Issue Date: October 2008

Ventilation: move that air
Frank Kehr

All boats need ventilation, but most don’t get it. Proper ventilation is important for both the maintenance of your boat and your personal comfort. Most of us with boats that have enclosed living spaces control the comfort side by using fans and air conditioning, but when it comes to the maintenance aspect things can get a bit sketchy.

The last thing we do before leaving our boats is to secure and lock the hatches and doors or put the cover on. This is when problems begin. As a result of the difference in temperatures between water, air and hull surfaces, the unattended boat is constantly generating moisture inside, promoting an ideal environment for mold, mildew and musty air. These temperature differences vary as the day progresses, and the process is accelerated in humid climates.

Boats that live on trailers in the backyard should be covered and, as such, also require vents. Proper ventilation is more than moving air. It should equalize the humidity level inside and outside the boat, preventing damage to interior fabrics, electronics, wood, metal and fiberglass.

As stated above, ventilation can be broken down into two categories: maintenance and comfort. For the purpose of this article let’s deal with maintenance type, which generally means replacing the air inside the boat at least once per hour. Maintenance ventilation can be broken down further into “active” and “passive.” Active vents typically are mechanical in nature — using fan blades to move air — and are powered either through the boat’s 12-volt system, solar array, internal batteries or a combinations of these. They force outside fresh air into the boat or exhaust stale air from it. Passive vents rely on wind and air currents to circulate air, without moving parts.

The most basic passive vent is a louver. Typically made of either stainless steel or plastic, they are inexpensive, easy to install, and available in a variety of shapes and sizes. Louvers typically are installed in lockers, bilges, deck boxes, lazarettes and behind refrigeration and electronic equipment. They allow compartments to be securely closed, yet still allow air to flow. If the door to a stateroom or cabin is normally closed, it should be vented for intake and exhaust, just like cabinetry, drawers and all closed compartments. When venting compartments, I install one louver high and one low to promote air circulation through convection.

Cowl and clamshell vents are commonly used to vent bilges or as intake air supplements for active vents. They are available in several shapes, sizes and profiles. Cowl vents can be connected to 3- and 4-inch-diameter hoses so the air flow (intake or exhaust) can be directed as needed. The cowl vent’s large bell-like opening can be positioned to face the breeze, and these are capable of funneling large volumes of air into the boat. When facing downwind, they create a draft as the breeze passes by, exhausting air from the inside of the boat.

Some cowl vents can provide a path for water intrusion, which, depending on their location, may create a problem. Dorade boxes provide a mounting surface for cowl vents and incorporate either a water-sensitive valve that opens or closes automatically to let air in and water out, or have baffles and drains built in to eliminate water intrusion below deck. Cowl vents that are well-positioned and installed on dorade boxes provide great passive ventilation.

Any vent that allows air movement to or from the boat’s interior should be fitted with screens. You can find cowl vents and accessories from West Marine (www.westmarine.com ), Nicro (www.marinco.com), Plastimo (www.plastimo.com ), Beckson (www. beckson.com ), Perko (www.perko.com) and others. Prices range from about $30 to several thousand dollars, depending on size and construction materials. They are favored by traditionalists for their salty appearance. You will always find cowl vents on large commercial ships.

Another form of passive ventilation is a round cabin/hatch vent such as those from Nicro, Lewmar (www.lewmar.com), and Beckson. They require round cutouts of 3 to 4 inches in diameter and can be installed on almost any horizontal surface. This style vent isn’t as efficient as a cowl vent, but it is much less obtrusive, projecting only an inch or two off the deck. They typically move 200 to 600 cubic feet per hour and usually have shut-off dampers. I have priced passive hatch vents at around $25 to $55. If I were considering this type of installation, I would spend the extra money and opt for active vents of similar configuration.

When it comes to active ventilation, the most common product for recreational boats is offered by Nicro. Nicro has been in the ventilation business for more than 30 years and offers a line of powered ventilators that work well and are straightforward to install. The cabin/hatch vent described above has been modified and is now outfitted with an electric fan and interchangeable blade that allows you to select either intake or exhaust. These ventilators are available with solar, battery or 12-volt DC power, and provide around 700 cubic feet per hour to 2,000 cubic feet per hour of air flow, depending on the model. An advantage of the Nicro system is most of its installations require only a 3- or 4-inch-diameter opening for the snap-in base plate. Once installed, the base plate accepts almost all of Nicro’s products and accessories, from a 3-inch PVC cowl vent to a two-speed 12-volt DC fan.

How much ventilation does your boat require? You cannot have too much, and even a little helps a lot. Nicro says a typical 30-footer contains approximately 800 cubic feet of air. To calculate your boat’s air volume, multiply interior length times beam times average height times 70 percent (0.7). Look at available product ratings as a guide, then go bigger. It is best to have vents at both ends of the boat — one for intake and one for exhaust. Where my boat is docked, the bow gets the majority of the breeze, so I use the forward ventilator as intake and the aft as exhaust.

Covered boats require ventilation, as well. Unfortunately, my Boston Whaler spends much of the week covered in the backyard. The cover is weatherproof and has several passive vents installed. These clever little devices from Airlette Manufacturing (www.airlette.com ) snap into the flexible cover and have insect screens, along with removable hoods to prevent rainwater from entering. The hoods are easily removed to roll the cover snugly without damaging the vents. I’ve also installed them on the cover for my RIB, which is on davits at the stern of my trawler. Everything stays dry, clean and well-vented. Without the vents in the cover, there was always a mold buildup inside the boat after a week or two. At less than $10 each, they save a lot of scrubbing and time.

There aren’t any mysteries about boat ventilation, except why more boaters don’t take advantage of the products on the market that can make life aboard a bit better and improve the overall condition of the boat and its equipment.


Read the other story in this package:

Issue Date: October 2008

Nicro Day/Night Plus solar-powered vent
Frank Kehr

If you own a boat with enclosed spaces or an open boat that’s covered when not in use, you should be familiar with the Nicro line of ventilation products. Nicro has been producing both active (powered) and passive (redirects air movement) ventilation for more than 30 years.

A product I recently added to my boat is the Day/Night Plus vent, which has been improved and moves up to 1,000 cubic feet per hour (24,000 cubic feet per day), providing continuous fresh air to your boat’s interior. The Day/Night Plus is totally self-contained, requiring no outside source of electricity, and it can be installed through almost any hatch or deck surface where there is a reasonably flat surface. It may seem obvious, but be sure the selected location doesn’t pass through electrical wiring, plumbing or other obstructions.

The Day/Night Plus provides 24-hour operation by using an integrated nickel-metal hydride (NiMH) battery and a photovoltaic solar array. The solar array powers the unit’s fan during daylight hours and provides charging to the NiMH battery, which in turn powers the fan during hours of darkness. The product literature indicates that the fully charged NiMH battery will operate the vent for up to 40 hours.

The battery’s life span is typically between two and three years, while the photovoltaic array should last 20-plus years, according to David Colclough, from Nicro technical support. When the time comes, a replacement battery is available either directly from Nicro or through Radio Shack.

I checked the fan speed while it was operating in daylight and charging the solar cell. The fan was turning 122 rpm. I covered the solar array for 24 hours and left the fan running on battery power, with a resulting drop in fan speed of only 4 rpm. Like all active Nicro vents, the Day/Night Plus includes interchangeable fan blades to provide either intake or exhaust air.

The Day/Night Plus is designed to fit directly on the hatch or deck surface and mounts on its own base plate, which must be installed correctly to ensure proper operation and watertight integrity. If the deck surface is cambered, be certain there is no more than a half-inch of curve over a 12-inch length of deck surface. (Place a 12-inch straight edge on the deck location and rock it, then rotate it 90 degrees and repeat.) For deck camber greater than a half-inch, a compensating shim will need to be installed.

The installation of all Nicro vents requires only basic hand tools and either a sabre saw or drill with a large hole saw. (A jigsaw will likely be more convenient for most boaters.) Since the vent operates on both solar and battery power, there are no electrical cables to run, simplifying the installation.

I have previous experience with other Nicro products and, being confident in their quality and design, I had no hesitation in cutting a hole in my solid teak aft cabin hatch. I was installing the 4-inch-diameter vent, which required a 4-3/4-inch hole. I marked the center of the hatch and cut out the required hole using a hole saw. If you use a sabre saw, I recommend covering the deck area with wide masking tape to prevent the saw base from marking the deck. (You also can apply the tape directly to the saw base.) Use a compass to mark the diameter of the hole and carefully cut along the line. Regardless of the method you choose for cutting, clean up the edges of the hole with sandpaper or a file.

There are several choices for finishing the portion of the vent in the boat’s interior. Nicro offers trim rings of plastic and teak; soft, protective rings for hatch installations; and snap-in screens. The vent exterior is offered in white and stainless steel.

Begin the installation by mounting the selected trim ring from the interior. Back on deck, fit the base plate into the hole to confirm alignment. Mark the three mounting holes. Remove the base plate and drill the mounting holes, being careful not to drill through to the interior of the boat. Rough up the mounting surface and the bottom of the base plate to promote good sealant adhesion; 100-grit sandpaper works well.

Apply a quarter-inch bead of silicone sealant to the underside of the base plate and to the surface where it will sit. Slide the base gasket over the base plate (optional for hatch installation), align the fastener holes, and set the assembly onto the deck. Place the cover — which includes the fan motor and blade — battery and solar array over the base and carefully install the final screws. Be sure not to squeeze out the sealant or distort the base plate by overtightening.

The new Nicro Day/Night Plus includes an on/off switch inside the fan housing. To access the switch, gently place a finger on the fan hub until the blade stops turning, then press the rubber-covered switch. Shutting off the fan enables you to operate the green water shut-off damper. There are two ears on the inside edge of the fan housing. Pushing the ears up moves the damper about a half-inch up, where it seals on the vent cover; pulling the ears down allows air to flow through the vent.

I installed the Day/Night Plus in early April, and by late June I hadn’t seen any water intrusion either from heavy storms or my heavy-handed deck washing. When installed according to the excellent guide provided with the unit, the vent provides good watertight integrity and enhances vessel ventilation. There was a substantial improvement in interior air flow on my trawler, as evidenced by the lower interior temperature and lack of “closed boat aroma” following the boat being locked up for a week.

Don’t be misled if you place your hand at the vent location and don’t feel rapid air movement. These units aren’t designed to create a wind tunnel. They slowly move volumes of air that may be imperceptible — and they work very well. I had two older Nicro vents on my previous boat, and they worked continuously in the five years I owned her. One was in the forward hatch as air intake, and the second was in the head as exhaust. Being installed on a sportfisherman, these units saw much more seawater over the deck than my Day/Night Plus will, but there was never a water intrusion issue.

Nicro provides plenty of technical information on its Web site regarding application, sizing and quantity of vents recommended, which is based on vessel configuration and size. Ventilation on board is certainly one place where more is better. The products work well and last in the marine environment.

The 4-inch Nicro Day/Night Plus retails for around $160 and is available from most major chandleries. For information, contact Marinco Electrical Group, Napa, Calif., at (707) 226-9600, or visit www.marinco.com .