Ventilation
By Joe Parker

Keeping your boat dry for livability and longevity

You decide to head down to your boat to take advantage of a beautiful Saturday afternoon in late August. You haven’t had a chance to use your boat in about three or four weeks, and you are really looking forward to catching up with your friends at the harbor.

You trot down the dock, hop aboard and slide back the hatch. The smell that hits you just about knocks you off the boat and into the water. You look inside and are stunned by the mess. The inside of the boat is a tropical swamp. There is mildew on the liner and cushions, and the smell is a mixture of bilge water, mildew, and musty life jackets.

Inviting ? NO.
Avoidable ? YES.

The problem is that the boat has not been open in a long time, and the ventilation system is not well designed nor implemented. You have often thought that you should add some vents, but the problem has never been this bad. Now it is time to figure out how to prevent this mess from happening again.

When choosing ventilating equipment, you should consider a number of factors: Where do you keep the boat, at a dock or on a mooring? What the climate is in your area for each of the seasons? Are there some vents that can be replaced or modified to be more efficient? What is the interior volume of the boat? Is there space on the deck for additional vents? And, what are the cosmetic requirements? Once you have analyzed the possibilities, you can make informed decisions.

There are basically two kinds of ventilation equipment. Passive, means the wind passing over the vent will extract air from the cabin or bilge. Active, means some form of power source is used to run a fan to move air through the vent. Either type, or a combination of both, can be used to create an effective ventilation system.

Passive vents

Passive vents include the traditional cowl vents, clamshell vents, louvered hatch boards, and the mushroom type vents. A cowl vent may include a water trap or dorade box. The dorade box is a water trap that was designed by the Sparkman and Stephens design group and first used on a sailing yacht called Dorade. A passive vent works reasonably well on a nice breezy day, but on those hot, still days in August, they do not move much air. They also work well as intake vents for systems that include active vents.