Our service yard highly suggests dye penetrant testing of all exposed shaft tapers whenever props are removed for servicing. A dye penetrant test of the shaft tapers will identify any cracks in the keyways, or elsewhere on the taper that may not be visible with the naked eye. Chemical cleaning and magna fluxing is a better non-destructive test method and should always be done when the shaft is removed from the vessel.
It takes approximately 30-45 minutes to perform the dye penetrant test and is well worth the cost. A cracked shaft that goes unnoticed could result in many expensive repairs for vibrations, lost propeller(s) and/or a damage to hull and other running gear. Shafts typically break when reversing, so be aware of this when approaching your mooring or backing down on a fish after a vibration has been noticed and seems to be getting worse. You may save yourself the cost of a propeller and much more.