The Order Experienced Divers Clean a Hull In, and Why

By Tomas Iglesias, Yacht service diver, South Florida. Reviewed by Dana Whitcombe, technical reviewer.

Hull & Bottom Cleaning | Marine Salvage & Recovery August in Fort Lauderdale: 9 a.m., 90 degrees already. I'm in the water on a 110-foot Hatteras, holding a 4-inch stiff brush and spitting out the taste of diesel and salt. The owner is standing on the swim platform in boat shoes, watching me. He asks why I'm starting at the waterline instead of jumping straight to the props. I knew the answer because I'd learned it the expensive way — after a year of scrubbing boats in order that worked, but wrong. There is a sequence to cleaning a hull. It isn't about what's easiest. It's about what the water does to what you're working on. After fifteen years of scraping barnacles off running gear and polishing gelcoat in every slip from Bahia Mar to Las Olas, I can tell you the order matters more than the brush you use.

Read the hull before you touch it

Drift down from the waterline to the keel, running a gloved hand over the surface. Look for blisters, gelcoat crazing, loose anodes, damaged shaft seals. Feel for soft spots. If you start scrubbing, you'll smear fouling over a crack and miss something that turns a $500 clean into a $20,000 repair. You also need to know the condition of your antifouling paint before you put a brush to it. Half the boats I work on have paint that's already failing. The other half have anodes that are ready to fall off. Both show up better before the water gets dirty.

Start at the waterline, work down

Clean the upper zones first, then drop. Your brush kicks up silt and creatures. If you start low, you're working blind in your own cloud. Starting high keeps the water clear as you descend. Plus, the waterline is where growth is worst — sun, splash zone, oxygen. So you give it the most time while your arms are still fresh. I see guys go straight for the bottom and then wave a brush around in brown soup. They're guessing where the barnacles are. I don't guess.

Props, shafts, and anodes always last

The running gear is after the hull is clean. These are metal exposed to electrolysis and they're what moves the boat. You want the water clear when you're working on them, because you're feeling for pitting, hairline cracks, and worn anodes. If you knock something loose, you want to see it fall, not lose it in filthy water. Also, once the hull is clean, you can see the actual waterline and set your dive depth. A prop last means you're not standing on sand while you're scraping a wheel. You're floating free.

Brush with the grain, not in circles

Scrubbing direction matters. You're trying to remove growth, not paint. Antifouling paint is sacrificial. Circular scrubbing acts like sandpaper and thins it. One-direction passes with the water flow lift off the slime without grinding the copper out of the paint. The difference shows in a season. A boat I clean twice a year keeps its paint for five years. A boat that gets circled to death needs a haul-out and a new bottom after two. That's a five-figure job nobody wants to pay for.

Finish with your hands, not the brush

After brushing, run a gloved palm over every square foot. Your fingers feel a barnacle base that a brush missed. You also check you haven't bare-spotted the paint. A smooth hull is the real product. A soft glove tells you if it's done. I catch something on almost every job — a stray goose barnacle hiding in a keel joint, a spot where the paint wore through to glass. The brush gets the bulk. The hand gets the truth.

Frequently Asked Questions

Why not clean the props first to get them done? Because you'll kick up silt and sand that can scratch the running gear, and you'll be feeling for damage in murky water. Clean hull first, then props in clear water. How often should a boat get this done? Depends on water temp and salinity. In South Florida, every 60-90 days will keep the growth manageable. Some boats in brackish water need it monthly. You'll know by running a hand down the side. Does scrubbing hurt the bottom paint? It can if done wrong. Circular scrubbing and hard bristles will wear the paint. That's why direction and pressure matter. A light pass with a stiff brush removes fouling, not copper.