Fog

Visibility reduced to less than 1,000 metres by suspended water droplets.

This creates a serious reduction in visual reference and makes it harder to judge distance, speed and the movement of other vessels. Navigation usually relies more heavily on radar, sound signals, compass headings, GPS, AIS where fitted, and careful plotting. Speed should be reduced to suit the conditions, with extra attention given to lookout by sight and hearing. The sound signal requirements for restricted visibility apply, and the skipper should allow more sea room wherever possible.