What is Relative Humidity?

Master the Navigation, Seamanship, and Shiphandling (NSS) – Officer of the Deck (OOD) Phase 2 Exam with engaging flashcards and multiple choice questions, complete with hints and explanations. Prepare comprehensively for your test!

Relative humidity measures how close the air is to being saturated with water vapor at the current temperature. It’s not just how much water vapor is present (that would be absolute humidity) and it isn’t the air’s temperature itself. The key is the saturation amount: the maximum water vapor the air can hold increases with temperature. So relative humidity is the actual amount of water vapor divided by that maximum, expressed as a percentage. For example, if the air contains water vapor at a level that’s half of what it could hold at that temperature, the relative humidity is about 50%. If the temperature rises without adding moisture, the air can hold more vapor, so the relative humidity drops; if it cools, the relative humidity rises toward 100% as saturation is approached. This concept is essential for understanding condensation, dew point, and comfort conditions in ships and work areas.