If you leave your boat in the water for a season, or always, you will need to clean the bottom periodically.  Algae, barnacles and other slimy growth slows down your vessel and increases the fuel needed to move her.  While there is no “one” answer for bottom cleaning, there are a few general principles that can be applied.

bots on the hardCredit: geographic.org

How often

The short answer to this is – it depends.  Many different factors affect how fast gunk is growing on the bottom of your boat, and you’ll need to consider all of them before deciding to clean or not.

  • Movement.  If you use your boat often, vs leave it stationary in the marina, growth occurs more slowly.  The growth is kind of washed away as the boat moves through the water.
  • Temperature.  Generally growth occurs more quickly in warmer water, more slowly in colder water.
  • Salt.  Boats kept in the ocean vs a freshwater lake or river tend to have more vegetation growing on the bottom of the vessel.
  • Pollution.  Runoff from fertilizer or sewage plants (ewww) create a water environment that is more conducive to vegetation, and boats that spend a lot of time tin these types of areas will grow a beard more quickly than a boat in a cleaner area.
  • Paint.  Specifically the age of your paint.  Antifouling paint that is used on the bottom of boats has a lifespan.  Over time the biocides used in the paint leach out in to the water and the paint loses it’s effectiveness.  Older paints need to be cleaned more often.
  • Visual.  If you see stuff growing, it’s time to clean regardless of all the other factors.

What you use

A very good practice is to clean frequently with the softest material possible.  By doing this you maintain your protective paint as long as possible.  A simple solution is to nail a piece of carpeting to a board, or even attach it to a flat mop head. Use this as a gentle wiping pad to remove the buildup on the bottom of your boat.  If you need to scrub, you’ve waited too long.  Be aware that if you have ablative paint on your boat, scrubbing the algae away is also scrubbing the paint away.  A boat with hard paint, or that’s going to be repainted anyway can be cleaned with a pressure washer (carefully!) or scrubbed.  If the paint comes off while cleaning, it’s past time to repaint.

How do you do it

Diver cleaning propCredit: Flickr, Official US Navy Imagery

You need to be next to the boat, which means you have three options.

  • First option.  Tie up to a dock and use a pad attached to a long, bent pole.  You can get most of the growth off this way (if it isn’t badly overgrown) by putting the pole in the water and gently moving it up and down along the sides of the boat, underwater.  This requires a fair amount of strength and you won’t be able to see if you’ve gotten all the areas clean, but it’s not a bad choice for a boat that’s just a bit slimy.  Wash the side of the boat near the dock, then untie, turn the vessel around, and tie up with the second side towards the dock.  Depending on how wide your vessel is, the stern and bow may be difficult to get to.  You can try some tricky maneuvers such as tying the stern loosely and pulling the bow closer to be able to reach nearer to the end.
  • Second option. Dive, or snorkel.  Ideally you are tied up to a dock, but you might be able to stabilize the boat enough by anchoring at both bow and stern.  Use a handheld pad to wipe down the sides of your vessel and get all the slime off.  As long as you’re in the water, check your props and zincs.  Clean or replace as necessary.
  • Third option.  Take the boat out of the water.  If you can put your boat on a trailer and pull it out of the water, do that.  Otherwise you’ll need a boat yard with an appropriate crane to haul your boat out of the water, or some nerve to beach your boat during low tide to give you access to the bottom.  Wipe down the bottom while wet and use a hose to get rid of some of the gunk you’re wiping off.  If you decide to use a pressure washer, be very careful about damaging the paint on the bottom of your vessel.  Really, your best choice is elbow grease and gentle water flow from a hose or a bucket.  Again, inspect the bottom and clean/replace whatever needs it.

Anti-fouling paint: hard vs ablative

The bottom of your boat is painted with one of two types of paint, either ablative or hard.  Ablative paint tends to be less expensive, but also have a shorter lifespan.  Expect to repaint your boat bottom every three years, or sooner if you do a lot of scrubbing.  Hard paint can last five years or more, depending on the formula, and there are no current restrictions about cleaning.

Ablative paint is softer and is designed to slowly slough off over time.  The biocide used, usually copper is newly exposed each time some paint is removed.  As you would expect, a substance that kills growth in the bottom of your boat will also kill growth in the water, and many marinas are implementing regulations about cleaning boats that have been painted with ablative paints.

Hard paint is designed to allow the biocides to be released slowly without removal of the paint.  Some also contain Teflon or other “slippery” substances that inhibit growth without killing it.  While soft paint can be relatively easily scrubbed off and reapplied, hard paint requires effort to remove.  Most people just add another layer, much as you would do when painting your house.

If you’ve recently purchased your boat, or are going to paint a used boat for the first time, make sure you know what’s already on the bottom before you start.