Barnacle-Proofing Underwater Metals

— By Jan Mundy

No antifouling on this outdrive results in excesive drag, slower speeds and increased fuel consumption. An antifouling specially formulated for aluminum outdrives, such as Trilux Prop & Drive, is the solution.

According to the experts at Interlux, there is an antifouling method to protect bronze and stainless-steel shafts, struts, props, trim tabs, thru-hull fittings and even stern thrusters from barnacles. Painting these areas requires special attention to initial surface preparation in order to improve adhesion.

The idea is to isolate the copper in the antifouling paint from the bronze of the strut. The cuprous oxide in the antifouling paint is less noble than the bronze in the strut and if you don’t prime properly, the paint’s antifouling properties will be compromised. The result of not properly priming the bronze could be loss of antifouling protection and the strut will become fouled or burn back may occur. Burn back looks just like it sounds, the paint looks as if it has been burned in concentric circles emanating from the strut or thru-hull or strainer.

Final coat of Interprotect 2000E applied to running gear.

The longevity of this system will probably not equal that of the remainder of the boat bottom, due to the abuse of the service speeds (rpm) these parts must withstand. However, excellent results have been obtained using the following steps. First, degrease the metal surface with Interlux Fiberglass Solvent Wash 202 or Special Thinner 216. Next, bring metal to a uniform bright finish by sandblasting with non-ferrous blast media, such as clean silica sand, or grind using coarse to medium emery cloth. Solvent wipe to remove blast or sanding residue. Immediately, apply one thin coat of Interlux Viny-Lux Primewash 353/354 thinned 25% with Viny-Lux Solvent 355. If this is not done within 24 hours of blasting or sanding, you’ll need to reblast or sand with coarse emery cloth. Primewash is a metal etcher containing vinyl butyral resin, phosphoric acid and a little bit of zinc chromate. The acid cuts through the oxidation and the vinyl resin gives the primer something to hold onto and the zinc chromate adds some anticorrosion protection. Metal etchers are the weak link in the chain and instructions must be followed very carefully.

Allow Viny-Lux Primewash 353/354 to dry a minimum of one hour but no more then 24 hours and apply four coats of Interprotect 2000E/2001E following dry times on the label. If fairing is necessary, fair between first and second coats of Interprotect.

If you don’t want to prep the gear down to bare metal, coat the surface with two to three coats of a single-part primer, such as Primocon and then apply the 2000E. Apply two to three coats of a non-vinyl antifouling paint. Hard antifouling paints work best such as Fiberglass Bottomkote or Ultra for this application. On aluminum use Trilux 33, Trilux or Tri-Lux II. Note: if dry times for Interprotect cannot be followed, use the following alternate system. Apply four coats of Primocon YPA984 over the Viny-Lux Primewash 353/354. On rivets and welded seams apply a minimum of five coats. Finish with at least three coats of antifouling paint.