Choosing the best boat props, or boat propellers, involves a number of key factors. The most important factor is engine revolutions per minute (RPM) at wide open throttle (WOT) while the boat is carrying the normal load. In other words, the best boat props will allow a boat carrying a normal passenger load, full tanks of fuel, and necessary cargo to run at maximum, factory-rated RPM at WOT regardless of boat speed. Always check with the engine manufacturer to find the factory-rated RPM for a particular engine when choosing boat props.
There is a common misconception that a boat at full throttle, or WOT, is going at the greatest possible speed, but this is not the case. It is possible for a boat to be at WOT but not be moving as fast as the boat can go. For example, if a small boat were towing another vessel at WOT and doing 8 knots (4.1 meters per second), then the tow line was cut, the WOT would not change, but boat speed would increase dramatically.
The best boat prop is the one that enables the boat’s engine to achieve but not exceed the maximum factory-rated RPM while all other engine parameters, especially temperature, remain normal. Boat props that are too great in diameter or have too much pitch will result in failure of the engine to reach maximum factory-rated RPM. Excessive RPM, which can result in a total, catastrophic failure of the engine, indicates that an increase in pitch or diameter of the boat prop is needed.
Other important factors in choosing the best boat props include cost, material, and operating conditions. Boat props are typically made of aluminum, composites, stainless steel, or bronze. Aluminum and composite boat props are the least expensive and are normally the choice for outboard motors. Composite boat props have the advantage of having replaceable blades, so if one is damaged, the entire prop does not have to be changed. Stainless steel boat props are used on both inboard and outboard boat engines and are more costly than aluminum; bronze boat props are for larger, commercial vessels such as cargo ships or fishing boats.
An important consideration when choosing the best boat prop is the environment in which the boat operates. Rocky conditions, reefs, and sand bars are notorious for damaging boat props, so aluminum or composite boat props are the best choice in such environments because such materials will give or even break, while stainless steel will transfer the damage to the gear case. It is cheaper to replace the prop than the gear case. Stainless steel boat props are best in deeper waters where there is less of a chance of striking an object. Stainless steel props are more durable than aluminum.
Boat props can vary in the number of blades. Whether it has two, three, four or more blades, the pitch and diameter of the propeller is still the deciding factor in making the best choice. The number of blades on a boat prop makes only a negligible difference in the performance of the engine and is a choice based solely on the taste of the boat owner.