Automatic tacks/jibes performance analysis

I've recently finalized my R scripts to analyse all our racing data. Unfortunately I can only find the data from 2013, but that already quite a few races!

As an example I'll use some newer data that we got during a recent practice (the same I used to make the videos overlays)

From these NMEA records, I compute the rate of turn of the boat, the standard deviation over the heading for the last minute. Using these two measurements along with the speed over water and apparent wind angle I can detect pretty accurately tacks and jibes.

Using the standard deviation and rate of turn I can see when we started our tack.

Using the speed over water, I assume the tack being done/completed when we reach 90% of the speed we had before, and therefore recover our speed. I use 90% because it's a threshold we reach most of the time, if I used 100% with the wind fluctuations I cannot observe these 'stops' all the time.

The plot above represents from top to bottom: Speed over water, Heading and Apparent wind angle

The vertical bars represents:

• BLUE : Tack or Jibe detected
• RED : Beginning of the maneuver
• GREEN : End of the maneuver

Now the interesting part is to calculate how much distance we lost performing that maneuver.

We can do that by integrating over time the speed loss (which is equivalent to calculating the area of the speed dips on the top plot)

When doing that I can calculate how much distance we lost over the competition due to our maneuvers. This is a very important metric, we can try to optimize our tacks and reduce that value!

What I'm interested to see is the distribution of these values. When running the same algorithm for the whole 2013 NMEA data I recorded this is what we find:

This graph shows that most of our tacks are making us loose between 1-3 boat lengths over the distance we would have done without performing the maneuver. This is very good !

Now you can also see that some of our tacks are really bad... There are some that are performed slowly and makes us loose 6 boat lengths or more... This has to be fixed!

What needs to be fixed is the variability of how we execute these. We should be consistent, perform it with the same team, in an almost exactly same way in order to reduce the tail of the chart above.

Tacking in 2-3 boat lengths is a well known rule of thumb, but we need to work on never get slower than that, because you only need one of these bad tacks to ruin your race!