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El día 10 de diciembre del 2021 a las 02:20 horas navegando al Rumbo de aguja= 142º con velocidad de la máquina = 12 nudos, se obtiene Marcación del Faro de Cabo Trafalgar = 052º Babor. Al ser 02:50 horas, se obtiene Marcación del mismo Faro = 122º Babor; desvío = - 6º. Viento del NE que nos abate 6º. Situación a las 02:20 horas.On 10 December 2021 at 02:20 steering Ra = 142º at 12 knots (deviation –6º, NE wind causing 6º leeway), Cape Trafalgar bears 052º Port relative, and at 02:50 it bears 122º Port relative. Find your position at 02:20:
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Correct answer: c) l = 36º 10.5' N L = 006º 08.2' W
Why it is correct
In 2021 dm ≈ −1º; with deviation −6º, Ct = −7º and true heading is Rv = 142º − 7º = 135º. True bearings to Trafalgar (from Rv, before leeway) are Dv₁ = 135º − 52º = 083º (02:20) and Dv₂ = 135º − 122º = 013º (02:50). With a NE wind on port (+6º starboard leeway), surface course is Rs = 135º + 6º = 141º (6 miles in 30 min at 12 knots). Shifting Dv₂ backwards 6 miles along 321º to intersect Dv₁ gives 36º 10.5′ N, 006º 08.2′ W.
Why the others are not
- a) Applies leeway to the relative bearings or gives the 02:50 position instead of the 02:20 position.
- b) Applies leeway to the relative bearings or gives the 02:50 position instead of the 02:20 position.
- d) Applies leeway to the relative bearings or gives the 02:50 position instead of the 02:20 position.
How to work it out in the exam
- Compute Rv = 135º, Dv₁ = 083º (02:20), Dv₂ = 013º (02:50) and Rs = 135º + 6º = 141º.
- Fit the 6 miles along Rs = 141º between both bearing lines and read the 02:20 position: 36º 10.5′ N, 006º 08.2′ W.
Where this question comes from
- Junta de Andalucía · 2021 · 1ª convocatoria · PY Módulo de navegación · question 11 Official paper · Official answer key
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Pending instructor review. Machine translation, not reviewed.