Boat Propellers | Fixed Hub Propeller or Removable Hub Propeller

Most modern outboard motor propellers and stern drive motor propellers have a rubber or plastic and metal inner hub that fits tightly within the inner barrel of the propeller.  The main purpose of this inner hub is to grip the drive shaft and transmit the power to the propeller.  The reason that the body of the inner hub is made of plastic or rubber is to protect the gears and shaft of your motor’s lower unit from expensive damage should the prop strike a rock or other hard feature.  In this instance, the rubber or plastic will slip or fail, absorbing the impact.

About Propeller Hubs

Each hub will have an inner sleeve designed to mesh with the teeth (called splines) on a specific motor’s drive shaft.  The diameter of the sleeve and length of the hub will be specific to a drive shaft configuration and must match the motor you’re putting it on.  The same hub may fit several different motors by the same manufacturer, and can even fit other manufacturer’s motors if they use the same drive shaft assembly. 

When evaluating propellers, the first order of business is to know the make, model and year of your motor.  Most boat propeller finder tools or propeller technicians can use this information to get you to the right group of propellers that will fit your motor.  Knowing the spline count (number of teeth) on your drive shaft is helpful as it will alert you if you are considering incorrect propellers.  While it is usually pretty straight forward, be aware that some manufacturers like Mercury may have different drive shaft configurations for the same motor depending on where the motor was made, so knowing if you have an 8 spline drive shaft or a 14 spline drive shaft will be important.

The metal sleeve will be enclosed in a rubber or plastic unit that will fit into the inner barrel of the propeller.

Fixed Hub Propeller vs. Removable Hub Propeller

For “fixed hub” or “pressed in hub” hub propellers the rubber inner unit is compressed and permanently forced into the propeller at the factory.  These props are ready to go and often cost a little less than a removable hub system.  Many motors will be initially equipped with a fixed hub propeller by the manufacturer.  Replacement fixed or pressed in hub propellers will usually use the same mounting hardware.  Mounting hardware is usually not included with fixed hub propellers

For “removable hub” systems, the hub and propeller shell are purchased separately and can be inserted and removed from the propeller.  One of the biggest advantages here is for the seller, who can stock a few hubs and a few propellers, but by mixing and matching, they can provide a wider variety of options with a smaller number of part numbers.  The boat owner will need to initially purchase both a hub and a propeller shell.  If they desire to change propellers, they can purchase a new propeller shell and re-use the hub.  Conversely if the hub is damaged, but the propeller is good, the hub can be swapped out for a new one.  Most removable hub systems will use different hardware than fixed hub systems, but they will usually come with the mounting hardware included.  Mounting hardware for different removable hub systems is often interchangeable.

Slipped Hub

As mentioned earlier, hubs are designed to fail under impact to protect the more expensive gears and shafts of your motor from damage.  They will usually allow you to continue to operate under low speeds and gentle acceleration, to get you home, but under rapid acceleration or higher speeds, they will slip, allowing the drive shaft and hub to turn within the barrel of the propeller.  Under these circumstances, you’ll need to change out the propeller or hub kit.

Which Should You Choose? Fixed Hub or Removable Hub

The upshot is either style will work for you pretty much interchangeably.  However, you'll want to keep in mind that the hardware may be different. 

• If you've got a removable hub prop and you want to change to a fixed hub prop, you probably need to order original style spacers and thrust washers. 
• If you purchase a removable hub prop with a hub kit, it will usually come with the required hardware. 
• If you have a fixed hub prop and you want another fixed hub prop, you should be able to re-use your existing hardware. 

If you have questions on Boat Propellers, we are always happy to help. Contact us and let us know how we can be of assistance.

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