Sunday, March 30, 2008

Bottom Paint (Small Boats)

There are three (3) basic causes for bottom fouling:
Animal Fouling.
1. Critters such as barnacles and zebra mussels find boats, sitting static in their slips, an ideal surface upon which to attach themselves and multiply.
2. Plant Fouling
Just like barnacles, weeds also attach themselves to static surfaces. This occurs most frequently near the waterline where sunlight abounds.
3. Slime Fouling
This mess is created by algae that settle into a gooey medium and happily reproduces. An algae colony soon attracts other organisms which, combined with the slime, makes for a really ugly and slow boat bottom.
The best answer to this problem is antifouling bottom paint. These paints reduce or eliminate any marine growth that develops on your boat's underwater surfaces. Antifouling paints do this by using biocides (chemicals) that slowly release during the season to repel underwater aquatic life. Most of the antifouling paints use cuprous oxide (copper) combined with other mysterious stuff to get the job done.
There are a couple of basic types of antifouling paints. Each one has its pluses and minuses.
Ablative Antifouling Paint
This paint wears down much like a bar of soap as your boat moves through the water. As a result, fresh layers of biocide are constantly being exposed throughout the boating season. This type of paint works well in high marine growth areas and continues to work even with multiple haul-outs, just as long as any of the biocide remains. Because of the way it works, putting on 2 or 3 coats of paint initially is a good idea.
Another plus is that you can apply ablative paint over most other antifouling paints. The downside is that because these paints are relatively soft, you will be removing bottom paint with each brush stroke every time you scrub your bottom or waterline. Also, it wears away quickly on high drag areas such as rudders or other bottom appendages. Likewise, trailer rollers and bunks grind it off in a big hurry.
Hard Antifouling Paint
If you and your boat like to go "warp factor six with your hair on fire," then a hard antifouling paint would be a likely choice. This paint starts leaching out biocide upon contact with the water to prevent marine growth. However, after a period of time (say 6 months to a year), the paint starts to run out of "ammo" and becomes much less effective than it was when first applied.
In addition, hard antifouling paint will build up. Because the medium that holds the biocide does not wear off, it needs to be periodically, physically removed to prevent excessive paint build-up on the bottom. Some hard antifouling paints have Teflon added to further reduce surface friction.
Those of you with aluminum hulls should heed this caution. DO NOT put bottom paint containing copper directly over aluminum. If you let these two (2) dissimilar metals come into contact with each other and put them into water, you will have just built yourself a large battery! Immediately on contact with water, a process known as electrolysis corrosion will set in.