This article was originally published in February 2001 on SailNet.
It doesn't take a rocket scientist to understand that minimizing the friction between the boat's hull and the water surrounding it will promote better performance. So how do you achieve this? In our case, we were starting with a hull that was just a year old and had been kept in good shape with monthly cleanings by a diver. Hence we really didn't have that big of a job to get the bottom race-ready, but because we wanted to make sure that it was flawless, we were at it for a full two days. We arranged to have the boat hauled out the week before the event. Once the boat was out of the water and secured in the boat yard, we pressure-washed the hull to get any saltwater residue off. After that, the heavy work began.
We started the process by wet-sanding the bottom of the boat initially with 220-grit paper to knock off any remaining scum. Then went back over the entire hull from the waterline down with 600. We used three-inch sanding blocks and made certain that our sanding motion went only fore and aft. Some bottom-prep specialists would shun this method in favor of longer sanding boards, but we were working with a fair surface that didn't require that much sanding, so the blocks worked fine.
Then we took 800-grit paper to the foils—the rudder and the keel—and the forward third of the hull. The reasoning behind that comes from the theory that one third of the way aft on any part of the vessel is where turbulence begins, and the flow aft of that is less critical. Bob opted not to paint the bottom as it would be cleaned regularly by a diver, so after that we were essentially done. (It's not uncommon for owners of serious racing sailboats to eschew bottom paint and use innovative approaches like spraying McLube on the hull for a season of sailing.)
The proof of our success with the bottom of the boat wasn't just in how smooth it felt to the touch when we'd finished—and it did feel like the proverbial baby's bottom—but also in the fact that we went out and won all five races in that regatta. Some of those contests were sailed in 20-plus knots and others in five-knot zephyrs, but despite the conditions, the constant aboard Tern was good boat speed. I give the lion's share of credit for Tern's speed through the water to that superior bottom job. And even if the bottom wasn't actually as fast as we thought it was, just the fact that we weren't worried about that aspect of our preparation gave us additional confidence for getting around the racecourse. You should try it; you'll see.
Of course not every crew has it this easy. Most boat bottoms are encrusted with years worth of bottom paint residue and getting down to the gelcoat (or other original surface) takes time and energy. If you don't have the time or resources to do it all in one haulout, don't worry. If you find yourself in this position, just try to make at least a 50-percent improvement this time, and you'll be ahead of the game the next time you pull your boat out. Follow that practice and eventually your boat will have a bottom that's close to perfect, and you'll enjoy a lot better performance on the water.
Smoother is Faster
Not every boat can have a perfect bottom; that takes a significant investment in time, energy, and dollars. But almost every boat can have a better bottom, and whether you race or cruise, a better bottom essentially means free speed.
Dan Steadley, a Charleston, SC-based boat care specialist and the owner of Big Dog Marine, was the principal architect of Tern's bottom job. He recommends starting with an assessment of the work needed and then clearing the calendar for the bigger jobs because of the time they inevitably require. He says the best way to get a smooth finish on the bottom of your boat is to spend the proper time filling and fairing first, and then move to the sanding.
"We once brought a 12-year-old Beneteau First 8 back from the graveyard with a new bottom job. Basically we used orbital sanders to take all the paint off and take the bottom down to gelcoat. Then we gridded the bottom with four-inch squares using a wooden yardstick. After that we used a straight-line sander that's 12 inches wide and worked from the waterline down to the keel; we kept this up until we sanded off the surface layer and we found the low spots. Then we abraded those spots with 80-grit paper and filled them with a marine-surfacing compound made by 3M.
"After that," continues Steadley, "we repeated the process of sanding and filling according to the grid and did that six times. Once we had the hull faired, we sanded the surface with 220-grit paper and then we applied InterProtect 2000 as a barrier coat. Then we sanded that surface down to 400-grit paper and applied 545 primer to the whole boat. We first applied a tack coat and then two finish coats, sanding in between. Because the owner planned to dry-sail the boat, we didn't need to apply bottom paint, so we finished the area below the waterline by sanding it down to an 800-grit finish."
If you plan to leave your boat in the water, Steadly recommends spraying the bottom with an antifouling paint manufactured for performance like VC Offshore (particularly for colored finishes) or EP 2000 for white finishes. After spraying, he says, sand with 600 or 800 wet-dry paper and then burnish the entire area. Steadly says that he relies on information from the specialists at Taylor Ship Design in Annapolis, who tell him that working beyond 800-grit paper is probably superfluous for even the most serious racing team. If you're skippering a nuclear submarine, says Steadley, well, that's a different issue.
Paint the Bottom Yourself by Tom Wood
Barrier Coats for Blisters by Don Casey
Bottom Paint Compatibility by Dan DickisonSailNet Store Section: Sandpaper and Abrasives