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Sailing reference
The YouSail sailing glossary
Clear explanations of the language used in navigation, pilotage, weather, safety and life under sail.
2 terms
Page 1 of 1
Under Keel Clearance (UKC)
The water remaining between the bottom of the keel and the seabed
Calculated as charted depth plus height of tide minus static draught, then reduced by squat, heel, wave-induced heave and allowances for datum and survey uncertainty. Company and port policies commonly require a minimum of ten percent of draught, or a fixed figure such as 0.5 to 1.0 metres for small craft in known ground. For example, charted 3.2 metres with 1.8 metres of tide and 1.9 metres draught leaves 3.1 metres before dynamic allowances.
Read definition →Universal Time (UT/GMT) in Celestial Work
The single worldwide time standard all almanac entries are based on
All almanac tabulations are argued on UT1, referred to in practice as GMT and closely tracked by UTC, which is kept within 0.9 seconds of it. Since the sun's geographical position sweeps west at about 0.25 minutes of arc per second of time, a timing error of four seconds displaces a longitude line by roughly one nautical mile at the equator. Watch error and watch rate must therefore be logged and applied.
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