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En el Mar de Alborán hacia el Estrecho, HRB= 0100 en situación GPS= 35º 45,2’ N – 004º 50,3’W dan rumbo hacia el faro de Punta Carbonera (en la carta) en posición 36º 14,7’N – 005º 18,1’W con viento fresquito establecido del SE, a vela y velocidad media de 6 nudos. Calculan el rumbo loxodrómico directo:Heading for the Strait in the Alboran Sea at 01:00 ship’s time in GPS position 35º 45.2' N – 004º 50.3' W, a vessel sets course for Punta Carbonera lighthouse (36º 14.7' N – 005º 18.1' W) under a steady fresh SE breeze at 6 knots. What is the direct rhumb-line course?
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Correct answer: b) 322.5º
Why it is correct
Difference of latitude: ΔLat = 36º 14.7′ N − 35º 45.2′ N = +29.5′ N. Difference of longitude: ΔLong = 005º 18.1′ W − 004º 50.3′ W = 27.8′ W, with mean latitude 36º 00′ N and departure A = 27.8′ × cos 36º = 22.49′ W. Thus tan R = 22.49 / 29.5 ⇒ R = N 37.3º W ≈ 322.5º.
Why the others are not
- a) Does not match the ratio of departure (22.5′ W) to difference of latitude (29.5′ N).
- c) Does not match the ratio of departure (22.5′ W) to difference of latitude (29.5′ N).
- d) Does not match the ratio of departure (22.5′ W) to difference of latitude (29.5′ N).
How to work it out in the exam
- Find ΔLat = +29.5′ N and ΔLong = 27.8′ W between the two positions.
- Compute departure A = ΔLong · cos(mean Lat) = 27.8′ · cos 36º = 22.49′ W and tan R = A / ΔLat.
Where this question comes from
- Región de Murcia · 2019 · 2ª convocatoria · PY Tipo 1 · question 31 Official paper · Official answer key
- Región de Murcia · 2023 · 2ª convocatoria · PY Tipo 1 · question 37 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.