Prop/shaft diameter question

mogmog2

mogmog2

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Will a 1" prop fit satisfactorily on a 25mm shaft that has the same taper? Presumably a small amount of the boss would be past the taper. On a 20hp sailing yacht, is that a problem? Thanks
 
As it stands, I have nothing aft of the gearbox: I've found a suitable prop secondhand so could get the new shaft machined to fit. £50 is more appealing than >£300 so just exploring options.
 
mogmog2 said:
Will a 1" prop fit satisfactorily on a 25mm shaft that has the same taper? Presumably a small amount of the boss would be past the taper. On a 20hp sailing yacht, is that a problem? Thanks
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A sound machine shop can put the non standard taper on for you if you need to keep to 25mm for the sake of the stern gear. On price I would shop around, there are some fancy figures out there.
 
DownWest said:
It is only 0.4mm, so not a lot if the taper is right. 4mm on a 10:1 taper
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That's about 1/14th of the boss length so I was hoping it was insignificant. Based on the measurements given, the taper is 1:9. Does that mean its likely to be1:10 really and his measurements are our slightly?
 
doug748 said:
A sound machine shop can put the non standard taper on for you if you need to keep to 25mm for the sake of the stern gear. On price I would shop around, there are some fancy figures out there.
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I haven't got any stern gear yet - my old prop is lh & I now need rh. My shaft was knackered and the old Volvo coupling isn't worth rescuing. All I have is a cutless bearing. It occurred to me that I could just get a 1" shaft as I need everything and I'd just have to replace the cutless bearing which was ok although it wouldn't hurt to have a new one.
 
coopec said:
This table might help you work out what taper it is.

If you want to go to their website google "little machine shop reference tapers" (YBW obviously can't handle a link)

View attachment 82420

https://littlemachineshop.com/reference/tapers.php
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Thanks, but it's all in foreign ? and none of those are close to the dimensions I've been given (1" large end, 3/4" small and 2 1/4" boss): apart from the Jacobs, they're all about 4" long around 1" diameter. However, AFAICT, the taper is largely irrelevant - it's whether it's a really bad idea to have a small percentage of the prop boss not on the taper?
 
Sounds like the best thing is to go all metric. I don't think that the tiny bit of unsupported boss will be a problem at that sort of power however a decent machine shop could perhaps knock up a dummy taper on a short piece of 25mm shaft to try before you commit to buying a the whole shaft. Alternatively try and find somebody with a 25mm shaft who is taking their prop off this winter and try the prop on their 10:1 taper. May give you a better idea.

Yoda
 
mogmog2 said:
Thanks, but it's all in foreign ? and none of those are close to the dimensions I've been given (1" large end, 3/4" small and 2 1/4" boss): apart from the Jacobs, they're all about 4" long around 1" diameter. However, AFAICT, the taper is largely irrelevant - it's whether it's a really bad idea to have a small percentage of the prop boss not on the taper?
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I think that you'll find that,within reason, it is all about the matching of the tapers in the hub and on the shaft.
And unless I'm reading it wrong and having one of those moments then the taper in the hub is 1 : 20 ???
I read that on the half diameter the taper increases from 3/8 to 1/2 . a rise of 1/8. The hub is 2 1/4 long which divided by 1/8 =20.
 
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