Deck Vents: Nicros Water Trap and Plastimos Cool n Dry are Clever and Effective

Among mushroom-types, the Nicro PowerVent with interchangeable fans for intake and exhaust gives 24-hour operation. White PVC Dorades just dont hold up long-they discolor and get sticky-so we recommend ABI stainless or brass models.


Cowls are descendants of simple vent pipes on sailing ships, cousins to the famed Charley Noble over the galley. When ships acquired engines below, the need for air down there became acute.

Eventually, somebody decided that the pipes could be made to extract fumes more efficiently or even direct air below. Hence, the hood-like cowl. On working ships, they usually were made of welded-up galvanized steel, which if done properly can last for years and require no care.

When cowls migrated to yachts, they were made of spun brass with red or white throats. Later came chromed brass and then stainless. They are more often now made of flexible PVC. Its hard to say which is harder to keep looking Bristol-fashion…brass or PVC.

Why the throats are red or white is a mystery. (Plastimo, which likes to be different, has broken out of the mold by offering cowls with blue throats; blue was Napoleons color.)

A cowl, directionally adjustable in a horizontal plane to draw in or vacuum out air, usually is mounted on a baffle chamber, a simple double-chambered enclosure of teak or plastic that passes air but collects and drains off rainwater and spray. (Such baffles or water traps generally are called Dorades, after Olin and Rod Stephens famous 1930s ocean-racing yawl, Dorade.) More serious water is excluded by turning the cowl opening away from the wind or, in extremis, replacing the cowl with a deckplate.

The air moved by a cowl is limited by its size and, in addition, is gyved (hindered) by the Dorade, so to be effective cowls usually are found on boats in pairs, quartets or even more. A more recent innovation: To speed up sluggish air, cowls can be fitted with a fan driven by a small electric motor.

Some cowls are snap-ins. But having lost not one but two when, in both instances, a wandering jib sheet hooked under the lip and shot the cowl off into the wild blue, our preference is for threaded deck plates. The threaded models also have deck plate covers that make one more willing to go to weather when one might otherwise prefer to be home. (Youll regret it if you fail to keep the threads lubricated.)

How many cowls do you need? The respected book titled Desirable and Undesirable Characteristics of Offshore Yachts, written by the Technical Committee of the Cruising Club of America and edited by John Rousmaniere, states that the total square inches of cowl intake faces should equal the boats beam multiplied by its waterline length.

A search of the market turned up an interesting variety.

Brass and Stainless Cowls
West Marine offers 3″ and 4″ cowls in either spun sheet brass or stainless. They have painted white throats. Made in Taiwan, they come with sturdy cast deck plates with O-rings and big deckplate keys.

The base on the 4″ brass model is threaded all the way through, so the deck plate cover fits either on deck or from below. That also means that, when sailing in heavy weather with the covers in place, a second cover could be used to reduce leaking (which these cowls tend to do when the O-ring disappears or wears out). Alternatively, a cowl can be stowed upside down inside the boat. Because cowls are hard to stow, the latter is an attractive idea if the cowl does not become a menace to skulls.

The two brass models are $140 and $150. The stainless versions are $160 and $216.

A & B Industries, Inc., known as ABI, also offers 3″ and 4″ cowls in both brass and stainless. Except for the 4″ brass cowl, they are identical. In fact, ABI now supplies the 3″ brass and both stainless models to West. All of the ABI cowls have a knurled locking screw inside the deck plate that can be tightened to prevent rotation or removal of the cowl. ABI took some pains to state that their cowls have powder-coated white throats that wont chip or discolor.

ABI shows suggested retail list prices for its two brass models as $228 and $315. The stainless models, with chromed bronze bases, list for $227 and $316. However, they are available through West Marine at the lower prices.

Rondal makes aluminum and stainless cowls and Paul Luke has cast aluminum and bronze cowls; all are expensive.

Plastic Cowls
Theyre not as carefree as their makers claim, especially as they age and discolor, but PVC cowls are the overwhelming choice aboard most modern boats.

The plastic cowls come in an amazing variety of shapes and sizes. Prices vary from as little as $20 for a small low-profile cowl with a plastic snap-in deck ring and a simple cover about like youd get on a carton of cottage cheese to about $255 for a big all-weather Vetus with a built-in Dorade made of cast aluminum, a stainless mushroom vent in the base, an interior finishing ring and a stainless screen.

The cowls dealt with here as representative models are from Martec, Nicro, Plastimo and Vetus. Except for Martec (whose primary business is folding props), all are very active in the cowl business.

The Martec Dri-Vent cowl, invented about 30 years ago by David Walter Beck, is unique. It has a soft plastic insert in the 3″ throat that forms a trap for casual water that is then drained by two holes in the back of the cowl. Hard water collapses and closes the air passage. The cowl snaps into the deckplate, as does the cover. Both have O-rings. It sells at discount for $58. A Martec Maxi-Vent (the same but without the Dorade) is $48; a small one called the Mini-Vent is $36.50.

Nicro is a big producer of vents. It sells standard and low profile cowls, 3″, 4″ and 5″, snap-in or threaded.

Among its best ideas is a water trap base (for the 3″ models), a sort of spring-loaded mushroom vent that closes when hit with solid water. When the water drains away, the top lifts to resume air movement. It can be manually locked in the closed position. The water trap can be retrofitted to any 3″ Nicro cowl.

Any of the 3″ and 4″ snap-in cowls can be replaced by Nicros widely known Day&Night 2000, a solar-powered ventilator with Ni-Cad batteries for night-time ventilation. (Nicros first solar-powered vent was Practical Sailors Product-of-the-Year when it came out in 1984; the company then was called Nicro-Fico.)

Nicro was the originator of the PVC cowl ventilator; it maintains high quality standards in its entire extension line.

The standard models from Plastimo, the French manufacturer of marine gear, includes no less than seven different shapes in four sizes (70, 75, 80 and 120 mm) with red or blue throats. Except for one of the large cowls, all are snap-ins. Plastimo also offers two sizes (75 and 90 mm) of a low-profile cowl mounted on a Dorade made of rigid ABS plastic.

As all of this equipment was being gathered up for evaluation, Plastimo brought out an entirely new Dorade that shuts itself off if water overwhelms the cowl. Called the Cool n Dry, it is very similar to the Nicro water trap vent. Instead of Nicros domed mushroom, Plastimos version has a large flat dish on the top that acquires weight enough when filled with water to overcome a large soft spring and lower the dish down on a rubber gasket. As the water drains away via three small holes in the rim of the dish, the dish rises and air flow is restored. (It also can be manually opened and closed with a separate spring-loaded trigger mechanism.) It is available as a complete assembly in four cowl shapes or separately, for any existing 60 or 80 mm Plastimo cowl.

The new automatic Dorade is very ingenious, but with a separate spring for the tricky off mechanism and a gasket seal which could be defeated by a bit of debris (which might also collect in the dish), the Plastimo seems a bit complicated when compared to the simple, rugged Nicro.

Actual usage aboard boats (always the best test of all) is certain to come quickly and will provide the answer to whether Plastimos new version is better than the Nicro, which has been around for at least five years .

We had no luck finding cowls made by Sea-Dog (nor could we contact Sea-Dog), but Vetus, the huge Dutch marine gear maker, as usual, very efficiently sent off representative examples of its very extensive line of high-quality ventilating equipment.

The Vetus cowls come in four shapes and three sizes. To their great credit, all screw in securely, the bases and rings (with big finger-sized knurling) are anodized aluminum and all come also with stainless steel mosquito screens, cover plates and interior finishing rings.

Each model and size can be fitted to a teak Dorade box or to a Vetus Dorade in which is fitted a stainless steel Vetus mushroom ventilator. The ventilator (three sizes to match the cowls) can be opened and closed from inside (very quick, very handy) with a big knob operating a bronze screw.

The Dorade base on the largest model is cast aluminum painted white and the cowl can be removed via the ring mentioned above. The others have fiberglass-reinforced nylon housings with the cowls that rotate but are not removable; if one is broken off, the mushroom provides good closure.

The plain Vetus cowls range in price from $106 to $167. The same with Dorades (which include a stainless mushroom) are, at discount, $88 to $255.

Mushroom Vents
More effective than is generally realized, passive mushroom vents work by developing a vacuum when a breeze passes over their domed heads, which can be raised or lowered to increase the opening to the pipe. They are especially good in heads or over the galley. In the latter instance, the rising heat from cooking helps.

ABI imports a heavy (6 lbs.) 4″ mushroom available in cast bronze or chrome. Considering the machine work involved, it is surprisingly inexpensive. Complete with a deckplate key and cover, the bronze version is $161, the chromed $18 more. It has a threaded adjustment post and two turning handles, one to lock the dome in place.

The Vetus mushroom, the same one that is used in their cowl ventilators, is spun of heavy stainless plate. The adjustment post is bronze and the top contains a gasket that provides a tight seal. The Vetus mushroom comes with an interior finishing ring and a mosquito screen. There are three sizes available-3″ ($60), 3-15/16″ ($78) and 5-1/8″ ($103).

For domed ventilators, theres Beckson, Vetus and Nicro.

Becksons venerable Vent-O-Mate comes in one size (3-1/2″), two models. The innards are the same, but the domed cover can be either plastic ($23) or stainless ($48), which has a bug screen. The Vent-O-Matic can be closed and locked manually. It also admits some light.

Vetus makes a 3″ passive dome with a stainless cover that is available solid or with a clear plastic insert to admit light. This one you can jump on. It cannot be closed. It lists for $66. (In the August 1 issue, Nick Nicholson reported in the Offshore Log that this ventilator needed repairs when some spot-welds failed, apparently because of saltwater corrosion.)

If more air is needed, the Vetus ventilators can be fitted with an electric fan, 12V or 24V, that is virtually noiseless and moves 42 cubic feet of air per minute. The 12V model draws but .22 amp and its brushless motor has a life expectancy of 50,000 hours. Its $93.

Vetus has strong feelings about ventilators. It uses mushrooms in its cowls, but maintains that domed ventilators should not be closable, to keep the inside and outside temperature and humidity the same and thus prevent condensation.

In its catalogs, it also says:

Ventilators powered by solar cells are, in our opinion, not useful since they start operating when it gets warmer during sunshine hours when the air can absorb more vapor. They should, in fact, operate at night when the air is cooler and condensation takes place, but they don’t do that.

Not in agreement with that is Nicro, which makes seven different domed ventilators, six of which have fans powered by 12V, solar or Ni-Cads, in two sizes (3″ and 4″) with white or black plastic or stainless steel covers.

The smallest and simplest is the Airvent 500. Its only moving part is a plastic push-pull cylinder that serves as a damper/closer. It costs about $22 (another $22 for a stainless cover). Its just a few pieces of plastic engineered, molded and assembled so that, when caressed by a breeze, it develops a surprising amount of suction. Itll move 600 cubic feet of air an hour in a 15-knot breeze. The top has a transparent insert that admits light.

The top-of-the-line is Nicros PowerVent 3000, a 4″ vent that is solar powered, but also has a Ni-Cad battery charged by the sun to operate at night. This square vent ($132) will move 900 cubic feet of air an hour, day or night, has interchangeable fan blades for intake or exhaust, can be closed from inside, can be switched off and comes with a trim ring and insect screen.

In between are several other models: solar/passive, 12V/solar and two-speed 12V models. The most powerful, the 12V model, can move 33.3 cubic feet of air per minute or 2,000 cubic feet of air an hour. Further, most of these can be snapped in place of a Nicro cowl ventilator. Nicro also has optional trim rings (including teak); hole liners; hose and bulkhead adapters, and screens.

To close out this epic on ventilation, here are two gadgets deemed irresistible. They are called Charlie Nobles. We know what they put in dandyfunk, but take this as a reader challenge: Who exactly was Charlie Noble? Our dictionary says its slang for a smokestack or galley exhaust.

ABIs 3″ exhaust vent is a box-headed ventilator with a slotted internal pipe that draws out air but excludes water. The 4-pound ventilator, available in bronze or chrome, screws into a 6-pound deck fitting whose in-the-cabin portion is a ribbed flange that accepts a 3″ pipe, if desired. The vent and deck fitting, including a nice finishing ring, cover and key, will set you back about $300.

Finally, its perhaps silly (mostly because it seems fragile) but shown in the photo on the preceding page is a rotating Charlie Noble that resembles those ventilators that used to be on chicken houses. It fits on any 3″ deck plate (but might blow off). Made of sheet stainless, the coolie hat with a wind vane swivels with the wind and sucks air up its 3″ pipe. Imported by ABI, it lists for $65. We tried it out and it weathercocks in as little as 5 knots of wind.

Nick Nicholson
Nick Nicholson is a boatbuilder, racing sailor, and circumnavigator. He began his career at Practical Sailor as an Associate Editor in 1979, and has been Editor-at-Large since he left full-time work in the early 1990s to finish building a 40’ cutter in his backyard, and subsequently sail it more than 40,000 bluewater miles. The voyages of Calypso were chronicled in the Offshore Log section of Practical Sailor during that circumnavigation. He has also raced from the US east coast to Bermuda more than 20 times, winning numerous navigator’s trophies in the process. In recent years, he has primarily worked as a race official and technical rules advisor in the Volvo Ocean Race and the America’s Cup. He also chairs the Technical Committee for the Newport Bermuda Race.