La Redneck Yacht Club

If you've started researching a new boat prop, you may have run across a number of arcane terms. "So you have a 15" pitch, is it a cupped blade? What's the rake?" It can be a little intimidating, but it isn't as complex as it sounds once you've decoded the jargon associated with boat props.

Boat Prop Parts:

First off, the typical prop is composed of 3 or 4 blades arranged around the hub. The hub serves to connect the prop blades to the drive shaft of the engine. The blades themselves are angled to screw through the water, pulling the boat forward. The leading edge is the side of each blade that is cutting through the water. The trailing edge is the opposite side.

You may see "splines" discussed. These aren't technically part of the boat prop, but are the teeth on the drive shaft. The prop hub will be designed to fit a shaft with a specific number of splines.Boat Prop Features:

Each boat prop will be defined by its diameter and pitch. This will often be expressed as two numbers in inch measurements, for example 14.5" X 12" and is usually stamped somewhere on the hub. T he first number is always the diameter, which is twice the distance from the center of the hub to the end of the blade. The second number is the prop pitch. Pitch is the theoretical distance the prop will travel through the water in a single revolution. Our 12" pitch prop would travel 1 foot forward for every revolution. I mentioned that pitch is the theoretical distance the prop would travel because in the real world props will experience prop slip. Slip is the difference ratio between the pitch and the actual distance traveled. Slip can be as little as 10% for really efficient planing boats, to as high as 80% for heavy work boats.Rotation is expressed as either right hand or left hand. Most boat props are right hand rotation, but a left handed prop may be used on one engine when double engines are used to counteract the motor torque that tends to pull the steering to one side.Cupped blades are a special treatment where the trailing edge of the prop blade is curved. This can provide better performance under certain circumstances.

Rake is another term you may hear. Rake indicates the angle of the blades from the hub. A rake of 0' indicates the blades are 90 degrees perpendicular to the prop hub. A rake of 20 degrees means that the blades sweep back from the hub 20 degrees from perpendicular. Negative rake points the blades forward towards the front of the boat and is occasionally used to add strength to high performance props.

Now that you've got the basic lingo down, it will be much easier to discuss your propeller needs with your marine supply expert. Before you get started, it is always a good idea to make notes about your engine's make, model HP and year. Y ou should also take a look at your current boat prop and identify the material (usually aluminum or stainless steel), number of blades, the diameter and pitch. With that information in hand, you should be ready to find the prop that is right for you boat and boating style.