Common Propeller Terms

1. LEADING EDGE - The edge of the propeller nearest to the boat cuts through the water first, starting at the hub it extends to the blade tip.

2. BLADE TIP - This is the farthest point that a propeller extends from the center of the hub to the outer radius of the blade.

3. TRAILING EDGE - The edge of the propeller farthest away from the boat where the water leaves the blade.

4. CUP - The cup on a propeller is designed to help lock the propeller in the water to reduce slippage and prevent cavitation. The cupped area is located on the trailing edge of the blade starting approximately 1" from the hub extending out to the blade tip.

5. PUSHING FACE - This is the face of the propeller blade away from the boat. More commonly called the PITCH FACE which faces the pitch block when repairing.

6. NEGATIVE FACE - This is the face of the propeller blade toward the boat.

7. BLADE ROOT - The thickest area of a propeller where the blade and the hub are joint together.

8. HUB - The center of the propeller that fits over the propeller shaft.

9. OVER HUB EXHAUST - Exhaust gasses flow over the hub and blades.

10. THRU HUB EXHAUST - Exhaust gasses flow through a barrel of outer hub to prevent exhaust gasses from flowing over the blades of the propeller.

11. RUBBER HUB - inner hub bushing made of hard rubber, molded to a splined spindle to protect the drive train when shifting.

12. ACR/DIFFUSER RING - The flared ring used on through hub exhaust propellers. The ACR/Diffuser ring prevents the exhaust gasses from backing up on the blades which produces cavitation on take-off.

13. CAVITATION - The introduction of air on the propeller blades resulting from running a damaged propeller, or from sucking air from the surface of the water. A cavitating propeller is actually slipping and produces very little thrust.

14. PITCH - The theoretical travel of a propeller through a mass per revolution. EX: a 19" pitch propeller moves approximately 19" per revolution.

15. STRAIGHT PITCH - The pitch is constant or the same from leading edge to the trailing edge of the propeller.

16. PROGRESSIVE PITCH - The pitch increases from the leading edge to the trailing edge. EX: Leading edge measures 17", trailing edge measures 17" pitch - this is a 3" regressive pitch.

17. VARIABLE PITCH - The pitch increases from the leading edge to the trailing edge, and from the hub to the outer tip.

19. RAKE - The angle of the propeller blade in correspondence with the propeller shaft.

20. FORWARD RAKE - Blades are angled toward the boat. Commonly used for inboard propellers and small outboard propellers.

21. AFT RAKE - Blades are angled b back or away from the boat. This type of rake is used to help lift the stern of the boat on take-off, and on top end will help to lift the bow up - improving performance.

22. PARABOLIC RAKE - The off center development of a propeller blade used to make the rake concave or convex.

23. DIAMETER - The overall width of a propeller.

24. RIGHT HAND ROTATION - The propeller turns clockwise on the shaft.

25. LEFT HAND ROTATION - The propeller turns counter-clockwise on the shaft.