It seems like all the commercial mud motors use props that are hard fixed to the shaft, with either a threaded shaft/prop or a hexagonal drive shaft.

On my homebuilt I have a smooth shaft/hole and the prop and shaft are drilled for a shear pin. My thinking is something's gotta give if the going gets tough, and I'd rather it be the shear pin instead of barber poling the drive shaft or damaging something else.

How do you guys deal with impacting immovable objects? I run waters with a lot of rocks. The nice thing about a long tail is the end of the tail can move if the prop hits something hard, unlike a surface drive or outboard which tend to stay put and exert a lot of force on the prop.

Greg

Shear pins are a thing of the past did'nt you ever have a old boat motor. If I had shear pins on my mud motor I would be changing them every 5 minutes. I hit the object and move on I got 400+ hours on the motor and haven't broke anything yet on it

As far as mud motors not sure if they ever built ones with shear pins but I know most Outbopard since the Mid 80s went to the rubber hud style props. Those shear pins seemed to bust on every stump you would hit, I remeber as a kid haveing a bag full in the boat with me just for a weekend on the river

you should have a key somewhere between your prop and your enigne.

An American longtail doesn't have any keys to shear when you hit something underwater, it has a keyway that the set screw for the u-joint sits on but it is a hard metal.

You have to throw traditional outboard logic out of the window when thinking of mud motors, the free floating up down pivot along with a more balanced frame, stronger props, and a longer rake on the skeg make alot of difference.

With the long shaft on a longtail it acts like a torsion bar and absorbs alot of shock from hits, it would surprise you.

A threaded or hex style prop like on american mudmotors has proven itself effective for years with plenty of people using them in conditions like yours on the rivers in Alaska, it also makes it much easier to re-prop if you have a standard design. Why did you grind the cup out of yours?
Also, look into a rock guard that godevil offers, it takes alot of direct hits off the prop.