Dear Blackjack owner,
I have found that prop breakage comes from over-tightening the prop to the drive dog and also the alignment of the flex shaft and spacing.
The flex shaft will expand when it is rotating, so you need to check spacing between the thrust washers on the propeller strut and the drive dog. I leave a 1/16th or 1/32nd gap just for that reason and the same for the flex shaft tube.
Try not to tighten the prop very tight against the drive dog.
This is what I do: Replace the broken prop and slide itup to the the drive dog.
start screwing on the propnut untilit is finger tight. use a wrench to hold the shaft still, then see if I can move the propjust alittle, not a lot of slop, just a little. This should be enough to allow prop flex.
I have the BJ that has the outdrive onthe stern and I kept breaking props and stern drives until I sat down and called Pro Boat about this and the tech told me what todo.
Tightening the prop against the drive dog likeyou might torc a bolt on a car engine is not the thing todo.
Just finger tight and maybe a 1/16th of a turn with a wrench is all you might need.
Works for me and I still have the plastic prop on mine.