Marine Glossary

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dew

Water condensed onto material objects (as opposed to air particles) on the ground or on a vessel. For this to occur, the temperature of these objects must have fallen below the dew point of the surface air. This usually takes place as a result of radiation cooling during the night or early evening. When the dew point is below freezing, hoarfrost forms rather than dew. The conditions favorable for dew formation are:

(1) a radiating surface well insulated from the heat supply of the earth or vessel upon which the dew can condense,

(2) a clear, still atmosphere with low specific humidity in all but the lower surface layers (this allows for more efficient radiation cooling), and

(3) high relative humidity in the surface layer of air.