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More on Prop Nuts and Torque

makomark

makomark

Silver Medal Contributor
"heard back from the tech staf

"heard back from the tech staff at a prominent supplier of underwater hardware...(Yes, they provided the custom castings for my current vessel). He was kind enough to supply a recommended torque value, for a 1.5" dia shaft (aquamet22 with their brass prop nut package), which was 337 #*ft. If you assume the load and material factors are constant, and scale for the thread change and shaft diameters, the values for the 'common' shaft diameters follow:
shaft (") torque (ft*#)
1.5 337
1.375 238
1.25 159
1.125 98

He also verified that their recommendation is consistent with the majority of the data on the internet - prop, thin nut, thick nut, cotter pin."
 
"Mark,

You were right on...

"Mark,

You were right on.... Quick question...Does filling in any space of thread between the big nu and the cotter pin, have any merit?

Reason being, I question whether or not any additional opportunity for those nuts to really grab and spin, might they have not also sheared the cotter pin and then have slipped EVERYTHING off of the shaft including the prop?"
 
"Al:

Can't say I though

"Al:

Can't say I thought much about that....the scenario you describe has happened more than once. I bet the prop shop could give you a better feel for how frequently it occurs.

I did receive that prop paper Dave offered in your post. After a quick review of it, in the context of your Q, I'll have to say there is some merit to the safety wire concept. I know guys that work on airplanes for a living and they'll tell you, properly installed, it is very reliable (sorry for preaching to the choir). I'm thinking of getting one of them to visit before the spring launch in 2010."
 
Wanna know how much torque to

Wanna know how much torque to use? As much as you can! Period. I'd fire any mechanic who worked for me and used a torque wrench on a prop nut.

Jeff
 
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