Propeller Maintenance and Replacement

Propellers require relatively little servicing. Many people remove their propellers at the end of the season and store them inside. This protects the expensive propeller from theft and ensures that it won’t become frozen in place due to corrosion. Trying to remove a prop from a corroded spline can end up damaging either the prop, the spline, or both. Removal is straightforward. Straighten out and remove the cotter pin, then unscrew the keeper nut. Beneath that is the prop nut, the unscrewing of which wil l require a special wrench or a big socket on a ratchet. To prevent the prop from turning when you unscrew the prop nut, use a block of wood to hold it steady, bracing the wood against the lower unit. When the nut is off, you should be able to pull the prop off the shaft, revealing the thrust washer beneath. If the prop won’t come off easily, you can use a hub puller. These have two claws to hook under the lower edge of the hub, and a large screw that you tighten against the prop shaft. Be gentle with aluminum props, as some parts of the hub are thin and can easily be damaged.

Remove and grease the thrust washer, and clean and regrease the hub splines and the shaft. Use a marine grease made specifically for this purpose. Small nicks in the edges of the prop blades can be careful ly smoothed out with a fine-toothed file and blended into the surrounding blade area. Inspect the aft surfaces of the blades for small pits, which are a sign of cavitation and a sure indication that your prop isn’t pitched right for your boat and motor combination. If blades are badly nicked or bent, or if you want to change the pitch of the blades, take your propeller to a competent prop shop. Sometimes they can even weld broken blades back onto the hub—although how likely is it that you’ll find the broken blade? If the rubber insert has come free of the metal hub of your outboard or I/O prop (this is called a “spun hub”), a pro can replace the insert. Be sure to get a quote before repairing a prop. In many cases the cost of repairing an aluminum prop is close to the cost of a new prop, especially if your marine store is having a sale.

You will need several pieces of information to purchase a new propeller. The first is the propeller diameter—that is, the diameter of the circle described by the tips of the blades. The second is the pitch, which in effect describes the angle of the blades but is measured in inches, not degrees. Imagine a wood screw with a spiral thread. Turning the screw once will advance the screw into the wood by a certain amount; in similar fashion, one rotation of a propeller advances it through the water. Because water isn’t solid, the propeller will slip to some extent, but slip is ignored when determining pitch.

You also need to know the make, model, and year of the engine, because the configurations of the prop shaft and splines differ from engine to engine. In many cases, the replacement prop will come without a hub, and you must purchase a separate hub kit to match the prop to the engine. This is an ideal setup for the retailer, as he has to carry only one model of prop for each pitch and diameter and match the props to the engines with a hub kit. It is also ideal for the consumer, as these hubs also act as a fail-safe mechanism. If the propeller hits a rock or debris, the hub breaks before the prop does—most of the time.