Why do barnacles grow on sailboats?

Boat hull cleaning water pressure washer barnacles antifouling and seaweed

I’m just coming back from playing on the lake with my family and friends.   I saw grime and sludge on many of the boats sitting at the dock. This made me curious.

Why do barnacles grow on sailboats? Barnacles are a marine growth just like shellfish that grow on sailboats by secreting a glue-like substance that attaches them to the hull. This glue-like substance can have a tensile strength of up to 5000 pounds per square inch.  As you can imagine, getting these off your boat takes a lot of work.

Understanding these small creatures will save you time and thousands of dollars in damage. Here is what you need to know.

Barnacle Growth on Sailboats

Barnacles are little crustaceans related to animals such as crabs lobsters and shrimps. Over 1,200 species live on earth. The most common barnacle boat owners face is the acorn.

The acorn barnacle can live five to ten years and grow to half an inch.  Their biggest predators include sea worms, marine snails, and a few species of birds.

Barnacles like active intertidal zones. They live on rocks, pilings, boats, and buoys.

Even moving objects such as whales and turtles find these little critters attached to their underside.

Barnacles feed by filtering water and consuming microscopic organisms. Barnacles are hermaphrodites, meaning they have both male and female sex organs. Baby barnacles come from adults fertilizing a neighbor with a retractable tube containing sperm which can reach outside its shell 6 to 8 inches to a nearby neighbor.  They may reproduce up to six times a year.

Most barnacles live in shallow waters in the ocean of 300 ft (100 meters) or less. However, some species may live at depths of 2000 feet or 600 meters.

Baby barnacles may float in the ocean until they find something to attach.

Are there various kinds of barnacles that grow on boats?

There are a few kinds of barnacles. A common shelled version and naked barnacles. Naked Barnacles live as parasites on or in other invertebrate animals. Another barnacle that has no shell lives inside holes drilled into corals or shells.

The barnacles that sailors must contend with form in calcium deposits underneath the paint making them difficult to scrape off the boat.  They grow a shell that acts as a leg-like attachment.

Do barnacles hurt my sailboat?

Barnacles slow a boat by increasing drag as the boat moves through the water. If you are under a time constraint for your passage keeping a clean hull by getting rid of the barnacles should be a high priority.  Some estimates show barnacles can cut your speed by 40%.

Barnacles also create issues for boat owners by growing in the inlets of the boat. As barnacles grow, they made block the inlets cooling the engine or shower and commode. If your engine uses seawater for cooling and they block your inlet, the engine can overheat and lock up. This may cause you to replace your engine at a cost of thousands of dollars.

Sailboat owners should also monitor water outlets that exit at or below the waterline. Barnacles grow here as well too. If these holes become blocked discharged water from the boat and back up into the cabin or cockpit causing damage.

Beyond the inlets and outlets, barnacles can penetrate the gel coat of your boat. The penetration comes from the hard shells. This increases the application frequency of antifouling to the bottom of the hull of the boat.

Another challenge barnacles create is throwing the prop off balance. They grow on a prop making it unbalanced. This imbalance may create a vibration coming through the driveline. If ran too long with the vibration, you may end up replacing bearings or bushings in your driveline.

What can I do about barnacles on my sailboat?

While you try eliminating barnacle growth, making the work easier to get them off the hull should be the goal for a sailboat owner. Dealing with these crustaceans happens in different stages.

If you are out at an anchorage and see growth on the underside of your boat, scrape the hull while stopped. In this situation since the boat is in the water, you need to keep proper swim gear, brushes, and scrapers to make the job fast. When the boat owner is inexperienced with sailing or scraping the hull, he should consult a professional scraper or have the boat removed at a convenient time to remove the barnacles.

For those boat owners who have experience sailing and comfortable swimming under the water, frequent scrapes or brushings can help keep the barnacles to a minimum.

While at your home port and removing the boat for the sailing season or other maintenance activities, it is common practice to have the hull sprayed and scraped once removed from the water.  The pressure washer removes most of the barnacles, but the hard shells as noted earlier may have remnants attached to the hull.

In either case, the owner must be careful about gouging into the antifouling and Gelcoat from the scraping activity. This is one reason having a good brush to remove the barnacles is important besides having a reasonable scraper.

After removing your boat from the water and scraping the bottom, it is not uncommon for the hull to have a new antifouling. The antifouling will not prevent barnacle growth, it slows down the growth. They have found copper is a deterrent for barnacle growth.  Do not be surprised if you come across a copper-based paint or copper bottom boat.

AUCKLAND, NEW ZEALAND – May 19, 2021: Yacht on dry dock stand being repaired with antifoul. Auckland, New Zealand – May 13, 2021

Boat owners have a trade-off to make as it applies to antifouling treatment to deal with the barnacle growth. It may cost more up-front to buy a higher-grade antifouling treatment, but it may save you time and scraping fees.

When applying antifouling to the boat hull, much sanding will take place. The hull will have the gel coat showing. Then it is made smooth to reduce drag through the water. Then 2 or 3 coats of primer will be applied to the hull followed by the coats of antifouling paint.

Is there an environmentally friendly way to address barnacles on my sailboat?

It concerns the environmentally friendly about the effects of copper bottoms or copper-based paints on our oceans. A new paint with the ivermectin molecule has produced great results and slowed the growth of barnacles. Someone may do this with a low concentration of the molecule at .1%. The effect will last a long while and replace the copper used in current paints. Studies show that much lower substance leech takes place into the water of this new molecule versus copper.