To be effective, boat ventilation must do more than just circulate air - it must also equalize the humidity inside and outside your boat. A well-ventilated boat discourages mold, mildew, musty air, dry rot, and foul odors, helps keep you and your crew comfortable, and is safer; the chances of an explosion are minimized.

For comfort aboard, every boat should have exhaust vents in the head and galley, and intake ventilation in the main cabin to maintain a steady flow of air. To prevent damage to fabrics, wall coverings, paint, metal, and the hull when the boat is unattended, you need only exhaust a relatively small amount of foul air, as long as it's done on a steady, hour-after-hour basis during daylight hours.

Active or Passive? Active systems, like solar and 12vDC vents, push air mechanically with fan blades. Passive systems use wind and air currents, but no moving parts. They include cowl vents, clamshells, louvers, and vent plates.

Passive Vents, like Nicro's Lo-Vents, PVC cowls, and clamshells, are inexpensive systems that can be installed for either intake or exhaust. They're a great choice for small areas like chain lockers or lazarettes.

Louvered Vents, the most basic and least expensive vents, are available in stainless steel or ABS plastic. These are used for ventilating fuel lockers, bilges, deck boxes, lazarettes, or behind electronics. Installed in hatch boards, they can provide intake air flow from the pressure drop created by solar-powered vents.

Solar Vents provide intake or exhaust ventilation without draining your 12-volt supply by using the sun's energy to power a fan. Install two or more, and you can switch them from intake to exhaust and back simply by changing the two fan blades provided. The less expensive models have the lowest cost per cubic foot for air volume moved, and are ideal for extracting heat during the day. Solar vents come in 3" and 4" sizes. The 4" size moves about 40% more air, and should be used on boats 40' and over.

Day/Night Solar Vents are the most versatile vents, moving more air in 24 hours than any other solar vent. Equipped with a rechargeable Ni-Cad battery, they store solar energy to work up to 48 hours without exposure to the sun. They are recommended for exhaust in the head, galley, lazarette, sail locker, or deck boxes, and for intake and exhaust in aft and main cabins, pilot houses, nav stations, and forepeaks.

Two-Speed 12vDC Vents are the most powerful topside vents. They are designed for boats with multiple battery systems, a battery charging system (110-volt, solar, or wind) or shore power, and for boats where vertical installation—usually in the head or galley - is a must.

Combo 12vDC/Solar Vents are ideal for live-aboards and cruisers because they use solar power during the day to preserve battery power, and at night give a higher air flow rate

Opening Ports with Insect Screens are another excellent way to increase your comfort aboard. You can install screens in just about any exterior vent.

Windscoops are an inexpensive, non-mechanical, easy-to-stow source of fresh air. Put in a hatch screen to keep out the bugs.

Cabin Fans circulate air and equalize humidity while aboard. Many models are available: Battery-powered portable models that won't drain the ship's battery (and can be used in the cockpit or at home), 12vDC oscillating fans, compact models that fold out of the way when not in use, and convertible fans that are either 12vDC or use batteries.

Bilge Blowers are the most important ventilation system source for boats with engine rooms. Dangerous fumes can accumulate in the bilge, creating a situation ripe for a fire, or more likely an explosion. High-capacity 12vDC bilge blowers are required to clear fumes before starting engines and while operating below cruising speeds. Passive vents should also be installed to keep the engine room clear while operating at higher speeds.