The global weather pattern
On the ocean scale the winds fall into belts: the steady trade winds either side of the equator, the calms and squalls of the doldrums (the Intertropical Convergence Zone), the variables, and the westerlies of the higher latitudes. Overlaid on these are the great ocean currents, which help or hinder a passage and shape the sea, and the seasons of the tropical revolving storms — hurricanes, cyclones and typhoons — which occur in known regions at known times of year and must be avoided. Reading this large-scale picture is what ocean planning is about.
| Feature | What it means for the passage |
|---|---|
| Trade winds | Steady following/reaching winds for the classic downwind routes |
| Doldrums (ITCZ) | Light airs, calms and squalls; a belt to cross efficiently |
| Westerlies | Stronger, more variable winds and depressions in higher latitudes |
| Tropical storm season | A region and time of year to avoid entirely |
| The wind belts and hazards that shape ocean routes. |
Routeing charts
Pilot or routeing charts present the climatology month by month: the average wind direction and strength, the ocean currents, the frequency of gales and calms, and the tracks and frequency of tropical storms. The ocean navigator uses them to choose the season and the route so the boat rides favourable winds and currents and stays clear of the storm regions in their season. Ocean routeing is, above all, about being in the right ocean at the right time of year.
WARNING — Plan around the storm season Tropical revolving storms occur in defined regions and seasons. The single most important rule of ocean routeing is to plan the passage so the boat is never in a storm region during its storm season.