Review of Hypervent Condensation Preventer

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What Hypervent Is

Photo © Tom Lochhaas.

As shown in this photo, Hypervent is a flexible structure layer that can be cut to shape and laid flat under cushions or mattresses inside the boat. The white core is composed of a pattern of thick nylon coils that resist compression, bonded to a thin waterproof polymer fabric. The open spaces in the coiled structure allow air to circulate within the 3/4-inch layer.

Circulating air brings warmth into an area where typically the bottom supporting boat structure is cool due to the boat's hull in water that is usually cooler than the air. When warm, moist ambient air comes in contact with the cooler fiberglass or wood surface beneath a cushion or mattress, condensation forms - and if the cushion or mattress presses directly on that surface, the condensation has little chance to evaporate. That's when mold and odors begin.

Hypervent helps prevent this problem in two ways:

  • It allows warmer air to circulate below the cushion or mattress, preventing the cooling that starts the condensation process.
  • When condensation does occur, or other moisture seeps into the area, the circulating air promotes evaporation and drying before mold gets a toehold.

Continue to the next page for installing Hypervent and an evaluation of how well it works on my sailboat.

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Hypervent Installed under Vee-Berth Mattresses

Hypervent Installed
Photo © Tom Lochhaas.

Hypervent comes in a roll 39 inches wide, sold by the yard by online vendors such as Defender Marine. The vee-berth area on this traditional 38-foot required less than 4 yards total. Simply measure the area carefully, and make a paper pattern if needed for an irregular space. It's good to cut the Hypervent material a little smaller than the space, to allow air to enter easily around the outside edges. Use a Sharpie marker to draw your pattern on the fabric side of the layer.

The bristly nylon coils are easily cut with a sharp knife or heavy scissors. Do not do this cutting on your boat, however, because small pieces of nylon will be left lying about that could easily find their way into your bilges and jam up a bilge pump.

Lay the Hypervent sections in place with the fabric side up and the nylon coils against the fiberglass or wood surface on which condensation normally forms. The weight of the mattress or cushion will usually keep the sections in place, or you can use duct or similar tape on the fabric side to join them in one piece.

Does It Work?

Remember that Hypervent works only by allowing air circulation. If the edges are open to the air, it works well as advertised. But if the air spaces at the edges are blocked, such as with a heavy blanket over the mattress that fills in the space around the outside edges, then air cannot get underneath and the system cannot work. (I discovered this myself by trial and error! This is not a magic product that solves all moisture problems by itself: you have to work with it to ensure air can circulate.)

Hypervent is similar to a product sold in Australia called Hydravent. Both are much easier to use than older, more rigid products of rubber or plastic that are assembled to create a similar air space below a mattress or cushion.

Other Tips and Tricks

In most marine environments moisture can be a problem throughout the boat. In addition to using Hypervent beneath cushions and mattresses, take other steps to keep your boat dry and mold-free:

  • Dorades and other vents help move air in and out of the boat when it is closed up.
  • For boats with shore power, an electric ventilator fan or dehumidifier helps a lot through the season.
  • Solar-powered vents help boats away from electrical hookups.
  • If power is convenient for winter storage, use a dehumidifier - or even a low-watt incandescent light bulb - to prevent condensation that occurs in a covered boat with temperature changes.
  • With boats shrink-wrapped for the winter, use vents in the shrink film to let air circulate under the cover (leave a boat hatch open for air to get inside).
  • Several chemical products are available to absorb moisture and lower humidity. For a covered winter boat, an inexpensive solution is a bucket inside half-filled with calcium chloride (sold for sidewalk ice melting), which will absorb lots of moisture.