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Lesson 6 - Tides

Overview

  • Learn how tides work and why they matter.

  • Covers patterns, tide tables, streams, and weather impacts.

  • Stay safe and plan effectively on the water!

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What are tides?

  • Tides are caused by the Moon and Sun's gravity.

  • Two tidal bulges form on Earth: one near the Moon, one opposite.

  • Geography and rotation shape local tides.

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Tidal Changes

Daily Tides:

  • Semi-diurnal: 2 highs, 2 lows daily.

  • Diurnal: 1 high, 1 low daily.

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Half-Monthly Tides:

  • Spring Tides: Larger ranges.

  • Neap Tides: Smaller ranges.

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Using tide Tables

  • Standard Ports: Times and heights of tides provided.

  • Secondary Ports: Adjust times and heights from nearby ports.

  • Use graphs to estimate water depth for safe navigation.

 

Rule of Twelve

Estimate tidal heights between high and low water:

  • 1st hour: 1/12th.

  • 2nd hour: 2/12ths.

  • 3rd hour: 3/12ths, and so on.

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​Tidal Streams

  • Tidal Diamonds: Show stream direction and speed on charts.

  • Tidal Atlases: Maps with arrows for strength and direction.

  • Use for planning efficient routes.

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​Weather impacts

  • High pressure = lower tides.

  • Low pressure = higher tides.

  • Winds can push water higher onto coasts.

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Practical Navigation Tips

  • Always double-check tide calculations.

  • Use software for real-time data.

  • Plan for time zones and weather.

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