Technical Boat propeller lingo

Pitch – the theoretical distance in inches that a propeller moves forward in one revolution. Think of a screw in wood. If you increase the angle of the threads, it will move further into the wood in one turn.

Diameter – the diameter in inches of the circle that the blade tips will cut. Or, the distance in inches from a blade tip to the center of the prop, multiplied by two.

Propeller Size – props are named by the diameter inch number, followed by pitch inch number (i.e. 14 x 19 or 14″ diameter x 19″ pitch).

Blade – the part of the prop that acts as a paddle.

Elliptical Blade – one that’s elliptical in shape.

Tapered Blade – a blade that is tapered in shape. (As opposed to round ear or elliptical.)

Cupped Blade – a blade that has a lip built into its trailing edge. (Most do) The lip generally helps a prop hold water. It also adds the equivalent of about 1/2-inch to one-inch of pitch.

Polished – a prop that has had the steel polished from a dull to a shiny finish.

Hub – the center part of the propeller. The hub, as an actual part, is the piece that fits inside the barrel of a prop and what the shaft slides into. If you strike something, the hub breaks free of the barrel and spins so that you don’t damage the drive-train. The word hub is also often referred to as the size of the barrel. (i.e. 4.5″, 4″, 3″, 2.75″)

Skew – a blade whose shape sweeps in a curve that follows its rotation is said to have a skew.

Rake – if a blade sticks straight out of a hub, in other words, is perpendicular to it, that prop has no rake, or zero rake. If the blade leans back more towards the trailing edge of the prop, it is said to have rake. If it leans way back, it is a high rake prop. Rake can be measured in degrees.

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