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Downwind VMG Max@160 AWA

Yes, much deeper than we’ve been sailing!

Today, Skootch, Gadget, Lazy Sheet and I went out for a technical practice — two hoists, half a dozen jibes and two douses.  Good practice!  By the end, we were getting much smoother.  Some of the learning:

  • Mastman should face forward, beside the mast starting with the pole directly in front of him
  • The people on the sheet and guy need to watch the mastman to ease enough line at the right times.
  • Whomever is securing the guy, needs to bring the sail all the way to the pole to control it
  • Mastman should walk the pole forward to the desired angle as soon as it is made on the mast.

And between each jibe, we sailed at three or four different angles to the wind, playing with the pole position (forward/aft, up/down) at each angle to optimize boat speed.  We were looking for the best VMG downwind. (VMG is Velocity Made Good, and really means how quickly are we getting to our destination — the leeward mark)

Out on the water, it is fun to sail hot angles — lots of boat speed, and a great feeling of power with full sails and a bit of breeze coming across the boat.  But once I brought all the data home, and crunched some numbers, it became apparent that this is not the quickest way to get to the leeward mark.  What is?  The answer (for wind speeds in the 6-10 knot range) is somewhere around 160 degrees of apparent wind.

And there’s more to it than that — the pole should be brought quite far back (between 2:00 and 3:00) and raised up above horizontal.

What will it feel like?  Here’s a summary of data at approximately 8 knots of true wind speed:

Observed Results Computed
5 5.9 90 130 7.7 8 3.2
5.8 6.4 90 132 8.6 8 3.9
4.9 5.8 100 136 8.2 8 3.5
4.7 4.7 120 150 8.1 8 4.1
3.3 4.5 150 163 7.5 8 3.1
3.5 4.7 150 163 7.9 8 3.3
3 4.4 155 165 7.2 8 2.9
4.3 3.8 150 166 7.8 8 4.2
3.8 4.3 155 167 7.9 8 3.7
4.3 4.8 155 167 8.8 8 4.2
4.3 4.4 160 170 8.5 8 4.2
4.7 4.2 160 171 8.7 8 4.6
3.4 5.1 165 171 8.3 8 3.4

Comparing the two bold lines, you can see that the boat was sailing much slower (BS=Boat Speed) at the apparent wind angle (AWA) of 160 degrees, but the VMG was 18% faster.  On a downwind leg of 24 minutes, that would save us over three minutes!  This is a good comparison, because the true wind speed (TWS) was about the same for these conditions.

There’s another important insight here:  the True Wind Angle (TWA) is about 170 degrees, which means our jibe angles will only be 20 degrees — in other words:  Jibe before the mark is at 11:00am

Next step — confirm this in a race, and keep collecting more experience on trimming the spinnaker, and more data!

And an important note:  we will still sail hotter angles, but we will use that mode for tactical and strategic purposes:

  • to get away from other boats,
  • to get into clear air,
  • to get into and stay into more breeze

And to build boat speed before heading deep.

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