This has been really helpful so thank you everyone. I will get some high tensile 7/16" bolts and try fitting them on instead of the M10's which may only be stainless anyway. Persumably I can use locking nuts and tighten as much as possible to stop this happening again?
The bolts at the rear of our prop shaft recently sheared off. We went to buy some new bolts for it and were told we needed 60mm high tensile M11 bolts. They didn't have any, so we have fitted M10 for now and she is running okay. I cannot for the life of me find any M11 bolts anywhere online or elsewhere. Does anyone know where I can get them, or what I should do? Thaks Tom