looking at the picture, what is supporting the propeller shaft near the propeller? that might be why you keep breaking things.
the reason i keep breaking things is i run into solid objects like light posts and such when im dry running
. the solid shafts i make arent quite true, so any extra stress on the part seems to weakin it and eventually break it.
a flex shaft would have a bit more give than a solid shaft and a lesser chance of breaking.
as for support, i can pick the boat up from the shaft and it doesnt budge,thats 7 kg of weight.
thanks for the info guys keep it comin!