It doesn’t take a big load of barnacles on the lower unit or stern drive to slow you down a knot or two. A decrease in speed translates into a loss in fuel efficiency, which means you’ll be paying more at the fuel dock than necessary. If your drive sits in the water in high-fouling areas, you’ll need to coat it with a good antifouling paint for aluminum.

This outboard trim/tilt assembly was used to conduct a three-product test of antifouling paints for aluminum. Pettit Alumacoat SR paint was applied to the assembly’s cylinder-shaped ram, while the Interlux and the West Marine aerosol sprays were applied to left and right portions of the unit’s housing.

What We Tested

At PBR, one test often leads to another. For our long-term test of our Mercury OptiMax 150-hp outboard, we recently replaced the aluminum trim/tilt assembly (see PBR March 2006). The lower half of the old assembly was caked with barnacles, which…