Any number of factors can affect the wind near land on coastal voyages, says Dick Everitt.
When planning a coastal voyage we might have to allow for the wind bending a bit, writes Dick Everitt.
The ‘forecast’ wind direction is for the open sea, but near land all sorts of odd things can affect it.
In summer, as the land heats up, air rises and the pressure reduces so cooler air over the sea flows straight in towards the land. This is known as a sea breeze and can ‘bend’ the forecast wind quite a way offshore – say 10 miles in northern Europe and up to 100 miles in very hot climates.
In light airs, the English Channel can experience north and south sea breezes blowing towards both the English and French coasts at the same time. So always read pilot books very carefully and seek local knowledge because some breezes are very predictable and often veer (or back, in the Southern Hemisphere) over the course of the afternoon, which could affect your choice of a quiet anchorage.
Just sheltering behind a small island might not work as wind can bend around it, and even split and come in two directions at once.
It’s not only the direction of the forecast wind that can be affected but also the strength. It’s not uncommon for a Force 7 to develop as the land heats up in hot countries, which could affect your landfall: you don’t want to tackle a tricky entrance with a near gale up your stern.
Mind you, if you wait until evening the effect can wear off as the land cools, and a ‘land breeze’ might blow out over the sea.
Lumps of land can also affect wind quite dramatically. Narrow gaps which look like an enticing short cut can be very choppy, especially if you are going with the current and the wind isn’t.
The wind can funnel through these gaps and accelerate, so it might be better to go around the long way in clear water.
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Cliffs also bend onshore winds so they flow along their length, and these could ‘head’ you if you stand in too close to the shore. Likewise, forecast strong offshore winds blowing over high cliffs can tumble and become bands of alternate ‘offshore’ and ‘onshore’ winds.
Also, take care near mountains: cold air rushing down valleys can form violent katabatic winds which could upset your landfall.
Be prepared for all of the above, especially if sailing in the Med this summer: the extra heat can quickly change the wind conditions.
As published in the August 2012 issue of PBO.