Systems+Engines

Fresh air below

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Despite all the progress in sailing gear and equipment certain aspects of life at sea never change. Keeping water out, maintaining good boatspeed, preserving and conserving food stores, and carrying adequate spares for the inevitable failures that occur are all perennial priorities. Plus one more thing; having a good supply of fresh air below.

Someone once observed that gentlemen do not sail to windward. If this is true it might also be said these so-called gentlemen should restrict their cruising to harbors and coves lying between the two 30th parallels. And though most long-distance cruisers do try to operate between those latitudes, the fact is most production sailboats are designed, built, and sailed in higher latitudes. Northern Europe, North America, New Zealand, Australia, South America and South Africa are all in the 40s and 50s.

What this often means—assuming a boat doesn’t have air conditioning—is that it’s hard to get a good supply of fresh air below both at sea and in port. This can be especially true when going to windward even in moderate winds and seas. Although cruisers use many devices to funnel fresh air below, probably the most common is one that has been used for centuries, the windsail or scoop.

In 1936, Rod and Olin Stephens devised a water-trapping device for the deck ventilators aboard their breakthrough yawl Dorade. That innovation, still in wide use today, is called the Dorade vent. But because these vents are usually fairly close to the deck their effectiveness is limited. Air behaves like a fluid and when it moves along a surface it is slowed by friction. As a result only a small portion of the air moving across a sailboat’s deck has enough force to enter a Dorade ventilator and work its way below past the baffled water trap. A taller ventilator can improve performance, but if it’s rigid it will be bulky and disturb sails and crew on deck.

My answer is a scoop that is light and tall enough to sit in unobstructed air so it directs the maximum amount of air below. It is also waterproof and can be left in position even though there might be water and spray running around on deck. My air-scoop design combines modern materials (polyvinyl chloride, or PVC, Velcro, and plastic battens) with an old concept—a luff rope that fits into a fixed slot. A number of years ago I was aboard a Swan 36 racing from San Francisco to Tahiti. Though the boat had a number of Dorade vents they were not very effective and there was always a lack of fresh air below. After the race we rested in Tahiti and contemplated the voyage home. I took out a pencil and designed a windsail I thought would do the job. Although that first Tahiti model was a bit crude it turned out to be very effective. We set it as soon as we cleared Papeete and didn’t take it down until we sailed into San Francisco Bay some 3,800 miles later.

During the trip, whenever the apparent wind got above three knots we had a steady supply of fresh air below. Despite the fact we were near the equator we actually had to close one of the hatches because there was too much air. At other times there was solid water running along the deck, but no more than one or two cups of seawater ever found their way below. Since then I’ve tweaked the concept and my final iteration is now on our 38-foot sloop Flashgirl.


How it works

The base of my windsail is secured in a groove machined into a plastic mount underneath a standard deck hatch. The hatches on Flashgirl are mounted on bosses to accommodate her cambered deck. The bosses have one flat side to fit the hatch; the other is curved to fit the deck. I machined a boltrope slot in my hatch bosses not unlike the slot in a headstay foil or slotted mast. The bosses consist of two pieces of PVC, each half an inch thick, that have been joined together. The entry or feed-in aperture for the slots around the hatch bases are located on the aft edge of the installation: the finished bosses a little bigger all around than the hatches they supports and are nicely rounded.

I shaped the two pieces of the bosses so they were slightly larger, both in width and length, than the hatches so the luff-rope groove would be clear of the fasteners securing the hatch and boss to the deck. The two pieces of the boss were joined mechanically with undersized flathead machine screws that were tapped into one of the pieces. The piece on which the machining is to be performed must be capable of lying flat on a bench, either side up.

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