2019 H0 Grib Plot Analysis with Yellow Brick Track

Brief - The attached analysis shows side by side comparisons of the tracks through the water for all the competitors in the 2019 Marion to Bermuda race. Select the yacht in the left column to show her plot. Each image illustrates, for one boat, two tracks:

1. The magenta line shows the positions as recorded by Yellowbrick.
2. The blue line shows the calculated track using Expedition routing software, version 10.10.18.

The images are saved from the Expedition display. A few comments on that display:

• Expedition displays a chart that is adjusted to show the race course from the start of Marion, MA to the finish off St. David's light in Bermuda.
• The Marion to Bermuda race has two legs, the start to Sow & Pigs Reef, and from there to the finish.
• There is a rhumb line in blue that shows the shortest great circle route for each leg.
• The display of wind is shown across the entire chart as a series of wind flags that indicate direction and velocity. The wind is represented in a GRIB file, produced by NOAA, that has records throughout the course of the race. Those records can be displayed at any time, using one hour increments.
• The wind field displayed for all the boats in this analysis is for 0900 Sunday EDT. Yellowbrick displays the position of the boat on its track at that time with an arrow.
• The calculated track from Expedition is the optimal routing track, indicating the fastest way to sail the course. Optimal routing uses the course layout and wind (GRIB files) and boat speed polars, in this case from the Offshore Racing Rule (ORR) used also to score the race.
• The blue curves that cover most of the chart are isochrones. Each isochrones displays where the boat could be after a fixed number of hours of sailing. Therefore, the distance between the isochrones indicates how fast the boat is sailing. (Isochrones that are close together show reduced boat speed.) These isochrones are separated by two hours.
• Along the blue optimal track there are wind vectors at the intersection of each isochrones that indicate the wind that occurred at that point in the race.

H0 GRIB file - The wind file being used for optimal routing is a string of "Hour Zero" models of the wind as created by NOAA using observations. These are NOT forecasts. Each Hour Zero record is concatenated with subsequent records throughout the race. Because H0 does not use forecasts the file used for optimal routing of a boat is not available until after the boat finishes.