odd shaft taper

[margitchris]

The story goes like this: old prop had been painted with bottom paint by a previous owner and was no good.
A prop was found on ebay, so I held my breath and bought it. When it arrived I discovered it was machined to a non-standard shaft taper profile.

"new" prop and gap

The thing is: the new prop fits. The bore at the forward and aft end of the prop hub fit the shaft and the keyway is the same size although the keyway only extends 3/4 the length of the prop hub. The only real issue is that there is about 1.25 inch gap from the aft end of the prop and the threads on the shaft. My idea is to cut the blades off the old prop ( it is a paperweight anyway) grind the hub smooth and even, then cut the hub to create a spacer between the prop and the threads on the shaft. Is this acceptable or must I get the shaft re-machined?

[TritonSean]

I can't see why that would not work... anxious to hear other opinions.
Sean

[margitchris]

amputated blades with rough hub.

Armed with one opinion and my gut, I proceeded to cut the blades off the old prop and roughly shape the blade-less hub to its new function.

[Squidd]

That should work fine... actually looks like the original was too far back and maybe hitting the skeg..?

Rule of thumb is 1-2 x the diameter of the shaft = free space.. so your second pic looks more in line...

Just want to confirm taper of shaft and taper of prop actually match or there will be vibration....

[Peter]

I recently ordered a new prop for the Ballad, and the maker told me all props are measured at the aft (small) end of the taper for size, and that the tapers are pretty well all standard. When I received my prop it went up the shaft a bit too far, past the threads. The small end of the taper was 0.015" too large causing this. The maker immediatly offerd to send a new prop, but the problem was solved by using 2 full-sized nuts and recessing the forward end of the first one to act like a washer ... problem solved.

Looking at your pictures i'd say the ebay prop is for a larger diameter shaft, explaining it's travel way past the end of the threaded portion.

[margitchris]

I double checked prop bore and it matches the shaft fore and aft. The prop, a Vetus, is unique in two ways: the hub is about 3/4 inch shallower than the prop I took off and the blade tips are swept aft to a higher degree. As it is, the prop fits my boat with the blade tips ending up in about the same place in relation to skeg and hull. My guess is that the Vetus prop was purposely bored with the taper starting further aft in the prop bore to accommodate the unusual blade rake. I took the prop to a shop to have it balanced and trued and the prop tech's pronouncement was that as long as it fits firm on the taper and the keyway matches ( it does) there should be no problem with using it. So, that's good enough for me.

[earlylight]

I had a boat that came with a similarly bored prop and there was a bronze collar added between the prop hub and the threads on the shaft. It performed well for the 18 years I owned the boat.....I say go with it as long as you have no vibration issues and it performs OK..