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El 22 de mayo del 2021, al corregir la carta nos sale una declinación magnética de 1º NW. Siendo HRB: 06: 00, situados al N/v de la luz del espigón de entrada del puerto de Tánger y al W/v del Faro de Punta Cires teniendo en cuenta una corriente de Rc =E e Ihc = 3 nudos así como un viento del W que produce un abatimiento de 4º, damos Rumbo y velocidad para situarnos a 2 millas de la luz de entrada del espigón de Tánger para llegar allí a HRB: 06:30. A rumbo el desvío= 2 NE. Se pide: Ra para dirigirnos a 2 millas al N/v de la luz de entrada del espigón de Tánger y VbOn 22 May 2021 (dm 1º NW) at HRB 06:00, due N true of Tangier breakwater light and due W true of Punta Cires in a current Rc = E, Ihc = 3 knots with a W wind (4º leeway, dev 2º NE), find Ra and Vb to reach 2' N of Tangier light at 06:30:
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Correct answer: a) Ra = 200º Vb = 10.6
Why it is correct
The start (due N of Tangier breakwater and due W of Punta Cires) is 35º 54.7′ N, 005º 48.2′ W; the destination (2′ N of Tangier) is 35º 49.4′ N, 005º 48.2′ W (5.3 miles along 180º in 30 minutes ⇒ Vef = 10.6 knots). With an east-going current (090º, 3 knots), the vector triangle gives Rs ≈ 197º and Vb = 10.6 knots. Offsetting the 4º westerly leeway and Ct = +1º yields Ra = 200º.
Why the others are not
- b) Does not account for covering the 5.3 miles in half an hour (Vb = 10.6 knots) while offsetting current and wind.
- c) Does not account for covering the 5.3 miles in half an hour (Vb = 10.6 knots) while offsetting current and wind.
- d) Does not account for covering the 5.3 miles in half an hour (Vb = 10.6 knots) while offsetting current and wind.
How to work it out in the exam
- Measure the 5.3 miles along 180º to 2′ N of Tangier (in 0.5 h ⇒ Vef = 10.6 kn) and counteract the current (090º, 3 kn).
- Offset the 4º westerly leeway and apply Ct = +1º: Ra = 200º and Vb = 10.6 knots.
Where this question comes from
- Junta de Andalucía · 2021 · 1ª convocatoria · PY Módulo de navegación · question 15 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.