Skill in predicting conditions at sea, by reading the weather and understanding the many types of forecast currently available, is essential for safety and for plotting a fast course when racing, or an enjoyable passage when cruising. Specially designed for reference afloat, this manual aims to help yachtsmen of both sailing and motor yachts to understand and appreciate their environment. It describes how weather systems develop; the effect of wind and storms on water; how to predict the wind, mists, fog and more extreme dangers; and how to plan a voyage to avoid adverse weather and follow the most favourable conditions.