If you boat in salt water, your boat’s bottom needs to be protected. If it’s not, everything from green slime to grass to barnacles could grow on it. Getting that stuff, especially barnacles and similar organisms, off is a chore once they take hold.
For decades, the shield against marine growth on a boat bottom has been bottom paint and the key ingredient has been copper. Unfortunately, copper that leaches off the bottom of a boat isn’t environmentally friendly, so alternatives have been developed.
So, should you contact a boat yard or other service facility to protect your boat — or tackle the work yourself? What you’ll quickly find is that the job is much more than simply buying a couple gallons of paint and a brush or roller.
“If you’re going to do it in your driveway, get familiar with the product,” said Ben Stewart, general manager at South Coast Shipyard in Newport Beach, CA. “It’s not a couple hundred-dollar deal to paint it in your driveway. There are drying times, over-coat times, and you need to be sure you don’t put wet paint back on your trailer and the hull drives to the bunks or rollers.” There are also local, state and federal regulations for properly disposing of the bottom paint that comes off when you clean the hull bottom with a pressure washer or similar process.
Step by Step
Most bottom-paint customers bring their boats to South Coast Shipyard by water. The first step in the process is yard personnel hauling the boat. Then the bottom is pressure-washed and hand-prepped with a mild abrasive like a 3M Scotch-Brite pad.
“It’s mostly a visual inspection of the condition of the boat,” said Stewart. “We want to note the condition of the paint and the type of paint that was previously used.”
He explained that there are different types of bottom paint for different types of boats. The decision focuses primarily on how often the boat is used. Stewart said that 99% of the boats that have their bottoms painted at South Coast are finished in Ultra-Kote from Interlux Paints, a hard, epoxy-based paint. Others are done with Sea Hawk products including Cukote, which is a softer ablative paint.
One thing that makes it easier for South Coast to remove bottom paint while abiding by all the clean-capture regulations is that the facility has a pit that holds 44,000 gallons of contaminated water. “All the water is contained in the pit,” said Stewart. “We pump it out and have settlement tanks and filters.”
When he talks to a private owner who’s thinking of painting their boat bottom, very often they’re not aware of the containment requirements. “People generally have no idea about the backside of compliance just with washing off your boat,” said Stewart. “Each municipality has rules for disposing of the product. The water and power district would not be happy about that water getting put into a sewer or commercial drain.”
Long Beach Marina posts environmental policies for self-employed workers and independent contractors who must register with and receive approval from the state marine bureau.
For paint and varnishing, spray application is not allowed on the property. For surface preparation, a vacuum cleaner must be connected to an electric sander and tarps must be used to collect scraping, debris and drips. Tarps must be stretched between the side of the boat and dock when working over the water. Vacuum dust and debris must be removed every time a tarp is moved or every hour.
To paint the bottom of the boat, environmentally friendly coatings should be used and proper application procedures need to be adhered to. Hulls can’t be cleaned for 90 days after paint application and the least abrasive cleaning pads should be used.
The reason why bottom paint needs to be re-applied is that it’s designed to be a sacrificial product. Its chemical makeup is such that it slowly leeches off a bottom to prevent growth from attaching.
“The way that bottom paint works is those chemicals that keep marine growth from adhering to the bottom are specifically designed to match leech rates so you don’t have too much sluffing off,” explained Stewart.
Ablative paint is designed to leech off a small amount of cuprous oxide that prevents growth from attaching to a boat’s bottom. This type of finish is better used on boats that go out frequently, like those used by a commercial or serious recreational fisherman.
Hard epoxy doesn’t leech as much, and because it has a more rigid structure, it prevents growth. When a boat isn’t used often, even if it has bottom paint, an owner is likely going to have to hire a diver to scrape the hull to keep it clean.
A paint is chosen based on many factors including the material from which the hull is made (also called the substrate), the frequency of the boat’s use and even the level of stray electrical current in the water if the boat is kept in a marina.
All things being equal, a bottom paint is expected to last about two years, but Stewart quickly pointed out, “It’s not unheard of for paint to last four years or for paint to last 14 months.”
After a boat comes into South Coast and it’s pressure washed, yard personnel inspect the bottom. “If the paint wears through to the primer, those areas need a new coat of primer,” said Stewart. “If it wears to the gelcoat, it gets two coats of primer.”
For re-coating, the standard is two full coats of paint for the entire bottom and a third coat from 12 to 19 inches from the waterline down. On a sailboat, the leading edges of the keel and rudder get an extra coat as well.
When a new boat gets its first coat of paint, the substrate is the most important factor when determining the type of product. With a new aluminum hull, for example, metals in the surface will react to the chemicals in the paint. Typically, a new aluminum hull will get two full coats of epoxy barrier primer.
“Especially for a first-time bottom paint, it’s important that the coats or primer are applied at the right mix ratio and allowed to dry between coats,” said Stewart. If applied properly, an ablative paint will require less attention from a diver if the owner runs the boat frequently because the growth will come off during operation.
Also, with ablative paints, it’s rare that the bottom would need to be stripped and re-coated, but these products don’t last as long as the hard epoxy and typically, they’re a little more expensive.
For a privately owned boat that doesn’t plane off and run at speeds above 20 or 25 mph, the modified hard epoxy paint is used. It doesn’t sluff off and, after, about 10 years, coating gets quite thick. When this happens, the only fix is to strip the old coating all the way down to the bare hull and start over.
To give boaters an idea of what they can expect to spend to have their bottom paint redone, for haul-out, bottom wash, prep, paint and launch, the price is about $100 per foot. For a new boat, a first-time application would be about $175 per foot.
For DIYers still considering tackling the job, Interlux Ultra-Kote is priced at $249.99 for a gallon on the West Marine website. Sea Hawk Cukote ranges from $312.99 to $324.99 for the same quantity. A gallon of Ultra-Kote covers 506 square feet, while a gallon of Cukote should be good for two coats on a 24-foot runabout.
