This prediction is based whether, when sailing, on the current wind given by your navigation instruments, or on the wind given by a Grib file. Datagram function can be used as well in navigation as during preparation on shore.
Datagram based on a Grib file:
Adrena is going to use the activated Grib file, that is to say the validated one among the various loaded Grib files, if you have several Grib files in your software.
Let’s take for instance a route between Cherbourg and Lizard Cape. We display the datagram, based on the Grib wind, by selecting the current as parameter.
We can notice two current reverses. Let’s focus on the first reverse, situated at the North of the British Isles. Below, we display the datagram based on the Grib wind, choosing TWD as parameter.
The wind direction evolution shows a 3° rotation on the left, which is negligible given the duration and the instability of the wind and its measurement.
Below we have displayed the datagram based on the Grib wind, selecting the TWA as parameter.
The TWA opens of 10°, which is not negligible and we will have to take it into account when navigating and making adjustments of the boat and sails.
In comparison of the wind direction evolution, we will have to take another factor into account: current evolution, as displayed below:
The current reverse is going to change the surface route, and thus the true wind angle (TWA)This is the way you can make the difference between a rotation due to the current and a rotation due to a weather phenomenon.
Another example: The datagram function can be used to prepare the coastal route of the day.
We have a quick and simple view of the route with the evolution of the wind direction according to the Grib’s data.We can even visualize the transit times, the current or the wind strength.
Real time datagram:
Adrena uses the wind speed and direction given by the navigation instruments to predict one parameter’s evolution between the boat position and the position you want, given by a right click on the mouse.
What will be the current evolution during the way through the Raz du Sein?
It is direct, visual and efficient information. This function is full of information and reactive in real time.
How to use the datagram function?
Two possibilities :
If you want to create a datagram between the boat position and a point on the chart, you just have to click right on the point of the chart that you are interested in: this point will be used as a destination point for the boat. Then you can whether choose to use the validated Grib (Datagrams based on Grib) or to use the true time wind given by your navigation instruments.
You can also work on a route before start.
In this case, you have to select Tools > Datagrams and select the Grib option or Navigations instruments Wind. If you are navigating, the ongoing Datagram corresponds to the route between the boat and the active WPT (whether this one is part of a route or not)..
To delete a datagram, whatever its type is, you have to click right > delete datagram.
Additional functions :
To get the TWA (True Wind Angle) to reach a point of the chart, you just have to click right on this point and in the lower part of the menu you will have several pieces of information about the route between the boat position and the point you have clicked on, including the TWA.
On the first line, in the image above, you will also notice the declination value. This value is available if you click right, on any point of the chart.