How To Tell If You've Spun Your Propeller Hub | Boating Magazine

How To Tell If You've Spun Your Propeller Hub

Prop Hub Slip and Diagnostic Tips

Method of marking a boat propeller so as to determine if hub has spun by simple visual inspection.

Marking A Prop To Show If It Has Spun Its Hub.

Method of marking a boat propeller so as to determine if hub has spun by simple visual inspection.

Kevin Falvey

The rubber inner bushing inside an outboard propeller’s hub is designed to absorb the shock created by shifting. The rubber hub bushing also serves as a “breakaway” should you strike something, allowing the prop to spin, and so protecting drive train components like gears.

Once a hub is spun, there generally remains enough friction to operate at low RPM –sort of a “get home” mode. But, when RPM is increased, the engine revs with little or no boat acceleration because the prop begins to spin. A spun hub feels like a loss of power with excessive RPM.

Sometimes, the hub only spins when the engine revs above a certain RPM, causing many boaters to wonder if they have spun a hub, are experiencing ventilation or cavitation, or are have some kind of gear or power issue with their outboard.

To tell if your hub has spun, mark a line on the back of the prop hub with lipstick. You can also score your mark using a file. With the mark in place over the inner and outer hub, it’s a simple matter to pull the prop and see if the mark has broken in two. If it has, you have spun a hub.

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