How does a prop shaft break?
- Thread starter THECUSCUS
- Start date
I had a new shaft made once for a small boat by the machine shop on a sub Sub Tender. The shaft key was installed by a "know it all" while I was on leave. He didn't listen when I told him not to use the old key be cause I could feel to much side to side movement in the keyway. I instructed him to have the shop make a new key. Well......he did it his way.
I came back off leave 2 weeks later and found out that the prop was laying some wheres on the Thames River bottom, and the new shaft was destroyed.
I came back off leave 2 weeks later and found out that the prop was laying some wheres on the Thames River bottom, and the new shaft was destroyed.
Thanks for explanations, but not really getting the last picture. Looks like a hack saw cutting shaft?
That is not what you are looking for. Look at the forward end of the keyway. I was just cutting the shaft threads to fit a feathering prop but the pic also showed a proper spooned keyway too..
another issue is that the OE did not closely spec the replacement shaft to match the specs and taper and keyway of the original. I've sent a stainless prop back to a 'reputable' shaft machinist who delivered me a shaft with the wrong length and improper taper and the wrong key way. this--- , despite delivering to them a boat manufacturer's p shaft tech drawings with precise length and taper dimensions in MM AND also OLD p shaft itself. totally unbelievable poor service..
it would be useful to confirm what the original p shaft specs were from Pearson and make sure the next p shaft matches. precisely.. and have your mechanic check proper facet on the coupling, and position of your engine mounts..
it would be useful to confirm what the original p shaft specs were from Pearson and make sure the next p shaft matches. precisely.. and have your mechanic check proper facet on the coupling, and position of your engine mounts..
That would be my guess also. I would guess also shaft is 302 or 304 SS. The prop would have to be turning clockwise in forward, looking stern to bow.
BTW "fresh water" comment does not mean no salt, but means new water bathing the SS surface to prevent stress corrosion cracking. SS need the Oxygen in chloride water to reduce that type of corrosion . Not zinc!
http://www.ssina.com/corrosion/stress-corrosion-cracking.html
Jim...
The key pretty much always extends into the threads. That shaft appears to have no spotting for the coupling set screws, an improperly cut keway and the PO re-used the coupling after slapping some paint on it, never a good idea unless a fit & face was performed. From the looks of the rust inside the coupling that was not done.... Oh and the face of the PSS carbon block appears to have a chip out of it and is a non-vented type, which means it is quite old.. Unfortunately this is an example of previous owner hackery 101..
Based on where that key sits, and where the shaft sheared, and lack of scarring at the head of the keyway, it seems that they prop was "key bound" and not properly installed thus the key/keyway was taking the entire load... It was only a matter of time..
New AQ 22 Shaft
New Coupling Fitted & Faced (preferably a split coupling)
A Properly Made Shaft by REPUTABLE SHAFTING SHOP
Lap Fit The Prop
Install Prop Correctly
Based on where that key sits, and where the shaft sheared, and lack of scarring at the head of the keyway, it seems that they prop was "key bound" and not properly installed thus the key/keyway was taking the entire load... It was only a matter of time..
New AQ 22 Shaft
New Coupling Fitted & Faced (preferably a split coupling)
A Properly Made Shaft by REPUTABLE SHAFTING SHOP
Lap Fit The Prop
Install Prop Correctly