Skip to main content

Winter Series Session 5: Oscillating Wind Shifts

So a few weeks ago I made a claim that we could gain 100 seconds in an average race by using oscillating wind shifts to our advantage.  The theory is clear:  when the wind is oscillating, we can shorten the course significantly by “tacking on the headers” to always be sailing on the lifted tack.  In the past, only the helmsman has been noticing knocks and lifts, but we have not really been keeping track of whether we are sailing in wind that is lifted or knocked relative to the median wind.  And that is the key.

This was hammered home by repeatedly playing the wind game.  It always tacked when the wind direction swept through the median direction (and even kept a rolling average of the median wind direction).  Great, it works on the computer — how to make it work on the water?

Well, turns out this is what the compass is for. Go figure!  I still remember the way Doug Folsetter’s shoulders slumped during leg one of the 2017 GHYRA when he asked where our compass was.  (actually, it was when I confessed that we didn’t have one).  He asked how we tracked the headers and lifts?  As usual, I didn’t know what Doug was talking about and mumbled something noncommittal in response.  He was too much of a gentleman to press the point.  But now I know what he was getting at!

With the boat trimmed, and steering to the tell-tales, the helmsman responds to the shifts in the wind by steering, and the heading of the boat varies.  The compass can show us clearly if we have deviated significantly from the original heading on any given tack.  In fact, the Velocitek uses the first 20 seconds or so after tacking to detect when we are in the groove and then begins to track deviations from that heading.  There are bars at the top that show if we have shifted 5, 10, 15 degrees or more.

Good, that will tell us how the wind changed since we tacked.  But surely we can do better than that!

Yes, we can.  First, we should follow Walker’s advice and write down these headings before the race and during the race.  That will give us an idea of the range of oscillations on each tack so we can make live decisions.

But we can do even better than that.  Our iRegatta app on the ipad tracks the TWD (True Wind Direction) as a function of time, updating it every 30 seconds and plotting a nice Wind History graph so we can see how much it has been varying on any given night and whether it is currently veered or backed relative to the median wind.  Bingo!

So now we know:  pay attention to how the wind direction changes, tack on the headers (ie: when the TWD oscillates through the median wind), watch the compass, write down headings, and check the Wind History every once in a while.  100 seconds, here we come!

Fun Facts:

  • On windy days, the oscillations are biggest (20 degrees!) and most frequent (every two minutes)
  • In moderate wind, expect 2-3 shifts in a beat
  • Have a look at other boats to see how the wind is affecting them.  If we are all on the same tack, we’ll feel more ‘side by side’ when on a lifted tack, and more ‘one behind another’ when headed….time to tack!
  • Oh, and boats on opposite tacks might tell us what wind is coming next.  Treat it like a persistent shift.  If they are lifted and we aren’t, tack now, and tack back when the header comes.

Leave a Reply

Your email address will not be published. Required fields are marked *