Understanding a Boat Propeller

Selecting a propeller for a boat is not a simple process. The parts of a propeller, their interaction and their suitability to the size of the engine can make all the difference to the speed, handling and load capacity of the boat.

Propeller Parts

A propeller consists of blades, typically three or four, that attach to a central hub at a point known as the blade root. The side of the blade facing away from the boat is the blade face; the reverse side is the blade back. The part of the blade that is nearest the boat and first cuts through the water is the leading edge; the opposite side, from which water leaves the blade, is the trailing edge.

How Propellers Work

As a propeller blade moves downward, it pushes water away and more water rushes into the space behind the blade. This creates a difference in pressure between the top and bottom of the blade, which effectively both pushes and pulls the propeller through the water.

Pitch

Pitch, which is usually included in a propeller specification, describes the forward movement of the propeller as it moves through a single revolution.

References

• Mercury Marine: Basic Propeller Parts
• Mercury Marine: How Propellers Work
• The Prop Doc: Propeller Basics