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Application of Boat Bottom Paint

by Bill MacKenzie

First of all I want to mention my first experience with bottom paint was on my 22' Mac 222 ( a '78 model) I purchased in 1986. I kept that boat in the water continuously from 1987 until 1996, except hauling it out from time to time to paint the bottom. Eventually I learned that two coats of bottom paint properly applied would last for three years. This longer life is probably due to the cold water temperature here in Puget Sound (ave. 50 degrees). My home port is Anacortes, WA. Despite 9 years of being in the water almost continuously the boat never developed blisters( with the only protection being anti-fouling paint) until the last year (I had not heard of barrior coat at that time) In 1996 when I hauled the boat out I discovered two pinhead size blisters below the water line. They were easily repaired.

In 1996 I purchased my 26X. I decided to apply a barrier coat to the bottom prior to painting with anti-fouling paint. Following are the steps I followed:

Getting Started

  1. I jacked up the trailer and boat.
  2. I placed supports under the hull and lowered the trailer.
  3. I removed the center board, and with a bolt thru the pivot pin hole and a line I suspended it from my garage ceiling so I could prepare and paint both sides at once.
  4. I washed the areas to be painted thoroughly with soap and water and rinse water.
  5. I washed the areas : hull bottom, centerboard and centerboard trunk interior with de-waxing solution. This is mandantory on new boats and is recommended on older boats in case there may be traces of the original mold release wax present on the surface of the gelcoat. I used Interlux brand 202 Fiberglass Solvent Wash. After this I applied masking tape at the water line.
  6. I applied the Interlux No Sand Primer to the areas to be coated and painted.
  7. I applied 4 coats of the Interlux 2000E/2001E barrier coat product to the hull, center board and centerboard trunk. I believe I needed 3 gallons. Be very careful mixing and applying this product according to instructions or you may waste it. It is very expensive.
  8. I applied 2 coats of bottom paint ( Interlux Bottomkote) , waiting overnight for the second coat. For the 26X you need 1 gallon and 1 quart total for 2 coats.
  9. I jacked up the trailer in order to remove the hull supports, and lowered the trailer.
  10. I performed steps (4) - (8) to the areas where the supports had been.

I repainted in 1999 and again in 2002. Those times I used West Marine brand Bottom Pro ( 2 coats)


For cleaning and applying de-waxing solvent inside the centerboard trunkI made swabs using 24 inch - 1"x1" sticks wrapped with toweling and string.

I painted mostly with paint rollers for the primer, barrier and anti-fouling coats. For inside the centerboard trunk you can paint the lower portion with a standard roller. For the upper portion Use a 1" diam. - 3 or 4 inch roller taped to a stick that will reach. For the top of the trunk use a 1" brush taped to a stick. You need a lot of roller covers because it is not worth while to clean them. You can clean brushes if you have some of the bottom paint thinner (not brushes used for Barrier coat , though).

You should use different colored paint for each coat inside the trunk in order to get proper coverage. Because of this I buy 1 quart of red and 1 gallon of blue. I paint the inside of the trunk with red first, then use the rest of the red as far as it will go on the hull, then start with blue for the rest of the first coat. The second coat, then is all blue. You will need a light to see Into the centerboard trunk.

For masking tape be sure to use the special kind for use on boats (avail. at West Marine) . Ordinary masking tape is very difficult to remove after it has been on as long as necessary.

For Repainting

  1. Clean off all the loose scum (slime) by thoroughly washing.
  2. Sand the painted areas. I found that wet sanding works good. You do not have to remove all the paint down to the barrier coat (or bare gelcoat if there is no barrier coat) If you are using a compatable paint. Just be sure there is no scum or loose paint flakes left. By wet sanding you do not have to use a dust mask and goggles. I found that the screen type sanding material used for sanding drywall plaster applications works very well. There are proper sized holders (handles) available for the sanding sheets.
  3. Wash the areas thoroughly with water and allow to dry thoroughly. Use care to make sure there is no water residue inside the trunk.
  4. Paint

If you have the time you can save a lot of money doing this job yourself and probably get a better job than what some shops might do.

Additional Information

  • You can not paint barrier coat over anti- fouling paint. A previously painted surface will have to have all the paint removed down to bare gelcoat before applying barrier coat.
  • Some types of anti- fouling paint can not be applied over some other types . You can learn about that by studying the information in the West Marine catalog. May be avail. Online also.

Bill MacKenzie

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