cowl vents for sailboats

This ventilation system was named after the yacht which was designed, navigated, and sailed by American naval architect James Stephens. The was the winner of the 1931 Transatlantic and Fastnet races.

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Sailing Whimsy

Adventures on a classic Pearson 35 sailboat

Monday, September 5, 2022

Installing a dorade box vent on my sailboat.

Adequate ventilation inside a sailboat's cabin is a must, whether in the hot tropics or colder climates where condensation becomes a problem. Being stuck inside a hot damp boat interior with no fresh air circulation is a miserable experience especially on passage, or even on a rainy day at anchor, when opening the portlights or top hatches is not an option. 

Whimsy will have 8 opening portlights (7 on cabin sides and an aft-facing one over the galley sink) but because boats tend to point into the wind, cabin-side opening portlights are generally not as effective in promoting air flow. A forward-facing portlight is also not an option as the force of waves crashing over the bow can possibly stove-in the area, not to mention the leaks. The solution is a Dorade box vent.

 Dorade vents are named after the Olin Stephens-designed sea-racing yacht  Dorade  built in 1929 when the Robber-Barons took up pleasure sailing, which is surprising because it seems like such a simple solution to a common problem that should have been invented much earlier: how to get air ventilation below deck without letting water in too.

A Dorade box vent basically consists of a rotating cowl that can be pointed into the wind, attached on top of a teak box that has an internal baffle,  which is placed over a hole on deck. The idea is that the internal baffle will keep out most of the sea spray and rain, which drains out from the bottom of the box, while the air moves over the baffle, down the hole & into the cabin. 

Getting air into the cabin is part of the deal; there also has to be adequate air exhaust routes for proper ventilation to occur. A Dorade box cowl can be pointed away from the wind too, creating negative pressure that will tend to suck air out of the cabin. This is why larger boats can have pairs of Dorade box vents: one facing fore and one facing aft, creating a continuous draft through the boat interior. 

Whimsy doesn't have the deck space for two vents and won't need one because the companionway as well as the yet-to-be installed aft-facing opening portlight over the galley sink, will provide enough of a passive air exit. They will in turn be protected from rain and spray by the yet-to-be installed dodger.

Parts for this project consisted of an off-the-shelf teak Dorade box, a cowl whose base just barely fit over the box, and a ring cut off of 5"wide PVC pipe.

The cowl is the most problematic part. One of the issues with Dorade box vents, other than their primary drawback which is taking up large tracts of deck space, is that the cowl can be a nuisance, fouling lines and banging shins. Traditional Dorade box cowls are fancy highly polished, hard metal objects with sharp edges that look pretty but a jibsheet caught around a Dorade box cowl can potentially rip it right off, and I'd hate to trip onto a cowl. Traditionally the solution was to build a steel cage around the vent to prevent all that, thus taking up yet ore space and not reducing trip hazards. 

Manufacturers came up with PVC cowls that are flexible enough not to foul lines and to not cut you open if you should fall on then, but the general consensus is that they don't fare well under the sun and also tend to stain, turn yellow or mildew. Vetus however has come up with soft but rigid cowls made of silicon, which supposedly fares better than PVC under the sun. I guess we'll see but the material doesn't feel floppy as I had feared.  Anyway I got the biggest cowl I could find to maximize airflow: the Vetus  Samoen  cowl with a gaping air scoop painted red and 5"-wide opening hole on the base. 

The installation of my Dorade box vent was pretty straight-forward as there aren't too many places to install one on deck. I was most concerned with making sure it did not interfere with any lines running aft to the cockpit. Then, installation was simply a matter of cutting a 5" hole on deck, and a slightly larger hole from below (for the cover plate). I went through the usual process of scooping out the balsa core material and filling the gap with epoxy filler. I had cut off about  2" length off of a 5"-wide PVC pipe to make a plastic ring; this was installed over the deck hole with about a 1" tall lip sticking up, acting as a dam to further limit water intrusion around the deck hole. Then a few coats of gel coat, and the quickly "varnished" teak box was stuck on the deck top with 3M 5200 only (I don't see any reason why it would need to be more securely fastened on deck, and additional fasteners just mean more holes for water penetration.) 

To close up the Dorade box vent from below, a 5" (internal diameter) waterproof plastic deck plate was installed from the interior under the hole. 

I decided to varnish the teak box. Though teak tends to be naturally weather resistant, I was concerned as the boards used to make my Dorade box were kinda thin, and so could use protection. I also like the glossy look of varnished wood. The quick-and-dirty varnish job was just two coats of epoxy (first one was Totalboat "penetrating" epoxy, as teak tends to be oily & not stick well to epoxy resin) followed by two coats of Interlux Perfection Plus to give it a glossy look, as well as to protect the epoxy from the Sun's UV.  The final coat was a spray of glossy acrylic from a can with additional UV inhibitors; not strictly necessary but helped deepen the gloss.. Of course there are drips and dust specks galore; I am working in a dusty boatyard. 

So, now Whimsy has pretty much maxed-out the natural ventilation options. Combined with multiple fans, there is not much else that can be done to improve ventilation below, but for a small screen on the cowl to keep out bugs.

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Simple Tips to Improve Boat Ventilation

As ventilation experts explored ways to make indoor spaces safer during the COVID-19 pandemic, we became curious about ventilation in our boats. What products and practices ensure that we maximize the volume of air exchange belowdecks, as measured in cubic feet per hour (CFH)?

While this exchange of fresh air provides direct benefit to our health, it also provides an indirect benefit by preventing the growth of mold and mildew. Generally, to successfully combat mold in any given space you need at least one air change per hour, and for boats from 25-40 feet that is about 700-1800 CFH. Good ventilation also helps remove warm moist air created during cooking that can condense on the inside of the cabin—creating the moist environment that mold loves.

We’ve looked at ventilation dozens of time over the past 10 years, but most of those previous studies focused on a particular product group—fans, hatches, vents, opening portlights, or air-conditioning systems. In the September 2020 issue we narrow the focus to passive ventilation—cowl vents, dorades, hatches, “wind scoops,” and other ways to boost the exchange of air on board without any mechanical assistance.

Boats are relatively small spaces, and you’d think that it would be easy to keep interior air fresh with a few ports and hatches. As it turns out, where you install your inlet and exhaust vents is as important as the kind of vent (hatch, port, or vent) you use.

Most sailors know that wind blowing across a uniformly smooth surface such as the leeward side of a well-trimmed sail creates a region of reduced pressure. Just as we can use the resulting suction on the leeward side of a sail to pull the boat forward, we can use pressure differentials in the air surrounding the cabin to maximize the ventilation belowdeck.

Understanding the pressure differentials created by the flow of wind over our boat’s deck is vital to the success of any passive ventilation scheme. Mapping this flow (see the below image), helps explain why some areas of the boat seem stuffier than others. It also explains why passive ventilation methods did so poorly in our testing.

Your boat’s cabin trunk has a number of pressure zones, and these zones change depending on the wind direction. At anchor, the front of the cabin trunk is an area of high pressure, and this pressure reduces slightly as you move aft. The pressure differential between locations along the cabin top on depends many factors, including the shape of the cabin and any items on deck that might interfere with flow. In general, the pressure is lowest just behind the front edge of the cabin trunk, slowly rising to neutral pressure as you move aft—depending on the extent of turbulence caused at the front of the cabin trunk or by other interruptions in the smooth surface that would disrupt the flow of wind.

The companionway area has the lowest pressure. Open a hole anywhere forward and air will be sucked out the companionway. In a breeze, the pressure differential is usually so great that air will push out through gaps in the weatherstripping, escaping even if the companionway hatch closed.

Maximizing air-flow through cowl vents is trickier than it might seem. Air-flow can be interrupted not only by insufficient pressure differential, but also by turbulence. The vertical cabin-sides, dinghies stored on deck, masts, changes in wind direction, and even other cowls can dramatically reduce the amount of wind that reaches the cowl.

The most complicated case is when you keep the boat at a dock with everything buttoned up. The wind can blow from any direction, and depending on the amount of protection afforded by the harbor and neighboring boats, the wind will be light most of the time.

Bottom line: Although many passive vents are rated by CFH, these ratings don’t tell the whole story. Flow will vary greatly depending on the location of the vent, and since the rated CFH is typically based on a 10 knot breeze, the rating won’t give a clear picture of air flow when your boat is at the dock. At many marinas around the U.S., the true wind at deck level is less than 5 knots most of the time.

For more on ventilation, see the September 2020 issue of Practical Sailor. If defeating mildew is your main objective, our eBook The Mildew-free Boat will cover everything you need. If boosting breeze belowdecks is your primary aim, the following related Practical Sailor tests will help you improve the flow of air down below.

Ventilation Can be Improved on Any Boat

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

Fabric Hatch Vents: The Breeze Booster Outdraws Windscoop

How to Measure Boat Humidity: Psychrometric Charts Do it Right

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Cabin Fan Test: Hella, Caframo Blow Best Breeze for the Buck

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On watch: this 60-year-old hinckley pilot 35 is also a working girl.

Because my last boat (a J/24) stunk of mold, I came up with a solution for my current 38’ sloop that I can recommend without hesitation. I’ve installed an inexpensive modular ‘daisy chain’ of DC USB ‘computer’ fans underneath and behind the boat’s beds, cabinets, and seating areas. The hidden & silent fans are UL Listed and connected to each other via USB-to-USB extension cables (with inline fuse). The fans are each rated to run for 10 years and I’ve run them continuously for the past 5 years with no problems. The fans are all oriented in harmony to increase airflow circulation belowdecks…in and around all of the many spaces where humid air tends to stagnate, and (combined with the Practical Sailor recommended Eva-Dry 2200 dehumidifier) have completely eliminated ‘that boat smell’ caused by mold, etc.. The fans are each rated to run for 10 years and move 64 cubic feet per minute of air, and entire system cost me less than $100 on Amazon. I can recommend it without hesitation.

In light air, no fetch, anchor off the stern. Leave the dodger and Bimini up. Open all hatches, put up the mosquito netting, and the dodger / Bimini act like a BIG wind scoop. The breeze is great and is especially welcome below when the bugs on deck are wrecking your romantic dinner.

We’ve been very pleased with the performance of Karecel fans, which are small and recharge with a USB plug. They have 3 speeds and are nearly silent. We got them from Amazon and the come in black or white. For the price ($18), you can’t beat them.

Your comment above: “The companionway area has the lowest pressure”, conflicts with your diagram showing average pressure at the companionway. Where’s the truth?

If there is one area that needs intensive product improvement it’s marine ventilation! solar vent fans havent been properly updated since the 80’s (and the prices are utterly unjustifiable). There are of course beautiful and justifiably pricey scoops etc in Bronze etc but most of the plastic and resin originated items just don’t address the need for forced air and energy sources most available to small to medium size yachts….Solar solar solar! modular design! micro connectors to discreetly run solar power to various fittings….scoops that really seal, fans that blow and are efficient actually last 5 years! no lousy rusting parts! The biggest culprits are the companies managing the few solar fan products out there….Someone needs to take the challenge and design a growing array of good (affordable) devices to render the interior of yachts habitable! W ith plastic casting and current solar technology there is no excuse for the scarcity of effective devices!

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boat cowl vent 16922

... constant quality supply wof several flexible vents per year. The most essential features of Plastimo vents are : material flexibility, resistance to UV-rays, easy mounting, smooth and glossy aspect. Model ...

boat cowl vent 54.C

Brass cowl ventilator DimensionsØ 56 - Ø 120 mm Height220 mm Brass cowl ventilator Finish .L Polished .C Chromed

fabric wind scoop 1010

... Thanks to its 4-chamber system, our wind scoop creates optimal air circulation and does not have to be adjusted to any wind direction. The special material causes very little noise and is UV-resistant. The ...

stainless steel cowl vent 1134 series

Mirror polishing. Stainless steel deck plate. White powder coating (on request blue or red).

stainless steel cowl vent 01.850

made from polished stainless steel AISI 316L CODE - A - FIXED - PRICE 01.850 - Ø 72 mm - Ø 5 x 35 mm - 30,00 €

fabric cowl vent BP914

fabric cowl vent 1101405

boat cowl vent DP-LP series / DP-HP series

Add extra ventilation with this adaptable deck plate. Cowl vent may be removed and standard smooth center plate installed to keep deck clear and watertight. Eash unit includes both vent ...

boat cowl vent 03306

PVC FLEXIBLE VENT WITH COVER A 95 mm B 160 mm C 235 mm

boat cowl vent H6500 Series

FEATURES-DORADES•Hand and elecltopcJished 18-8 norwnagnefic stainless steel.•Snag-free, low profile design.•Teor drop opening for optimum circulation.•Stairless sreel deck plate provided with Oing•Additional deckplates available separately.

boat cowl vent classic

ORANGEMARINE wind scoop classic allows the maximum aeration of the anchored boat . It is stiffened by a slat and held in position by a halyard.

stainless steel cowl vent DORADES

18-8 non-magnetic stainless steel. Hand polished and electro-polished chrome plating to protect against corrosion. Snag-free design. Low profile with tear drop opening to allow maximum air to enter the dorade box. Stainless steel Deck ...

freestanding wind scoop

Freestanding windsock with single attachment, no halyard required. Quickly fits all deck hatches on sailboats, powerboats and catamarans. Its rod structure maintains the profile and improves air circulation. An optional mosquito net is available.

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boat cowl vent 4876

Traditional cowl vent € 113,00 Specifications Article number: 4876 21,5 x ø 12 cm Air opening: ø 5,6 cm

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A boat cowl vent is a through-deck fitting generally taking the form of a curved tube with a flared mouth. It is designed to direct exterior air below decks for ventilation purposes. Fabric wind scoops serve the same purpose when installed over deck hatches. The models offered on NauticExpo are intended for leisure craft.

The close quarters found below decks on many recreational vessels all require ventilation. Cowl vents are designed to provide the necessary air circulation.

Such devices are generally metal or plastic. Some, such as dorado vents, have an elbow or other system to prevent rain or seawater from entering. Vents can be round, rectangular, ovoid or another shape. Most models swivel, allowing them to be turned into the wind regardless of its direction. Fabric wind scoops are suspended above hatches to maximize below-decks ventilation. They are extremely light and easy to stow once removed.

Rigid, fixed boat cowl vents cannot be moved after installation. Choose the size and installation point carefully. For more flexibility, consider a fabric wind scoop. It is efficient, easy to use and requires no additional hole in the deck.

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• Jan 9, 2023

Installation Instructions for cowl vents, dorade boxes and guards.

The first step is to decide which deck location(s) will be suitable to mount the dorade, mushroom ventilator, and dorade guard if one is being installed at this time.  You need to consider the traffic patterns commonly used to move about the boat.  Can you go around the ventilators or do they become an obstacle nuisance.  Before you start drilling into the deck consider for a moment what is below.  Is there any electrical or plumbing that needs to be avoided.   Can the opening in the deck be clear of all bulkheads.  Will the airflow that enters into the space below provide adequate ventilation. Can you mount a trim ring to the headliner?  Do you have good access to the knob of the Low Profile Ventilator to adjust the amount of airflow into the cabin space.  You must determine the thickness of the deck to decide whether you can thru bolt the fittings of the ventilator or do you need to mount it using sheet metal or wood screws. 

You have chosen the site to drill the opening in the deck.  Is the deck flat or does it possess some amount of camber to deal with.  If it is flat then you can proceed to the first step.  Here you will decide if you want to reduce the height of the dorade box keeping in mind that if you choose to use a Low Profile Ventilator you will need to consider the maximum height of the open ventilator to clear the bottom of the dorade.  Once you drill the opening it is suggested that you seal the core of the deck with either epoxy or polyester resin.  You can proceed to mount the Low Profile Ventilator.  It is quite light and can be mounted with screws.  You should first add a bedding compound like butyl Tape or 4200 caulking compound before securing the ventilator for waterproof protection.

If your deck has a camber to it you will need to decide if you want to leave the bottom of the dorade flat or to cut the bottom of the dorade to compensate for the camber.  This can be easily done with a protractor and marking the angle of the deck unto the surface of the dorade.  There are a number of tools that can be used to cut the dorade ranging from a bandsaw to a hack saw.  If you are comfortable and proficient you can also use an electric skill saw.  Be sure to use face and eye protection which ever method you choose.  Apply epoxy or polyester resin to the raw fiberglass edge.

Step number two involves mounting the Dorade box.  Before you begin, it is important to make one or more weep holes in the sides of the dorade where the seawater can escape through the weep holes where the dorade sits on the deck.  You have been provided with (2) Heavy Duty  stainless steel angle brackets to secure the Dorade to the deck.  Fasten the brackets to the inside wall where the Dorade edge meets the deck.  Calculate the center of the dorade over the Low Profile Ventilator.  Continue now to mount the brackets to the deck.  I would advise thru bolting the fasteners because of the added weight of the Cowl Vent and the unlikely possibility of wrapping lines around the vent.  They also become valuable hand holds when moving about the boat particularly when the sea and things get dicey.

Step number three involves mounting the Deck Plate to the top of the Dorade.  If a hole has not been drilled into the top, now is the time to measure for the center of the dorade so that a hole saw can drill the appropriate size hole.  For a 3" Deck Plate a 3-1/2" hole saw will be used and for a 4" Deck Plate a 4-1/2" hole saw is used.  Because you are drilling into polyester fiberglass it is imperative to use a hole saw with a strong blade.  Otherwise you will quickly destroy the unprotected blade.  Before mounting the Deck Plate, use a small amount of butyl tape or 4200 to the surface of the dorade.  Also seal the exposed fiberglass surface of the dorade with epoxy or polyester resin.  Mount the Deck Plate to the Dorade with screws, lock washers and nuts that have been provided.

Step number four describes mounting a Dorade Guard to the deck.  The Dorade Guard offers many benefits to the safety of the crew and protection of the Cowl Vent and Dorade from lines, sails, emergency rafts, wayward dinghies  other gear often hand tied to the Dorade Guard.  It has been designed to be mounted in several possible positions in relation to the Cowl Vent.  It can be mounted looking forward or turned 180 degrees to face aft.  Sometimes it is positioned to face starboard or to turned to face the port side.  Which ever position is used most importantly it must be strongly secured to the deck with a minimum of 3/16" fasteners thru bolted with a backing plate.  Once again epoxy the holes in the deck and bed the guard feet to the deck with butyl tape or 4200.  Keep in mine that the dorade guard has been fabricated with 1" tubular Type 304 stainless steel with a wall thickness of 0.060".  It has one welded joint connecting the three legs.  It is strong but does have its limitations.  It will provide many years of service if you treat it accordingly.

This is a brief description of the installation of the Ventilation Package consisting of the Cowl Vent, Deck Plate, Dorade, Low Profile Vent, and Dorade Guard.  I am certain that there may be additions and comments which I encourage.  Thank you for your business and smooth sailing.

If you have any questions or would like to place an order please call me at +1 (415) 895-8395 or visit www.buchanmarine.com

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Good ventilation aboard provides a number of benefits to both the crew and passengers. It provides a source of fresh air in any weather conditions, helps to prevent bad odors and mildew, and can even save somebody's life by removing carbon monoxide in the case of an emergency. If a non-open vessel is outfitted with a gasoline inboard motor , the ventilation system having a blower is a legal requirement. Commonly, the vent layout includes special channels (ducts) that have openings known as air inlets and outlets. Typically, these openings have different kinds of plastic or metal vents available in various shapes and designs.

There are louver, cowl, mushroom, and other types of vents that can be installed on the deck, walls, or other constructions. The square of vent holes and their location have to meet specific requirements. For instance, air outlets should be installed above any possible bilge water level. In our online store, you will find a large assortment of boat vents offered in different kinds and sizes. They are made from high-quality plastic, stainless steel, brass, or other materials and feature appealing finishes, so you will certainly find the products that suit your project best.

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Low Profile Cowl Vent with Deck Plate

Purchase options and add-ons

• HIGH QUALITY MATERIAL - Made and cast from 316 Stainless Steel Vent and Deck Plate Dorade as it can resist rusting, corrosion from marine environment, saltwater, acidic elements, and high temperature.
• DORADE VENT - The Cowl Vent can be changed to a Deck Plate Cutout 3-3/8", Deck Plate 4-7/8" when not in used. The Deck Plate have a rubber o'ring gaskets to make sure on water goes thru the boat.
• BOAT VENTILATION - Vent Opening Dimensions 4-1/4" x 2-1/2" which can help to circulate the fresh air within the cabin of the boat.
• DECK VENT - Polished and Mirror finished Low Profile Cowl with the Height Above Deck 3-5/8" with the weight of 6 lbs. Can be easily maintained through the use of fiber cloth and cleaner.
• FRESHER AIR - Steamy air permeates everything inside the cabin, fostering rot, corrosion, and mildew that are damaging to boat, gear, and locker contents. The cowl prevent hull blisters.

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Product Description

(1) Cast stainless steel cowl vent including deck plate ring, cap and key. Casted with 316 stainless steel eliminating corrosion in the marine environment. The vent is polished and has stainless mirror finish. The interior is painted white. This vent threads into a stainless steel deck plate. The deck plate is also casted 316 stainless steel. This vent and deck plate cap has a rubber o'ring gasket to insure water will not leak. The deck plate has a star pattern on the cap, the star pattern is the same size as most winch handle star pattern 11/16" (17.5mm)

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Customers like the appearance and quality of the cowl vent. For example, they mention it looks great, is well made, and has an excellent design. Some appreciate the sturdy flanges and the fact that they are made of high quality material.

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Customers are satisfied with the quality of the cowl vent. They mention that it is made of high quality material, and is extremely well-made. They also appreciate the sturdy flanges and the fact that they are American-made and look great installed.

"...Installation and sealing is easy with their sturdy flanges . I chose to use butyl tape since the solid flange allowed for easy compression." Read more

"I am pleased to have found these extremely well-made cowl vents as a replacement to the (most-recent) pair of cheap-o "Sea Dog" vinyl-plastic vents...." Read more

" High quality material , these will oulast the vessels life, will replace original equipment able to lock in place will not be lost to Neptune." Read more

" Very high quality and finish ." Read more

Customers are satisfied with the appearance of the marine vent. They mention that it looks great, has excellent design and workmanship, and is well-engineered.

"...They are well made, wonderfully polished and packaged extremely well. (The cloth bags were a nice touch!)..." Read more

"...that these Buchan Marine vents are durable, well-engineered and aesthetically pleasing; a significant step above their cheap-o "sea dog"..." Read more

"Incredibly disappointing. The external stainless steel is beautiful , but the paint on the inside of the cowl peeled away after only 1 year...." Read more

" Great looking stainless cowl vent for the great price" Read more

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Exceptional Quality + American-Made + Look Great Installed

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Ventilation

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• Hatches (7)
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Marine Ventilation

Proper boat ventilation practices are required for several important reasons. USCG regulations require potentially explosive fuel fumes be removed prior to engine starting. This is especially critical after refueling. These regulations apply to all gasoline engines including outboards.

Suitable ventilation of passenger areas, particularly enclosed areas, is crucial to prevent carbon monoxide poisoning. Boats with the right cabin vents will have cleaner, fresher smelling cabins. The right configuration minimizes the appearance of mildew and mold. Adequate ventilation of the head area will also go a long way towards preventing unpleasant odors.

Boat Ventilation Systems

Gasoline Engine Ventilation: Gasoline fumes are volatile, heavier than air, and potentially explosive. Gasoline vapors naturally settle in bilge areas if not properly ventilated. The operation of a bilge blower is necessary to evacuate any possible gas fumes from this enclosed space. Marine specific fuel fume detectors should be installed in enclosed areas as a safety precaution.

Passive or Natural Ventilation: A natural ventilating system typically consists of a minimum of two ventilator ducts connected to cowl vents or an equivalent device. Air intake ducting runs from the open atmosphere to the bottom of the bilge compartment. In addition, the system will have exhaust ducting leading midway from the bilge or near the carburetor out to the open air. Larger boats may require multiple vents and ducting in order to provide adequate under-deck ventilation. A passive system will only function when the craft is underway, therefore, a powered ventilation system is needed prior to engine start-up. Natural systems are required for enclosed fuel tank compartments.

Powered or Forced Ventilation: The USCG revised the regulations in 1980 to require powered ventilation systems on gasoline fueled inboard, inboard/outboard boats. This regulation did not apply to boats built prior to that date. However, it's a good idea to ugrade older gas powered craft to modern systems. This regulation also does not apply to diesel installations. Diesel is not a volatile fuel like gasoline. However, leaking diesel fuel can catch fire, so fume detection is a good idea.

Ignition protected bilge blowers should be operated for at least four minutes before starting engines. The bilge area should also be checked for the possibility of liquid gasoline from leaks and any vapors present.

SAFETY NOTE: Only fuel tanks designated 'for below deck use' should be used in enclosed area. Above deck tanks should NEVER be placed or installed in enclosed areas. Above deck tanks are red in color and are not impermeable to gasoline vapors.

Propane gas Ventilation: Propane gas is similar to gasoline fumes in that it is heavier than air and will sink to the lowest available areas. For this reason, propane tanks should be installed in proper lockers that are sealed from boat interior areas and vented outside of the boat's hull. Marine specific propane gas detectors should be installed as a safety precaution.

Engine Air Intake Vents: Many power boats feature a ducted system to moves fresh air from outside the hull through louvered grills, dorade boxes, air duct hoses and then directly to engine air intakes. It is important that these systems are designed and installed to minimize the possibility of water intrusion.

Passenger Area or Cabin Ventilation: Cabin fans, opening portlights. and deck hatches are important elements of a well designed ventilation system. A solar powered deck vent is an excellent way to circulate fresh air into head compartments. Continually flowing fresh air will help prevent mildew and mold. A combination of powered and passive air vents will ensure adequate flow of fresh air is maintained, even when the boat is unattended.

Carbon Monoxide Precautions: Carbon monoxide poisoning is an insidious, odorless, invisible killer. Carbon monoxide gas (CO) is clear and odorless, often present without the appearance of clouds of exhaust smoke. All boats with gasoline engines, gas powered generators, stoves, heaters or even charcoal grills are potentially at risk for CO poisoning. Engine exhaust system leaks, whether gasoline or diesel, are a potential source of carbon monoxide fumes. All exhaust connections should be routinely inspected for cracked manifolds, damaged pipes, deteriorated hoses, loose clamps, etc. These inspection procedures also apply to generators and all propulsion engines. Hoses should be double clamped for safety. Seal all engine bulkhead compartments to prevent CO gas leakage into passenger areas. Consider installing a carbon monoxide detector as a safety precaution.

Common Boat Vent Types

Cowl Vents are available in a variety of styles, sizes, and materials. Vinyl cowl vents are a popular choice due to their classic appearance and reliable performance. Vinyl vents work well on deck due to their soft rubber construction. Stainless steel vents work well in locations not liable to see continuous foot traffic. A Dorade box is often used to permit air flow while shedding water. Mosquito screens are a popular accessory, to keep fresh air flowing and insects out.

Mushroom Vents are more difficult to install but offer a lot of versatility. Mushroom vents often have a low profile design, making them desirable for deck mounted and hatch mounted applications. Available in passive and solar powered versions.

Clamshell Vents are the simplest in construction and to install. They are not designed to be directly connected to hoses. Clamshell vents need to be selected and installed carefully as they do not shed water effectively.

Louvered Vents are designed specifically for engine air intake applications. Most are rectangular shaped, and intended to be installed on flat surfaces. Available in stainless steel or ABS plastic construction.

Portlights are designed to be opened for ventilation and sealed shut for heavy weather conditions. Mosquito screens are available to keep the bugs out. Also known as portholes, they can be found in a variety of shapes; round, lozenge, rectangular and oval. Typical port lens material is acrylic; some ports use polycarbonate (Lexan) lenses.

Deadlights are also known as portholes. Unlike Portlights, Deadlights are fixed, in that they admit light but are not designed to be opened. They have no ventilating properties. No screens are needed.

Boat Hatch Types

Deck Hatches are designed for through deck and cabin top installations. They feature heavy duty aluminum frames and rugged acrylic or polycarbonate lenses. They are all capable of ventilation functions and can be locked securely for offshore use. The larger ones may also serve as emergency escape hatches.

Access or Inspection Hatches are constructed from resin or plastic, making them suitable for mounting on bulkheads, cockpit sides, center consoles or where foot traffic is unlikely. Available in locking and non-locking versions, they provide offer handy access to lockers, storage bins, fishing tackle, etc. Access hatches must be installed on flat surfaces.

Additional Marine Ventilation Resources

The Chapman Book of Piloting and Seamanship is the essential guide for power and sail boaters. Chapman features an extensive chapter describing the requirements of safe ventilation systems for gasoline powered vessels. In addition, there is a detailed write up of how to safeguard against carbon monoxide poisoning.

Need help or have questions? The FAQs in our Help Center cover most account, order, or product-related topics. Click to call or chat with our Total Support Team.

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