prop play

[pepmyster]

Hi guys! After the boat went on the hard, I looked around and found a
very slight looseness on my startboard prop. Just a readjustment? I did get stuck on a sand bar during
the summer, but tested it after wards and there was no vibration.

[Viper]

Is the prop moving independent of the shaft when you move the prop?

[km1125]

Hard to tell from the video which way it's moving. Is it up and down the shaft or around the shaft?

If around the shaft I'd remove it and check the keyway and key to see if there's any distortion. You might have a key that's damaged and allowing some loose rotation.

If the prop is that loose is should be a breeze to check. Pull the cotter pin, pull the nuts and slide it off and take a look. You won't even need a puller.

[Viper]

Looks like the prop might also need to be fitted to the shaft by lapping both mating surfaces. This fit should be checked anyway.

[Midnightsun]

If you turn up the volume you can hear the clunking noise as he moves it. Not normal at all!

My take, the securing nut/lock nut is not touching the prop or insufficiently tightened to allow the prop to engage the taper properly. The clunking leads me to believe the keyway cutout on the prop may be damaged and should be inspected. Agreed, a lapping or at least a test with blue marking die should be done to verify taper fitment.

Bottom line is the taper itself should hold the prop in place even under way. The nuts and keyway are there as a safety backup.

This is a great video showing prop fitment. Although he is convinently setup on a lathe, the same can be done by spinning the prop under the boat on the hard.
https://www.youtube.com/watch?v=2ozh4JjoWm4


Real world, on the hard lapping method. https://marinehowto.com/lap-fitting-a-propeller/

I have been around lathes and drill presses for most of my life. Tooling is held in place by a taper fit, no key ways, no nuts, just push on and you're done. This is called a Morse Taper. They do not fly off otherwise you would hear about accidents due to this which just do not happen. The prop/shaft taper works on the same principal however the taper is slightly different.

For anyone interested, history of Morse Taper which has been around for a heck of a long time by the way. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3779551/

[pepmyster]

QR_BBPOST Is the prop moving independent of the shaft when you move the prop?

Yes, independent to the shaft. Shaft does not more, just the prop. Ever so slight but I caught it.

[Viper]

Watched it again and I just caught something. Not 100% sure but I slowed the video close to the end and I noticed that the nuts might be reversed. You can just catch enough of a view and it's not a good angle but it looks like the jam nut (narrow) is on last. It should be up against the prop with the large after it. Not having it this way can result in the nuts loosening off.

Did I see it right? Is the small nut on last?

[Midnightsun]

Odd you mention the nuts as I looked into this a few years back and yes the small nut goes on first. I looked at several boats on the hard and the majority had them reversed. Seems to be a common mistake.

[km1125]

QR_BBPOST Odd you mention the nuts as I looked into this a few years back and yes the small nut goes on first. I looked at several boats on the hard and the majority had them reversed. Seems to be a common mistake.

That's one of those "what kind of oil do you use" debates. I've seen arguments for both methods.

...
The nuts and keyway are there as a safety backup.
...

They're probably also pretty useful when you're running in reverse gear.

[Viper]

All the credible sources I've looked at agree that the "Jam" nut, small nut, goes against the item being secured. The jam nut is smaller for a couple of reasons. Without getting into engineering jargon, in simple terms, this is so that when you tighten the large nut against the jam nut, you actually distort the jam nut and its threads. This distortion is what jams the nut in place and helps prevent it from backing off. The distortion also works to apply backward pressure against the large nut to keep it from backing off the jam nut. I can tell you that when done properly, it usually takes a lot more effort to remove the jam nut than it does to remove the large nut. On occasion, one will actually ruin the threads of the jam nut trying to get it off, hence many recommend replacing the nut every time it's removed. You don't get this type of mechanical advantage if you put the jam nut on last.