Tapered Prop on Straight Shaft

[MGRodems]

I've been looking for a prop for my sailboat for a while and found and received one from ebay that has a tapered shaft (not advertised). My shaft is 7/8" straight and the prop is tapered from 1-1/8" up to? It was listed as 1-1/8" and I was going to put an adapter sleeve in place.

Is there a way to accommodate this prop or should I return it? My 28hp engine has a 3.2 reduction gear, so the prop will spin at less than 1000 rpms.

[fstbttms]

If you truly have a straight shaft, you cannot install a prop with a tapered bore on it.

[Cheechako]

Most props are for tapered shaft, but as you found out, not all. return it.

[Steve Bean]

If the shaft is "straight," what determines the position (fore-and-aft) of the prop? I'll ask this question at my local boatyard.

[brianlara 3]

TO ALL INTENTS AND PURPOSES, IT. CAN'T. BE. DONE. !!!
Send. It. Back !!

[pcmm]

Originally Posted by MGRodems

I've been looking for a prop for my sailboat for a while and found and received one from ebay that has a tapered shaft (not advertised). My shaft is 7/8" straight and the prop is tapered from 1-1/8" up to? It was listed as 1-1/8" and I was going to put an adapter sleeve in place.

Is there a way to accommodate this prop or should I return it? My 28hp engine has a 3.2 reduction gear, so the prop will spin at less than 1000 rpms.

Sounds like the prop is the wrong size for your shaft. you should be buying a prop bored for a 7/8" shaft. if your shaft has no taper at the end, how are you going to fit a prop. They all have a taper machined into them. it almost sounds like someone may have cut the previous prop off and cut the shaft to do it.

[chris95040]

Originally Posted by MGRodems

I've been looking for a prop for my sailboat for a while and found and received one from ebay that has a tapered shaft (not advertised). My shaft is 7/8" straight and the prop is tapered from 1-1/8" up to? It was listed as 1-1/8" and I was going to put an adapter sleeve in place.

Is there a way to accommodate this prop or should I return it? My 28hp engine has a 3.2 reduction gear, so the prop will spin at less than 1000 rpms.

Well, the RPMs don't really have anything to do with anything. That little prop is presumably going to push your boat somewhere and it needs something to push against. How are you locating a prop fore/aft on a straight shaft?

[boden36]

It depends whether your straight shaft has a shoulder on it. If there is a shoulder , then there is no reason why an adapter bush can't be turned up. Use material compatible with the shaft and prop and make it with a split in it so the taper on the prop presses the bush against the shaft when the nut is tightened. The split could coincide with the keyway, and you would use a deeper key.
An easy job for an experienced machinist.

Regards,
Richard.

[MGRodems]

Thanks for the comments. I just realized my shaft is tapered inside the prop. The prop I received is 1-1/8" tapered and the bore just looked too large. I plan on putting an adapter sleeve in it to make it fit.

[fstbttms]

Originally Posted by MGRodems

Thanks for the comments. I just realized my shaft is tapered inside the prop. The prop I received is 1-1/8" tapered and the bore just looked too large. I plan on putting an adapter sleeve in it to make it fit.

I don't believe you will find a 1/4" sleeve off-the-shelf. Key stock in the dimension you would need may be problematic as well.

[MGRodems]

Actually, I found the bore reducing bushings first knowing that I can go from 1-1/8" onto a 7/8" shaft. Hopefully the key is not a problem. I should be able to find a larger key.

[fstbttms]

Originally Posted by MGRodems

Actually, I found the bore reducing bushings first knowing that I can go from 1-1/8" onto a 7/8" shaft. Hopefully the key is not a problem. I should be able to find a larger key.

FYI- you will need a step key, not a straight one.

[capt-couillon]

Just as a matter of note... Contrary to popular belief, the key in the prop/shaft interface is a "failsafe" rather than the primary means of transmitting torque from the shaft to the prop. The torque is transmitted via the interference fit between the tapers, when properly torqued.

Propeller tapers are often not to any standard which makes this game a challenge. There are 4 common tapers used - 1 in 10 , 1 in 12 , 1 in 16 and 1 in 20 and then there are odd back yard ones. The most widely followed dimensions for tapers is the internationally accepted standard S.A.E. taper dimensions which is 1 in 16 up to and including 5 1/2" diameter shafting.

Also critical is the amount of draw - i.e. the overhang distance at the nut end so the prop tightens on the taper properly.

If you find the key or keyway worn when replacing or servicing a prop, it usually means the taper has not been fit properly, inadequate draw, or a prop nut that has loosened in service or was not properly torqued on installation.

A properly installed prop should be lapped into place ensuring continuous contact (at least 95%) over the full length of the taper. Particularly important when installing used props, or installed on shafts with wear. All except new shafts will show some wear in the taper, and even new are not necessarily right when purchased.

Sadly, this aspect of prop installation is usually ignored. Buy it, slap it on, and go. Asking a 1/4" key (std for a .875 shaft) to accept the stress of a diesel engine pushing tons of boat is asking for problems in the future. Seems a bit nit-picky, but a bit of time and attention to start will save the cost of new shafting and machine shop time in the future. Not to mention possible catastrophic failure under full stress of emergency power in a critical situation.

Just sayin...

[toddster8]

My boat came to me with a straight shaft and a prop with some kind of reducing sleeve. When the shaft wore out, it was a cascading discovery of expensive things to replace.

BTW: If anybody needs a 7/8" prop with a straight 3/4" sleeve, let me know. The local consignment shop wont even take props.

[Suijin]

Originally Posted by MGRodems

Thanks for the comments. I just realized my shaft is tapered inside the prop. The prop I received is 1-1/8" tapered and the bore just looked too large. I plan on putting an adapter sleeve in it to make it fit.

Just make sure all the parameters work; that the tapers are all the same, that the fit is good and the nut tightens the prop on the bushing and bushing on the shaft, and that you have a key that fits. Personally I would keep looking for the right size prop but if has a good tight tight low tolerance fit I suppose you'll be all right.

It does not t take much bad fit in either the prop or the coupling to cause runout and wear on your cutlass bearing and transmission.