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