LogScanner Race Analysis

How LogScanner measures your overall performance

Since the LogScanner output is produced by a robot and not a knowledgeable human, it doesn’t include any insights. That’s your job. You can add notes to the log and they will be included in the report. Otherwise, the report is just a bunch of measurements and pictures.

Overall Performance

An overall score is achievable by comparing performance against a standard – polars. There are other things that also deduct from winning like going the wrong way, misjudging the wind and current, starting badly and infractions. However those things are outside the current world of measurement. You can see the results of many of these things by looking at the chart, but the conclusions are yours to make.

By using the strip view, it is actually possible to get an overall performance score for the entire race. Polars model the boat’s performance, so by summing the difference between actual speed (thick line) against modeled boatspeed (thin line – polar speed), the accumulated performance difference can be calculated. In other words, a single number can be assigned to your performance.

The result is knots – which depends on wind speed and angle. So here is how to get around that one. Adjust the polar calibration until the total gain/loss for the race is zero (or close to). Then the polar calibration (in this case 1.02) is a normalized performance score. In other words, the boat’s overall performance was 2% above what the polar said it should be.

 Where was performance below par?

With the polar calibration set as described above, the chart view shows where performance was below par (red line) and above (green line). Here we’ve centered on the first leg which is upwind. The first thing to notice is that port tacks are above par (mostly) while starboard tacks are always below par. Notice also that the boat has been positioned on one of the starboard tacks, and the wind arrow looks pretty wide. Hmmm. better look into that more closely.

Stripchart view

Here we see a tack from port to starboard (true wind angle goes from – to +). When on port tack, boatspeed is pretty close to target speed. but on starboard, it is 1/2 a knot low. And by looking at the chart view, you will notice that this is not a one-time issue. How do you get a clue about why this is happening? Read about RaceCam.

Next post…

LogScanner posts

• RaceCam video
• LogScanner overview
• How to load a log file
• Looking at tacks
• Checking laylines
• RaceCam
• GeoGons
• LRgons
• Using LogScanner