Almacen Naval

Boat Propeller or Wheel

Definition of  Commonly Used Propeller Terms

Cavitation: A phenomenon of water vaporizing or boiling due to the extreme reduction of pressure on the back of the propeller blade.

Diameter:  The first number listed when describing a propeller. Is two times the distance from the center of the hub to the tip of the blade. Also can be described as the distance across the circle the propeller makes when rotating.

Pitch: The second number listed when describing a propeller.  Propeller pitch is the theoretical forward movement of a propeller for one revolution, assuming that there is no prop slip. For example, a 21 pitch propeller will theoretically move 21 inches for every revolution. Propeller slip occurs with every propeller, but the amount of slip varies depending on propeller design. More aggressively and efficiently designed propellers will slip less.

When selecting a propeller pitch for your boat, it is important that the propeller runs at the upper end of your engines wide-open-throttle RPM range. If you want your RPM's to increase, go down in pitch. To decrease RPM's, go up in pitch. As a general guide, for every 2" of pitch, RPM's will change approximately 400 RPM's.

Rake:
Propeller rake is the degree that a propeller blade is angled in relation to the hub. Props with higher rake typically have better speeds and greater lift. The better performing propellers typically have between 20 - 30 degree rake angles.

3 Blade vs. 4 Blade:

Performance boats:  3 blade fastest but in some cases the 4 blade will deliver more bow lift to achieve faster speed.
Fishing Offshore boats:  3 blade is fastest.
3 Blade Raker: Has curved blades for better bite and hole shot and can be run at higher engine height.

Advantages of a 4 Blade:
A 4 blade can be trimmed high to achieve higher transom height, which will achieve higher speeds.
A 4 blade propeller has less slippage. Due to better hole, a 4 blade will stay on plane at lower RPM, and will improve gas mileage.

We sell Boat Propellers by Michigan Wheel

download the latest Michigan Wheel Product Catalog, it is full of valuable information.  http://www.miwheel.com/MIWheel/Catalog/default.asp

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