The choice of a prop affects what performance your boat shall achieve. You will thus need to look at the prop size, number of blades, material used to make it, its rpm at wide open throttle, and the functions of the boat.
The size of the prop is an important factor. Installing the wrong size could damage the boat and its engine. It shall also mess up its ventilation and cavitation. The prop’s diameter and pitch determine the size. These are normally stamped on its hub. The first digit you see it the diameter followed by the pitch. With a powerful enough boat, a higher pitch shall boost the speeds travelled. A larger diameter enables the boat to reach higher acceleration.
A prop may have between three to five blades. As the blades increase, so does its performance. Racing boats use three bladed props for their top-end speed. It is even better if they are cupped blades. Cupping is the curve at the blade’s end. This is what will keep ventilation at bay and help make the boat turn sharply. You may also have to think of the rake of the blade. The angle of the blade with the propeller hub affects the boat’s performance.
You need to then think of the material used to make the prop. You will have an easily accessible and affordable option in aluminium. It is the lighter choice that shall also keep the boat safe when you hit obstacles. It however easily rusts and cannot stand salt water. Stainless steel is, but it comes at a price. It is more durable and can withstand the effects of salt water. You can, however, be sure it will destroy the engine if you hit an obstacle. You shall need to have a composite and plastic prop for emergency cases.
As for the rpm at the wide open throttle, there is a specification for each engine. This is what will guide you when you are making your choices.
You also need to think of your purpose for getting the boat. There are props designed for different types of boats, such as pontoons, bass boats, as well as those meant for skiing, fishing, racing or leisure. You should then think of the water where the boat shall travel. Some of these props are meant for the lakes, rivers, and other slow waters. Others are designed for the high seas. There are also the flat heavy boats used for transporting passengers and goods. You will also see those meant for high performance such as for racing.
When you are aware of all these factors, it becomes easier for you to choose the right boat prop.