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A HRB 19:00 estamos a 6 millas al Este verdadero del faro de Punta Europa. Desde aquí damos rumbo a Ceuta (luz verde de la bocana), teniendo en cuenta que existe una corriente de Rc = E e Intensidad horaria = 2 millas. Calcular el rumbo verdadero y la velocidad a la que tenemos que navegar para llegar a Ceuta a HRB 21:00.At HRB 19:00 you are 6 miles due East true of Punta Europa lighthouse and head for Ceuta (green entrance light) in a current setting Rc = E at Ihc = 2 knots. Calculate the true course and speed needed to arrive at HRB 21:00:
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Correct answer: c) Rv = 213º V = 7.6 knots
Why it is correct
From 6 miles due East of Punta Europa (36º 06.5′ N, 005º 13.3′ W), to reach Ceuta green light (35º 53.8′ N, 005º 18.6′ W) in 2 hours (19:00 to 21:00), the current (Rc = 090º, Ihc = 2 knots) will set the vessel 4 miles East. Joining the tip of that 4-mile current vector to Ceuta gives a water track of 15.2 miles in 2 h (speed V = 7.6 knots) on true course Rv = 213º.
Why the others are not
- a) Does not divide the distance by the 2-hour passage time or fails to counteract the east-going current.
- b) Does not divide the distance by the 2-hour passage time or fails to counteract the east-going current.
- d) Does not divide the distance by the 2-hour passage time or fails to counteract the east-going current.
How to work it out in the exam
- Plot 6′ E of Punta Europa, lay off 4 miles (2 h at 2 knots) East and join to Ceuta: Rv = 213º.
- Measure that vector's length (15.2 miles in 2 h) and divide by 2: V = 7.6 knots.
Where this question comes from
- Junta de Andalucía · 2016 · 2ª convocatoria · PY Módulo de navegación · question 16 Official paper · Official answer key
Try it: Navigation calculations
Pending instructor review. Machine translation, not reviewed.