Jul 202010
 
Propeller Assembly

An interchangeable hub propeller assembly

On the Propshaft

A typical recreational boating propeller is mounted on a splined propshaft with a thrust washer, spacer, washer and nut, with some provision to keep the nut from turning loose, such as tabs on the washer or an additional cotter pin. There are exceptions, like the shear pin systems that were once widespread, but now most are as discussed here.

Thrust Washers

Various thrust washer shapes. Not all are splined.

Thrust Washer

The thrust washer is mounted on the propshaft, between the lower unit and the propeller, and it may or may not have splines. It’s an important component of a boat propeller’s installation, because it fits the shaft in such a way that will not allow either itself or the propeller to move forward under thrust, thereby transferring thrust to the shaft and protecting the gear housing and its seal from contacting the rotating propeller.

A matching taper on the propshaft and the washer is one effective design that stops a thrust washer from moving too far forward.

The thrust washer also helps to keep the propeller centered on the shaft when the soft inner prop hub fails to do so under adverse high-torque conditions.

Hub

Inserted in the prop is a splined inner hub, which serves as a shock absorber between the prop blades and the shaft. A good prop hub should keep the propeller precision-centered on the propshaft, dampen vibrations and help protect the shaft from the severe shock of striking a submerged object with the propeller.

Prop Hubs

A Rubex interchangeable rubber hub (left) and a pressed rubber Solas hub

There are two basic types of hub (in addition to some rare specialty hubs): a pressed rubber hub or an interchangeable hub. The pressed hub is semi-permanently forced into position by a high pressure press in a prop shop. By contrast, the interchangeable hub is easily inserted by the prop installer. Each propeller is designed to use one type or the other. While pressed hubs are made of rubber, interchangeable hubs are sometimes made of a more rigid material, but we find that rubber interchangeable hubs offer better vibration dampening.

What’s the difference between Rubex and Solas? Most Solas propellers are of the pressed rubber hub type and a few have specialty pin drive hubs. All Rubex props use interchangeable rubber hubs. There you have it!

Next: Spacers and more in Part 2

  4 Responses to “Understanding Boat Propeller Assemblies (Part 1)”

  1. Your info is not very helpful.
    I buy a Yamaha F20, I have a light boat and want to go as fast as the engine allows.
    So which propeller do I need?

    I like aluminum.

    Thanks for your info

    Hans

    • For top speed from your 20hp, our Solas Amita 3 blade aluminum propeller is the most appropriate of the Solas blade styles. It is available from our dealers in a range from 7 to 11 pitch as found in our prop finder. The higher pitches will move the boat faster than the lower pitches, but you want to make sure you don’t over do it or the engine will have a hard time getting the boat on plane when you have a full load.

  2. have yamaha 350 and would like to try my mirage props need to buy the hubs can you help me thank you ### ### ####

    • Big outboard! I forwarded your question to the Solas USA office via email along with your phone number. Thank you for your inquiry.

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