prop nuts

[njlarry]

Anyone know the correct torque for prop nuts? I have a one inch stainless shaft, the thicker nut is 1 1/2 inch, the thinner nut is 1 1/4 inch.
Second question, when the nuts are two different sizes which one goes against the prop? I read Maine Sails excellent thread on installing prop nuts that instructs placing the thinner nut against the prop but they are both the same size. All of the boats in the yard I looked at with two different sizes had the bigger diameter thicker nut against the prop. Those few that had the thinner against the prop all had two 1 1/2 inch nuts.

 

[woodster]

thinner nut goes on first always ......don't know the torque for that but i always put a block of wood between the prop and the hull and crank down on the nut then the same thing on the larger nut ...after all its a 3/4 thread or 5/8 thread ...then set the cotter pin and trim properly ...oh and don't forget to lap the prop to the shaft ...

 

[Charles Erwin]

Here is a guide from Western Branch Metals. If you call them they will probably be able to give you a number for torque value which will be different for different shaft material, diameter and the nut alloy. If one had to guess I would probably use the standard bolt torque values for 316 stainless. but these values strike me as a bit high

Western instructions say that you seat the lapped propeller with the thicker one, remove it, and then place the thinner one followed by the thicker one. So does the US Navy specifications for fasteners. Anyway if the thinner nut is too small in diameter you can get a replacement matching diameter nut cheap enough.

The important thing is to create well lapped surfaces because it is the friction at these surfaces - not the clamping force of the nut(s) - that makes the assembly solid.

Charles

 

[Capt jgw]

The the thinner one goes on first and the size wrench they take is irrelevant. Torque depends on shaft and nut material, and would be the same as a bolt and nut of the same thread size. If they're not the same material use the lower of the two values. You can google "torque values" to get the torque tables. Example: 3/4" 316 stainless is 131 foot pounds.