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Water-saturated air is a potent
gas that permeates nearly everything in the interior of a sailboat.
The visible effect of this dampness is mold and mildew below,
but as damaging as these fungi can be, they are not the most serious
consequences. The moisture fosters rot in unprotected interior
wood, accelerates corrosion, degrades electrical wiring, and even
contributes to saturation of the fiberglass—the cause of
hull blisters. Simply stated, wet air ages your boat prematurely.
Your boat needs some way of venting
that moist air, even when it is sitting in the slip with all hatches
and portlights dogged down tight. But just a single vent is inadequate
to let the cabin “breathe.” In a house, you’d
open two windows to get cross ventilation, and the same is true
aboard a boat; you need at least two well-separated ventilators
so wet air can flow out as dry air flows in.
Two vents of any type beat no vents
at all, but the most efficient passive vent is the cowl vent—a
vertical pipe with a bell-like horizontal opening. Standing proud
above the deck and facing into the wind, this type of vent funnels
a great deal of air below, but it can also admit rain. Facing
away from the wind, the cowl vent becomes a powerful extractor.
For a boat on a mooring, a single cowl facing aft, used in concert
with some other rain-excluding opening—perhaps a louvered
hatch board—can do an admirable job of exchanging the air
in a closed boat.
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| A lot of
production-built boats don't come equipped with sufficient
ventilation. The field of cowl vents and Dorade boxes
that sit atop the deck of this Baltic 72 may seem like
overkill, but when you consider the volume of air needed
to keep moisture in check, they're just adequate |
For a boat in a slip, facing the
cowl aft will not exclude rain since the wind is just as likely
to blow from that direction. In this case, the cowl vent will
need to be mounted on a water trap or a Dorade box, either of
which will prevent rain from coming below. A pair of cowl ventilators,
each mounted on a water-trap Dorade box (with one facing forward
and one facing aft), is even more effective. In nearly all conditions,
this configuration sets up a beneficial flow of air in one vent
and out the other.
A notable alternative for closed-cabin
ventilation at the dock or on a mooring is the solar-powered ventilator.
Using an integral solar panel to run a small fan during daylight
and, in some units, to recharge internal batteries that keep the
fan running after dark, a single solar vent, paired with a cowl
ventilator or a sizable louvered vent, can effectively exchange
the entire volume of air inside the typical sailboat 10 to 20
times
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