Bottom Paint: Types, Costs, and When to Redo It

Bottom paint (antifouling paint) stops barnacles, algae, and other marine growth from attaching to your hull. If your boat sits in the water, you need it. If your boat lives on a trailer or in dry stack, you probably don't. A bottom job on a 30-foot boat runs $1,500 to $3,000 at a boatyard, depending on the paint and the condition of the existing bottom.

Two main types

Ablative paint wears away slowly as the boat moves through the water, constantly exposing a fresh layer of antifouling. It works well on boats that move regularly. When it's time for a new coat, you can paint right over the old surface with light sanding. Most recreational boats use ablative paint. Popular brands include Interlux Micron and Pettit Hydrocoat.

Hard paint doesn't wear away. It releases biocide from a fixed surface. Hard paints are smoother and faster, which is why racing boats and high-performance hulls use them. The downside is buildup. After several coats, you need to strip the old paint back to bare gel coat, which adds $50 to $100 per foot to the job.

There are also copper-free paints for use on aluminum hulls (copper causes galvanic corrosion on aluminum) and in areas where copper-based paints are restricted, like parts of California and Washington state.

How often to repaint

In warm water (Florida, Gulf Coast, Southern California), most boats need a new coat every 12 to 18 months. Marine growth is aggressive in water above 70 degrees, and even good paint loses effectiveness after a season.

In cooler water (Northeast, Pacific Northwest, Great Lakes), you can go two to three years between coats. Growth slows below 60 degrees and nearly stops below 50.

Between paint jobs, regular bottom cleaning keeps growth in check. A diver with a scrub pad costs $100 to $200 per visit and should come every two to four weeks in warm water.

What a bottom job involves

The yard hauls the boat and pressure-washes the hull. A worker sands the existing paint to give the new coat something to grip. If the old paint is peeling, blistered, or built up too thick, it gets stripped. Then two coats of antifouling go on, with the waterline taped off. The whole process takes two to four days.

Most yards won't let you do your own bottom paint. Environmental regulations require proper containment, disposal, and sometimes licensing to handle antifouling paint. Some DIY-friendly yards do allow it, but they charge a fee for the use of their containment area.

Cost breakdown

Haul-out and blocking fees are extra, typically $4 to $12 per foot each way.

Do you need bottom paint

If your boat stays on a trailer or in dry stack and gets rinsed after every use, you don't need antifouling paint. Some owners apply a barrier coat (like Interlux Interprotect) to protect the gel coat from osmotic blisters, but that's different from antifouling. If the boat goes in the water for more than a few days at a time, paint it.