While on a course of 152°T, a light bears 9° on the port bow at a distance of 11.6 miles. What course should you steer to pass 3 miles abeam of the light leaving it to port?
• Relative bearings and transfer to true bearings when altering course • Using basic trigonometry to form a right triangle with the closest point of approach (CPA) as one leg • CPA distance vs. present distance from the light and how that affects required course change
• If the light is 9° on your port bow while you are steering 152°T, what is its true bearing from you now? • How can you draw a right triangle where one leg is the desired CPA (3 miles abeam) and the hypotenuse is the current distance (11.6 miles)? • Once you find the angle between your present line of sight to the light and the line of travel to CPA, how do you convert that into a new true course?
• Confirm the true bearing of the light from your vessel before any calculation • Make sure you correctly identify which side (port) the CPA will be on and whether the triangle leg is perpendicular to your track at CPA • Double-check that your final answer is a true course, not a relative bearing or a new bearing of the light
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