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