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Plumbing & Ventilation
Your boat's heating, ventilation and air conditioning systems provide climate
control, keeping you cool in tropical summer weather, dry in muggy August
humidity, and toasty-warm during the last October cruise of the season. They
guard against odors associated with mold and mildew, extend your cruising
season, and enhance the value of your investment in your boat. What follows
will help you design the systems for ventilating and air conditioning your boat.
Proper ventilation is important for the maintenance of your boat, and is a ne-
cessity for the comfort of you and your crew.
A good ventilation system will:
Active and Passive Ventilation
Vents fall into two categories: passive or active.
, such as cowl
vents, clamshell vents, louvers, grilles, ventilating sails, ports and hatches, provide
an access path for air to enter or leave the interior of the boat. As long as either
the boat or the air itself are moving, they work just fine. Of course, on those hot,
still days when the only things moving are the mosquitoes, they're not much help.
, such as Nicro's Day/Night Plus Solar Vents, incorporate a fan
to keep air moving even when the boat or breeze is still. Solar energy or ship's
power is used to power the fan depending on the ventilator. These vents come with
both intake and exhaust fan blades for flexibility in creating your ventilation system.
Designing a Ventilation System That Works
A properly designed ventilation system provides adequate air circulation
throughout the boat without allowing water from waves, spray or rain to come
aboard. Experts recommend that your ventilation system should provide at
least one air change every hour. This means provisions must be made for both
the intake of new air and the exhaust of old air. Set up your system to provide
a "cross flow" of intake and exhaust ventilation wherever possible. If you only
add one active ventilator, use it for exhaust.
A typical 30-footer has about 800cu.ft. of belowdeck interior volume. Unfortu-
nately, this space is often broken up into distinct cabins or compartments that
may restrict the free movement of air throughout the boat. Therefore, simply
installing a pair of vents rated for 800cu.ft. per hour of airflow may not be ad-
equate to get the total ventilating job done. Each cabin and head should have
some kind of ventilation, especially if the space can be closed off from the rest
of the boat. Louvered doors, or vent grilles in solid doors, help air circulate
into lockers, forepeaks and other isolated areas. During wet or rough weather,
you'll need to be able to shut off or remove vents to prevent water from finding
its way below. Racing boats may need to use vents that can be removed while
the boat is in use in order to keep the decks free of possible snags.
Do You Need an Air Conditioner?
Air conditioning systems will be one of the largest electrical amperage draws when
you are under way, but use modest AC current when connected to shore power. At
the dock, a 5,000-16,000Btu AC-powered system draws between 4 and 13 amps.
Under way in a powerboat, these amperages are manageable. Under sail or at
anchor, you'll need a sizable inverter and the battery banks to support those loads,
or a genset. What makes these electrical investments worth considering? Summer
cruising locations that combine high heat, humidities in the 80% to 90% range, and
the presence of mosquitoes or other insects, requiring screened cabin areas that
restrict ventilation. Air conditioning opens these locations to comfortable boating.
AC Air Conditioning
Hatch mounted portables:
Your alternatives start with a portable unit, a good
choice for cooling the small cabin of a cuddy cabin powerboat or overnighter
sailboat. Similar to window-mounted home portables.
like the FCF Series or EnviroComfort air conditioners are typ-
ically the best choice for boats up to 40'. All of the major components are mounted
on a single chassis, which is installed in the living area under a bunk or settee, or
in a locker. They require thru-hull connections to draw cooling water into the unit.
, also known as split systems, are usually found on boats up to
80' in length. A condensing unit is mounted in the engine room or other mechanical
space, and connected by copper tubes to an air handler in the living area.
Heating/Cooling or Cool Only
Central systems and some self-contained units, like the FCF Series and Enviro-
Comfort air conditioners, heat as well as cool. They pull heat out of the water
to warm the interior of your boat. Though affected by water temperature, they
can cool your boat in 90F waters and heat your boat in waters as low as 40F.
Pompanette Air's new 12-volt Air Conditioner
provides straight cool only. A
complete installation kit is standard. Total run time depends on the type and
condition of your batteries. In general, a typical pair of group 27 batteries
provides about 3 1/2 hours of continuous operation.
from Webasto (FCF Series Air Conditioners) and Dometic (Enviro-
Comfort Reverse Cycle Retrofit/Compressor Kits) allow you to replace your old
unit and re-use the old plumbing and ducts. They fit into a similar footprint and
are charged with environmentally safe refrigerant.
Sizing Your AC System
Air conditioning systems are rated in Btu, or British Thermal Units, a universal
measure of heating and cooling. To calculate the number of Btu needed to
cool or heat your space, follow the steps below, then select the unit with the
capacity you need. The interior space fits into three categories-
cabins where the hull slopes inward toward the keel and there are minimal port
lights and hatches;
areas on the main deck with small or shaded
areas with large glass surfaces and direct sunlight.
Pick the load factor (Btu per sq. ft. per hour) for the space to be cooled:
Moderate/Tropical Moderate/Tropical Moderate/Tropical
Factor: 60 80
90 120 120 150
Select Moderate Factors
where the maximum air temperature is 95F, maxi-
mum water temperature is 80F, and moderate humidity exists.
where maximum air temperature is 110F, water temperature is
100F, and high humidity exists.
Measure the area (length x width) of the space to be cooled.
Multiply the Factor selected in Step 1 by the area from Step 2. Ex-
ample: A below deck cabin in moderate climate (Factor 60) has 100 square
feet of area to be cooled. 60 x 100 = 6,000Btu. A 6,000Btu unit is the minimum
size for this cabin. If there is more than one space, perform these calculations
for each space, and then add them together.
Select an air conditioning unit that is rated equal to or 10% to 15%
larger than your total calculation. A unit that is oversized too much can "short
cycle," and may not run long enough to remove the humidity. A multiple unit
system is required to produce 16,000Btu or greater.
Solar vents, like the Day/Night Plus
vents, run 24/7. They can be
used for both
intake and exhaust
Hatch Vent is 100%
works with hatch
circulate air through
the engine compartment.
Solar vents freshen the
V-berth and deckhouse
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