also works as a sheer section if the prop catches a line etc to prevent damage to the drive. If the op has had issues with this over the years without knowing it may have sheared years ago. The idea being that one can still get in to port . But if one carries on motoring it will finally let go completely and the prop will just spin.

A few props - I thought it was many Gori and Volvo come to mind - but the Op mentioned a shaft and I assumed it was not a sail drive - and then it cold be any prop.

But it was my first thought, which I then discarded (as I cannot recall a failed polymer sleeve having failed)

Jonathan

 

[Daydream believer]

But it was my first thought, which I then discarded (as I cannot recall a failed polymer sleeve having failed)

Would they report to. You any way?
My Brunton has a rubber bush and it was replaced at its last service. That may have been them being careful but I had told them of a serious issue with a polythene sheet that the cutter could not deal with along with numerous weed encounters that took some time to shift and a net that required a haul out
Bruntons can be used on shaft drive as well as sail drive

 

[Neeves]

Would they report to. You any way?
My Brunton has a rubber bush and it was replaced at its last service. That may have been them being careful but I had told them of a serious issue with a polythene sheet that the cutter could not deal with along with numerous weed encounters that took some time to shift and a net that required a haul out
Bruntons can be used on shaft drive as well as sail drive

No, that was not suggested

But such things might be reported on YBW

Jonathan

 

[B27]

No matter whether RH or LH prop. When driving ahead, the propeller is pushing the boat, and is therefore pushing onto the taper on the shaft.

But in one case the shaft is trying to tighten the nut, in the other it's trying to loosen it?

Driving ahead could also push the prop against the P bracket, while driving astern would pull it away?


Essentially, if it's a tapered shaft, I would suspect the prop is not properly mounted on the taper.
Maybe it's damaged/doesn't fit.
Maybe the key is holding the taper apart
Maybe the nut has bottomed out on the end of the shaft before pushing the prop adequately onto the taper.
I'm sure there are other possibilities.

Basically, the prop should refuse to come off the taper without using a puller.


I would double check the shaft is going round, this could be a gearbox problem. The shaft might go around when lightly loaded but not under proper load? Does the gearbox get hot?

But you don't want to mess around while you have such a problem, a loose prop is easily lost and rarely found.

 

[Daydream believer]

But in one case the shaft is trying to tighten the nut, in the other it's trying to loosen it?

Driving ahead could also push the prop against the P bracket, while driving astern would pull it away?Essentially, if it's a tapered shaft, I would suspect the prop is not properly mounted on the taper.
Maybe it's damaged/doesn't fit.
Maybe the key is holding the taper apart
Maybe the nut has bottomed out on the end of the shaft before pushing the prop adequately onto the taper.
Basically, the prop should refuse to come off the taper without using a puller.

But the op reports that the prop issue has only just happened. So unless it has first come loose in some way. Ie the nut has loosened whilst going astern and pulled the prop off the taper. the only thing that may have happened is that it has hit something or caught some weed etc and sheared the woodruff key.

 

[B27]

I f the prop is mounted properly, the woodruff key won't matter. It's there to enable the nut to be tightened initially, it should be the taper which does the driving in operation.
But there are probably a lot of badly fitted props about, divers find the odd one now and then.
It's also not a trivial amount of torque to correctly tighten the nut on even a medium sized yacht shaft.
So there are probably a lot relying on the key, and/or whatever locking mechanism retain s the nut.
There's also metric and imperial, 25mm is a lot like an inch but the standard taper angle is different.
The wrong angle will work, 'sort of'.
I assume it's a normal fixed or folding prop, more exotic beasts may have extra failure mechanisms

However, the only boat I've known which manged to lose drive ahead was due to the cone clutch in the gearbox being worn out, allegedly due to sailing with the motor in Ahead.

 

[Daydream believer]

I f the prop is mounted properly, the woodruff key won't matter. It's there to enable the nut to be tightened initially, it should be the taper which does the driving in operation.
But there are probably a lot of badly fitted props about, divers find the odd one now and then.
It's also not a trivial amount of torque to correctly tighten the nut on even a medium sized yacht shaft.
So there are probably a lot relying on the key, and/or whatever locking mechanism retain s the nut.
There's also metric and imperial, 25mm is a lot like an inch but the standard taper angle is different.
The wrong angle will work, 'sort of'.
I assume it's a normal fixed or folding prop, more exotic beasts may have extra failure mechanisms

However, the only boat I've known which manged to lose drive ahead was due to the cone clutch in the gearbox being worn out, allegedly due to sailing with the motor in Ahead.

Can you explain why the taper ANGLE would be different on a metric or imperial shaft please

 

[Stemar]

Can you explain why the taper ANGLE would be different on a metric or imperial shaft please

No particular reason other, I presume, than convenient measures in each system, but they are. A prop set up for one will be wobbly on the other.

All the OP can do is take the prop off and have a look. Our Snappie had a tapered shaft with a woodruff key. I'd expect this key to be damaged or missing. A loose prop nut could do that. When everything's sorted, if the slots in the nut won't align with the hole in the shaft with the nut tight, you either need a thicker/thinner washer, or you can grind a little off the bottom of the nut. (Been there, done that)

 

[Daydream believer]

No particular reason other, I presume, than convenient measures in each system, but they are. A prop set up for one will be wobbly on the other.

No. —-
Please explain the statement made by B27 as I requested in#27.
I am just intrigued and would like to understand this new, to me, learning
I want know why one will be wobbly on a shaft with the same taper angle note angle ,or pitch if you like, if one shaft is 1 inch and one is 25 mm. surely the taper just runs a few mm further up the thicker shaft. A prop designed for a 1 inch shaft will still fit a 25 mm one but sit slightly further up the the taper. One might need a couple of washers behind the nut. But so what. The taper angle is still the same. It is NOT different.

 

[Tranona]

No. —-
Please explain the statement made by B27 as I requested in#27.
I am just intrigued and would like to understand this new, to me, learning
I want know why one will be wobbly on a shaft with the same taper angle note angle ,or pitch if you like, if one shaft is 1 inch and one is 25 mm. surely the taper just runs a few mm further up the thicker shaft. A prop designed for a 1 inch shaft will still fit a 25 mm one but sit slightly further up the the taper. One might need a couple of washers behind the nut. But so what. The taper angle is still the same. It is NOT different.

As usual a lot of misunderstanding here. Imperial props generally have a 12:1 taper and metric 10:1, although mixed are not unknown as for example on some Westerlys in the early 80s which had 25mm shafts with 12:1 tapers.

On a shaft drive as mentioned several times the drive is transmitted by the taper interface so correct torque on the nut is important. The key is only for location - important for balance to ensure the prop always goes back in the same location. On my current boat the shaft was machined to match the prop and balanced as an assembly. It also has a 30mm shaft but a 25mm 10:1 taper because the prop hub is not big enough to take a 30mm.

Rubber bushed props are a red herring. They are only used on saildrives which have splined shafts rather than taper. So a Bruntons prop for a saildrive will be bushed and for a shaft drive solid with the appropriate taper to fit the shaft.

 

[B27]

Can you explain why the taper ANGLE would be different on a metric or imperial shaft please

Imperial might be one inch in a foot, metric might be 1mm in a cm?
The US tends to use inches and decimals of inches, so I wouldn't assume they'd be the same.
There are loads of different 'standards' for tapers, used for different purposes in different industries,
And loads of things which are non-standard.

 

[Daydream believer]

Imperial might be one inch in a foot, metric might be 1mm in a cm?
The US tends to use inches and decimals of inches, so I wouldn't assume they'd be the same.
There are loads of different 'standards' for tapers, used for different purposes in different industries,
And loads of things which are non-standard.

I said— if you read my post— same taper angle.
I am fully aware that one can introduce any standard one wishes. I have several I use on my lathe & milling machine for collets etc.
I often turn a taper to fit some mandrel or other and so long as they match it is pretty much irrelevant what diameter whether 25mm or 1 inch. Just need to be true

 

[alahol2]

I said— if you read my post— same taper angle.
I am fully aware that one can introduce any standard one wishes. I have several I use on my lathe & milling machine for collets etc.
I often turn a taper to fit some mandrel or other and so long as they match it is pretty much irrelevant what diameter whether 25mm or 1 inch. Just need to be true

Read what Tranona said.
The STANDARD taper on a 1" (Imperial) shaft is 12 to 1
The STANDARD taper on a 25mm (Metric) shaft is 10 to 1
So different taper angles.

 

[Daydream believer]

Read what Tranona said.
The STANDARD taper on a 1" (Imperial) shaft is 12 to 1
The STANDARD taper on a 25mm (Metric) shaft is 10 to 1
So different taper angles.

irrelevant to the point I was making

 

[B27]

irrelevant to the point I was making

Whatever point you thought you were making, you failed.

 

[Daydream believer]

Whatever point you thought you were making, you failed

Clearly so .

 

[footsoldier]

I'm sure the O.P. must have found all that most illuminating.

 

[Bilgediver]

Once

Fingers x , unfortunately can't get back to boat yard till Sunday,to get prop off, would you know if it has likely damaged inside of prop ?

When the prop is removed you can inspect the condition of the shaft and bore of the prop. If only minor damage then might be able to recover the surface by lapping in with smooth grinding paste. If seriously damaged a machinist could probably recover the tapers in a lathe.