The depth of a sinking lure is heavily dependent on the speed of the lure through the water. When there is a significant water current, the speed with respect to the water is different than the speed given by the GPS.

Trolling Angles can show the speed and direction of the rig with respect to the water by comparing the GPS and the water current. This gives you the knowledge to control the boat speed to accurately achieve the desired lure depth when using weighted lines or downriggers in tidal currents and large rivers,

The GPS control shows the speed of the boat, and shows an error flag when it differs significantly from the Speed assigned to the calibration.

If the option “Adjust Speed for Water Current” is set, the GPS control shows the speed and direction components of three related vectors:

• Speed Over Ground (SOG), as given by the GPS.
• Current, as entered by the user.
• Speed Through Water (STW), as calculated by Trolling Angles.

Since the Over Ground vector is the sum of the Current vector plus the Through Water vector, the STW is calculated by subtracting the Current from the SOG.

The only trick in this process is to determine and enter the Current speed and direction. You may be able to find the current at certain locations as measured by government current gauges. On a calm day, you can let your boat drift as you read the speed and direction from the GPS.

Or, you can use the Trolling Angles Water Current Gauge.