
Lesson 6 - Tides
Overview
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Learn how tides work and why they matter.
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Covers patterns, tide tables, streams, and weather impacts.
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Stay safe and plan effectively on the water!
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What are tides?
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Tides are caused by the Moon and Sun's gravity.
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Two tidal bulges form on Earth: one near the Moon, one opposite.
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Geography and rotation shape local tides.
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Tidal Changes
Daily Tides:
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Semi-diurnal: 2 highs, 2 lows daily.
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Diurnal: 1 high, 1 low daily.
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Half-Monthly Tides:
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Spring Tides: Larger ranges.
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Neap Tides: Smaller ranges.
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Using tide Tables
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Standard Ports: Times and heights of tides provided.
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Secondary Ports: Adjust times and heights from nearby ports.
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Use graphs to estimate water depth for safe navigation.
Rule of Twelve
Estimate tidal heights between high and low water:
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1st hour: 1/12th.
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2nd hour: 2/12ths.
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3rd hour: 3/12ths, and so on.
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​Tidal Streams
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Tidal Diamonds: Show stream direction and speed on charts.
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Tidal Atlases: Maps with arrows for strength and direction.
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Use for planning efficient routes.
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​Weather impacts
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High pressure = lower tides.
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Low pressure = higher tides.
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Winds can push water higher onto coasts.
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Practical Navigation Tips
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Always double-check tide calculations.
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Use software for real-time data.
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Plan for time zones and weather.
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