Your engine revs but the boat doesn't move—or moves sluggishly. The prop looks fine. What's happening? You may have a spun hub.
What Is a Prop Hub?
Most outboard and sterndrive props have a rubber or plastic hub pressed into the center. This hub serves as a shock absorber and a sacrificial element—if you hit something, the hub is designed to slip or shear, protecting the lower unit gears from catastrophic damage.
Signs of Hub Failure
- Slipping under load: Engine RPM climbs but speed doesn't increase, especially when accelerating hard
- Inconsistent performance: The prop works fine at light throttle but slips at WOT
- Visual damage: Cracked, melted, or extruded rubber visible around the hub
- Burnt rubber smell: Overheated hub material has a distinctive odor
Why Hubs Fail
- Age and heat: Rubber degrades over time, especially with repeated heat cycles
- Impact: Hitting a rock or log can damage the hub without visible blade damage
- Over-propping: Engines that lug under load stress the hub
Repair Options
Press-in a new hub: For about $30-50, a prop shop can press out the old hub and install a new one. This is often done as part of a repair service.
Interchangeable hub kits: Flo-Torq and similar systems use a replaceable hub insert, making future swaps easier and allowing you to change prop brands without buying new hubs.
Pro Tip: Carry a spare prop with a good hub. A spun hub in the middle of a river trip ends your day.
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