My answer to Why do speedboat propellers need to be changed so frequently?
Answer by Desmond Last:
There are two reasons. The most common reason is that the hub that is the center of the propeller has a pressed rubber hub. This will have sheared.
The rubber hub allows the initial force which is an immediate load to be absorbed and transferred without shearing the shaft.
The rubber hub also prevents the output or gearbox shaft from shearing should the propeller gets caught on a rope or seabed.
Tip:Always use marine grease when putting the propeller onto the shaft and ensure you use a new cotter or split pin – only use a stainless steel pin.
The other reason propellers get replaced is that the blades can get broken.
Money Saving and Breakdown Tip: Carry out a regular inspection of the area behind the propeller on outboard and stern-drive leg driven boats. Fishing line gets caught behind the propeller which will tear the gearbox shaft seals.
Boat buying Tip: When buying an outboard or stern-drive gearbox always drain the gearbox oil to see if it contains water – it will be milky white. If it is then the gearbox will have to be internally inspected to ensure the bearings and gears are still serviceable.
Another Tip: Make sure you have the right size pitch of propeller for your engine and boat. The wrong pitch will cause over-revving or a lack of acceleration and top speed.
Tip of Tips:Never buy any boat without an inspection by a marine professional.