OVERVIEW

This chapter aims to explain tides in such a way that you develop an understanding of what’s going on. It covers sources of tidal information and how to use them, and also indicates how you can make your own informed estimates of what may be happening in a particular place.

a) why we need to understand tides (movement and depth of water)

b) what causes tides; the pattern of tidal oscillation - springs, neaps and tidal period; the movement of water that occurs

c) information and prediction of tidal heights; the terms used; tide tables; tidal curves; information for secondary ports; complex tidal areas

d) information and prediction of tidal streams; what are tidal streams; tidal stream atlases; information on charts; thinking about what’s happening

e) glossary

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INTRODUCTION

“There is a tide in the affairs of men, Which, taken at the flood, leads on to fortune.” Shakespeare, Julius Caesar

Most people are familiar with the idea of tides. The sea comes in over the sand when you are on the beach, and then goes out again.

Tides are of particular interest to yachtsmen because of two distinct facts:

• the depth of water at a particular place - or indeed, whether there is any water at a particular place - changes, and it is important to know the depth to avoid going aground

• the tides cause movement of the water, and it is important to know about this in order to navigate (this is referred to in Chapter 1). In fact sometimes the water’s movement can create a dangerous environment for the boat.

The good news is that these effects are predictable. Because they are important to mariners, tidal heights and movement have been carefully observed over the years, and predictions published. From this we can get tidal information about the exact places and times we are interested in.

This chapter explains:

• tidal theory - the tidal patterns and what causes them

• the sources of tidal information and how to use this information, including the terms used when talking about the tides.

It’s not necessary to understand the causes of the tides in great detail, but a little knowledge does help in understanding their general behaviour.