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Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.
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Yellow buoy marking a feature that is not a navigation hazard
Yellow throughout, with an X-shaped yellow topmark where fitted, and a yellow light of any rhythm that cannot be confused with white cardinal, isolated danger or safe water rhythms; Fl Y 5s is typical. Special marks indicate spoil grounds, outfalls, cables, military exercise areas, recreation zones, data buoys and racing marks. Their shape may optionally reflect the lateral system, but they carry no navigational meaning beyond identifying the feature described in the pilot or on the chart.
Read definition →The reasons a log reading may not match reality
Marine growth on the impeller or in the housing slows rotation and under-reads. Aeration from pitching or a bow wave passing the sensor gives erratic readings. Heel lifts the sensor towards the surface, so a boat can log differently on each tack. Positioning the transducer in disturbed flow near the keel or a step yields a consistent scale error. The boundary layer itself means the sensor always sees water slightly slower than the free stream.
Read definition →Your real speed along the ground once tide is counted
Speed made good is the length of the ground track divided by the elapsed time, differing from speed through the water by the along-track component of the tidal stream. A yacht logging 5 knots with a 1.5 knot fair stream makes good 6.5 knots; against it, 3.5 knots. Over a passage with a turning stream the net effect may be small, which is why an average is taken over the whole leg rather than instantaneously.
Sailing reference
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.