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A HRB = 15:00 estamos al Sur verdadero del faro de Pta. Camarinal y al Oeste verdadero del faro de Pta. Paloma. Situados, damos rumbo a Tánger (farola del espigón), teniendo en cuenta una corriente de Rc = W e Ihc = 3 millas. Declinación magnética = 3º NE y desvío de la aguja = –3º (menos) Calcular el rumbo de aguja y la velocidad del buque para llegar a Tánger a HRB = 18:00.At HRB 15:00 when due South true of Punta Camarinal and due West true of Punta Paloma, you head for Tangier breakwater light in a West current of Ihc = 3 knots (dm 3º NE, dev –3º) to arrive at HRB 18:00. Find Ra and Vb:
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Correct answer: a) Ra = 149º Vb = 6.4 knots
Why it is correct
The start (S of Camarinal, W of Paloma) is 36º 04.0′ N, 005º 47.9′ W. Over the 3 hours (15:00 to 18:00) to Tangier breakwater (35º 47.4′ N, 005º 48.2′ W), the West current (270º, 3 knots) sets 9 miles along 270º. Joining the tip of that 9-mile vector to Tangier gives a water run of 19.2 miles in 3 h (Vb = 6.4 knots) along true course Rv = 149º. Since Ct = +3º − 3º = 0º, Ra = 149º.
Why the others are not
- b) Does not offset the 9 miles of west-going current over the 3-hour passage.
- c) Does not offset the 9 miles of west-going current over the 3-hour passage.
- d) Does not offset the 9 miles of west-going current over the 3-hour passage.
How to work it out in the exam
- Plot 36º 04.0′ N, 005º 47.9′ W, lay off 9 miles (3 h at 3 knots) West and join to Tangier: Rv = 149º (Ra = 149º).
- Measure that vector's length (19.2 miles) and divide by 3 hours: Vb = 6.4 knots.
Where this question comes from
- Junta de Andalucía · 2020 · Convocatoria de e · PY Módulo de navegación · question 17 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.