Prop shaft key and coupler key material ?

[Patrick of M]

My stainless shaft had a steel key and a bronze propeller. The key will need to be cut out, as it is not moving, basically seems welded in after 15 years in salt water. On the other end , the shaft coupler key even though visibly rusted freed up easily. Coupler is mild steel.

1. It seems a bronze/brass key is the obvious solution for the prop end?

2. I'm guessing bronze/brass key is not recommended at the coupler end, just another steel key?

Cheers.

[nhschneider]

I install stainless steel keys on my prop shaft.

Fair winds and calm seas.

[ItDepends]

A plain steel key on the propeller end of a bronze propshaft is a disaster. A bronze key would be fine, stainless also, assuming you keep your zincs in good shape.

On a straight shaft (like on the transmission side) the key is vital to actually transmitting the torque. A steel key here makes sense. It is strong, and isn't immersed in salt water (we hope!)

On the prop side, with a tapered shaft, essentially all the torque is transmitted by friction between the prop and shaft--assuming everything fits properly and installed well. The key is insurance and should be under little or no load. In this case a softer metal key works just fine. If the key is needed to keep the prop from rotating relative to the shaft, something is wrong with the fit.

[Patrick of M]

Thanks all. Makes sense.

[c.K.]

Originally Posted by Patrick of M

My stainless shaft had a steel key and a bronze propeller. The key will need to be cut out, as it is not moving, basically seems welded in after 15 years in salt water. On the other end , the shaft coupler key even though visibly rusted freed up easily. Coupler is mild steel.

1. It seems a bronze/brass key is the obvious solution for the prop end?

2. I'm guessing bronze/brass key is not recommended at the coupler end, just another steel key?

Cheers.

and when installing a new key use some anti seize grease

[Patrick of M]

Absolutely, I'm an anti seize freak. Slows me down during re-assemblies, but whenever I need to go back, the trouble free ease is well worth it.