As the cold weather draws in for the winter, many boat owners use this as an opportunity to put their boats into storage for the coldest months. This could be paying to store it at a climate-controlled boat storage facility, or just dumping it in the back garden under a boat cover. This is a great opportunity to inspect a boat for propeller damage. Nicks and chips aren’t much to worry about as they can be repaired relatively easily, but eventually you’ll get to a point where the damage is so severe that it cannot simply be bent back into shape.

It doesn’t matter how careful you are with your boat, at some point you will strike something with your propeller and it will be damaged. Continuing to use a damaged propeller can lead to advanced wear of the internal components of the drive shaft and engine. Damaged propellers create vibrations that can slowly diminish the functionality of motor parts, as well as reducing fuel efficiency and overall performance.

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This is why it’s important to regularly check your prop for damage. Holes in the protective paint on aluminium propellers or dents in stainless steel props require attention. It’s especially important to check your prop regularly if you boat in sandy or rocky areas. To help your prop resist damage, avoid shallow waters and be careful when loading and unloading. Power loading can sometimes kick stones and rocks up from the bottom of the water that can damage the prop.

If your propeller is problematic and beyond repair, you’ll really notice the difference when you replace it. A new propeller should get rid of any vibrations and will also make the boat more fuel efficient. It will also help the boat’s motor to last for longer.

If you’re looking for a new boat prop there are some key terms you need to learn. It can be confusing for newcomers as there are a number of different elements to consider when selecting a new propeller.

Propeller Hub

The hub connects the propeller with the drive shaft. Each hub is designed to fit with a particular drive shaft system which can vary by manufacturer. That said, there are two main types of boat prop hubs; fixed and removable. Fixed hubs are the most common, and cost-effective solution. The hub is fixed into the core of the propeller. Removable hubs are separate from the propeller, and several props can be fitted to a single hub. If you change your prop regularly for some reason then removable hubs are the best option.

Splines

A drive shaft has a number of ‘spline’ or ‘teeth. It’s important that the number of splines on the drive shaft match the number of spline on the hub. This is how these two items fit together, so if the splines don’t match you have selected the wrong propeller.

Blades

Prop blades are connected to the hub and turned by the motor, creating propulsion. 3 and 4 blade propellers are the most common. 3 bladed propellers tend to be a bit cheaper, and will provide more top end speed and pitch options than 4 bladed propellers. 4 bladed propellers help to lift the stern of the boat and generally offer smoother operation and more efficiency at mid-range speeds. Boaters with a removable hub often change to 4 bladed propellers if they are trying to achieve smoother acceleration. The extra blade means the propeller can move more water, but will also create more drag, which can have a detrimental impact on speed.

Pitch

Propeller pitch is the distance the prop will move through the water for each full rotation. A propeller with a 50” pitch will advance 50” for every complete spin on a solid surface. Obviously on the water the boat will move more slowly than this. Pitch can also be used for things like screws, which will advance a few millimeters for each complete rotation with the screwdriver.

It’s crucial that the pitch and diameter of the propellers are carefully calculated. If the pitch is too large, the propeller becomes heavy and will require more power than the engine can each. Equally, a pitch too small then the propeller will not be able to dispatch the engine’s full power.

To find the right pitch a number of elements need to be considered, including power, RPMs, gear reduction, the size of the boat and its intended use.

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Alan Cairns writes on a number of subjects including outboard motors and motor boat fuel efficiency. Image used courtesy of Spigoo.

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