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The Bottom Line

Although I’m loathe to acknowledge my naivet concerning such matters (especially since I’m 61 years old and have owned boats all my life), my approach to in-water bottom cleaning was plain as dirt—if not downright cavalier—until recently. It went something like this: When growth on chines and running surfaces slipped past the faint-slime stage, I’d simply dial up a marina-recommended dive service and have ‘em fall by with stout hearts, dive gear, and a bag of tools.

Ignorance is bliss, of course. And I was blissfully enjoying my bottom-cleaning misconceptions until three years ago, when Betty Jane’s top speed dropped off radically during the summer months due to (it turned out) a performance-degrading oyster infestation on her propeller. Given the money I’d been lavishing upon my dive service at the time and the extra moolah I’d have to pour into dealing with the infestation, I decided to examine dive services and their procedures, capabilities, and guidelines with a lot more passion than I’d ever examined them with before.

My first finding engendered gratitude. Apparently I’d been fortunate over the years, having stumbled onto careful, experienced divers by sheer dumb luck. “I think the slap-dash approach will eventually get a person into trouble, though,” advised Rob Johnson of Pow’r Scrub Underwater Services, a decades-old dive service in Panama City, Florida, which was scrubbing at the time—and continues to scrub today—Betty’s nether regions. “Whether a guy uses a machine to remove growth or hand tools, his expertise and work ethic are critical—a sloppy job’s gonna remove bottom paint, expose or scratch gelcoat, and cause accelerated haulouts and maybe blisters.”

“So how do you find a good diver?” I asked. “Word of mouth,” Johnson proclaimed. “Pick somebody that folks in neighboring slips are happy with, a guy you see working around the marina, not somebody with nothing more than a big phone-book ad.”

My second finding zeroed in on bottom-paint thickness, a subject to which heretofore I’d paid little attention. Steve Goldberg of Del Rey Divers of Marina Del Rey, California, another dive service guy I’ve known from way back, told me straight-out that the single coat of bottom paint that I’d been applying is simply not enough to withstand the tightly scheduled (every three weeks in the summer) cleanings he recommends. “You need to do two coats on every haulout, not one,” Goldberg advised, “and then apply a third coat to the sensitive places.”

Examine the drawing above, and you’ll see there are several of these areas. Most important is the swathe that extends from the boat’s waterline down to her chine and continues on from the chine toward the centerline of the running surface for about a foot. The object is to thicken the paint in this area, since the sunlight that gets through here more readily encourages marine growth and the physical impact of cleaning it must therefore be more intense. The same reasoning applies to the bow and the transom areas, which are also shown in the drawing.

Running gear’s another matter, however. It turns out there was an easy explanation for why Betty’s propeller became infested with oysters while the aspects of her bottom visible from the dock remained comparatively clean. During a haulout some months prior, I’d dealt rather cursorily with Betty’s propeller. Instead of applying an epoxy barrier coat first, I’d directed the yard to simply slap on some hard, copper-laden paint. The upshot, Goldberg theorized, was that the paint’s cuprous content soon reacted galvanically with the prop’s metal, thereby nixing all anti-fouling properties, leaving the bottom relatively clean, but the prop open to the oyster onslaught.

This article originally appeared in the April 2009 issue of Power & Motoryacht magazine.