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Old 24-06-2024, 05:21   #1
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Prop spacer or new shaft?

I bought a new prop for my boat, 12x8 standard taper (like my boat is now), however, the new prop slides up past the threads before stopping. Do I need to have a machine shop fix this/build me a new one, or is there a spacer I can add to fix this? Picture attached
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Old 24-06-2024, 07:46   #2
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Re: Prop spacer or new shaft?

maybe your new prop is wrong

is the prop still in the taper of the shaft
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Old 24-06-2024, 08:09   #3
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Re: Prop spacer or new shaft?

The taper specs include the length of the taper, start and end diameters, and the length of the threads. If it doesn't fit, either the prop or the shaft is wrong.

There are both SEA and ISO standard tapers, maybe you have one of each? You could check that yourself. But an anycase, I would probably take both the prop and the shaft to a shop to be checked.

https://www.propellerpages.com/?c=tech_info&f=tapers
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Old 24-06-2024, 15:56   #4
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Re: Prop spacer or new shaft?

Quote:
Originally Posted by Sailor_Grant View Post
I bought a new prop for my boat, 12x8 standard taper (like my boat is now), however, the new prop slides up past the threads before stopping. Do I need to have a machine shop fix this/build me a new one, or is there a spacer I can add to fix this? Picture attached
You can easily fit a spacer between the nut and the propeller hub BUT the bigger problem is how close to the stern bearing and deadwood that makes the propeller, it looks way too close. You could get it back a little if you install a drive saver or flexible coupling (R&D) between the gearbox and the shaft coupling, that would push the shaft back about an inch.
It actually looks like the prop is still not home fully on the taper, you need to take out the key and do a bit of work with bearing blue to see what the real fit and engagement looks like.
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Old 24-06-2024, 16:51   #5
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Re: Prop spacer or new shaft?

Somebody did not measure the taper properly when the prop was ordered. A new prop or shaft with proper taper is the only answer. Spacers are a patch job destined to fail and do other damage.
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Old 24-06-2024, 19:40   #6
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Re: Prop spacer or new shaft?

This is a bit of a dogís breakfast. As people have said, the taper of the prop, or the shaft, or both, are wrong.

A prop and the shaft should be an exact match. On a properly installed prop, the friction between the shaft and prop should be transmitting the lionís share of the torque, and the key really is just a safety feature. The prop and the shaft should touch EVERYWHERE. Ideally they should be lapped.

I believe I see daylight between the back of the prop and the shaft. That tells me that they are a total mismatch and will never work properly. It is time to call in a professional to get this sorted out. But based on what I see, that prop needs to be sleeved, and rebored, as a minimum.
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Old 24-06-2024, 22:36   #7
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Re: Prop spacer or new shaft?

Since this seems to be a new prop, have you contacted the seller/manufacturer? Maybe they will simply exchange it for the correct prop, after you take some careful measurements of the existing taper.
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Old 25-06-2024, 04:47   #8
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Re: Prop spacer or new shaft?

There does exist propshaft taper adapters, which would shove the prop "aft" into the proper position on the taper - assuming both your prop and propshaft are the same i.e. they are both SAE or ISO as previously mentioned. (SAE is usually 1:16 or 0.750 inch/foot, and metric shafts 1:10 for small, standard running gear like shown here)

I would consider using one as a temporary measure but probably wouldn't leave it as a permanent fix. As mentioned earlier, the included angle on a properly fitting "standard" small propshaft taper is self locking and you would lose that with a nylon bushing...

https://www.generalpropeller.com/Nyl...-Reducers/NB02
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Old 25-06-2024, 04:57   #9
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Re: Prop spacer or new shaft?

add proper rope cutter end story,
or short shaft from inside if possible
or order ne propeler
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Old 25-06-2024, 14:08   #10
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Re: Prop spacer or new shaft?

"I bought a new prop for my boat, 12x8 standard taper (like my boat is now)"

The size may be correct and the taper may be correct, but it looks like it was machined for a bigger diameter shaft than yours...
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Old 25-06-2024, 14:37   #11
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Re: Prop spacer or new shaft?

It looks to me like the prop was cut for the wrong size shaft. Same taper but different diameter.
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