Boat Prop Guide: The Basics
The perfect propeller can optimize boat performance from multiple angles, but there’s a lot more to propellers than the size and number of blades. Tack on material, diameter, pitch, cup, rotation—do you feel like we’re speaking a different language?
Not to worry. Consult ATC’s boat prop guide below for help starting your research for the right prop and its intended body of water.
Matching Prop Size to Your Engine
Prop size measurement is expressed in two sets of numbers, as outlined below:
1. Diameter: A prop’s diameter indicates the distance from its midpoint or hub to the tip of its blade multiplied by two. Propellers with larger diameters are better suited for vessels with larger engines; the same goes for smaller diameters and smaller motors.
2. Pitch: Pitch is a dimension given in inches that describes how far the propeller will move forward with one revolution. It can be helpful to think of pitch as speed. A lower pitch has more pull power while a higher pitch operates at higher RPMs and allows the boat to go faster.
The key here is to make sure that the pitch you choose doesn’t exceed what your engine can handle. To make sure that your prop pitch matches your engine’s ability, locate your boat’s wide open throttle (WOT) number in your operator’s manual. This number indicates the recommended RPM range at which your boat should operate.
Your boat’s required pitch can change depending on how many fellow boaters and their gear you have on board. Because of this, it’s wise to bring along two props with different pitches for when the boat is loaded up or down.
Prop Type and Additional Considerations
Rotation direction: Rotation direction, or whether the propeller will spin right or left, is determined by your boat’s powertrain. A right-hand propeller must be replaced with a right-hand prop and vice versa.
Cupping: Cupping indicates the curvature of the blade’s edge. Cupped propellers can increase rotational efficiency, reducing slippage underwater.
Number of blades: Three-blade props are the most popular for recreational boating where top-end speed is required. Larger boats that add another blade to the mix with a four-blade prop will draw power at lower RPMs.
Prop Material
Inboard/outboard or outboard boat props are typically made with either aluminum or stainless steel.
Aluminum: A cost-effective, reliable, low-maintenance propeller material, manufacturers tend to favor aluminum props on stock vessels. If you were happy with your OEM aluminum prop and own a small- or medium-sized boat, aluminum is a good material choice for your replacement.
Stainless steel: Though a bit more expensive, propellers made from stainless steel have a significant leg up when it comes to performance. Hardier than aluminum, a stainless steel prop tends to last longer and withstand damage. Stainless steel props come in a range of sizes, including larger diameters, and make great props for heavier boats.
Get More Details on Boat Prop Selection
We hope you found our introduction to new prop shopping helpful! Get more information on the best methods for matching up the right propeller to your boat and engine with our free eBook Top 5 Ways to Ensure Outboard Engine Peak Performance. As you may know, the right prop is just step one. This eBook also dives into tips on fuel types, how to create your own boat maintenance plan to keep your engine running its best, and much more. Get yours now!
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