The original Dorade ventilators were designed in ??? a year of two after Dorade was built in order to bring in air when the spray was flying and the decks awash(Dorade and boats of her era, the freeboard is so low that from the modern RIB you step DOWN on to Dorade’s deck) and all hatches were dogged down. The ventilators (photo from Mat Brooks) stood a full 3’ above the deck. The dorade box only had to adsorb and get rid of rain and spray, no problem as the drain holes in the dorade box were adequately large.
In contrast on the modern yacht the so called Dorades are so low, so close to the deck they gather in little air. In heavy weather the low ventilors gather a lot of wate. The drain holes in the dorade box are too small and often miss placed so that the modern dorade in most cases can only be described as a heavy weather water scoop designed to make below decks un inhabitable (wet bunks) and ruined electronics when nave station floods.
To demonstrate to yourself that the low dorade is useless as an air gatherer, hold a piece of wool yarn 6” above the deck, no movement, 12” above the deck, some movement, 18” above the deck, if there is any wind the yarn is streaming aft. The only decent ventilator available from stock is the Frank Luke aluminium ventilator 4” in diameter, 9 “ from the top of the box to the bottom of the mouth, “ 15” to the top of the ventilator. Mounted on top of a 4” in high Dorade box, the ventilator is high enough so that it does not gather solid water, only spray and is high enough to gather air. The luke ventilator is descended from the moyle vermalite (british salt water resistant alloy) that I imported for installation on Ondine in 1955.
The lip on the Luke ventilator is so small that there is no danger of a flogging sheet throwing a half hitch around the ventilator and tearing it out. If a flogging sheet does throw a half hitch around the ventilator it will probably throw itself free, if not, it can easily be lifted off. In the 45 years that the moyle ventilators(salvaged from the wreck of the ONDINE wrecked on the north side of Anegada reef, the salvage is another story too long to relate here) and in the ten years Luke ventilators were on L’ll Iolaire until lost in hurricane Ivan, we never had trouble with sheets throwing a half hitch around the ventilator and not coming free. Thus with Luke ventilators there is no need for the ugly and expensive to custom make croquet hoops to be mounted over the ventilators.
It is possible to cure the flooding problem by fitting proper Luke ventilators to existing dorade boxes, by enlarging and re locating the drain holes in the existing dorade box.
All too often you see dorade boxes built into the side of the cabin house with the drain hole on the outboard side. This is fine in port, but at sea, if you are sailing in heavy weather on the same tack for a fairly long time, since they taught us in school, water does not run up hill, the windward dorade box gradually fills up with water until the water level in the box is higher than the standpipe inside the dorade box and water floods below instead of overside. Put your dorades to the BUCKET test. Go for a sail, strap her down hard on the wind, then about20 seconds apart, throw four buckets of water at the windward dorade. I”ll bet few beers(Heineken of course ) that the box will flood and water will go below decks.
To cure this problem plug up the outboard drain hole or holes, then cut holes in the AFTER end of the Dorade box. Two holes, make sure they are big enough to stick your thumb into the holes.
If your boat does not have dorade ventilators, buy the luke ventilators and fabricate dorade boxes of fiberglass or wood. The boxes should be a minimum of 4” high, better 6” high, minimum 14”long if you are using 4” ventilators, stand pipe in box 3” high. If this is done, you can enjoy below decks in heavy weather with fresh air and no water.
Make the top of the box of lexan, Lucite, plexiglass to let light down below. Also, fit two holes in the top of the box. The after hole makes the dorade work as rain or spray is drained out while air passed forward to the down spout. The forward hole covered with plug, in periods of hot weather when no rain is expected, re move the cap from the forward hole, move the ventilator to the forward hole which will give straight thru air flow instead of being slowed by baffels when ventilator is in the after hole
When cold weather comes, and the dorade is pushing too much cold air below decks, partially close off the down spout with a sliding door OSY ! pg 276
Photos can be suppliedPROPER DORADE VENTILATORS