Boat Propeller Technology

Choosing the right propeller requires some knowledge of the technology.

Your boat's propeller converts the engine's output to the driving force that propels your watercraft through the water. Fitting the right propeller requires some knowledge of the technology involved.

Pitch

Pitch is the forward movement a propeller would make in one revolution if there was no slip. In practice most propellers operate at about 80 percent efficiency, meaning they lose about 20 percent to slippage.

Diameter

Diameter is the circle described by the rotating propeller. Larger boats need larger diameter propellers. Propeller specs generally list diameter x pitch, in that form.

Rake

Blades of a propeller are angled back from the hub, or center section, to provide lift.

Thrust

Thrust is generated when the propeller moves water from front to rear and discharges it at an increased velocity.

Materials

Composite propellers are least expensive but generally cannot be repaired. Aluminum propellers can be easily repaired, are mid-range in price, and are the most common. Stainless steel propellers are the strongest and heaviest, but repairs are difficult and initial cost is higher.

Blade Count

Three- and four-blade propellers are most common, with some two- and five-blade designs marketed for specialty applications. Three-blade designs provide more top end speed and are good for general purpose boating, while four-blade propellers give improved mid-range performance and power.

References

• Mercury Marine: How Propellers Work
• Coastal Prop Technology, Inc.: Choosing & Tuning Props
• Boatbuilding: History and Design of Propellers
• CWS/Outboardsales: Propeller Basics

Resources

• Bam Marine: Prop Slip Calculator