The top line below the Home and Menu buttons shows the course for which you are calculating the data (Boat to 001); along with the range and bearing of the mark (‘from the boat’ for the current leg, or ‘from the previous mark’ for the next leg).
The next two lines show the True Wind Direction and Speed, and the Tidal Direction and Speed. When the green box to the right says that these are ‘Live’, it means that they are showing the most up-to-date calculated values. However, they can be changed to any value for tide or wind, speed or direction. The table below shows the sailing data for the leg in whatever tide and wind that you have decided to use.
In the far left-hand column, we have the data labels for the two right-hand columns; Heading, COG (Course Over the Ground), Boat Speed (target/polar), SOG (Speed Over the Ground), TWA (True Wind Angle) and then AWA (Apparent Wind Angle), Apparent Wind Speed (AWS) Distance and Time left on the leg. The second and third columns are then the calculated values of this data for port and starboard tack respectively.
If you want to look at a different leg, then you can toggle between them using the Prev, Current Leg and Next buttons on the bottom of the display.
There will be some variability between different chart plotters – for instance to calculate the AWA and AWS the app will need a polar table installed (see Race panel – Starting)
Ok, so how do we make good use of all this data? In the case of the current leg it’s particularly useful when the wind is shifty. When you are going upwind or downwind, tacking or gybing it’s essential to know how much time you have left on each tack. This is vital tactical information as the general rule in a shifting breeze is to stay away from the corners of the race course.
Without the What If? screen, you might get close to a corner and not even realise it. The What If? app can tell you how far you are from the layline at the extremes of the wind shift pattern. For instance, in the What If? screen shown to the left, the boat is on port tack on a big lift with a True Wind Direction (TWD) of 080 degrees. The What If? says that there is 5mins and 25secs to go on port before the starboard tack layline.