See full version: Choosing the Correct Boat Propeller
Finally, material is an important consideration for your propeller. Aluminum props are a great balance of cost, performance, and durability. Stainless steel is five times stronger than aluminum, dramatically improving performance and durability. Stainless steel propellers offer better acceleration and are less likely to be damaged from striking objects in the water. Stainless steel props will outlast aluminum multiple times over. more
Before you dive into choosing a propeller, understand your boat’s intended use. Consider your average speed, load, and boating location. If you will be using the boat for multiple applications, you may need to switch props. The propeller choice directly affects the engine RPM and therefore its performance. Choose a propeller that puts the engine RPM at the midpoint or higher of the wide open throttle (WOT) range with a normal load. This operating range will translate to the highest horsepower available from your outboard. Refer to your engine operating manual for the operating range.
Once you know the operating range, consult the propeller guide for your engine to pick a combination of pitch, blade number, and material. Choose a range of propellers to perform a water test. Test the props under the same conditions that you would typically use the boat—same load, gear, and water. Set the trim angle so the boat has optimum speed on top of the water.
Pitch is the distance the propeller will move the boat after one revolution (not accounting for slip). A lower pitched propeller will create more power due to more engine RPMs, but the boat will move slower. A higher pitched prop allows the boat to move faster by travelling a farther distance with each rotation. When choosing a propeller, choose a pitch that will keep the engine RPM in its recommended operating range. Going under the range will cause the boat to lug, while going over can cause engine strain. here
The fewer number of blades a propeller has, the more efficient it is. However fewer blades will also increase the "vibration" you will feel. That’s why three blade propellers are the most common for general purpose boating. Three blades props provide the best combination of performance, speed, and efficiency. Some manufacturers also create four and five blade propellers to increase acceleration and reduce ventilation. A four blade propeller will improve handling and control for high-performance applications. Five blade propellers are good for rough water conditions and tow sports. more
It’s also quite common for people to discover that what they thought was an aircraft propeller is something else entirely. “People think that they have airplane propellers,” Ryan says, “but they’re not. Airboat propellers, for example, are usually much wider across the blade. They usually have flat ends. In other words, the blades don’t round out at the end or come to a point, they’re cut off flat. The other thing we get called about a lot are test clubs, which were used to test engines. Those blades don’t have any twist to them like an aircraft propeller. Instead, it’s a fixed airfoil. Sometimes they’re two blades, but they can have four or more. We also get calls about metal propellers that turn out to be from Hartzell fans. It looks like a little airplane propeller, but it’s only about two feet long and has either a half inch or three-quarter inch hole in the middle so you can attach it to an electric motor. They usually have Hartzell stickers on them that say Hartzell Propeller Fan Company. When people call and ask where it came from and I say, ‘well, it came off a fan,’ they’re usually kind of disappointed!” more
Here at Hartzell, we often get calls, emails, and messages from people interested in identifying historic wooden aircraft propellers. Hartzell Technical Representative Kevin Ryan has been on the front lines of fielding these types of calls for us at our prop shop. Here’s a great story from the Naples Daily News about a recent WWII propeller that he helped identify.
Distinguishing Modern vs. Early Wooden Propellers
Assessing Propeller Value here
One hundred years ago, when early aviation engineering was still in its infancy, fixed pitch propellers were your only option. A fixed pitch propeller has its pitch determined at the factory when the propeller is made. Its blade orientation was tested and built for a specific airplane to offer the optimal blend of performance and efficiency. Fixed pitch propellers were the norm until about World War II, when both pilots and aeronautical engineers began pushing aircraft to higher performance levels. [links]
In earlier posts we’ve covered how different types of propellers – such as fixed pitch propellers and variable pitch propellers – operate. But today we’re going to break down the differences in a single post. [links]
As the names imply, the core difference between the two prop designs involves the orientation of the blades relative to the propeller hub. Pitch affects the way a propeller blade will slice through the air. A low (fine) pitch positions the blade of the propeller in a slightly more vertical position from ground level. This configuration generates more thrust and is ideal for take-off and ascent. At cruising altitude, a more horizontal, high (coarse) propeller pitch allows the prop to move through the air more efficiently. This conserves fuel and reduces strain on the engine. more
Though born out of wartime, the benefits of variable pitch propellers made them appealing to commercial aircraft designers. In a variable pitch propeller, the blade pitch can be manipulated directly by the pilot in the form of cockpit controls, or automatically based on the speed of the engine. On aircraft with automatic control, blade pitch is continually adjusted as the propeller adapts to altitude, engine RPM, and other parameters. The blade pitch is typically regulated via a hydraulic or electrical system. Varying pitch allows the propeller to maintain the ideal blade orientation for the exact flying conditions.
Rake angle is measured in degrees. Rake is the amount of degrees the propeller blades angle perpendicular to the propeller hub. Rake can be slightly negative (leaning towards the boat), or positive (leaning away from the boat). The range of degrees could vary from -5 to +30 degrees. An average rake angle for most outboard propellers is 15 degrees. Rake can be progressive meaning it increases as you move out from the propeller hub to the blade tips. Or rake can be flat maintaining its degree of angle continuously from propeller hub to blade tip. Higher rake angles help to improve some boats ability to operate in aerated water situations by causing the water to adhere to the blades better than a prop with lower rake angles. The centrifugal force the propeller creates, throws the water outward and the higher and/or progressively raked propellers can hold and control that water better, increasing the thrust rearward. Higher rake angles can also help to hold a boats bow higher in the air, reducing hull drag and increasing speeds. However, low rake propellers can be a better choice for light weight fast hulls that carry the bow on their own since they direct thrust with less drag and can increase efficiency. [links]
Diameters are limitless. Most propellers have a diameter predetermined by the manufacturer as correct for the pitch, horsepower and application it was designed for. Diameter changes can affect the “attitude” of the boat or the way the boat carries itself. Generally, the lower the pitch of a propeller, the larger the diameter will be. Propellers running at deeper depths can be smaller in diameter while performance applications that surface the propellers while running can use larger diameters. Trained custom propeller shops can adjust diameter to aid in the operation of your specific vessel and its set-up. [links]
Pitch is the theoretical forward travel of any given propeller. This forward travel is measured in inches. The pitch stamped on the propeller tells you how far forward the propeller would move in inches if it was turned or screwed into a solid media such as cork or the ground. more
Just as the word suggests, rotation determines the direction a propeller revolves around the axis of the propeller shaft. Rotation is determined by looking at the propeller from the rear of the boat. A right hand propeller will turn clockwise therefore moving down to the right hand side. Contrary, a left hand propeller will rotate counterclockwise or down to the left while looking at the propeller from the rear of the vessel. Changing rotations on single, twin, or triple engine applications can affect the boats performance too.
Pitch is the final “gear ratio” adjustment on any given boat. Pitch controls the engine revolutions per minute or “RPM”. Adjusting pitch for any given situation can change a boats performance anywhere in the rpm range and give the boater the desired performance they need while keeping the propulsion system working as the manufacturer engineered. here
Pitch can be “True” or “Progressive”. True pitch describes a propeller that measures the same pitch from the leading or beginning edge to the trailing or following edge. Progressive pitch describes a propeller that starts low in pitch at the leading edge and increases its pitch as the water travels towards the trailing edge. Both styles of pitch offer benefits depending on the type of boat and engine package or set up a person uses. more