UK Marine Screen (photo by G. Allen, Met Office)
If a louvered screen is to be used, two should be provided, one secured on each side of the
vessel, so that the observation can always be made to the windward side. In this way the
thermometers can be completely exposed to the air stream and uninfluenced by artificial
sources of heat and water vapor. As an alternative, a portable louvered screen can be used,
being hung on whichever side is to windward, to gain the same exposure. The muslin and
wick fitted to a wet-bulb thermometer in a louvered screen should be changed at least once a
week and more often if it becomes dirty or contaminated by salt spray, if any spray has
reached the instrument, the muslin and wick should be replaced by new ones. It is advisable
to do this in any case after bad weather.
