Discover Boats

For people with no previous association to boat propellers, the terms that are used when speaking about different types of propeller and propellers parts can seem quite confusing. This write up aims to increase your basic knowledge when it comes to dealing with boat props.

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.

The drive shafts teeth are referred to as splines, and these arent part of the propeller itself. A hubs design ensures that it fits into a drive shaft keeping in view the number of splines it has.

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.

Rotation of a propeller can be right or left hand, and most boat propellers come with right hand rotation. Left handed rotation is generally found aboard boats that require heavy steering wherein the motors torque is countered using double engines.

A cupped blade is used to describe blades that have undergone special treatment wherein the trailing edges are curved. This is known to elevate performance levels in specific scenarios.

The rake refers to the blades angle from the hub. A negative rake indication shows that the blades are pointed forward (towards the boats front), and this is generally done to strengthen high end props.

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.