![]() We are 5 nautical miles from the target at 1030hrs. If we know the length of one side (our course covered, A to B) from our log reading, we then know the length of the side B to C.Ī to B = 5 nautical miles, therefore B to C = 5 nautical miles. We have a baseline of a triangle, A to C and the two remaining sides (A to B and B to C) are equal in length because we have an isosceles triangle with two equal internal angles. We know triangles have a total of 180° internally, therefore the remaining angle must = 40°. The value of all three angles added together always equals 180°. This 100° forms the angle at the top of our isosceles triangle.Īll triangles have three internal corner angles. We cut that line with the double angle of 080°, therefore 180° – 080° = 100° remaining. The Isosceles Triangle – how does it help us in Navigation? So we have to add 13☎ to all the Compass bearings to obtain the True bearing for the chart work. We have used a total Compass error for the above example of 13☎. Remember: to be able to plot the fixed position on a chart, convert all bearings to TRUE. By using 045° as your initial angle, by the time 090° (abeam) comes up, you could be in the danger zone! 030°), you can predict your clearance off the headline on arrival. By using an initial angle off the bow less than 045° (e.g. you may have to avoid a danger that is lying off a headland. ![]() This method is easier, but it is not predictive, i.e. As before, the distance run will equal your distance off the target. When target is abeam, note the time and log reading. When the target is 045° off the bow, note the time and log reading, double the angle off the bow will be 090° or abeam. Swing your arm from pointing at the bow to pointing abeam of your boat. When you get the chance, have a go it’s actually quite simple and straightforward.Īnother useful method is to guess 045° off the bow using your arm. So you can say, ‘At 1030hrs we are 5nm from Nobby’s Head Lighthouse, which is on a bearing line of 267☌.’ The number of sea miles covered (assuming no current or leeway) equals the distance the vessel is from the target.When the same target (Nobby’s Head Lighthouse) bears 267☌, note down (again) the time and distance run (from the log).Ĭourse steered = 347☌, target bearing = 267☌, distance run = 5nm, time of second bearing = 1030hrs. ![]()
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