![]() ![]() 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 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. Or rake can be flat maintaining its degree of angle continuously from propeller hub to blade tip. Rake can be progressive meaning it increases as you move out from the propeller hub to the blade tips. An average rake angle for most outboard propellers is 15 degrees. The range of degrees could vary from -5 to +30 degrees. ![]() Rake can be slightly negative (leaning towards the boat), or positive (leaning away from the boat). Rake is the amount of degrees the propeller blades angle perpendicular to the propeller hub. Trained custom propeller shops can adjust diameter to aid in the operation of your specific vessel and its set-up. Propellers running at deeper depths can be smaller in diameter while performance applications that surface the propellers while running can use larger diameters. Generally, the lower the pitch of a propeller, the larger the diameter will be. Diameter changes can affect the “attitude” of the boat or the way the boat carries itself. Most propellers have a diameter predetermined by the manufacturer as correct for the pitch, horsepower and application it was designed for. In other words it is the distance across the circle the blade tips make as you rotate the propeller.ĭiameters are limitless. Diameterĭiameter is the total outer circumference of the propeller measured across the center of the prop. 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. Pitch controls the engine revolutions per minute or “RPM”. Pitch is the final “gear ratio” adjustment on any given boat. Both styles of pitch offer benefits depending on the type of boat and engine package or set up a person uses. 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. True pitch describes a propeller that measures the same pitch from the leading or beginning edge to the trailing or following edge. 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. ![]() This forward travel is measured in inches. Pitch is the theoretical forward travel of any given propeller. The descriptions and picture listed below will describe those basic parts, and help you to understand some of the distinctive characteristics of those propeller parts that can vary, causing different reactions. However, there are many variables within those basic parts. All propellers have the same basic parts. This momentum change is caused by a pull push affect of the blades and the pressure differential from low to high and is the basis for the creation of thrust. Thrust is created as the propeller pulls water into the front of it, (the boat side) and pushes it out on the back side. ![]() It is the part of the boat that transfers the engine horsepower to the water. PropellersĪ propeller or “prop” is the final piece of the engine and its drive train. Here is some terminology so you can talk “prop”. Top-end, hole-shot or cruising speeds, your rig needs to be propped right. Maximizing the performance of your boat is not just getting the right motor for your boat your prop plays a big role in its performance. ![]()
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