Wind Flows - leeward mark

Wind Flows – Leeward Mark Rounding

Drone video helps us to capture scenarios showing decisions being made and clearly show the result. In this case, we saw a leeward mark rounding that might be helpful to share. We also roughly modeled the scenario with wind tunnel software to see what we might learn from the fluid dynamics involved.

In this case, MC2007 is rounding the leeward mark closely trailing MC2748. MC2007 decided to duck MC2748 to leeward even though there was room to go above or closely follow them.

Watching the rest of the boats rounding, all boats closely followed the prior boat around the mark.

There are a few concepts that are vital here:

  1. There is disturbed air surrounding MC2748 above, trailing and leeward.
  2. Sailing behind or above MC2748 retains the freedom to tack to Starboard as soon as a good lane appears, even if sailing in some disturbed air.
  3. Sailing to leeward limits options and puts MC2007 decidedly in MC2748’s wind shadow.
  4. Dropping to leeward also gives away distance up the course that will have to be regained.

Here’s how the skipper remembers the decision:

My intent was to come in wide and exit closer to the mark so I could come inside (MC2748).  Half way around the mark I thought that (MC2748) was pointing and I was going to get stuck with low boat speeding trying to point too.  That’s when I veered off and tried to reach a bit to keep boat speed up.  Oh well…the video tells the story.


We’ve probably all been there. The video shows the angle that MC2007 achieves versus the combined paths of the boats that took that same side of the gate. Many times these decisions are made quickly. Could this scenario help us to make a quick decision next time that provides a better result?

Shaping Your Mainsail, Part 1: Angle of Attack

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