March 16, 2006 - Ventilation without Inundation
by Michel & Jane DeRidder

An unaired boat grows old before its time.

On dank, humid vessels electronic failures abound, camera and binocular lenses grow threadlike fungal decorations, aluminum goes powdery, bronze turns green, fastenings bleed through flaking paint, and rust streaks everything. Crew comfort and well being is seriously affected by lack of ventilation below decks. Both heat and cold are more likely to be felt if air is motionless or stale. Clothing becomes musty. Towels go sour. Judgment is impaired. Heads ache.

The discomfort brought about by a stagnant atmosphere can be relieved by fresh air. Besides spiraling the comfort factor, a free flow of fresh air through a vessel keeps away dry rot, the only treatment for which is surgery. Good ventilation as a preventative measure beats that.

Although an obvious solution to so many maintenance problems and a major contributor to a happy crew, good ventilation is all too often undervalued or ignored. To let in air without letting in water is the secret of nautical longevity. To arrive at this ideal state of affairs may be easy enough in port or at anchor - though even there problems exist - but to attain ventilation without inundation is something else again in a seaway, particularly when going to weather when the choice is all too often clear cut. Stale, still air, or sodden bunks? Suffocate, or saturate? Or both?

With most yacht orifices whose function is to air the boat, the trouble is they are equally efficient at bringing in water. Portholes are a good example. Either they're left open when they should have been closed, or they leak around the edges, or let water come dribbling or cascading in when opened. A porthole designed to go on outward-leaning ship sides automatically drains outside, but when the same porthole is used on cabin sides sloping inwards, it collects water which pours into the boat when the port is opened. We try to make sure that books, radios and so on are located where they cannot be doused. For many years we had no opening portholes so as to avoid inadvertent soaking of valuable gear with salt water (on boats everything is a compromise). Even now, we have only one opening port, and that in the galley where the occasional splash won't cause any damage, a blessing worth waiting far too many years for.

We are not as comfortable dockside as we might be. We are far better off lying at anchor lined up with the wind to get a flushing of air through our sealed self. There's no air conditioning on the doughty dragon. In hot weather, to get more breeze in the cockpit, we sometimes anchor by the stern. (Magic Dragon does not swing as much when stern to.) We have a windscoop to funnel air down directly through the companionway into the main cabin. In very calm conditions when air does not circulate, we have six fans in various parts of the boat, obtained here and there over the years, plus two more in the engine compartment.

Hatches are the best way of airing our boat. On some of the Caribbean charter boats it was interesting to note that huge hatches had been cut out over dining areas, ones that could be raised, removed, or propped up in any of four directions to scoop air. These hatches were often situated under permanent sailing awnings so that they could be kept open in drizzle. One I remember was under a cockpit table. We've experimented with webbing hinges (made of seat belting) with pop button fasteners to enable a couple of our hatches to be opened fore or aft, to port or starboard.

Hatches can have their efficiency increased by using wind scoops - sail cloth poltergeists cut and formed for maximum draw, battened for stiffness, suspended perhaps from a halyard. Wind scoops can also be used at sea to encourage air to find its way below decks when the going is light and temperatures soar. They may be equally clever at scooping up rain and spray, so they should be easy to haul down at a moment's notice. We've seen some marvelous ones. We have a few of our own, not as effective as some, but helpful.

It is pleasant to be able to keep hatches open even when it is raining. Slanted louvers built of quarter-inch painted plywood allow us to keep hatches open in all but driving rain, though we find they do cut the air flow to some extent. A cruising friend had a big hatch in the shower which could be left open in rain or spray without soaking anything that matters too much. It made a great deal more sense than the system on the character ketch which we'll call SLUICE that friends of ours delivered back to California from Tahiti. Water came in everywhere, jetting in from between planks, squirting in through deck seams, percolating in via the cabin deck joint, seeping in around portholes, hatches, what-have-you. The only dry place on the whole boat was the shower. There they stored their diminishing supply of dry clothing sealed in plastic bags as they pumped their way across the Pacific.

If wind and weather is such that hatches must be kept closed, then dorade ventilators are amazingly effective, providing they are big enough. Named after the ocean racer DORADE, these are air scoops with water traps designed into them. Ideally dorade vents should be of sufficient size and number to keep a current of air moving through the entire ship. At sea in lashings of spray and rain, at anchor during downpours, or tied up to docks when hatches and ports are locked for security, dorades may be the only source of ventilation. The dorade box or water trap must provide sufficient drainage to allow water to escape without unduly affecting the passage of air. The dorade scoop necks must be long enough to avoid the worst of the green water on deck. The scoops should, of course, be free to turn 360 degrees so they can be turned into the wind to gulp air, or away from wind to avoid solid water. When conditions deteriorate and water courses on deck, dorade ventilators may have met their match, for if water is forced in more quickly than the ducts can drain it out, the vents may exude trickles of sea water into the boat. At this stage of the proceedings you either arrange shower curtains and towels to catch the occasional dribble, or else you have some means of closing them off. (See Changes over the Years for pictures and info about closing off dorade vents in storm conditions)

Dorade maintenance.

If you have a cockpit dodger that can withstand the elements, you can keep the main hatch open even in heavy weather. We rate storms by the number of storm boards it is thought wise to have in the main hatch opening in case of a breaking sea splashing into the cockpit. One-board storms are a rarity. Two-board storms are almost unheard of. The third board has yet to be used. The trouble with the storm board system is that, once again, the human error is the one most to be feared. The temptation is to put the boards in too late (after the washout and mop-up, that is) or to take them out too early in a burst of optimism, not allowing for a rogue wave. You don't want to be caught out with your storm boards down!

When the weather is so bad that our ports and hatches are battened down, dorades sealed off, storm boards two-deep dropped into their slides, our 12-volt fans keep air moving. At such times a good book can help us forget our misery. As a last resort there's always sleep - and the knowledge that it can't last forever.