To reduce humidity and prevent the growth of mold and mildew it is important to ventilate your boat.  Hatches, ports, vents and interior fans can be used to create cross ventilation. Installing clam shell ventilators or solar-powered ventilators is another option. Many boaters use dehumidifiers. There are two types of dehumidifiers: low-wattage electric heaters and absorbent materials. Low-wattage electric heaters like the West Marine Air Dryer with Fan and Goldenrod devices warm the air in enclosed spaces to reduce condensation and mildew. Absorbent materials utilize calcium chloride crystals to remove moisture from the air and deposit it into a tub or sachet.  AC-powered cabin heaters can also be used to warm the air and keep your cabin dry.