How to navigate using waves
Yachting Monthly|March 2021
Developing a thorough understanding of what the waves are telling you can provide you with a ‘sixth sense’ when it comes to navigation, says Dag Pike
Dag Pike

When voyages of discovery were being made 500 years ago and navigators had to make landfalls without any charts, being able to read the waves was a valuable navigation technique. Indeed many of the ancient sea-going cultures also relied on waves for navigation. The waves breaking on the rocks or reefs of an island would often be the first sign of land, but there are also more subtle and varied ways of reading the waves too. Learning to interpret them is an art rather than a science, but is one that will give you an invaluable sense of your surroundings, and will alert you to danger when something doesn’t feel right.

Electronic navigation has taken over our lives as navigators, even before GPS in the days of Loran C and Decca. Satellite navigation is more accurate than ever, and with the advent of satellite receivers that can derive a position from several separate satellite constellations, they also have redundancy built-in. A Chartplotter screen gives the impression of indubitable accuracy, but datum shifts or, more likely, inaccurate or out-of-date chart data can throw a spanner in the works. Add in shifting coastlines, river mouths, and sandbanks, and it would be foolish to rely solely on what the little glowing screen tells you about your location.

SPOTTING SHOAL PATCHES

If there is shallow water and there is a swell running then you will almost certainly see the waves breaking on the shallow patches. The problem of course is, what comprises a shallow patch? Much will depend on the size of the waves but you can be fairly sure that there will be breaking waves in any depth of less than 2.5m (8ft) when there are ocean waves rolling into the shore and these will allow you to identify the shallows.

Think about making an approach to a shallow entrance with a shifting seabed in onshore wind, such as the Deben on the East Coast, Chichester Harbour bar, or Caernarfon Bar in North Wales. The charts and buoys may tell you one thing, but if there is breaking water across the entrance ahead, it would be foolish to plow on regardless, and better to standoff. Patches of broken water, however, may confirm where the shallows are and reveal where the channel has shifted to.

FINDING DEEPER CHANNELS

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