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Para una embarcación que se sitúa en la marca especial al Este de la Línea de la Concepción, calcular el rumbo de aguja (Ra) para pasar a 4,2 millas del faro de Punta Almina, teniendo como desvío de aguja para ese rumbo 3,5ºE y declinación magnética la obtenida en la carta náutica de enseñanza del Estrecho de Gibraltar para 2021.From the special mark East of La Línea de la Concepción in 2021, calculate the compass course (Ra) to pass 4.2 miles off Punta Almina lighthouse with compass deviation 3.5º E:
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Correct answer: b) Ra = 155º.
Why it is correct
From the special mark East of La Línea (36º 09.6′ N, 005º 19.2′ W), the outer tangent to the 4.2-mile arc east of Punta Almina has Rv = 157.5º. In 2021 charted variation is dm = 0º 58′ W ≈ −1º; with deviation +3.5º, Ct = +2.5º and Ra = 157.5º − 2.5º = 155º.
Why the others are not
- a) Does not subtract Ct = +2.5º (variation −1º, deviation +3.5º) from true course Rv = 157.5º.
- c) Does not subtract Ct = +2.5º (variation −1º, deviation +3.5º) from true course Rv = 157.5º.
- d) Does not subtract Ct = +2.5º (variation −1º, deviation +3.5º) from true course Rv = 157.5º.
How to work it out in the exam
- Draw the tangent from the special mark E of La Línea to 4.2′ off Punta Almina: Rv = 157.5º.
- With variation(2021) = −1º and deviation = +3.5º (Ct = +2.5º), compute Ra = 157.5º − 2.5º = 155º.
Where this question comes from
- Ministerio de Transportes (Madrid) · 2021 · Convocatoria de febrero · PER Test 5 · question 43 Official paper · Official answer key
Try it: Navigation calculations
Pending instructor review. Machine translation, not reviewed.