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A la Hrb 17:42 horas una embarcación se sitúa 7 millas al W verdadero del faro de Cabo Espartel, navegando en zona de corriente desconocida al rumbo de aguja 30º con una velocidad de 12 nudos, siendo la Ct = 5 (-). A la Hrb 19:02 horas la embarcación se sitúa en la oposición de los faros de Punta de Gracia y de Espartel a 9,4 millas del faro de Punta Paloma. Calcular el rumbo de la corriente (Rc) y su intensidad (Ihc).At Hrb 17:42, 7 miles due West true of Cape Spartel lighthouse, a vessel steers Ra = 030º at 12 knots (Ct = –5º); at Hrb 19:02 it fixes its position on the Punta de Gracia–Spartel opposition at 9.4 miles from Punta Paloma. Find Rc and Ihc:
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Correct answer: d) Rc = 144º and Ihc = 4.2 knots.
Why it is correct
From 7′ W of Spartel (35º 47.5′ N, 006º 04.1′ W), with Rv = 030º − 5º = 025º, in 1h 20m (1.333 h) at 12 knots you run 16 miles along 025º to a DR at 36º 02.0′ N, 005º 55.8′ W. The 19:02 fix (Gracia–Spartel opposition at 9.4′ from Paloma) is 35º 57.5′ N, 005º 51.7′ W. From DR to fix is 5.6 miles towards 144º ⇒ Ihc = 5.6 / 1.333 = 4.2 knots.
Why the others are not
- a) Does not divide the 5.6-mile drift by 1.333 hours (1h 20m) or reverses the current direction.
- b) Does not divide the 5.6-mile drift by 1.333 hours (1h 20m) or reverses the current direction.
- c) Does not divide the 5.6-mile drift by 1.333 hours (1h 20m) or reverses the current direction.
How to work it out in the exam
- Compute the 19:02 DR (16′ on Rv = 025º) and the fix on the Gracia–Spartel opposition at 9.4′ from Paloma.
- Measure from DR to fix: Rc = 144º and drift = 5.6′ in 1.333 h ⇒ Ihc = 4.2 knots.
Where this question comes from
- Ministerio de Transportes (Madrid) · 2020 · Convocatoria de diciembre · PY Test 1 · question 37 Official paper · Official answer key
Try it: Navigation calculations
Pending instructor review. Machine translation, not reviewed.