Prop Shaft Size?

[Eddie]

I just had a passport 41 surveyed. They found the 1 1/2 inch shaft was turned down to 1 inch just before passing into the coupling. The engine is a 62 hp yanmar 4jh2-te. Questions 1. Will this shaft hold up without shearing? 2. not sure if there is room to cut off the 1 inch end of the shaft, then place a new coupler, maybe flexible coupler and still mount prop. 3. anyone know if rudder needs to be dropped to replace the shaft?

[James S]

I think there are several things that help determine the shaft size....if its unsupported for some distance a thicker shaft would help eliminate "whip" in its length.

With just the info you have supplied, and with no personal knowledge of the Passport 41 I would think the end being turned down to 1" would be OK.

Originally my 48ft boat had a 72 hp engine with a 23" three bladed prop and an 1-1/4" shaft....this lasted for 30 years and about 30,000 miles.

What did the surveyor have to say about it?

[Chief Engineer]

That's a new one for me.

I would be very suspicious of that.

Loosing 1/3 of the shaft size?

Sounds like somebody was too cheap to buy the right coupling.

[captain58sailin]

They should have turned the coupler and enlarged the hole instead, usually there is plenty of metal in the shaft hole on the coupler.

[GordMay]

Originally Posted by Chief Engineer

That's a new one for me.

I would be very suspicious of that.

Loosing 1/3 of the shaft size?

Sounds like somebody was too cheap to buy the right coupling.

As the Chief Engineer notes, the shaft has been reduced to 66% of it’s original diameter.
This results in a reduction of cross-sectional shaft area to 44% of the original area.
I “believe” that the result is about 44%* of the original shaft strength (tortional).

* Perhaps even less, due to stress concentration factors.

[Chief Engineer]

I love it when somebody does the math at 0538........

[Cheechako]

I dont know the PP 41 undershape. I assume it is skeg hung rudder...? If it is, then the skeg is your issue .... removing the rudder wont help right?.....