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“Tiny Tiny STOCS”: Optimizing sail trim

On the longer races of the GHYRA, we had two chances to repeat something really interesting about sail trim (check out the reports from 2016 and 2017).  On those days, the wind was steady and light, and each time, we were able to get a lot more boat speed by systematically optimizing every aspect of sail trim.  We left the experience with a great sense of gratification from coaxing more speed out of the boat in a virtuous cycle:  more boat speed created more apparent wind and that additional wind allowed us to create more boat speed. (and the apparent wind shifted forward, so we had to adjust for that, or the boat would slow down again).

It also showed us that PERSPECTIVE’s boat speed is very sensitive to tiny adjustments.  These adjustments are so tiny that you can’t see the effect on sail shape or the tell-tales.  The sails looked as good at 3 knots of boat speed as they did at 4 knots.  All the tell-tales were flying in both cases.  The verdict?  Our eyeballs and tell-tales are only crude indicators of sail trim.

Which means that on the shorter legs of our typical races there is a lot more untapped boat speed to be found.  How to find it?

Lazy Sheet and I were talking about this on the weekend.  How could we make this kind of tweaking part of our culture? How can we get our eyeballs off the sail shape and onto the speed meter to find that extra 10% of speed on each and every leg?  (remember, races are won and lost on 3-5% of differences in speed across the course).  We propose this algorithm:

Upwind (adjust your STOCS for bigger gains)

  1. We tack
  2. We gain boat speed
  3. We head up
  4. We use sail shape and balance to adjust our trim
  5. This is our baseline
  6. NOW we invoke “Tiny tiny STOCS”.  Check the boat speed and apparent wind speed, then optimize one parameter at a time, making just 1cm of change in one direction. For example:  mainsheet out 1cm, pause to measure speed, if better, try another cm, if worse undo, try in 1cm…continue until no change.
    1. main Sheet
    2. Traveler
    3. Outhaul
    4. genoa Car
    5. genoa Sheet
  7. And once one cycle is done, we immediately start the next cycle.

Downwind (do favours – DUFAVOS  – to get ahead)

  1. We gybe
  2. We head up
  3. We gain boat speed
  4. We settle on our course
  5. We adjust the pole & mainsail using our eyes and trim the sheet accordingly
  6. This is our baseline
  7. Now we invoke “DU tiny tiny FAVOS”
    1. pole Down/Up
    2. pole Forward/Aft
    3. boom Vang
    4. Outhaul
    5. main Sheet
  8. And once one cycle is done, we immediately start the next cycle.


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