PS Advisor June 2009 Issue

PS Advisor: Waterline Stains Revisited

Can clear antifouling paint solve this problem?

I own a 1978 Columbia 9.6, which I sail on freshwater Lake Erie four to five months each summer at Sandusky Harbor Marina in Ohio. My problem is keeping the 1-inch white bootstripe between the bottom-paint line and the molded-in black stripe clean. After three or four weeks, the scum buildup requires heavy brushing or sanding to remove.

Application of PoliGlow Acrylic Coating
Practical Sailor readers have reported good results warding off waterline stains with a regular application of PoliGlow acrylic coating. We are currently testing PoliGlow and similar products on a 1974 Javelin.
What about applying Trilux prop antifouling (clear 9387887) before launch? Would this work without damaging the fiberglass? Do you have any other fix?


Charles A. Riddiford,
Charisma, Columbia 9.6
Taylors, S.C.


If what you are seeing is green or brown algae, or even barnacles, then your waterline has crept upward. In that case, you can either shed some ballast, apply antifouling paint up to your new waterline, or incorporate your summer scrubbing routine into your fitness program.

Clear antifouling paints have not performed well in our bottom paint tests, and the waterline is a favorite place for marine life to multiply, so we’d recommend something more potent.

It sounds like what you are dealing with is oil, dirt, and contaminants on the water’s surface staining the gelcoat just above the static waterline. Adding antifouling paint well above the waterline won’t fix this and would likely have cosmetic consequences. There are no UV inhibitors in antifouling paint, so it can be prone to fading, chipping, or peeling. Clear antifouling paints can appear yellow on a white hull.

Our advice would be to buff and seal the gelcoat below your molded-in bootstripe as best as you can. A boat of that age is likely to have very porous, oxidized gelcoat, so this may require some wet sanding, followed by a buffing compound like 3M Imperial Compound and Finishing Material and/or a micro-finishing glaze like 3M Finesse-It II. Finally, seal your polished gelcoat with a hard, durable wax. We like Collinite 885 Fleet Wax. ("Offshore Log: Gelcoat Maintenance" elaborates on this routine in the "Tools and Techniques" section online at

If you go the route of conventional wax, by the end of the season, you may have to reapply the wax (hard to do in the water) or resort to scrubbing again. A waterline stain cleaner will reduce the amount of scrubbing required. We have tested some waterline stain removers that claim to have little or no impact on the environment, one of them is Star brite Sea Safe Hull Cleaner, which performed well in our November 2007 test.

The acid gel cleaners like Spray Nine Boat Bottom Cleaner worked best, but these are more caustic. A chemically assisted hull cleaning project is best done out of the water. Be sure not to get any hull cleaner on your bottom paint, which it will remove.

This advice does not apply to painted bootstripes, which should not be scrubbed, but can be protected by recommended sealer waxes. Ultimately, an old boat will need re-striping.

Comments (1)

Posted by: Robert D | March 18, 2013 5:59 PM    Report this comment

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