Spring Commissioning: The Underwater Checklist
By Tomas Iglesias, Yacht service diver, South Florida. Reviewed by Amanda McCallister, editor.
Hull & Bottom Cleaning | Propeller Removal & Repair Last March, I pulled into a slip on New River and found a 42-foot Hatteras with a prop fouled so thick it looked like a brick of barnacles. The owner had just bought it and asked for a 'quick look' before sea trial. I spent 45 minutes chipping that crust off, and he stood on the dock the whole time shaking his head. Spring commissioning in Fort Lauderdale is a rush. Boats come down from the Northeast, or they've sat in a shed all winter, and everyone's in a hurry to get in the water. But the underwater side is where the cheap fixes turn into big ones. A torn prop blade, a seized sea cock, a zinc that's gone completely — these are ten-minute inspections if you're systematic. I've done this dive work for 15 years, from Port Everglades all the way down to Government Cut. Here's the checklist I run through on every spring dive, and it's not the whole list — it's the part that saves you from the expensive surprises.
Running Gear: Props, Shafts, Cutless Bearings
Props get the most attention, and for good reason. A 1/4-inch nick on a blade edge will shake the whole boat at cruising speed. I've seen an owner blame a seawater lift for a vibration that was just a plastic line wrapped around the shaft. So first, unwrap the line. Then run a gloved hand over each blade. You'll feel a ding before you see it. On a four-blade 30-inch prop, that's ten minutes. The shaft tells its own story. Brown or black staining near the cutless bearing means sand has worked into it. Grab the shaft right next to the bearing and try to move it up and down. If you feel more than a hair of movement, that bearing is done. Cutless bearings are cheap — a Duramax or Johnson bearing for a 1.5-inch shaft runs $50 to $150. That's a lot better than a bent shaft or a ruined transmission. Then check the prop nut and cotter pin. I've found loose prop nuts time and again — that's a prop trying to walk off in reverse. Marine-grade thread locker is your friend here, and a new cotter pin is twenty cents. Also look for dimple signs on the prop hub, which means the prop has spun on the shaft.
Through-Hulls, Sea Cocks, and Strainers
Every through-hull is a potential sinkhole. I check strainer baskets first. On a 40-footer, you'll typically see five or six openings: engine intake, generator, A/C, heads. That's a lot of ways for water to get in if one hose clamp lets go. I've worked on boats where the A/C strainer was so packed with growth it barely flowed. That kills an air conditioner fast. Sea cocks need to turn — period. A seized ball valve is not acceptable. I open and close each one underwater, and if it's stiff, I note it for the owner. Also check the hoses that connect to them. A 45-foot motoryacht can sink at the dock in less than an hour from a burst head discharge hose, I've seen it. The hull is the strong part; the fittings are where boats die. One digression: a good diver learns his boats like a mailman learns a route. I have a 70-footer at a marina on the Intracoastal where I've replaced the same shaft zinc twice a year for five years. The owner finally let the yard rewire the bonding system after they found the old prop in a basket. That's how it goes.
Zincs and Stray Current
Zincs are your sacrificial metal, but only if they're the right alloy. In saltwater you want zinc or aluminum, not magnesium. I've seen magnesium anodes on boats in brackish water turn to cottage cheese in a month. And I've seen bronze props so pitted they looked like chicken skin because the owner never checked the anodes. Spring is when stray current shows up the worst. Marinas with old wiring can leak DC or AC into the water. That'll eat an anode in weeks, and it can take the shaft and rudder with it. The classic sign is a zinc that's wasting fast next to a prop that looks brand new. A Performance Metals zinc shouldn't disappear in a season. I use a silver-silver chloride reference cell to read hull potential, but if the numbers are wrong, you need a marine electrician, not a diver. And don't assume more zinc is better. Too many anodes can overprotect and cause paint to blister. It depends on the boat's bonding system. I'll tell you what I tell every owner: measure, don't guess. A zinc that's lost 50% by spring has done its job. One that's almost gone means you've got a problem.
Hull Clean and Antifouling Touch-Up
Marine growth in Florida is relentless. In three months, heavy fouling can cost you a knot or two depending on the plant. That's noticeable at the helm. Acorn barnacles are the main offender, but you'll also get slime and little oysters on the rudder. I scrape with plastic scrapers to avoid cutting bottom paint, and I hit running gear a little harder. Some divers use a razor on props, but that can strip the antifouling coating. Then I look at the bottom paint. Bare spots get marked with a grease pencil so the yard can touch them up while the boat is still in slings. That's the time to fix it. If the antifouling is uniformly thin, you're better off doing a proper haul-out and a fresh coat of something like Sea Hawk or Pettit. A diver can only clean what's there — I'm not going to pretend a quick scrub makes old paint new. And remember, in Florida, in-water hull cleaning is regulated. You can't scrape antifouling paint into the marina. I use a fine-mesh bag and a shop-vac, and I rinse the scrapings into a filter. That's the law, and it's not hard to do right.
Frequently Asked Questions
When should I schedule a spring underwater check? If your boat's been sitting more than three months, get it done before you really run it. In Florida, growth doesn't wait. For a boat that wintered in northern water, as soon as it's splashed here is plenty. Can I do this myself with a snorkel and mask? You can, but safety and visibility matter. In a marina with zero-current, a mask works. But if you're not comfortable changing a zinc underwater or dealing with a stuck sea cock, raise the flag for a dive service. It's not worth a panic. What's the biggest thing people miss? The bondings. I've seen props fall off because the zinc was fine but the bonding wire was disconnected. A good diver checks electrical continuity, not just the anode. How much does a spring dive check cost? Pricing varies by length and location, and it's usually based on a per-foot rate or hourly. Call it somewhere between the cost of a haul-out and a sea trial — most owners find it cheaper to prevent than to rebuild.