26 March, 2017
The end of the prop shaft is normally tapered and has a keyway in it as well to transmit the torque from the shaft to the propeller. Retaining the propeller on the shaft is done by lock nut.
The lock nut can occasionally come loose when the shaft rotates in the opposite direction to the thread. This can result in the loss of an expensive propeller and all drive!
There are many different ways of securing the propeller nut including; castellated nuts with split pins; drilled nut with split pin; cone nut with lock bolt; a tab washer bent over or; locks nuts.
Lock nuts are not so common in the UK but its worth noting that when fitted, the half nut (the thinner nut) should be fitted first with the full nut last. This seems counter intuitive but actually splits the load correctly between the two nuts.
Each method has its advantages but should never be overlooked when refitting a propeller and should always be checked when the vessel is lifted for any maintenance. Also check for play in the keyway by turning the prop by hand.