It’s sort of a given these days that most boaters heading out in local waters won’t necessarily be carrying paper charts with them. In the shallows surrounding the coastal regions of the southeast, particularly on the ICW, this is a mistake. One trick I often practice in the extremely rare case of GPS failure (more than likely that failure would not involve the GPS technology at all, but would rather be an instance of operator ineptitude where I dropped the thing overboard) is creating and using danger bearings.
This technique requires a rudimentary knowledge of how to read a chart and use a hand-bearing compass. Though rarely needed in practical terms, practicing this technique will keep your skills sharp, keep your head in the real-world and keep a reserve plan in your back pocket should the need for it arrive. Plus, they’re fun.
What are Danger Bearings?
Danger bearings are really useful when navigating from open water into restricted water. I’ll use Hillsboro Inlet in Pompano Beach as a prime example.
The Hillsboro Lighthouse sits on the beach to the north of the inlet, a rock jetty extending south and then curving west off the northern beach. To the south, another rock jetty extends southeast in a straight line. The entrance is narrow, often riddled with a strong current and a shallow reef lurks just beneath the surface to the south.
I’ll use the lighthouse as my point of reference. I should be able to see it long before I see the jetty, day or night, and I can take compass bearings on it from the boat. On the chart, we’ll draw bearing lines to create a ‘safe’ zone in which I want to keep the boat. The bearings that mark the limits of my safe zone are my danger bearings.
From the lighthouse, draw a line on the chart that just clears the reef to the north. This will be my southern limit, my danger bearing, approximately 285º magnetic. It’s clear to the north, so my safe zone is basically between my bearing of 285º on the lighthouse to the south, and the beach to the north.
If I’m offshore and approaching the lighthouse from the southeast and take a bearing on it, I need to keep that bearing below 285º – as I approach that number, it means that I’m approaching the point at which the reef is between me and the lighthouse – danger. Anything north of this – bearings less than 285 degrees – is safe. I can run right up onto the beach before I’d hit any other dangers.
Chartwork like this is arguably obsolete in practical terms, but a little knowledge never hurt anyone.