I have a 1985 wellcraft scarab I (21') that has a 350/260 and an alpha drive style drive from sterndrive engineering. The drive is only 4 years old but as I was getting on plane this last week, the propshaft broke clean off on the prop side of the carrier bearing resulting in the prop, and remainder of the prop shaft, sinking to the bottom. Also, I was running a 21 pitch prop of unknown diameter (on the boat when I bought it). My question is, is the broken shaft just a result of a defect or is there an underlying issue? In other words, if I simply replace the shaft, will it be ok or am I likely to just break it again?

Thanks,
Jake

I am now doing a Failure Analysis on the shaft for my Engineering Capstone Project at MSU.
Now that I am getting started with it, I have realized that having some broken shafts to compare
to mine would be very helpful for identifying defects in the micro-structure of the steel.

If anyone has a broken shaft that they would be willing to part with, please let me know as I am very interested.

Thanks,
Jake

Only thing left of my prop and prop shaft








poly shaft from the drive from a few years ago.




All I can provide is pics..

That motor shouldn't break anything..including an SEI.

Thank you for the pictures! That will definitely help my research.

That is what I assumed also. I am now trying to find the root cause of the failure but i ended up replacing the shaft with a mercruiser shaft

Damn . I would be snagging deals out of classifieds on gen 1 alphas for spares at this point