I keep a motorcycle outdoors under a waterproof cover, but noticed that with morning dew the bike is still noticeablely wet on the inside of the cover.
Meanwhile a buddy has his bike in a plywood shed that is by no means air tight but has 4 walls and a roof, but no insulation or air handling fans/AC and he says dew is never an issue..what’s the difference?
In: Planetary Science
Water from the air condenses onto things that are cold, and things get cold at night because they radiate their heat away to the blackness of space, which gives nothing back. Dew tends to form on clear nights, because on cloudy nights, the clouds radiate energy back to the ground. If your friend’s shed is near trees or a building, those would block the view of the night sky, which would reduce cooling.
Cooling by radiating heat away is not very fast, compared to cooling by conduction (touching something else that’s colder). So big heavy things with a lot of thermal mass don’t cool enough overnight to form dew, while thin, lightweight things like grass, or your motorcycle cover, could cool enough to condense water.
Another reason that your motorcycle gets wet might be that it’s touching the tarp directly. Your friend’s shed might get dew on ceiling, but the bike is a few feet below the ceiling so the water doesn’t transfer.
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