Shaft Straightness

The tolerance for permissible variation from straightness of a shaft is maximum 0.006 in/ft.

To check shaft straightness, use a dial indicator inside the boat, forward of the strut, just aft of the bearing and forward of the propeller.

To check the trueness on the taper, the propeller must be removed.

Shaft whip is due to an undersized shaft diameter.

If the propeller has previously hit something, the shaft is usually bent right at the transition between the straight part of the shaft and the start of taper.

Trueness and alignment issues typically get worse as RPM is increased.