🔍 Key Concepts

• Relative motion along a track line when taking bearings of a fixed object • Use of the ‘four-point bearing’ / abeam bearing method to find time and distance of closest point of approach (CPA) to a light • Speed–time–distance relationships when converting time differences into distances traveled

💭 Think About

• How can you represent the ship’s track and the light’s bearings on a simple sketch, with the light fixed and your course as a straight line? • What does it mean geometrically when the light is ‘abeam’ of your vessel in terms of the bearing relative to your course? • Given two bearings and the times they were taken, how can you turn the change in bearing into a proportion of the track run, and then convert that time into distance using your speed?

✅ Before You Answer

• Be clear about the relative bearing when the light is exactly abeam of your course of 307° T. • Carefully convert the time intervals between observations and abeam time into minutes, then into distance using 20 knots (1 knot = 1 nautical mile per hour). • Double-check your interpolation or proportion between the two observed bearings and times so that the change in bearing is treated as changing at a steady rate along the straight track.