Selecting the right propeller is an important factor in maximizing your boat's performance.
Many people do not understand how a prop works. It is important to understand how they work to be able to choose the correct propeller for your boat.
This is providing your engine is running correctly. The prop directly affects performance and rpm’s. Pick the wrong prop and your engine may turn too many rpm’s or too little rpm’s, either way you could do significant damage to your engine. The prop is the last link between your engine and the water. A perfectly maintained engine and hull are useless if the prop is wrong type, size or damaged.
PROPELLER BASICS
1. Diameter-Prop diameter is the distance from the center of the hub to the blade tip, multiplied x 2.
2. Pitch and Rake- Prop pitch and rake describe the placement of the blade in relation to the hub.
A. Pitch is expressed by the theoretical distance that the prop would travel in one revolution. For example if the prop is a 20 pitch it would move 20 inches in one revolution. This distance is only theoretical, during actual operation, the prop achieves about 80%.
B. Rake is specified in degrees and is measured along a line from center of the hub to the blade tip. A blade that is perpendicular to the hub has 0 degree of rake. A blade that is angled from perpendicular has a rake expressed by its difference from perpendicular. Most props have rakes ranging from 0 to 20 degrees.
The number of blades used on a propeller is a compromise between efficiency and vibration. A one blade propeller would be the most efficient, but have a high level of vibration. As blades are added efficiency decreases and so does the vibration. Most props have three blades, representing the most practical trade –off between efficiency and vibration.
Propellers are made from several different materials. The materials are chosen for strength, corrosion resistance, and economy. Stainless steel, aluminum and bronze are most commonly used.
1. Bronze is quite strong but rather expensive.
2. Stainless steel is more common than bronze because of its combination of strength and lower cost.
3. Aluminum is less expensive but lack the strength of steel.
4. Plastic props may be used in some applications, usually small outboards and trolling motors.
Direction of rotation of the prop depends on your application. There are right hand and left hand props. This usually comes into play with twin engine inboard or stern-drive boats. To tell the difference between a right hand and a left hand prop you can look at the blades and observe the angle of the blades. A right hand prop angles from the upper left to the lower right. The left hand prop is opposite.
Another factor to consider is the way you use your boat, for example skiing, cruising, or just all out. The lower the pitch the better out of the hole performance, but lower top speeds. The larger the pitch, out of hole performance, but will get more speed.
Usually a change in 1 inch in pitch will change rpm’s by approximately 300.
You will also want to make sure the boat is at its heaviest when you prop it. Have all gear and persons you would normally have on board.
But remember it is very important to stay within your engines top rpm range
Many people do not understand how a prop works. It is important to understand how they work to be able to choose the correct propeller for your boat.
This is providing your engine is running correctly. The prop directly affects performance and rpm’s. Pick the wrong prop and your engine may turn too many rpm’s or too little rpm’s, either way you could do significant damage to your engine. The prop is the last link between your engine and the water. A perfectly maintained engine and hull are useless if the prop is wrong type, size or damaged.
PROPELLER BASICS
1. Diameter-Prop diameter is the distance from the center of the hub to the blade tip, multiplied x 2.
2. Pitch and Rake- Prop pitch and rake describe the placement of the blade in relation to the hub.
A. Pitch is expressed by the theoretical distance that the prop would travel in one revolution. For example if the prop is a 20 pitch it would move 20 inches in one revolution. This distance is only theoretical, during actual operation, the prop achieves about 80%.
B. Rake is specified in degrees and is measured along a line from center of the hub to the blade tip. A blade that is perpendicular to the hub has 0 degree of rake. A blade that is angled from perpendicular has a rake expressed by its difference from perpendicular. Most props have rakes ranging from 0 to 20 degrees.
The number of blades used on a propeller is a compromise between efficiency and vibration. A one blade propeller would be the most efficient, but have a high level of vibration. As blades are added efficiency decreases and so does the vibration. Most props have three blades, representing the most practical trade –off between efficiency and vibration.
Propellers are made from several different materials. The materials are chosen for strength, corrosion resistance, and economy. Stainless steel, aluminum and bronze are most commonly used.
1. Bronze is quite strong but rather expensive.
2. Stainless steel is more common than bronze because of its combination of strength and lower cost.
3. Aluminum is less expensive but lack the strength of steel.
4. Plastic props may be used in some applications, usually small outboards and trolling motors.
Direction of rotation of the prop depends on your application. There are right hand and left hand props. This usually comes into play with twin engine inboard or stern-drive boats. To tell the difference between a right hand and a left hand prop you can look at the blades and observe the angle of the blades. A right hand prop angles from the upper left to the lower right. The left hand prop is opposite.
Another factor to consider is the way you use your boat, for example skiing, cruising, or just all out. The lower the pitch the better out of the hole performance, but lower top speeds. The larger the pitch, out of hole performance, but will get more speed.
Usually a change in 1 inch in pitch will change rpm’s by approximately 300.
You will also want to make sure the boat is at its heaviest when you prop it. Have all gear and persons you would normally have on board.
But remember it is very important to stay within your engines top rpm range