Captain Ron's

Sailing and Cruising Pages

Emergency Prop Repairs

Ever spun your prop? This happens to outboard propellers when the rubber bushing in the hub gets old and tired. It just strips. In the old days, small outboards had 'shear pins' ... smallish soft bronze pins that fit through a hole in the prop and drive shaft. They provided the prop with a safety if the prop hit something hard; the pin would just shear off ... you lost propulsion but the prop usually survived. The modern technology to provide similar protection, is to hub the props with a heavy rubber compound. The compound also cushions the lower unit from stress due to acceleration as the rubber hub flexes when you add power.

If this hub wears out at an unexpected time, your motor revs but you don't go anywhere. Probably if you slow down, and take it easy on the throttle you can nurse your boat home at slow speed as the rubber will still turn the prop but it just won't handle a bigger load. In an emergency, I have removed the prop from the shaft and made a temporary repair with machine screws.

Typically the repair takes three screws for a three bladed prop. You drill and tap through the prop into the bronze hub bushing (usually splined) between the blades of the prop, at an angle perpendicular to the drive shaft. Insert the screws into the tapped holes. If they stick out a little, that's ok, but you can trim the screws to protrude minimally. Then leaving the screws loose, reinstall the prop on the shaft and tighten the screws. This locks the inner hub bushing to the external prop casting. You should be careful to make sure the inner bushing is still straight and centered in the prop, otherwise you'll get vibration that could damage the lower unit.

The problem with this repair is that now if you hit something, your prop doesn't have any give to it so you will likely damage the gears in the lower unit. Be very careful driving around with this rig, be gentle with the throttle and no sudden acceleration but it will work until you can get a new prop. By the way, once you've done this repair, a rebuilding service likely won't rebuild the old prop ... but you'll still have a useable spare.