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A HRB = 17-00 en situación verdadera l = 36º-07,0´N, L= 005-57,4´ W, damos rumbo al Fº de Cabo Espartel, Vhb = 7 nudos. A HRB = 19-00 se toma Dv del Fº de Pta. Malabata 138º y simultáneamente Dv del Fº de Cabo Espartel 210º. Calcular Rc e Ihc.At HRB 17-00 in true position l = 36º-07.0' N, L = 005º-57.4' W you head for Cape Spartel lighthouse at Vhb = 7 knots; at HRB 19-00 you take Dv Punta Malabata = 138º and Dv Cape Spartel = 210º. Calculate Rc and Ihc:
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Correct answer: b) Rc = 074º, Ihc = 2.25 knots.
Why it is correct
From 36º 07.0′ N, 005º 57.4′ W towards Cape Spartel lighthouse (35º 47.5′ N, 005º 55.5′ W) true course is Rv = 175º. In 2 hours (17:00 to 19:00) at 7 knots you run 14 miles to a DR at 35º 53.1′ N, 005º 55.8′ W. Intersecting Dv(Malabata) = 138º and Dv(Spartel) = 210º gives the observed fix 35º 54.3′ N, 005º 50.5′ W. From DR to fix is 4.5′ towards 074º ⇒ Ihc = 4.5 / 2 = 2.25 knots.
Why the others are not
- a) Does not measure from DR to fix or fails to divide the 4.5-mile drift by the 2 hours.
- c) Does not measure from DR to fix or fails to divide the 4.5-mile drift by the 2 hours.
- d) Does not measure from DR to fix or fails to divide the 4.5-mile drift by the 2 hours.
How to work it out in the exam
- Plot the DR 14′ towards Spartel (35º 53.1′ N, 005º 55.8′ W) and the fix with Dv = 138º and 210º.
- Measure from DR to fix: Rc = 074º and drift = 4.5′ in 2 h ⇒ Ihc = 2.25 knots.
Where this question comes from
- Junta de Andalucía · 2015 · 3ª convocatoria · PY Módulo de navegación · question 13 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.