Hiring a Diver for In-Water Hull Cleaning: How Often, What It Does to Your Paint, and What to Ask

Record the paint brand, product, type (hard or ablative), color and the date it was applied in your BoatMend boat profile. Give a copy to your diver. Also note what type of zinc your boat uses: zinc, aluminum or magnesium alloy, and the shapes and sizes (see sacrificial-anodes).

Many marinas allow only insured, approved divers, or require a vendor permit. Ask the office before hiring anyone. A diver who works there regularly already knows the rules, the water and where shore power is.

Examples from California:

• San Diego Bay: the Port of San Diego requires a bay-wide in-water hull cleaning permit for any business doing in-water hull cleaning, and best management practices (BMPs) for anyone doing it. In Shelter Island Yacht Basin, where copper levels exceed water quality standards, the Port temporarily paused in-water cleaning of copper-painted boats from December 19, 2021 to February 9, 2022, working with the Regional Water Quality Control Board, and has been pushing boaters toward lower-copper or copper-free paints.
• All of California (the paint itself): since July 1, 2018, the California Department of Pesticide Regulation caps how fast copper antifouling paints labeled for recreational boats may leach copper. DPR's notice explains that it based the cap on boats cleaned no more than about once a month, using best management practices with soft carpet pads. Paint sold in California for recreational boats should already meet it; ask your yard if you bought paint elsewhere.
• Marina del Rey (Los Angeles County): a 2018 ordinance requires commercial and private hull cleaners to use BMPs, hold a Commercial Service ID and complete BMP training. Certified divers display a burgee from the county.

Los Angeles County says the BMPs for in-water cleaning were first developed in 1990 under the Sea Grant program by the California Professional Divers Association. In practice they mean using the gentlest method that works and avoiding the paint plume. If you're not in California, ask your marina and your state's environmental agency whether similar rules apply where you keep the boat. Rules change: confirm the current ones.

Ask:

• Are you insured, and approved or certified for this marina or harbor?
• What do you use on hard paint, and on ablative paint? (Soft cloths or soft pads on ablatives; the stiffer tools only on hard growth such as barnacles.)
• Do you clean the prop, shaft, rudder, trim tabs, through-hull screens and intake grates?
• Do you change zincs, and do you supply them or do I?
• Do you send a written report with photos after each visit?
• How do you make sure the engine and thruster are off and shore power is disconnected while you work?

There is no single right interval. Divers commonly work on a monthly or every-few-weeks rotation in warm saltwater during the growing season, and less often in winter or cold water. Base it on what the diver finds:

• Hard paint: clean as often as growth appears; light slime comes off easily.
• Ablative paint: clean as rarely as possible. Practical Sailor found the panel that was never cleaned kept fighting growth long after the scrubbed panels gave up. For cruisers, it suggests only occasional gentle wiping of fouled spots, with more cleaning near the end of the paint's life. A boat that runs often at speed sheds soft growth on its own.
• Running gear and zincs can be checked on every visit even when the hull itself is left alone.

Tell the diver what's on the bottom and ask them to use the softest method that removes the growth. Barnacles should be popped off one at a time, not scraped across a whole panel of soft paint. If the diver sees a cloud of paint coming off, they're removing too much paint. Hard tools belong on bare metal running gear and on hard growth, not on soft paint.

A good report includes:

• Date and how much growth (light slime, weed, barnacles) by area: waterline, hull sides, bottom, keel, rudder.
• Zincs: each one's location and how much is left (for example "about 50%"), and which ones were replaced. Most guidance is to replace anodes at about half their original size (see sacrificial-anodes).
• Prop: cleaned or not, any dings, bent blades, missing paint, fishing line or rope on the shaft (see fishing-line-prop-shaft).
• Shaft, strut, cutless bearing and rudder: any play, cracks or unusual wear seen.
• Through-hulls and intakes: screens clear or clogged.
• Paint condition: bare spots, peeling, blisters, paint wearing through at the leading edges.
• Photos of anything unusual.

Zincs that suddenly wear much faster than usual can point to an electrical problem on your boat or a neighbor's. Zincs that barely wear at all may not be connected well, or may be the wrong alloy for the water. Either way, look into it (see sacrificial-anodes and hull-potential-survey).

• Fouled raw-water intake: check the strainer and engine temperature next time out (see raw-water-strainer).
• Prop damage or vibration: plan a prop repair (see propeller).
• Paint wearing through: start planning the next haul-out and bottom job. Cleaning bare spots won't stop growth.
• Line on the shaft, play in the cutless bearing, loose through-hull: schedule a yard visit soon.

Run the boat on your next outing and compare speed and fuel use with your log. A clean bottom should bring back lost speed (see hull-speed-loss-diagnosis). Watch the engine temperature: a cleaned intake should run normal.

Over the paint's life, the diver's reports show how fast it's wearing. Use them to choose your next paint: if you get heavy growth and frequent cleanings, a harder or more scrubbable paint may suit you better; if the boat is in a copper-impaired harbor, ask about copper-free options. Discuss it with your yard before the next haul-out.

Save every report in BoatMend. A clean history of diver visits, zinc changes and paint condition helps when you haul out, sell the boat or file an insurance claim.