How to Stop Marine Growth
On Outboard Motor and Stern Drives Lower Units

mercathode prevent corrosion on lower units

Pettit Marine Ultima Eco antifouling for outboards

Even though outboard motors and stern drive live in the saltwater there are a number of things you can do to prevent the growth of slime and barnacles. Want proof? The clean as a whistle sterndrive pictured above just spent the previous eight months in the waters of Raritan Bay, protected with Pacifica Plus.

Slime, barnacles and other marine growth on lower units is a curse. They slow a boat, waste fuel and destroy handling. The good news is lower unit salvation can be found in anti-fouling paint. Only there's a catch. You can't use cuprous oxide on an aluminum drive or it will corrode. In other words, if you have a fiberglass boat you can't use the same copper based anti-fouling on the hull as the lower unit. No problem.

Both Interlux and Pettit Marine offer copper-free barrier coats, namely, Pacifica Plus from Interlux and Ultima Eco from Pettit. Both of these anti-fouling paints contain Econea and Zinc Omadine, a highly potent combination. Jargon Buster: Econea is a metal-free pharmaceutical that completely breaks down once it leaves the paint film (resisting fouling). And Zinc Omadine is highly-effective against soft growth. These two additives pay big dividends in multi-season protection.

Interlux's  Pacifica Plus antifouling for outboards Both paints can be brushed or rolled applied and can also sprayed (using a Pre-Val sprayer). The advantage of brushing over spraying is as simple as the sea is salt: Rolling or brushing applies more active ingredient by virtue of its higher wet/dry film thickness. Some boatyard experts argue that a brushed or roller application is more effective throughout the season than spray. There is also the issue of economics. Spray anti-fouling consists predominantly of thinner so that viscosity is thin enough to spray out the nozzle in a fine mist instead of clumps. So why spray in favor of rolling? Because it can sometimes be difficult to get to all the nooks and crannies on a lower unit with a brush. Spraying can do a more thorough job.

Pacifica Plus is available in pints of black and gray while Ultima Eco is available in quarts. A pint is usually enough to paint a drive. No matter what finish is destined to be applied to a lower unit surface preparation is the key to the paint being able to work its magic. So painstakingly follow the directions on the label. Then read them again. For safety sake be sure to wear gloves, eye protection and work where there's plenty of fresh air.

Interlux's  TriLux antifouling for outboards One particularly worthy option is Trilux 33 spray antifouling for outboards (from Interlux). The coating comes in an aerosol can, which means painting is very easy. First, coat the surface with the special primer, followed up by a top coat. The net result is a hard, durable coating.

Soon to be released is Pettit's Hydrocoat Eco also boasting multi-season protection all the while yielding a VOC content less than half that of California's strictest regulations. Advantages to its use include convenient soap and water clean up, easy application, no heavy solvent smell and compatibility with just about any other coating that may have been laid down on the hull.

No matter what finish you'll be applying to a lower unit, surface preparation is the key to the paint being able to work its magic. So painstakingly follow the directions on the label. Wear gloves, eye protection and work where there's plenty of fresh air.

Finally, one low-tech old-school method for keeping marine growth at bay is to wrap the drive leg in a heavy-duty trash bag floating in the water. Pour a gallon of bleach inside the bag to kill any growth. Crazy as this method sounds, it works.

© Copyright 2013 by Tim Banse