Decoding Boat Propeller Terminology

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Decoding Boat Propeller Terminology

For someone who is new to the world of boat props, the terminology used in describing various types and parts of boat propellers can be quite confusing. Given below is a brief description about various terms that you might come across in trying to find yourself a suitable boat propeller.

The parts of a boat prop: The normal boat propeller is made of either three or four blades which surround the hub. The hub, in turn, connects the blades of the propeller to the engines drive shaft. The blades are angled in the way that enables them to screw through water, thereby moving the boat ahead. The leading edge refers to the end of the blade that cuts through water, and the opposite side is referred to as the trailing edge.

Spline: This refers to the teeth of the drive shaft which is not really a propeller part. The design of a hub allows it to fit a shaft in accordance to number of splines.

Features: The classification of a boat prop essentially depends on its diameter and pitch. This is normally displayed in inches with two numbers (for example, 14.5 x 12) and is usually found stamped on the hub. The diameter is referred to by the first number and is the distance from the center of the hub to the end of the blade. The pitch of the prop is denoted by the second number, and gives the distance that can theoretically be traveled by the prop on a single revolution. For instance, a 12 pitch prop can travel about one foot on a single revolution. Pitch is generally referred to as a theoretical number because slips in pitch can be experienced in varied circumstances. A slip is the ratio difference between the distance that is actually traveled and the given prop pitch. The slip could vary under the same conditions; for example, while a heavily loaded work boat could show a 70% slip, a well maintained boat could experience a 10% slip in the same waters.

The rotation can be either left or right hand. A majority of the boat props have right hand rotation. You can expect to find a left handed one on engines wherein double engines are needed to counter the motors torque which can lead to pulling the steering in one direction.

Cupped blades refer to blades whose angles have been specially treated and their trailing edges are further curved. This is done because it increases the props performance under specific circumstances.

The rake is used to refer to the angle created by the blade and the hub. A negative rake would indicate that the props blades point forward and this is normally done for adding strength.

Also, if you intend to buy yourself a new boat propeller, you should ideally make a note of your engines specifics which would include the model, the make, and the horse-power; as well as the propellers specifications like its material, pitch, diameter, blades, etc. With this information in hand, your hunt for a boat propeller should get considerably easier.