Module 10 - Chartwork
Leeway
Wind and sea can make a vessel move sideways to leeward, so its track through the water differs from its heading. The amount depends on vessel type, loading, point of sail, speed, wind, sea state and steering. There is no universal angle suitable for every yacht or motor vessel; use the exercise value, vessel information or an estimate checked against observations.
For an EP, begin with the heading actually steered and apply the estimated leeway towards the leeward side to obtain the track through the water before adding tidal movement. With wind on the port side, the leeward displacement is towards starboard. With wind on the starboard side, it is towards port.
For a CTS, the direction reverses because the problem is solved backward. Once the required water track is known, steer to windward by the estimated leeway so the vessel's leeward slip produces that track. Continue comparing observed course over ground and position checks with the plan; changing wind or sea may require a revised estimate.
- Leeway moves the water track to leeward of the heading
- The angle varies with vessel and conditions
- EP: apply leeway from heading towards leeward
- CTS: correct the heading from required water track towards windward
- Monitor and revise the estimate from observed progress
Optional quick check
Section 7 of 7
Wind is on the port side and the required water track is 078°T. With 5° estimated leeway, what true heading should be tried before compass correction?
Continue studying Chartwork
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