Soft Growth vs Hard Growth: Why One Cleaning Costs Triple

By Tomas Iglesias, Yacht service diver, South Florida. Reviewed by Amanda McCallister, editor.

Hull & Bottom Cleaning | Marine Salvage & Recovery Sliding down the side of a 50-foot Tiara last Tuesday, I ran my palm over the bottom paint. It felt like 80-grit sandpaper. That's soft growth. A fuzz of algae and biofilm that'll turn into barnacles if you give it a few more weeks. I've seen it a thousand times. And I've seen what happens when people ignore it. Here's the thing about boat bottoms in Fort Lauderdale. We've got warm, nutrient-loaded water. Soft growth builds in days. Hard growth can follow in weeks. The difference in cost? Call it three times. I know that seems like a lot. It's not a mark-up. It's just work. I'm not talking about a haul-out. I'm talking about a diver in the water, doing a proper hull scrub. This is the part of the job that separates the bottom-cleaning business from the toothbrush-and-Flitz crowd. Let me walk you through it.

Soft growth — what it really is

Soft growth is the community of microscopic organisms that settle on any submerged surface. You're looking at diatoms, slime-forming bacteria, and juvenile algae. To the touch, it's slick and gooey at first, then it gets fuzzy after a few days. In warm water, that fuzz can be a quarter-inch long in two weeks. The reason it's cheap to clean is that it hasn't bonded to the paint. The organisms are just living on the surface, not burrowing in. A nylon brush or a 3M Scotch-Brite pad on the end of a pole is enough to wipe it off. Ten minutes on a 40-footer, give or take. I've done it in five when the water's flat. The cost model for this work is simple: per foot. I charge $5 per foot for a routine slime clean. That's $200 for a 40-foot boat. It comes out to about $4 to $6 per foot at most yards. The diver surfaces with green wash-down and a clean boat.

Hard growth — the barnacle brigade

Hard growth is a different animal. Barnacles, mussels, tube worms. They set up house with calcium carbonate plates. They dig into the paint, or at least cement themselves onto it. When you try to scrape them off, you're not pulling off a sticky film. You're prying a miniature fortress off a fresh epoxy finish. I once scraped a 34-foot cruiser that had sat in a canal for eight months. The bottom looked like a rock wall. The owner said it was just a little fuzzy. I dropped over the side and my scraper hit a barnacle cluster that sounded like a gravel driveway. I had to go through three sharpened putty knives that day. That's why hard growth costs more. It's not just the scraping. It's the amount of paint damage that happens in the process. Barnacles leave behind a calcium footprint that etches into gelcoat and bottom paint. To get the surface fully smooth, you'd need to grind it down and reapply barrier coat. Most of the time, you just chip them off, roughen the surface, and tell the owner to get a better paint job.

Why it triples: labor, tools, and aftermath

Let's talk numbers. Soft growth on a 40-footer: an hour in the water, if I'm being picky. Hard growth on the same boat: three to four hours. That alone triples the labor. But then you've got the tool costs. A soft scrubber is a $10 sponge. For hard growth, I'm carrying a stainless steel scraper, a putty knife, sometimes a chisel and a hammer. I've had to replace scrapers mid-job. Then there's the cleanup. The scraped barnacles sink like little rocks. I've got to catch them in a catch bag, otherwise they'll reattach in a week. That's more time. And there's the actual physical toll. My neck and back are done after a hard-growth job. Soft growth is easy, rhythmical. Hard growth is like doing a hundred push-ups underwater. So you bet the price is triple. The typical rate for hard growth removal runs $12 to $18 per foot. On a 40-footer, that's $480 to $720. That's before we talk about the bottom paint repair. I've seen a full barnacle scrape and spot repaint hit $1,200. For a boat that would've cost $200 for a monthly scrub.

What affects the price besides growth type

Water temperature is a big factor. In July, a slime clean might turn into a barnacle job if you've been away for three weeks. In January, you might get away with six weeks. The location matters too. A boat on the New River – we call it a nursery for growth – will foul faster than one tied to a floating dock in the Atlantic. Another thing: bottom paint age and type. A fresh coat of hard ablative like Petit Trinidad SR gives you a smooth, burnished surface that resists barnacles. But once the ablative wears out, the exposed gelcoat is a welcome mat. A soft paint like Micron CSC is great for sloughing off growth, but it's fragile. If you let it get hard growth, you're in for a mess. One more thing that nobody tells you: the boat's use pattern. A boat that runs every week keeps the film from building. A boat that sits still is a reef. I've told dozens of owners, 'Start your engine, turn the wheel, but also get the bottom cleaned.' Actually, there's one captain I remember who insisted his bottom was fine because he had a 'self-cleaning' propeller. That was a 20-inch prop with barnacles the size of walnuts. I spent two hours on it. He called the office to complain about the bill. I've got his picture somewhere.

How to stop it before it starts

The best way to avoid the triple cost is to stay ahead. In South Florida, a monthly hull scrub is standard. Some high-end yards recommend bi-weekly in the summer. I've got clients who set a calendar reminder every 21 days. They never pay more than the base rate. If you're on a lift or have a dive buddy, you can scrub the slime off with a deck brush and a mask. It's not glamorous, but it takes an hour and costs nothing but sunscreen. The key is to not let it turn hard. And if you're buying a boat that's been sitting in a slip for six months, get a bottom assessment before you sign. A diver'll tell you quick if it's just fuzz or a barnacle reef. That'll inform your offer. Bottom line: soft growth is an inconvenience. Hard growth is a second mortgage. Ask around in Fort Lauderdale, and you'll find guys like me who'll price it honestly. Call it a cheap lesson: don't let the barnacles win.

Frequently Asked Questions

Can I just pressure-wash off barnacles on a lift? You can. But sooner or later you'll blast a hole through the gelcoat. Pressure washers at 3,000 psi are fine for soft growth. For barnacles, use a plastic scraper and some Barnacle Buster, or call a pro. How often should I have a diver clean my bottom in Florida? Every three to four weeks, year-round. In July and August, maybe every two weeks if the boat sits in a canal. The slime becomes hard growth in about three weeks. Is bottom paint supposed to prevent growth? It limits growth, but it doesn't eliminate it. Hard paints like Petit Trinidad resist barnacles longer but need a good surface. Soft paints like Micron CSC release product slowly. Both need regular cleaning if you want to avoid the triple cost. Do I need to haul out to remove hard growth? Not always. A diver can do it underwater if the barnacles are small and the paint is sound. But if you've got a thick layer that's already lifted the paint, you're better off hauling it, sanding, and recoating.