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Lesson 3 - Distance, Depth & Height
Distance
At sea, distance is measured in nautical miles or meters.
Speed
Mariners measure speed using knots, where 1 knot equals 1 nautical mile an hour.

Charter Depths​
- Spot Depth
- Contour Lines
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- Drying line
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Depth & Height
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Chart Datum
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Mean High Water Springs (MHWS)
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Highest Astronomical Tide (HAT)

Measuring Depth in Practice
Echo sounders are the standard tool. They work by sending high-frequency sound waves to the seabed and measuring the time it takes for the echo to return. This time is then converted into a depth reading.
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Dead Reckoning (DR)
Example:
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Compass reading = 090
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Distance Traveled in = 6 NM
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