Features July 1, 1998 Issue

Offshore Log: The Bottom Line

After six months in the tropics, keeping Calypso’s bottom clean proves to be a weekly—and bothersome—chore. Because it’s soft, Pettit ACP-50, one of our top paints in our annual tests, disappears quickly during scrubbing. What to do?

When Calypso was hauled at New England Boatworks last September for bottom painting, we decided to switch from Micron CSC Extra to Pettit ACP-50 bottom paint. Our experience in Florida in the winter of 1997 verified previous test results that showed CSC Extra to be only an average performer in tropical waters. ACP-50, on the other hand, has consistently tested at or near the top in warmer waters.

Switching paints, according to Pettit, called for a heavy hand or machine sanding with 80-grit paper, followed by a wipe-down with ACP-50 thinner. As expected, the CSC sanded easily, making the switch fairly straightforward.

NEB applied the new paint, using short-nap rollers. They reported that the ACP-50 dried so quickly to the touch that a follow-up brush smoothing after roller application was impractical. This resulted in a substantially rougher surface texture than the sprayed-on Micron CSC finish applied by Jamestown Boat Yard the previous year.

While drying quickly to the touch, ACP-50 dries slowly for re-coating, so that it took longer to apply the four coats of bottom paint that are specified for longest antifouling protection than we have experienced with other paints.

For our first two months in the tropics, the ACP-50 bottom stayed remarkably clean. With no scrubbing at all, we found only scattered patches of very light soft fouling, which wiped off with a sponge. We left most of this soft fouling in place to test for longer-term results.

After the third month, the bottom was generally clean, but began to show more patches of a much harder soft growth—a red, coral-like substance—that required light scrubbing with a medium Scotchbrite pad. Scrubbing with the abrasive pad removes clouds of bottom paint, so it remains to be seen how long the paint will hold up if we try to keep it really clean.

In addition, areas that see very little water flow—the rudder pintles, for example—began to grow stringy, grass-like fouling, although it, too, removed quite easily.

After six months in the tropics, the areas of the bottom that have not been scrubbed began showing significant fouling, including scattered barnacles. After a month without moving from Mt. Hartman Bay, Grenada, all of the bottom, including the areas previously scrubbed clean, were covered with a soft fuzzy fouling. This comes off fairly easily with a stiff bristle brush, and the areas which have been previously scrubbed clean—the rudder, for example—are easily brushed to a clean surface.

Areas which have not been kept scrubbed, however, are not so easy to clean. In fact, it has reached the point that we have declared the experiment over. After eight months—six in the tropics, two in New England—we are to the point that the bottom needs a heavy scrubbing with medium or coarse Scotchbrite pads to remove the tenacious harder fouling under the softer surface fouling.

Based on the condition of the paint in the areas that we have kept reasonably well scrubbed—the waterline, the rudder, and the prop aperture—a significant portion of our antifouling paint has been removed. On the leading edge of the rudder—an area of great turbulence under either sail or power—we are down to the signal coat of contrasting color. The waterline, which received an additional coat of paint, still appears to have a fair amount of life left.

We have decided to give the bottom a very thorough scrubbing before heading to Trinidad, our next stop. Calypso will be hauled in Trinidad in early fall to repaint the bottom and clean and wax the topsides before heading west toward the Panama Canal

Just how bad are Caribbean waters for fouling? Very bad, indeed. Water temperature is around 85°F —about 30°C. A weekly scrubbing of the waterline above the antifouling is required to remove algae.

The speed impeller, coated with a thin antifoulant designed for transducers, needs to be picked clean of seed barnacles every week. We could remove the impeller when in port, but its location well below the waterline allows a fountain of saltwater into the boat every time we do. Going over the side to clean the impeller is simpler.

The unpainted bottom of the inflatable dinghy must also be scrubbed once a week to 10 days, or you end up with a terrible mess. Seed barnacles start to grow in a week, and by two weeks they are so tenacious that it is a major task to remove them. The grass that grows on the dinghy bottom is even harder to get off.

On two occasions we have really let the bottom of the dinghy go—three weeks without scrubbing. The result has been nightmarish. The only way to remove the long grass and other marine growth on the bottom is scrubbing with a stiff brush using full-strength chlorine bleach. Needless to say, this requires heavy rubber gloves and eye protection. It’s no wonder that the smart cruisers haul their dinghies out of the water every night.

The unpainted MaxProp requires a weekly polishing with a Scotchbrite pad, and both the big hull zinc and the Dynaplate grounding plate are scrubbed at the same time. The rough surface of the Dynaplate is particularly difficult to keep clean.

Maintaining the bottom of a boat in the tropics is no simple task. We are undoubtedly more concerned about keeping the bottom clean than most cruisers. The reduction in efficiency from a dirty bottom is significant under either sail or power.

Will we re-paint with ACP-50 when we haul? That remains to be seen. Ablative paints like ACP-50 work best on boats that are constantly underway. Cruising boats do a lot of starting and stopping—usually, a lot more stopping than starting. It may well be that a hard paint with a very high copper content, a paint that can be scrubbed frequently without removing much of the paint film, is a better choice for the typical cruising sailboat.

In any case, our original plan—to spend two years in the water until we do an extended haulout in New Zealand—is unrealistic, if we want to have any bottom paint left on the boat. The simple truth is that today’s bottom paints do not seem to be good enough for true multi-year service in tropical waters.

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