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Capt. Dan's Coastal Navigation Course: Danger Bearings   Exercises and References Bowditch on Danger Bearings p. 121 Exercises coming soon DB key coming as well     DANGER! Understanding Danger Bearings may be the most important thing you'll learn in ASA 105. At least it's likely that you'll apply this technique frequently as it can be used on your GPS, chart plotter, radar as well as any compass you have aboard. It works at night and, with the aid of electronics, in fog and bad weather. And it's easy. All you have to know is Right and Left. In the schematic, you'll see that we're headed towards Exotic Destination on a heading of 350M at 7 knots. With no current, steering error or anything else to throw us off, we'll have a safe transit. But if some factors do throw us off, we don't want to go left of course. Faraway Light is in the distance. It's not our destination, but it can help us get there by keeping us off Martin's Reef. You can see that if we stay to the Right of 350M bearing to Faraway Light, we're in the clear. If we stray to 350M or left of it, we're likely to run smack into the reef. In this case, to remain to the right of 350M, we will not accept a bearing more than the Danger Bearing. Some navigators note on their charts, NMT 350M. No More Than 350. The course and the Danger Bearing do not have to coincide as they do here. They're totally independent factors. In an instance where you wanted to remain left of the Danger Bearing, you'd accept NLT, No Less Than the Danger Bearing. In the Catalina chart, you can see a tactic we used to safely enter the Isthmus at night. We established our Course to Steer and denoted a No Less Than bearing to keep us well away from the shore. We turned turned toward the harbor when the Fl 2.5s light was was on a bearing of 144 M. We didn't want to stray left of this course, and established another danger bearing, this time a No More Than bearing . Visibility was excellent that night, and we were able to pick up G1 shortly after we made the turn toward Fl 2.5s. Interesting to note on this chart that the Ferry route takes G1 to the right. We didn't and we wouldn't, but then we don't go to the Isthmus several times a day as the ferry does.   Danger Bearing on Radar Using this with some radar sets is exactly like the visual technique we just described. What kind of radar? One that allows you to display magnetic bearing on the bearing cursor. Our Jeanneau has that feature, our Catalina does not. On the Catalina, we have only relative bearing - so many degrees left or right of the bow. Apply that figure to the compass reading - subtract left relative bearings, add right - and you can keep track of your position with regard to the Danger Bearing.   Danger Bearing on GPS GPS makes this drill very easy. Drive your vessel so that the COG is your intended course. (Your course, of course, was plotted on an up-to-date NOAA chart. You didn't just plug in some coordinates and head out.) Use the "highway" display for easiest steering and you'll have no issues knowing if you're straying near a hazard. Many chart plotters display multiple vectors, including COG, ship's heading and bearing to the waypoint. It can be confusing and I do not rely on these vectors, but refer back to COG and my planned course. You can also use the Course to Steer (CTS) read out. You'll need to plot a danger bearing on the chart first, but then you'll know what your NMT or NLT bearings are with regard to CTS. If you have a cursor on the chart plotter and a bearing readout, you can also use that. Though I do not recommend it - I recommend using a NOAA chart and your plotters - you can establish a Danger Bearing with bearing readout. Using GPS is just as easy as visual determination of Danger Bear - maybe easier; however, I don't like to relyon GPS alone. I'm really comfortable only when I can verify my position in another way - be it visual or radar. That said, if there is a hazard to the right or left (or both) of your course, you'll probably detect the drift on your GPS before it's evident any other way. This is probably too obvious to mention, but Radar and GPS can also be used to establish a "no closer to" and/or "farther from" criteria much as you use your depth sounder for "no shallower than" considerations.   Return to Top