I just hauled my boat and noticed that both the prop nuts had backed off and the shaft key was exposed. I had the tin (locknut) right aft of the prop and the bigger nut on last, with the two tightened together. Did I screw up? Advice appreciated.
Which nut first?
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Pascal, there is no mechanical theory that justifies putting the skinny nut on first. It's not proper. The skinny nut does not unload the larger nut.
Show me the numbers.
The only reference I have found is in the Navy books and they refer to a jam nut that is 2/3 the thickness of the main nut.
Show me the numbers.
The only reference I have found is in the Navy books and they refer to a jam nut that is 2/3 the thickness of the main nut.
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I agree... Most manufacturer and shaft guys recommend the small but many yards do it the other way around. It s like 2 micron filters, oilf fiter brands, Honda gensets etc... Personally when a yard does it the other way, I don't care!
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According to Michigan Wheel, the wide nut should be the last one on.
http://www.miwheel.com/uploads/resources/Inboard_Installation_Process.pdf
http://www.miwheel.com/uploads/resources/Inboard_Installation_Process.pdf
I've seen both and care more about practical experience than theory anyway.
I could not show you the numbers, but have certainly read examples where it was backed up with more than just opinion that the little nut went first. I really don't know who's right myself. I do like Tony Athens method of wiring the nuts and you will find that he does big nut first! Actually the Tony Athens article on the subject is worth a start to end read, whether you agree with everything or not, he at least explains why he does what he does and any procedure is only as good as the empirical results it achieves over time (which any yard, right/wrong, knows over time the effectiveness of their procedure).
Point in fact, Tony has the opinion that the cotter key won't stop a prop from coming loose. I would have agreed with him in theory until I saw one that I discovered myself, on a boat that I had first hand knowledge of its running. Without a doubt it held until the boat was hauled and the owner did not know he was walking the edge. So while its clear the even Tony Athens opinions are sometimes not perfect, but on whole I still personally replicate his example. I think where one can get in danger is to experiment on their own boats by following half of one person's method with half of another persons. If you do that, you have no empirical results other than your own to back up what your are doing over time. Might work, might not and one data point whether it succeeds or fails won't be enough to predict future success.
So pick one method and do that.
I could not show you the numbers, but have certainly read examples where it was backed up with more than just opinion that the little nut went first. I really don't know who's right myself. I do like Tony Athens method of wiring the nuts and you will find that he does big nut first! Actually the Tony Athens article on the subject is worth a start to end read, whether you agree with everything or not, he at least explains why he does what he does and any procedure is only as good as the empirical results it achieves over time (which any yard, right/wrong, knows over time the effectiveness of their procedure).
Point in fact, Tony has the opinion that the cotter key won't stop a prop from coming loose. I would have agreed with him in theory until I saw one that I discovered myself, on a boat that I had first hand knowledge of its running. Without a doubt it held until the boat was hauled and the owner did not know he was walking the edge. So while its clear the even Tony Athens opinions are sometimes not perfect, but on whole I still personally replicate his example. I think where one can get in danger is to experiment on their own boats by following half of one person's method with half of another persons. If you do that, you have no empirical results other than your own to back up what your are doing over time. Might work, might not and one data point whether it succeeds or fails won't be enough to predict future success.
So pick one method and do that.
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Rob reading that set of instructions conflicts with the diagram, and does not talk to proper torque. Is there a torque spec for this based on the shaft?
http://www.fas.org/man/dod-101/sys/ship/nstm/ch075.pdf
When someone shows me that the torque applied will stretch the propshaft before it compresses the skinny nut I'll become a believer. Stainless is stronger than brass right?
http://www.fas.org/man/dod-101/sys/ship/nstm/ch075.pdf
When someone shows me that the torque applied will stretch the propshaft before it compresses the skinny nut I'll become a believer. Stainless is stronger than brass right?
In theory the thin nut should end up being on first. I always "set" the prop on the shaft by tighting the big nut on first, I can wrench it alot tighter than the thin nut, then if you want back the big nut off and replace it with the thin one and then put the big nut on. I keep the the big one on and tighten the thin one against it.
The theory of putting the thin one on first is that the last nut on relaxes the force on the first bolts threads and ends up taking all the load and that is true. No, you're not stretching the shaft, you're just pushing the first bolt.
The theory of putting the thin one on first is that the last nut on relaxes the force on the first bolts threads and ends up taking all the load and that is true. No, you're not stretching the shaft, you're just pushing the first bolt.
The nuts had deformed, but not broken the cotter key. I am thinking now that, perhaps, I had not fully seated the prop to start with. I will remove both nuts, thread the big one one first and tighten bigtime against the prop hub. Then I will remove the big nut, screw the jam nut tight against the hub, screw on the thick nut tight against the jam nut. Then, holding the jam nut with one wrench, use another wrench on the fat nut to jam them together. New cotter pin. Cross fingers. Check often.
Anything wrong with that? Thanks for the advice.
Anything wrong with that? Thanks for the advice.
Propeller Installation Procedure
In order to help ensure a vibration free operation, the propeller should always be properly mated
to the shaft taper. The tapers of both the shaft and propeller hub should be in contact over at least 70% of
their surface (ABS recommendation) area to transmit power effectively and without undue stress. The
following procedure is written as a guideline to help in the installation of the propeller on its shaft. In this
procedure, it is assumed that the tapers of both the shaft and propeller are made to the same
specifications and with a taper of 3/4” on diameter per foot.
Step 1: Remove the key from the propeller shaft. Examine it for any obvious
imperfections or burrs. If necessary, file the key to correct.
Step 2: Examine both the propeller bore and the propeller shaft for any obvious
imperfections or burrs. Again, correct if necessary.
Step 3: Put a smooth coating of Prussian blue liquid compound on the propeller shaft
taper.
Step 4: Install the propeller on the shaft taper (insure that the propeller is fully seated on
the taper), then remove the propeller. The amount of contact between the prop
hub and shaft taper will be indicated by the amount of Prussian blue that has
transferred from the shaft taper to the inside of the prop hub.
Step 5: To determine high spots between the prop hub and shaft, repeat Steps 3 and 4;
however, once the prop hub is on the shaft taper, rotate the prop hub one
rotation. High spots are indicated by streaks in the Prussian blue upon transfer.
If you do not have a minimum 70% contact (as indicated in Step 4) and there are
high spots as indicated in Step 5, use an appropriate lapping compound to
improve the fit of the propeller to the shaft taper. Repeat steps 3 thru 5 until
satisfactory results are achieved.
Step 6: Install the propeller snugly onto the shaft taper. Please note that the key should
not be in place during this step.
Step 7: Mark a thin line on the shaft at the forward edge of the propeller hub, or make an
accurate measurement of the distance from the large end of the propeller hub to
a strut or some other fixed point.
Step 8: Remove the propeller from the shaft.
Step 9: Re-install the key in the propeller shaft. If the propeller keyway has radiused
corners please note that the key has the matching radius.
Step 10: Install the propeller snugly onto the shaft taper and check to see if the propeller
moves forward to the line or measurement made in Step 7. If it does, skip down
to Step 11. If not, perform the following:
10a: Hold a light near the keyway on the large end of the propeller bore. Inspect the
keyway fit by checking for light around the keystock in the small end of the
propeller bore.
10b: There could be a small amount of light visible on the top of the keystock. If not,
the keystock may be jamming and preventing the propeller from going back to its
original postion. Remove the key, secure it in avise, and file a small amount from
the top of the keystock.
10c: There should not be any light visible on the sides of the keystock. If there is, the
keystock is under size and should not be used. The propeller could also be
jamming on the sides of the keystock. To check for this, carefully observe the
end of the keystock as the propeller is moved up the shaft taper. See if the
keystock moves slightly to one side during the installation. If so, a very small
amount should be filed from the side of the keystock in the area of contact.
Another way to observe this is to check the position of the keystock after the
propeller is up the taper. See if the keystock is pushed to one side or the other of
the keyway. If it is, a very small amount should be filed from the side of the
keystock in the area of contact.
10d: Replace filed key in shaft keyway with filed edge on top.
10e: Replace the propeller on the shaft and fit snugly on the taper. Check to see if it
reaches the line or measurement made in Step 7. If it does not line up then
repeat Step 10a through Step 10e.
Step 11: Check the fit of the propeller onto the shaft by inserting a 0.001” feeler gauge in
several locations on both ends of the propeller hub. If the gauge slides in more
than 1/8”, then the fit may not be good. Consider using a lapping compound, and
go back to Step 3 above.
Step 12: When propeller hub moves to the correct position, install the heavy hex propeller
nut on shaft and torque to seat the propeller. Remove heavy hex nut and install
the jam nut if your shaft is so equipped. Then re-install heavy hex nut and torque
as necessary
In order to help ensure a vibration free operation, the propeller should always be properly mated
to the shaft taper. The tapers of both the shaft and propeller hub should be in contact over at least 70% of
their surface (ABS recommendation) area to transmit power effectively and without undue stress. The
following procedure is written as a guideline to help in the installation of the propeller on its shaft. In this
procedure, it is assumed that the tapers of both the shaft and propeller are made to the same
specifications and with a taper of 3/4” on diameter per foot.
Step 1: Remove the key from the propeller shaft. Examine it for any obvious
imperfections or burrs. If necessary, file the key to correct.
Step 2: Examine both the propeller bore and the propeller shaft for any obvious
imperfections or burrs. Again, correct if necessary.
Step 3: Put a smooth coating of Prussian blue liquid compound on the propeller shaft
taper.
Step 4: Install the propeller on the shaft taper (insure that the propeller is fully seated on
the taper), then remove the propeller. The amount of contact between the prop
hub and shaft taper will be indicated by the amount of Prussian blue that has
transferred from the shaft taper to the inside of the prop hub.
Step 5: To determine high spots between the prop hub and shaft, repeat Steps 3 and 4;
however, once the prop hub is on the shaft taper, rotate the prop hub one
rotation. High spots are indicated by streaks in the Prussian blue upon transfer.
If you do not have a minimum 70% contact (as indicated in Step 4) and there are
high spots as indicated in Step 5, use an appropriate lapping compound to
improve the fit of the propeller to the shaft taper. Repeat steps 3 thru 5 until
satisfactory results are achieved.
Step 6: Install the propeller snugly onto the shaft taper. Please note that the key should
not be in place during this step.
Step 7: Mark a thin line on the shaft at the forward edge of the propeller hub, or make an
accurate measurement of the distance from the large end of the propeller hub to
a strut or some other fixed point.
Step 8: Remove the propeller from the shaft.
Step 9: Re-install the key in the propeller shaft. If the propeller keyway has radiused
corners please note that the key has the matching radius.
Step 10: Install the propeller snugly onto the shaft taper and check to see if the propeller
moves forward to the line or measurement made in Step 7. If it does, skip down
to Step 11. If not, perform the following:
10a: Hold a light near the keyway on the large end of the propeller bore. Inspect the
keyway fit by checking for light around the keystock in the small end of the
propeller bore.
10b: There could be a small amount of light visible on the top of the keystock. If not,
the keystock may be jamming and preventing the propeller from going back to its
original postion. Remove the key, secure it in avise, and file a small amount from
the top of the keystock.
10c: There should not be any light visible on the sides of the keystock. If there is, the
keystock is under size and should not be used. The propeller could also be
jamming on the sides of the keystock. To check for this, carefully observe the
end of the keystock as the propeller is moved up the shaft taper. See if the
keystock moves slightly to one side during the installation. If so, a very small
amount should be filed from the side of the keystock in the area of contact.
Another way to observe this is to check the position of the keystock after the
propeller is up the taper. See if the keystock is pushed to one side or the other of
the keyway. If it is, a very small amount should be filed from the side of the
keystock in the area of contact.
10d: Replace filed key in shaft keyway with filed edge on top.
10e: Replace the propeller on the shaft and fit snugly on the taper. Check to see if it
reaches the line or measurement made in Step 7. If it does not line up then
repeat Step 10a through Step 10e.
Step 11: Check the fit of the propeller onto the shaft by inserting a 0.001” feeler gauge in
several locations on both ends of the propeller hub. If the gauge slides in more
than 1/8”, then the fit may not be good. Consider using a lapping compound, and
go back to Step 3 above.
Step 12: When propeller hub moves to the correct position, install the heavy hex propeller
nut on shaft and torque to seat the propeller. Remove heavy hex nut and install
the jam nut if your shaft is so equipped. Then re-install heavy hex nut and torque
as necessary
- Joined
- Mar 2, 2000
- RO Number
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- 6,692
Do you lock the jam in place as part of step 12? If not you risk ruining the threads on the shaft or the thin nut when you tighten up the wide nut correct?
All of these steps lack attention to detail that will prevent damage when the thin nut is installed first.
All of these steps lack attention to detail that will prevent damage when the thin nut is installed first.
- Joined
- Mar 2, 2000
- RO Number
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- Messages
- 6,692
Note I provided a link.
At least the Navy spec has some mention of torque and correct installation. But it does not talk to whether or not the materials are the same. In other words, shear strength of the materials. Believe me I know.
I torqued a brass nut onto stainless and had to have it chased because the threads were ruined. The shaft was fine but, and you knew this was coming, I busted a nut. The nut would not spin freely until it was chased.
At least the Navy spec has some mention of torque and correct installation. But it does not talk to whether or not the materials are the same. In other words, shear strength of the materials. Believe me I know.
I torqued a brass nut onto stainless and had to have it chased because the threads were ruined. The shaft was fine but, and you knew this was coming, I busted a nut. The nut would not spin freely until it was chased.
It is not the nut but the friction taper, such as the Mores taper, that transmits torque. The key and nuts are back ups. The prop needs to properly seated on a clean taper then the key and nuts keep it in place especially in reverse.
- Joined
- Mar 2, 2000
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- 6,692
Exactly, but the torque applied to the nut is what ensures the fit is proper right? There is torque transmitted to the prop for propulsion, and torque applied to the nut with the shaft locked to ensure the nut is properly tightened. I am talking about the latter.
- Joined
- Mar 2, 2000
- RO Number
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- Messages
- 6,692
Provided the torque specs are clear for the sizes and materials I would agree except for the notion that is a construction site where the materials are all the same. We are talking stainless and brass. Some of the jamb nuts are quite thin and unless the prop is well seated threads will be ruined.