Mold is less of a problem than discoloration from soot. Some have the impression that cold prevents or slows the growth of mold but we have found some of our worst mold problems develop during the winter rather than the summer. If the discoloration is from soot, that can be very damaging to the gel-coat. Soot necessarily contains more or less sulfer which, when combined with the humidity in the air, forms Sulfuric Acid (think acid rain). Lingering on the deck, trapped in place by the particulates in the soot itself, this stuff will quickly eat into, and through, gel-coat. That can be remedied but not easily nor inexpensively unless its very minor.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."