Bottom Painting

Bottom Painting

by Conrad & Judy Kreuter

Q: Dear Boat Talk: I am getting my boat ready for spring launch. I know I have to paint the bottom of the boat. Do I need to paint the engine as well? JJ, Coram, NY.

Dear JJ: When a boat is kept in the water for an extended period of time, the bottom must be protected with bottom paint against marine growth such as barnacles. Most bottom paints are ablative. That is, a small amount of paint is sloughed off each time the boat is driven exposing a fresh concentration of the biocide material. The biocide material keeps the barnacles away from the boat bottom. Paint is like cod liver oil to the barnacles, they hate the taste. With ablative paints, the more the boat is used the cleaner the bottom. Most ablative paints last only one season and should be applied at the beginning of each boating season.

Unwanted critters not only attach themselves to the boat bottom but also to engine parts that are submerged in salt water. If your engine is an outboard and the trim and tilt system allows the lower unit to come completely out of the water at the dock, then antifouling paint is not required. On the other hand, if you have an outboard or stern drive that does not come completely out of the water, you must apply antifouling paint to protect against unwanted passengers. The bottom paint used on your boat cannot be used on these engine parts as they are made of aluminum. The paint used on your boat bottom contains copper as the active biocide ingredient, while the engine requires a paint that contains tin. Since these tin based paints are restricted use paints, they cannot be sold over the counter in large quantities without the proper license. They are generally sold in 16 ounce spray containers to the public.

When getting your outboard ready, you should touch up the bare spots and scratches with the original manufacturers paint to prevent corrosion to the aluminum parts. The antifouling paint should be applied to those parts the are in contact with the water when the engine is not in use. Painting the propeller is not necessary since once the engine is put in use the antifouling paint will wear off rapidly.

Stern drives should have both the lower unit and intermediate housing painted. Make sure to tilt the lower unit up and apply paint to the exposed inner parts of the intermediate housing to prevent unwanted tenants from establishing barnacle hotels.

In general, most boats should be launched after allowing sufficient drying time for the paint, usually, within thirty days. Read the label directions on the paint can for more specific details.

Q: Dear Boat Talk:What is involved in painting a boat bottom for the first time? PB, Port Jefferson NY.

Dear PB: To begin the process of applying bottom paint for the first time, you need to know where the water line will be on your boat. The correct way to do this is to launch the boat with the engine installed and a full tank of fuel. Allow the boat to sit for a few hours to establish a water line mark on the hull.

Remove the boat from the water and let the water mark dry completely. Use masking tape to follow the water line mark leaving about a two-inch space above the water line. This allows for the added weight of passengers and equipment on the boat. Clean the bottom of all debris and de-wax the hull below the water line. Wax is used when building the boat to help remove the boat from the mold after it has cured. Use clean rags to remove all of the wax. Commercial de-waxers are available in all marine stores.

Apply a bottom paint primer using a wide brush or roller. The primer prepares the boat bottom to accept the bottom paint. Allow the primer to dry before applying bottom paint using a paint roller. Remove the masking tape and you will have an even water line on your boat.