A very reactive speed over ground.

This HF GPS is a great alternative to the conventional speed sensor. It allows a very accurate measure of the starting line. Once we have supplied high frequency GPS to Open 60’ we have been able to work on all the data logged by Michel Desjoyeaux skipper of FONCIA. Actually, we have noticed significant differences between speed-over-ground and boat-speed in areas where there is no courant. The speed of the surface layer of water on the waves explains that difference. A wave consists in a transversal movement that carries energy, not matter. But in some cases, the upper layer of water moves in an elliptic way, generating an apparent wind which adds to the boat-speed (boat-speed being the speed at which the boat sails on that water layer).

Autopilot in Wind Over Ground mode!

While using the true wind mode the pilot does not take this apparent wind variation in consideration. The true wind angle value is affected by the movement of that water surface layer and the pilot should compensate. We have noticed that this water layer can reach speeds as 2 to 3 knots! This is quite significant. At a 126 ° true wind angle with 10 knots of apparent wind it gives a 10° variation of the true wind angle value. For an accurate true wind angle process, it is important to consider the speed of that “water layer”. In other words, use speed-over-ground data to process the values of true wind. This is possible with an ultra-high precision GPS.

User tips

Toggling speed data source is done in the Gyrographic setup menu. Once activated, the true wind mode on the pilot will implement that choice automatically.

Another good reason for using the High Frequency GPS: in case of failure of the boat speed sensor, the true wind mode remains available for the pilot.

This sensor is recommended for boats using the nke Gyropilot

It requires the True Wind Option on the pilot and the Ground Speed option on the Speed/depth interface.