Mold is a living organism that can form in dark wet areas. For many years the standard method of killing mold has been with bleach diluted with water. This method works well on most hard surfaces but is not recommended on a boat's gel-coated surfaces. Bleach can damage the color pigments in the gel coat. Vinegar is a much better alternative to bleach; it is safer, environmentally friendly and just as effective at killing mold. Simply fill a spray bottle with straight undiluted household white vinegar and spray it directly on the mold. The mold will disappear! It is important not to dilute the vinegar with water. Vinegar has a strong smell but the odor will fade away in a few hours. For more information on mold removal and other "green" solutions check out National Geographic's Green Guide.