Sailing in Current could be costing you 50 seconds/mile
If you don’t know where and how fast the current is going, you could be losing 50 seconds/mile and not know it
Another thing to realize is that current is much more variable than you think or current tables tell you. Back eddies, wind effects and harbor outflow make current do things you would never believe. And on a scale of minutes and a few hundred feet.
Having a real-time current readout is the only way to monitor it and use it tactically
Calculating current requires both GPS and paddle/compass input.
GPS based systems cannot calculate current
Current also changes true wind. This can cause confusion because, contrary to perception, performance (relative to the water) is not affected by current. There is no “lee-bow effect”.
How the Ockam system helps with current
At the boat, the blue arrow is the current speed and direction. On the right is the dCur arrow which is the amount of current going in your direction. In this case, it’s almost a knot against you (red arrow). If it’s in your favor, the arrow will be green.
In upwind sailing, the 90 degree difference in heading on the two tacks will change the current’s effect on your performance. If you know this, you can choose when to tack to increase its help or neutralize its effect. In this case, tacking to starboard will change the 1 knot of hindrance to 0.2 knots of help. Knowing this can help in your decision about tacking.
By the way, that “Ready to tack” banner is a report from the tack logger, which reports your tack score for training purposes.