Q&A: Keeping The Boat’s Interior Dry

Question: Is keeping the interior of the boat dry in the midst of prolonged damp, chilly weather, and/or sea spray just a matter of dorade vents, hull insulation and your Espar heater? Do you have success keeping the interior dry or does it inevitably get damp?

Note Morgan’s Cloud’s beefy dorade, outlined in yellow

Answer: If you already have a boat, there are some things you can do to at least help the problem:

  • Install an extraction blower over the galley. The stove is one of the biggest moisture generators, particularly since a byproduct of burning propane is water vapor. When we wintered over in Norway we installed a second bilge blower and a vent on the suck side of the blower over the stove and routed the blow side out a dorade. This really helped.
  • When installing a heating system you have to decide how much outside air to let into the supply side of the furnace. For example, the Espar on Morgan’s Cloud is installed in the lazarette right under a large dorade vent. If we close the dorade, the heater just re-circulates the air in the boat, which is more efficient than opening the dorade and letting the heater draw cold air in from outside. However, keeping the dorade at least partly open results in a MUCH dryer boat, since we are drawing in dry outside air, heating it—which drops its relative humidity—and forcing moist warm air out through other ventilators. The point being, you have to think about airflow and trade off efficiency against dampness. We found that in Arctic Norway, where we spent two winters, where the air was dry and cold, it was better to keep the dorades pretty much closed, but in London, England it was better to open almost all of them and get rid of the damp. (The winter in London was brutal for dampness, the worst we have ever experienced. In the end we bought a dehumidifier.)
  • Our biggest problem on Morgan’s Cloud, like most boats, is condensation forming on the hatches and ports. In Norway we covered both with plastic sheeting separated from the metal by bits of adhesive foam; in effect double glazing—not elegant but it worked like a charm. Update, 2007: During the last refit we designed and had built wooden bezels around each port that accept Plexiglas covers, which will do the same thing and are more elegant.
  • Make sure you have a heater that can be run in any weather offshore. I can’t tell you the number of boats we have met, even in the Arctic, that have to cap off the heater at sea because of worries about burning something on the chimney or getting water down it. Don’t let anyone sell you one of those ‘toy’ exhausts for an Espar that pokes out of the hull of the boat. Ours is on the aft deck, massively braced to the rails, and three feet high. The result is that we can run the heater in any weather.
Note Morgan’s Cloud’s massive heater exhaust—outlined in yellow—that we had custom made and well braced to the stern rail
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John was born and brought up in Bermuda and started sailing as a child, racing locally and offshore before turning to cruising. He has sailed over 100,000 miles, most of it on his McCurdy & Rhodes 56, Morgan's Cloud, including eight ocean races to Bermuda, culminating in winning his class twice in the Newport Bermuda Race. He has skippered a series of voyages in the North Atlantic, the majority of which have been to the high latitudes. John has been helping others go voyaging by sharing his experience for twenty years, first in yachting magazines and, for the last 12 years, as co-editor/publisher of AAC.

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