Nav in a nutshell: How to deal with wind shifts

Tacking inside a ‘cone’ can help you to harness changes in wind direction, explains Dick Everitt.

Nav in a Nutshell: How to deal with wind shifts
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When planning a trip to windward, we’ve already looked at lee bowing and touched on wind shifts.

A wind shift will either ‘head’ us – which means its direction moves towards the ‘head’ of the boat, so we can’t sail on that course anymore and we’ll have to tack – or the wind will become ‘free’, which means it moves slightly aft, so we can remain on the same tack and sail more directly towards our destination.

Tacking inside a ‘cone’ reduces the sea area we use, so we can take advantage of any favourable shifts that might occur – and we won’t be too far out if we’re ‘headed’ by unfavourable ones.

Setting up a ‘cone’ is straightforward with GPS: just tack each time the ‘bearing to waypoint’ is, say, 10° either side of a line directly downwind of the destination. However, some family crews prefer the equal tacks of a parallel ‘corridor’ to avoid the hectic work of the cone’s final short tacks; especially when they’re tired at the end of the day.

The ‘corridor’ limits are defined by ‘cross track error’ either side of the downwind line, but this can be fiddly to set up on some GPS systems. Whichever you choose, make sure you check the chart for any dangers that might lurk inside the tacking area.

How to deal with wind shifts

Gaining an advantage

If the weather forecast predicts a wind shift in a certain direction, it makes sense to favour that side of the cone, or corridor. The diagram shows what would happen if the predicted wind veered (moved clockwise) from west to nearly north-west and the advantage we could gain.

At the same time, if the wind shift doesn’t occur we won’t have lost too much ground.

This Nav in a Nutshell was published in the July 2012 issue of PBO. For more useful archive articles explore the PBO Copy Service.