Prop nuts

My prop is a little loose, and while getting a bottom job I was going to remove the prop and see if the keyway or key was damaged or if the nut was just loose. Is this a DIY job or am I about to screw something up?

I was going to use an impact to get the jamb nut off. How much do you tighten the main nut going back on?

cardude01 said:

My prop is a little loose, and while getting a bottom job I was going to remove the prop and see if the keyway or key was damaged or if the nut was just loose. Is this a DIY job or am I about to screw something up?

I was going to use an impact to get the jamb nut off. How much do you tighten the nut going back on?

View attachment 62467

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It's a DIY job......that doesn't prevent you from screwing it up.

Use 2 wrenches to loosen the jam nut. If the prop is loose, a prop puller shouldn't be necessary. To tighten, a block of wood between the prop blade and the hull. Tighten with a BIG wrench and maybe a cheater bar, no impact wrench.

Ted

When you are done; It looks like there is a hole in the shaft for a cotter pin, I would add one, you know, belt and suspenders.

Thanks for the help. Oh yeah there was a cotter pin. I removed it.

Right, definitely no impact wrench. There are a bunch of articles out there on how to correct install a prop. I had a bit of a wobble in my drive line, and it turned out to be due to an incorrectly seated prop. The tape needs to be spotlessly clean. D'Antonio has a good article on his site.

Propeller Installation | Steve D'Antonio Marine Consulting

Mostly agree with this, mostly disagree with another often quored expert.

If your nut is loose then your prop may have been "riding on the key" which can make the prop vibrate. This is the case when the key pushes forward in the keyway as you put the prop on so that it is the key itself that stops the prop from going forward as the nut is tightened, not the taper fit of the prop to shaft.

Put the prop on without the key and tighten the nut up a bit. Scribe a line where the prop stops on the shaft. Then reassemble with the key. Make sure that the prop stops at the scribed line.

And BTW there is much debate about the order of the big and little nut. Tony Athens, formerly of boatdiesel, believes that the little nut should go on first. See Propeller installation / Big Nut vs. Little Nut - Seaboard Marine for a full discussion of prop assembly.

David

Ahh. According to that DAntonio article. it appears my prop nuts are installed backwards.

I have a little play in the prop, so I hope the key and keyway are OK. Thanks for that additional info. And it does seem like I have a little more vibration than I used to.

I'm at a DIY yard in the middle of a bunch of shrimp boats so no yacht type experts here.

cardude01 said:

Hmm. So according to that article. it appears my prop nuts are installed backwards?

I have a little play in the prop, so I hope the key and keyway are OK.

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In reference to the nut order....not according to every expert but one I know of including the US Navy.

Take look at the link I posted.

Engineering principles are that the first nut snugs the prop and the big one tightened behind it actually takes the load as it pushes the thinner nut off its threads a bit. The bigger nut should be carrying the load, not the smaller.

Now if you do things differently, and epoxy the little nut after tightening the big nut, well I can't say that doesn't work, as there often are many different ways to do things and get the same result .(something lost on a few here)

Here it is again:

The thin nut goes on first…

*

I spent 11 years wrenching on submarines.**When I reflect back, I am still amazed at the amount of useful technical training that the Navy provided me.**One of my favourite technical manuals to this day is NavShipsTechManual*Chapter75, Fasteners.* Use it all the time.

*

To quote:

*

075-5.3.4 JAM NUTS (LOCK NUTS). Jam nuts are an older variation of the prevailing torque concept. They are not usually recommended for new installations due to the tendency to use an improper thickness for the jam nut and to install them in the wrong relative positions.

*

075-5.3.4.1 Jam Nut Assembly. The jam nut assembly requires a regular or main nut and a thin jam nut, as shown in Figure 075-5-5. The assembly is installed with the thinner nut between the thick nut and the bearing surface. The main nut has to be as thick as if no jam nut were being used, because the main nut carries all the working load. The jam nut is usually about 2/3 as thick as the main nut. If the jam nut is too thin, however, the threads in the jam nut area will be damaged as the main nut will pull the bolt threads partially through the jam nut. Conversely, if the jam nut is too thick, the main nut cannot distort the threads enough.

*

075-5.3.4.2 Tightening the Jam Nut. At assembly, first tighten the jam nut to the same or slightly less percentage of the preload torque specified for the main nut, based on the relation the jam nut thickness bears to the thickness of the main nut. Then hold it in position with a wrench while you tighten the main nut. For example, if the jam nut is 2/3 as thick as the nut, tighten the jam nut to 1/2 to 2/3 of the torque used for the main nut. Then, when the main nut is tightened to the preload torque specified for the bolt, it stretches the bolt (stud), thereby tending to pull it through the jam nut. Any vibration or load that tends to loosen the bolted joint will allow the bolt to shrink back to its original length, leaving the jam nut tight against the main nut. This creates the necessary prevailing torque to prevent the jam or main nut assembly from rotating on the bolt.

*

Chapter*75*can be downloaded here:*www.hnsa.org/doc/nstm/ch075.pdf

Regards,

*

Mike Pedersen

NORTHERN SPY, Nordic Tug 26

Powell River, BC

Ok. Thin nut first. I savvy now.

Hey while I'm at it is there something I can put on that prop to make it smooth again? The power washer got off some of the growth but there is still some calcium looking deposits that I would like to get off if I can do it without destroying the propeller.

Soft, fine grit flapper wheel or a medium scotch brite wheel is what I've used.

Soft wire wheel in fast drill of grinder...if not soft touch lightly...

cardude01 said:

.. it appears my prop nuts are installed backwards...

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Your prop has nuts? and they are backward?

If your prop is loose and wobbling, you have a problem. I won't try to describe the process here but the taper of the shaft and the taper of the prop bore are supposed to match perfectly. There's a process using a fine abrasive compound to make this happen. Look it up.

WesK said:

If your prop is loose and wobbling, you have a problem. I won't try to describe the process here but the taper of the shaft and the taper of the prop bore are supposed to match perfectly. There's a process using a fine abrasive compound to make this happen. Look it up.

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I would not describe it as loose and wobbling, but there definitely is some play back and forth. Yeah I saw that process described in that DAntonio article PSneed posted. Hopefully I don't need to do all that.

https://youtu.be/2jxX-yS-M7E

cardude01 said:

Ahh. According to that DAntonio article. it appears my prop nuts are installed backwards.

I have a little play in the prop, so I hope the key and keyway are OK. Thanks for that additional info. And it does seem like I have a little more vibration than I used to.

I'm at a DIY yard in the middle of a bunch of shrimp boats so no yacht type experts here.

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Thin nut first. No impact wrench. Find one of the shrimpers that is friendly (might cost you a beer or two) and he can enlighten you on the wobbly prop as well as some other things you might want to know. These guys know boats. Haven't done this to a prop on a real boat but laping compound does the trick to seat the prop correctly on my model race boats (up to 30k RPM).

First of all, I would put to you that we are all "prop nuts."

Secondly, Northern Spy, you must have been a good swimmer to wrench submarines for 11 years, especially if they were Canadian as I thought ours all sank...?

Xsbank said:

First of all, I would put to you that we are all "prop nuts."

Secondly, Northern Spy, you must have been a good swimmer to wrench submarines for 11 years, especially if they were Canadian as I thought ours all sank...?

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Moved to Canada after I got out of the US Navy in '96. West Ed mall had the bigger fleet then.

djmarchand;530882 See [url=http://www.sbmar.com/articles/propeller-installation-big-nut-vs-little-nut/ said:

Propeller installation / Big Nut vs. Little Nut - Seaboard Marine[/url] for a full discussion of prop assembly.

David

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I have used the Seaboard approach and favor the practices...they make sense to me.
I changed the cotter pin to SS seizing when I purchased Bacchus and do like that approach for the reasons stated.
I also believe - can't substantiate w/ data...just my opinion - that one of the more common reasons for "loose" fitting props is the lack of lapping of the prop to the shaft taper. When properly fit you can easily test by spinning the prop w/ the first nut snug but not tight - a slight hand tightening w/ 2 fingers will stop the rotation amazingly fast with a good fitting taper.

This is a great DIY project for anyone w/ some basic mechanical knowledge / skills... great hands on learning experience. If unsure I'd vote to have someone more familiar do it or help and observe for learning.

Does it appear from my video that I need a "re-lapping", if mine was ever in fact lapped. I had some work done by a yard two years ago and they removed the prop. This is the first time I've had the boat hauled out since then.

Is the lapping compound stuff available fairly easily?

cardude01 said:

Is the lapping compound stuff available fairly easily?

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Lapping compound & bluing readily available in a good auto parts store - NAPA, etc

Northern Spy we are going to have to meet - we are in West Sechelt and we are bobbing past PR in May.

My buddy's father just died, he was the project engineer at the PR mill.

I would not describe it as loose and wobbling, but there definitely is some play back and forth. Yeah I saw that process described in that DAntonio article PSneed posted. Hopefully I don't need to do all that.

https://youtu.be/2jxX-yS-M7E

Cardude01, if this is your prop in this video, you had better inspect the key and keyway also, it appears that both are worn.

Xsbank said:

Northern Spy we are going to have to meet - we are in West Sechelt and we are bobbing past PR in May.

My buddy's father just died, he was the project engineer at the PR mill.

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It is a pleasure to meet Northern Spy in person.

BTW, thanks for the education on the prop nuts. I had no idea and I am sure that I would have put them on in the wrong order. Now I won't.

mramoo said:

I would not describe it as loose and wobbling, but there definitely is some play back and forth. Yeah I saw that process described in that DAntonio article PSneed posted. Hopefully I don't need to do all that.

https://youtu.be/2jxX-yS-M7E

Cardude01, if this is your prop in this video, you had better inspect the key and keyway also, it appears that both are worn.

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Yes that's my prop. Pulling the prop tomorrow to inspect the key and keyway. Didn't have a big enough wrench today.

If the key is worn I was hoping I could just get a new key and be good. Don't know what to do if the keyway is worn.

CarDude01,
If the keyway is worn the best way to repair it is to have the shaft and prop machined to the next larger size key. There is of course the wrong way to do it, by putting in some shim stock to fill the gap.

Ummm... not sure I understand "thin nut first" relative to Cardude's pic....

In the pic, looks like the first nut is thicker than the second.

???

Also looks like the second is larger in "diameter" (?) than the first.

Useful to know the first nut is labeled the jam nut; I'd thought labeling was the other way around, second nut being the jam nut.

-Chris

The "lapping" compound is at NAPA as valve seating compound.

A good prop shop will have keys that are in 2 stepped sizes as well as oversized keys.

If the shaft key fit is tight , the prop folks will broach an oversized keyway , and provide a stepped key

Fairly easy to modify an oversized key by sliding the key along a file to get the exact fit.