If you’ve spent enough time around boats, especially boats with cabins, you know that there is a certain smell the moment you step inside. While not necessarily unpleasant, it is distinct and “boaty.” It’s that musty, moist smell that comes as a result of high humidity and low ventilation.
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Battle of the Bilge
For some boat owners, this smell is part of the package, a nostalgic reminder that you are in a cabin, not a living room; a stateroom, not a bedroom. But for others, it’s a smell that calls to mind mold, mildew and potential health risks.
Obviously, boats operate in moist environments, and moist environments are prone to mold and mildew. Combating that tendency requires a battle on both fronts — increasing ventilation and reducing moisture — and there are a wide range of products that can aid in either or both.
Standing Water in the Bilge
While increasing ventilation is relatively straightforward, reducing or eliminating excess moisture can be much more complicated. Recently, increasing attention has focused on the bilge as a major cause of moisture, and it makes sense. Nearly every bilge has some level of standing water in it.
A well-designed bilge pump system can make quick work of excess water in a boat’s bilge, but even the best-designed systems leave a pool of water around the intake, water that is too shallow to be pulled into the pump.
For stepped hulls, water can often get trapped in pockets and never drain back to the area of the hull where the main bilge pump is located. That water can range from a fraction of an inch deep to much deeper, and eventually, that water evaporates, rising through the decks as it does so. If you’ve ever spent time with your head in the bilge area of your boat, you’ve seen the black mildew that coats nearly every surface of that moisture rich environment.
Low-Volume Pump Systems
To address this, manufacturers have developed low-volume pump systems that are designed to eliminate all standing water in a boat’s bilge. These systems generally consist of a diaphragm pump (or several pumps) enclosed in a small box. The pump unit in the Bilge-B-Dry system carried by Boat Outfitters, for example, has a 5” x 5” footprint and stands 3” tall. Remote water pickups are attached to the pump unit via 1/4” plastic tubing and can be located wherever water collects in your bilge, up to about 25’ from the pump unit. Water is drawn from the pickup(s), through the tubing, and then pumped out into an outlet tube. The outlet tube can be plumbed into an existing overboard drain.
The Bilge-B-Dry system is available with up to four pumps to support four separate pickups. If you’re using the system on a small boat to evacuate water that collects in the bilge near the transom, one pickup is plenty. If you need to remove water from multiple areas — each hull of a catamaran, for example, or the steps of a twin-stepped monohull — choose a system with the corresponding number of pumps and pickups.
Not a Replacement for Conventional Bilge Pumps
It is important to note that these systems perform an entirely different function from conventional bilge pumps. Conventional bilge pumps remove excess water that enters the hull in the form of spray, rainfall, washdown water, plumbing leaks, small breaches, etc.
Their primary role is pumping water overboard to keep it from accumulating to the point that it might affect performance, buoyancy or stability. The smallest conventional electric bilge pumps are rated at around 350 gallons per hour. Larger recreational boats are normally equipped with multi-pump systems capable of moving many thousands of gallons per hour.
A typical dry bilge system, on the other hand, is intended only to remove the last small amounts of water that conventional bilge pumps can’t in order to minimize moisture-related odors, mold, mildew and corrosion in the bilge and elsewhere in the boat. That requires much less pumping capacity. A typical dry bilge pump can move only a fraction of the water a conventional bilge pump does. The Bilge-B-Dry system, for example, has a maximum rate capacity of 0.3 gallons per minute, or around 18 gallons per hour. These systems should never be thought of as an alternative to a conventional bilge pump system.
Applications
It’s easy to assume that dry bilge systems are useful mainly for large boats kept in slips or on moorings. But they also offer real benefits for boats that live on trailers, lifts or outdoor rack storage. Rainwater can and does find its way to the bilge on outdoor-stored boats, and once there, it can not only encourage formation of mildew and mold but can also contribute to corrosion of electrical connections and components and even soak into stringers and transoms.
Bilges aren’t the only places that hold water and cause odors and growth.
Keep in mind too that bilges aren’t the only places that hold water and cause odors and growth. On many boats, livewells, fish boxes, built-in coolers, ski lockers, and other closed compartments retain enough water even after draining to get stinky and slimy over time. Dropping a water pickup into them prevents that. Pickups can be installed with cable ties or screws but will also work without being fixed in place.
Easy Installation
The Bilge-B-Dry and similar systems are surprisingly easy to install. In most cases, installation is a matter of mounting the main pump unit in a dry, accessible location, connecting it to 12V power, connecting the pickup(s) using push-to-fit connections, placing them where desired and routing the output tube. The output tube can be connected to an existing overboard line or a dedicated above-waterline through-hull. Alternatively, on small trailer boats, it can be simply routed out over the transom or through a scupper while the boat is stored, then stowed while the boat is in use.
Keeping water on the outside of a boat is a constant battle against the elements, but even the best seals won’t protect your cabin from excessive humidity if your bilge has standing water in it. If your boat shares that musty or mildewy smell in spite of your best efforts, addressing the bilge may give you the edge you need to stay on top of it.