I bought the AIS to let me know what the ships around me were up to, and it works well for that, but on this trip I’ve been anchoring out almost every night and have been using the anchor alarm function. It’s given me real peace of mind each night. For instance, it was very windy last night and this morning, gusting to 30 knots, and hovering around 20 much of the time. There are boats all around me in the Nanaimo anchorage just south of Newcastle Island, and I wanted to be sure I wouldn’t drag into them.
This picture shows two days of being anchored in the same place. The outer circle shows the range I can swing before the alarm goes off, in this case 150 feet diameter.. The dots are GPS positions of the boat, taken every few minutes. The inner set of dots were after I anchored, when the breeze was mild. I let out about 90 feet of line because the depth was around 25 feet. Around 2 AM the wind picked up and I increased my scope about 30 feet for better holding – which is the cluster of dots further away from the center of the circle, where the anchor is. If I had dragged about 20 feet, the alarm would have gone off.
You can tell two things from this picture – the wind is from the NNE, and the Coot swings back and forth about 30% in the wind.