Props/keyways/shearpins

[Anchorite]

Have a std Vetus shaft, 30mm, with a 16" prop?. Have bought a secondhand
bigger Volvo prop, same taper....but the keyway is 10mm as against 8mm for
the Vetus. Two solutions: shape a piece of 2mm s/s to take up the play, or
drill through the Volvo hub (there's about 12 mm available on forward end) and
fit a shear pin.
Has anyone done something like this and of so what shear pin recommended?
Motor (inboard) is about 50 cv max, 2500 rpm max., prop 1250, behind semi-
long keel.

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[burgundyben]

I'd make up a 2mm peice of metal to go in the slot and not bother drilling the hole, remember that its the tapers being locked together that drive the prop, not the key. Thats why you need a puller to get the prop off.

Remeber that the little peice of metal will only be in compression never in shear as it wont be located in the shaft.

When fitting new prop to shaft you should use some valve grinding paste to 'lap' the two taper together, like a valve in a cylinder head, 1/2turns, 1/4 each side of keyway. Make sure very clean on re-assembly and taper should stick togther just by pushing on by hand.

If you do decide to drill and fit a pin get a cobalt drill to go thru the shaft and use drill on low speed. But dont bother, pack out the keyway.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[charles_reed]

You have the following solutions:-

1. Take out the shaft and have the keyway re-cut and a new key. Cost, if you know an engineering shop £12.
2. Have the keyway recut at 8mm on the propellor boss, to take your existing key. Probably a lot more expensive than #1.

The above two are engineeringly correct.
More of a botch:-

3. Make up a 2mm wide packer to fit into the keyway. OK if you've got the tools, patience, eyesight etc to get it right. I very much doubt you'll find a 3rd party to do it for you.

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[anderson]

the only real way to do this is to make a stepped key, ie make the key to fit the ten mil and then file down the key to fit the 8 mil.

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[webcraft]

Er . . .

Yes, it's a taper fit and maybe theoretically the keyway is never in shear. But . . .

I lost all forward motion on a Jeanneau Sunshine going into Portpatrick in bad weather, ended up getting towed in . . .

I assumed the prop had fallen off.

After the boat was towed back to her home port and lifted out of the water it was discovered that the prop was still there, just spinning helplessly round and round.

The keyway had sheared.

It was a new prop, but the owner had economised by re-using the old keyway. He says he won't do that again!

My advice is, get a new keyway made.

- Nick

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[Avocet]

I'd be very wary of the shear pin route. Depending on whereabouts it is it's just possible that you could start a fatigue crack and end up loosing the end of the shaft and the prop at an inconvenient moment. (Not that I suppose there is ever a "good" time to loose a prop!). The stepped key gets my vote but I'd probably dry the boat out and check it for tightness after one week and then after one month. I agree with the previous poster that the friction between the two does all the work - but only once it's all settled together. If there's anything preventing a PERFECT fit that subsequently disappears, the whole lot will end up relying on the key.

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[Anchorite]

Thanks to all: I've the patience, metal and tools to fab a filler. And
I'll go for lapping. I think Webcraft's 'new prop' must have been
inadequately fitted to be able to spin. The Vetus keyway is 50x8mm
which would require a 20 tonne bash to shear it. The forces in play
down there are under 500 kgs and even a dynamic load caused by
sloppy keyway fit wouldn't add much...it could strip the bronze in
the prop though.

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[Heckler]

if you dont want to recut the keyways (if the bigger prop is no good you will have to mess with the old one as well) make a stepped key, got to be a tradesman to do this however, take a key that is the biggest size and file a step in it. painstaking but cheap. dont drill and pin, the shear forces acting on it will, if the taper doesnt grip well, break it.
from a man who served an apprenticeship and made a living doing things like this.
stu

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[Plum]

One more thing...

You have had lots of good advice, but can I just add one more thing if you have not fitted keys before:

Obviously, you need to adjust the width of the key (or spacer) to fit the width of the slots, but please do make sure that you leave adequate clearance on the height of the key (or spacer) so that as the prop pulls up on the taper of the shaft the key does not bottom out in the slot and so stop the taper gripping correctly. This is most important and is probably the main reason why props come loose or keys get sheered. As has already been said, if all is set up correctly, it is the taper that does all the work, not the key.

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