Propellers 101: What the Terms Mean
The propeller is one of the most important factors that can have a significant impact on a boat’s performance. Knowing the parts of the propeller will help a boat operator better understand how one works. Going beyond the basics will add more knowledge to choose the best prop for our needs.
Hub
The hub of a propeller is the center barrel to which the propeller blades attach. On through-hub exhaust props, we distinguish the outer and the inner hubs that are connected by the ribs. In these propellers the engine's exhaust gases pass between the outer and the inner hub. The interior of the inner hub has a rubber sleeve that fits over the propeller shaft.
Diffuser Ring
A Diffuser Ring is the raised rim on the trailing edge of the outer hub on a through-hub-exhaust prop. Its role is to keep exhaust gases from feeding back into the propeller blades at low rpm, which would lead to the reduction of thrust.
Blades
The blades are the fins attached to the propeller's hub. Typical props have three or four blades, while performance-focused wheels can have up to five or six blades.
Blade Face and Blade Back
The “blade face” is the side of the blade facing aft that pushes the water and moves the hull forward. The blade face is known as the high-pressure side or pitch side. The “blade back” is the side of the blade facing the bow and the one that first meets the water. The blade back is known as the low-pressure side.
Blade Root and Blade Tip
The “blade root” is the part of the blade that attaches to the hub. The “nominal” pitch of a propeller is measured at this part of the blade.
The “blade tip” is the farthest point of the blade, measured from the center of propeller's hub. It separates the Leading from the Trailing Edge of the propeller's blade.
Leading and Trailing Edge of the Blade
The “leading edge” is the forward edge of the blade that first cleaves the water when the propeller rotates. It starts from the front part of the propeller's hub and ends at the blade Tip.
The “trailing edge” is the aft edge of the blade from which the water leaves the blade or flows away. It starts from the blade tip and ends at the rear portion of the propeller's hub.