February 2011 Feature Janet Groene

On the day we woke up with condensation dripping on our faces we knew something had to be done about the ventilation in our boat. Sleeping and cooking aboard day in and day out create moisture that must be dealt with on a liveaboard boat.
Here are thoughts on bringing more good air into your houseboat and exhausting more bad air. By "good", we mean dry air at a comfortable temperature. By "bad" we mean warm, humid air that feeds condensation, mold, dry rot and mildew. (We're assuming you already have sniffers to protect you against more deadly "bad" air such as CO buildup, gas fumes or a propane leak.)
Even in a bone-dry bilge, the moisture level varies season to season depending on the water temperature under the boat. When warm air settles into a thin hull in cold water, condensation is created in the bilge. When cold rain falls on a warm roof, indoor air condenses and beads on the ceiling. If your houseboat is brand new, moisture and other fumes may also be exhaling out of new materials and adhesives.

No matter how dry the outdoor air and how well insulated your houseboat, moisture by the gallon (yes, gallons) is created by human breathing, houseplants, burning fuels (the propane stove, the Sterno in the ventless fireplace) and by cooking, showering and running the dryer. The first step is to install exhaust fans over the stove, in the laundry and in bathrooms. If you have "exhaust" fans that merely filter and re-circulate, replace them with the type that exhausts air to the outdoors.

Your houseboat has two types of air flow. Natural flows come through hatches, wind scoops, vents and dorade boxes. Mechanical venting is via fans and blowers. Gotta vent? Here's how:
* Upgrade from passive vents, which merely waft ambient air through hatches, to solar or electrical vents with fans that really move the air.
*Don't forget to vent unoccupied portions of the houseboat such as lockers and the engine room.
* No matter what we did including posting a sign, family and guests simply would not flick on the exhaust fan when they were in the head. Hot showers were burdening the air conditioning and dumping much too much moisture into the air. Our solution was to wire the bathroom light switch or door so the exhaust fan comes on automatically when someone enters the head. That guarantees the exhaust fan will go on before the shower goes on and won't go off until the shower is off and the head door opened again.
* Brass, stainless steel and wood louver inserts for cupboard and closet doors increase passive air flow and can also be a handsome decorator statement. Find them in marine stores and catalogs such as
* Don't vent in a way that might allow air exchange between living compartments and areas where CO is produced.  Assure too that open hatches don't suck in air filled with your own or another boat's exhaust.
* Stay aware of how air is flowing through your boat underway, at anchor and at the dock. Then open and close windows and hatches and aim wind scoops accordingly. This could require multiple changes each day as winds change.
* Do everything possible to remove standing water from inside the boat. That includes the bilge, shower sumps and the refrigerator drain. If your anchor rode and chain stow inside the boat, you bring in a load of water every time you bring in the anchor. Improve drainage and venting in the chain locker. If possible dry anchor rodes and dock lines on deck before stowing them.
* What is a dorade box? Picture a horn-shaped air scoop or cowl, that sits atop a wood or fiberglass box. The scoop can be turned any direction to capture breezes. Inside the box are baffles, a drain, and an opening into the interior of the boat. If any water comes in with the air, it drains away on deck before the air enters the boat. Seen mostly on sailboats, energy-saving dorade boxes make good ventilation sense for houseboats too.
* Fabric air scoops, also called wind sails, are seen commonly on sailboats where they are tied high in the rigging to capture winds, which they then cram down through an open hatch. A wind sail might also be flown on your houseboat depending on whether and how you can rig it. Observe some designs in use at your marina. If you see that you can use a wind scoop on your houseboat, design one that can be stitched up by a sailmaker. See a commercial version at or and put "wind scoop" in the search window. One advantage to this energy-free vent is that it's fabric. When it's not need it stows flat in very little space.
Nautworthy News
Some of the best liveboard marinas are in the Caribbean, Mexico or overseas. If you're considering a move across waters you don't want to navigate yourself, BoatU.S. can put you in touch with a qualified delivery captain. Go to Captains are screened and the site will list their qualifications including licenses, references, insurance and experience.
About the Authors 
The Groenes lived on board for ten years. Send questions and comments to

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