9 Marine Growth Species That Change How a Hull Gets Cleaned
By Tomas Iglesias, Yacht service diver, South Florida. Reviewed by Dana Whitcombe, technical reviewer.
Hull & Bottom Cleaning | Marine Salvage & Recovery April 2018. I was kneeling on the toerail of a 50-foot Viking at the Lauderdale Marine Center, waiting for the haul-out to finish. The water was 78 degrees and every juvenile fouler in the Intracoastal had taken the hint. The owner, Gary, leaned over the rail and said, 'It's just barnacles, right?' It wasn't. I was about to prove it to myself by making the exact mistake I warn every client against: firing up the pressure washer before I'd done a hand-over-hand inspection. That one move blew off the adult barnacle shells but left their bases and a whole zoo of other organisms grinning up at me. It cost me two extra hours of hand scraping and a touch-up on the gelcoat. Since 2009 I've been a commercial dive in South Florida yards, cleaning everything from 30-foot center consoles to 200-foot motoryachts. The list of things that attach to a hull is long, but nine of them show up so often that they determine how I approach every single job. They fall into three groups, and each group forces a different tool and a different sequence. Here's the entire pack, in the order I fight them.
The Cement Company: Barnacles, Tube Worms, Bryozoans
Acorn barnacles are the street-level creatures of any Florida bottom. They cement themselves on with a calcium-carbonate base that grows wider than the visible shell. The classic beginner move is to power-wash them off, but that just removes the shell and leaves a rough, gritty base that still slows the boat. My rule is to use a stiff putty knife and slide it under the rim, not scrape straight down. If the base doesn't pop, it's already fused into the gelcoat and you have to treat it carefully to avoid lifting the finish. Once they're off, I run a stainless bristle brush over the spot to sweep away any remaining dust. Tube worms—serpulid worms—are the next layer. They build a spiral white tube out of calcite, and it's brittle. The problem is that the tube leaves a raised ring on the hull after it breaks off. That ring acts like a tiny excavator blade against the water, and it will shred a coat of bottom paint over time. So when I see tube worms, I don't just scrape once; I scrape, then brush, then wipe with a diluted acetic acid solution to dissolve the last microlayer of the tube base. If I skip that step, the next growth in line will anchor onto those rings. Bryozoans are the sneaky one. They grow as a lacy mat that looks like a fossilized doily. Underneath that mat is a hard, flattened crust that's almost like a limpet scar. A pressure washer blows away the lacy part and leaves the crust looking untouched. That's why I always spray the area with a commercial hull cleaner and let it sit for five minutes before I even touch the surface. The crust softens and comes up in sheets, and the gelcoat is fine afterward.
The Jelly Factory: Slime, Tunicates, Hydroids
Slime is the first thing you'll feel when a boat has sat for more than a month. It's a living film of diatoms and bacteria, and it feels like a fine sandpaper. If you pressure wash it, you're actually pressing the grit against the gelcoat and grinding a haze into the wax layer. The only way to remove slime properly is with a soft loop pad on a pole, and you have to keep rinsing the pad because it clogs up fast. This is also the step people skip when they think a diver is just going to 'wash' a hull. Colonial tunicates are the worst thing to tear. They're gelatinous blobs with two siphons, and they attach in sheets. If you brush them, they break into dozens of fragments, and every fragment that floats away can settle and grow into a new colony. I've tried all the tools, and the honest answer is a towel or a fine-mesh sponge. You press it against the tunicate sheet and lift. It takes twice as long, but you don't seed the whole marina with the same problem. I also keep a net bag over my waste bucket to catch the pieces. Hydroids are the little stinging ferns. They have nematocyst cells that can irritate your skin, especially around your wrists and neck. The bigger issue is their holdfast: a root-like base that stays in the gelcoat even after the stems break off. If you use a stiff brush, you just break the stems and leave the roots, and they regrow in a week. The method I trust is a paint roller with a short nap. I roll it gently over the hydroid mat, which lifts the whole structure including the holdfast, then I wipe the area with a cloth. And I glove up past the elbow.
The Tangle and the Fuzz: Algae, Mussels, Gooseneck Barnacles
Filamentous algae is the long, hairlike green growth that wraps around shafts, rudder posts, and bow thruster tunnels. On the hull it hangs in tufts; on running gear it wraps like a mop. You can't just scrape it off because it's slippery and it separates into fine strands that clog your scraper. The efficient way is a wide rubber paddle used like a squeegee to slap the algae off in sheets. On the shaft, I use a nylon brush and rotate the shaft by hand to work it off. If you let this stuff go for months, it can actually block water flow to a packing gland and cause overheating. Mussels have been a Gulf and East Coast problem for a while, and now the charru mussel is here. They attach with byssal threads that are so strong, they could hold a soft-shell crab in a hurricane. The shells pop off easily, but the threads don't. If you leave a patch of threads, it will collect everything from silt to barnacle spat. I always carry a serrated scraper just for mussel threads, and I go over the area twice. The second pass is dedicated to finding the little reddish spots where a thread has broken off flush with the gelcoat. Gooseneck barnacles are a different kind of barnacle. They grow on a stalk, and they attach by a fleshy pad that grips like a suction cup on a rough surface. They love the transom, rudder, and water intakes after an offshore trip. You can't pop them off with a scraper because the pad is too soft to catch an edge. You have to slide a knife blade under the pad and lift. If you break the stalk, the pad remains, and it's the perfect foundation for tunicates and bryozoans. So I always carry a diver's knife with a blunt tip, and I cut each one free, then lightly sand the spot with wet/dry paper to remove the pad's residual shadow.
Frequently Asked Questions
How often should I get a hull cleaning in Fort Lauderdale? For a boat that stays in the water, I recommend every four to six weeks in warm months and every eight in winter. If you run your hand along the waterline and feel a rough film, don't wait—that's slime, and it's already dragging. Can I use a pressure washer on my own bottom? You can, but it's almost never the best tool. It's fine for knocking off grass after a haul-out, but it will peel away barnacle shells and leave the bases, and the high-pressure spray can damage gelcoat and wax. I tell owners: pressure wash to cleanup, not to clean. Why does leftover growth matter if the boat comes out again in a month? Because each piece of leftover growth is a texture anchor for the next species. A tube worm ring or a gooseneck barnacle pad gives tunicates and mussels a rough spot to glue onto. If you miss a small patch, that patch becomes the origin of the next growth cycle.