April 20, 2014

Keep that inside air moving

I SUSPECT that a lot of boats down in the local marina will be bearing a heavy load of mold and mildew right now. We’ve had a lot of rain this past season and the inevitable drips from deck fittings have contributed to the kind of damp interiors that mold loves most dearly.

Because the outside air is so humid here in winter and spring, many boat owners think it only logical to seal the cabin tight so that no exterior air can get in. In addition, they will often leave a light bulb burning to take chill off the inside air.

But both these moves are wrong. Long ago, sailors and fishermen discovered that the two best defenses against mold, mildew, and dry rot are strong flows of fresh air and rock salt in the bilges.

Most amateur sailors would object to salt in the bilges, but the argument for good ventilation — no matter how damp the outside air may be — still holds strong.

The natural flow of air inside many sailboats is from aft forward, particularly if a main companionway dodger is fitted. So any intended ventilation should take advantage of this. If, for example you have Dorade boxes fore and aft, you might want to turn the forward cowls to face aft, so that they suck, rather than blow.  Similarly, the one nearer the stern should be turned to face the wind, so that they scoop wind into the cabin under pressure.

But not all boats are the same, of course, and I have had boats that demanded that the forward ventilators be turned toward the wind and the aft ones away from it.  Experiment with a smoldering joss stick inside the cabin to see what suits your boat best.  It doesn’t matter which way the air flows as long as there is a constant stream moving through.

Don’t ask me why mold doesn’t like moving air, even if it’s nicely damp and fairly warmish. I know it doesn’t make much sense, but it works. After all, sailing a boat doesn’t make much sense either. But it works, too, in its strange way.

Today’s Thought
The way of the Wind is a strange, wild way.
— Ingram Crockett, The Wind

 “My uncle had an accident the other day and now he’s got a wooden leg.”
“That’s nothing. My sister got engaged the other day and now she’s got a cedar chest.”
(Drop by every Monday, Wednesday, Friday, for a new Mainly about Boats column.)


Anonymous said...

Regarding salts, calcium chloride is far more effective at removing moisture; it is often used in air drying systems in industrial air conditioning systems. WQe get ours as "Road Runner" brand at the local Home Depot.

John Vigor said...

Dear Anon:

Old-timers strewed the bilges of their wooden boats with rock salt to ward off rot that could start in the many crevices able to hold fresh water.

It wasn't there to absorb moisture from the air; just to prevent dry rot.

John V.