Coastal Skipper Terminology

Set is the direction towards which a tidal stream or current flows; drift is its rate, normally in knots. Leeway is a vessel's sideways displacement through the water caused principally by wind. Each value is an estimate or observation tied to a time, place, vessel and condition—not a permanent correction.

A dead-reckoning position is advanced from a known position using the vessel's movement through the water over elapsed time under the chosen plotting convention. An estimated position adds estimated external effects such as tidal stream or current and leeway. A DR and EP are both constructed estimates with growing uncertainty; neither is a measured fix and an EP is not automatically more true.

A transit or range exists when two identified objects are observed in line. It can provide a useful line of position or directional check without a compass, but it is not an exact fix and one line cannot show movement along itself. A clearing bearing is a pre-planned bearing boundary used on a stated side of an identified object with a protected margin. Its usefulness depends on correct chart work, object identification, reference conversion, observation and continued monitoring.

A tidal gate is a timing constraint or opportunity where stream, height, sea state or another tidal effect materially changes feasibility or margin. It is not always an instant when passage changes from impossible to safe. A lee shore has wind blowing towards it and can erode sea room; a weather shore has wind blowing away from it and may reduce local fetch, but shoreline shape, topography, refraction, swell and changing wind can limit any shelter.

Fetch is the distance over water for which wind blows in a broadly consistent direction; wave development also depends on wind strength, duration, depth and other conditions. Met Office sea-state words such as slight, moderate and rough correspond to stated wave-height bands. They describe sea state, not the height of every individual wave or a guarantee of comfort or safety.

Under the COLREGs, underway means not at anchor, made fast to the shore or aground. Making way through the water means moving relative to the surrounding water. Rule 35 uses that distinction for sound signals in or near restricted visibility; it should not be treated as a shortcut for every lights or collision-avoidance rule.