This is the Interlux method. It has worked for us quite well. Little bit of work invloved but worth it IMHO:
PAINTING UNDERWATER METALS
Such as bronze and stainless steel, shafts, struts, props, trim-tabs and thru-hull fittings.
The painting of these areas requires special attention to initial surface preparation in order
to improve adhesion. The longevity of this system will probably not be equal to that of the
remainder of the boat, due to the abuse and RPM’s these parts withstand. However, excellent
results have been obtained utilizing the following system.
PAINTING TRIM TABS, SHAFTS, STRUTS, PROPS AND THRU HULL FITTINGS.
Degrease the metal surface with Fiberglass Solvent Wash 202 or Special Thinner 216.
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. Remove blast or sanding residue.
Apply one thin coat of Viny-Lux Primewash 353/354 thinned 25% with Viny-Lux Solvent 355.
Allow Viny-Lux Primewash 353/354 to dry a minimum of one hour but no more then
24 hours and apply three coats of InterProtect® 2000E/2001E following dry times on label.
(If fairing is necessary, fair between first and second coats of InterProtect®).
Apply 2-3 coats of Interlux® antifouling paint. Hard antifouling paints work best such as
Fiberglass Bottomkote® or Ultra for this application. On aluminum use Trilux® 33® or Tri-Lux® II.
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 weld seams
apply a minimum of five coats. Finish with at least three coats of antifouling paint. When painting
aluminum use Trilux® 33®, Tri-Lux® II Trilux® Prop & Drive or Trilux® antifouling paints.