Sail Smart by Chisnell Mark;

Author:Chisnell, Mark;
Language: eng
Format: epub
Publisher: Fernhurst Books
Published: 2012-10-25T00:00:00+00:00

DON’T PANIC!!

It’s a long time ago, but the most extreme and difficult conditions I ever faced were in Kiel Week way back in 1989. It was the British trials for the Admiral’s Cup team and the first real racing for a very carefully set-up instrument and computer system aboard the IOR fifty footer, Jamarella. It was half way through one of the inshore races, and according to the instruments we were sailing straight into the wind with an apparent wind angle of zero degrees and a breeze of 10 knots. Meanwhile the sails were full and the water was a glassy calm. Confused?

Don’t be – although this is a very extreme example, such apparent instrument anomalies are relatively commonplace. The crew’s response is just as common, ‘There’s something wrong with the instruments.’ It’s a phrase that has a special place in all my worst nightmares. But in this instance there was nothing wrong with the equipment. It was still telling us something useful but the message needed more interpretation. Producing good information when you cannot read the number directly off the dial is one of the key skills of the navigator. So what was going on that day in Kiel?

It was our friends from the apparent wind calibration section – wind sheer and wind gradient. There was little or no mixing of the wind aloft and down on the water so there were big differences in wind speed. It is perfectly possible that the wind 80 ft up is travelling at 10 knots, whilst at zero feet it is stationary – and that’s what the instruments were telling us. The masthead unit can only measure the wind speed where it is.

This information can be of use to the trimmers, they need to set the sails flat at the bottom for very light airs and full at the top for 10 knots. But we also need to take into account the wind sheer. We already know that as the wind slows, it backs, so that the wind at the masthead is considerably more veered than the wind at the water. This was why we were able to fill the sails on Jamarella even though the wind at the masthead was coming from dead ahead. The wind halfway down the mast was blowing from further to the left (we were on port tack) and filling the sails. Again the instruments were telling us all they knew, and the information was certainly of interest to the trimmers. It just needed interpreting correctly. So the next time the trimmer says ‘There’s something wrong with the instruments.’ Don’t panic! Not only are they quite possibly wrong, but they are the people who need the information most.

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