Axis Wakeboard Boat Forum

I have seen them fall out, knocked off but not sheer off like that.

Good call just buying the new one. Let your dealer handle the warranty and if it gets approved they can credit you back. If not at least you did not miss this entire time on the water.

The warranty got approved, but didn’t get an answer what the cause was. Not to worried since the boat handles again like new


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it looks like a classis example of a HCF failure. You have a sudden change in thickness to the shaft diameter, which causes a local concentration of the stresses, or "stress riser". The prop spins causing pulses of force every time the prop blades pass by. Assume 4 blades at 3000 RPM, that is 12,000 cycles per minute. Take the number of minutes of fun you have had and this could get into the millions of load cycles. Once the crack initiates, which could be from a metal defect, or a deep scratch, the force will be concentrated on the crack tip and it will slowly increase in depth. As the part deforms the crack growth rate increases.

Big round radii help to prevent this kind of thing by reducing available stress risers. This kind of failure of parts that spin, reciprocate, or are acted on by other parts that spin or reciprocate, is not uncommon and the reason that companies such as Magnaflux have done so well over the years.