Climate Control

The Carry-On Air Conditioner fits inside any deck hatch with a rectangular opening between 12" x 12” and 24" x 24" or a 15 ½" diameter round opening, using an adjustable fabric hood to seal the opening.

HVAC - Heating, Ventilation and Air Conditioning

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. We discuss heating on the previous page. What follows will help you design the systems for ventilating and air conditioning your boat.

Why Ventilate

Proper ventilation is important for the maintenance of your boat, and is a necessity for the comfort of you and your crew.

A good ventilation system will:

• Reduce moisture and humidity below deck when the boat is left unattended.
• Reduce the chances of musty air development caused by trapped moisture and humidity in the boat.
• Help electronics and fabrics last longer by maintaining a drier climate.
• Reduce the likelihood of blisters caused by moist air saturation of the hull.

Active and Passive Ventilation

Vents fall into two basic categories: passive or active. Passive ventilators, such as cowl vents, clamshell vents, louvers, grilles, ventilating sails, ports and hatches simply 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.

Active ventilators, such as Nicro’s MiniVent 3000 and 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. <Current image goes with this copy>

The Nicro Solar Vent is one of our favorite devices for bringing fresh air to the cabin. A solar cell and batteries allow 24-hour fan operation with no electrical hookups, and it works for either intake or exhaust directions.

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 belowdecks interior volume. Unfortunately, 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 adequate 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 of the boat.

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 percent 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 like the Carry On, a good choice for cooling the small cabin of a cuddy cabin powerboat or overnighter sailboat. Similar to window-mounted home portables.

Self-contained units like the FCF Series, EnviroCool or EnviroComfort air conditioners are typically 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. These units use a new type of R-417A or R-410A refrigerant, environmentally-safe products that won’t destroy the world’s high-altitude ozone layer.

Central Systems, 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.

A reverse-cycle system like this Webasto FCF5000 self-contained unit provides both cooling and heat. A seawater kit requires you to install a thru-hull, 115V raw water pump and associated plumbing. You also install supply and return grilles, ducts and other ventilation hardware.

Heating/Cooling or Cool Only

Central systems and some self-contained units, like the FCF Series and EnviroComfort 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 90°F waters and heat your boat in waters as low as 40°F.

EnviroCool Self Contained Air Conditioners provide straight cool only. A complete installation kit is standard, including all the pumps, hoses, ducts, fittings, and everything else you need. The pre-charged units are the right size for air conditioning the cabin of a small express or cabin cruiser, in the 25' to 40' size range.

Retrofit kits from Webasto (FCF Series Air Conditioners) and Dometic (EnviroComfort 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—Below Deck: cabins where the hull slopes inward toward the keel and there are minimal port lights and hatches; Mid Deck: areas on the main deck with small or shaded windows; Above Deck: areas with large glass surfaces and direct sunlight.

Step 1: Pick the load factor (Btu per sq. ft. per hour) that applies to the space to be cooled:

Select Moderate Factors where the maximum air temperature is 95°F, maximum water temperature is 80°F, and moderate humidity exists, Select Tropical Factors where maximum air temperature is 110°F, water temperature is 100°F, and high humidity exists.

Step 2: Measure the area (length x width) of the space to be cooled.

Step 3: Multiply the Factor selected in Step 1 by the area from Step 2. Example: 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.

Step 4: 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.

Choose a Ducting Kit: Single duct systems are good for small boats or other installations that don’t require a single A/C unit to cool/heat multiple cabins. A dual duct kit allows the boat owner to use one A/C unit to cool/heat two separate areas within the boat.

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