11 WHEN THE GOING GETS ROUGH


Working with the waves Waves are produced by the friction between the wind and water. At first glance it might seem as if the whole surface of the sea is moving bodily downwind, but this is not the case. Except for currents and other streams, the water is pretty much stationary – at least in the horizontal plane, though there can be plenty of vertical movement.


‘Fetch’ is the distance the wind moves over the water. The greater the fetch, the rougher the water will be.


But there is more going on inside each wave than the water simply rising and falling. There is also an orbital, wheel-like movement which can best be understood by imagining a single water molecule on the surface. As each wave passes, that molecule will be carried round in an almost perfect circle, ending up almost exactly where it was before. This means that the surface flow runs in different directions depending on where you are on the wave face – an important issue when it comes to handling a boat in tough conditions. Not all boats handle in precisely the same manner, but here’s some general guidance.


Motoring downwind


It might seem illogical but ‘following seas’ – meaning waves approaching from astern – present one of the most dangerous circumstances for small craft. This is because the wave’s surface flow will propel you off the crest and then rush up to meet you in the trough. The result can be to spin the boat around so it ends up broadside to the waves. This is known as ‘broaching’ and can easily lead to capsize. Very careful use of the throttle is called for. Ease it back as you approach each crest, then accelerate as you enter the trough to give you the power and steerageway needed to climb the next wave. Better still, choose a calmer moment to turn round and head upwind to another source of shelter. Avoid beam seas if at all possible.


The bow digs in ... the rotational forces in the wave cause a broach ... and a boat can be rolled 82


RYA Seamanship for Sea Anglers


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