Single-handing today I had a west wind which meant go south out of the Wood Islands Harbour if you want to come back on the same wind. All well and good except a rising tide in Northumberland Strait gives a 2-3 Kt current to the west. Running a broad reach…crosswise to the wind…meant the tide carried me to the west even though the sailboat pointed south.
After an hour I reversed direction…I could tack through the 180 degrees because the boat speed was high enough…about 5 Kts. Now, heading back toward the harbour, I noticed that when the boat pointed toward the lighthouse the little arrow on the GPS display pointed more to the west. OF COURSE, the GPS isn’t interested in the direction of the boat…just the net direction it finds the sensor going relative to the earth. You don’t need a course in vector math to recognize that the tide was moving me west as I sailed north. So I adjusted the autopilot setting until the GPS arrow was pointed toward where I wanted to go. Even though the boat pointed quite a bit east, the net direction was north! I’ve always known you could calculate the direction to point when in a cross current, but the GPS unit makes it even easier. My discovery for the day!