Situados en la oposición del faro de Isla Tarifa y Punta Cires y a 3 millas este último, ponemos rumbo al faro de Cabo Trafalgar. Sabemos que el rumbo de la corriente es SSW, su Intensidad Horaria 3,5 nudos y sopla un viento del sur que nos abate 3º. Nuestra velocidad de máquinas es 9 nudos y la CT=1º+. Calcular el rumbo de aguja que debemos poner y la velocidad que desarrollara nuestro barco.On the Isla de Tarifa–Punta Cires opposition at 3 miles from Punta Cires, you head for Cape Trafalgar in a SSW current of 3.5 knots and a South wind giving 3º leeway (Vm = 9 knots, CT = +1º). Find Ra and Vef:

Correct answer: d) Ra = 318º; Vef = 7.8 knots

Why it is correct

From 3′ off Cires on the Tarifa opposition (35º 56.6′ N, 005º 31.6′ W), the effective course to Cape Trafalgar is Ref = 300º. With a SSW current (Rc = 202.5º, Ihc = 3.5 knots) and Vm = 9 knots, the vector triangle gives Rs = 322º and Vef = 7.8 knots. With a South wind (+3º starboard leeway), Rv = 322º − 3º = 319º and Ra = 319º − 1º = 318º.

Why the others are not

• a) Does not simultaneously compensate for the SSW current (3.5 knots), leeway (+3º) and CT = +1º.
• b) Does not simultaneously compensate for the SSW current (3.5 knots), leeway (+3º) and CT = +1º.
• c) Does not simultaneously compensate for the SSW current (3.5 knots), leeway (+3º) and CT = +1º.

How to work it out in the exam

1. Plot Ref = 300º to Trafalgar and solve the triangle with Rc = 202.5º (3.5 kn) and Vm = 9 kn ⇒ Rs = 322º and Vef = 7.8 kn.
2. Subtract starboard leeway (Rv = 322º − 3º = 319º) and CT = +1º: Ra = 318º.

Where this question comes from

• Ministerio de Transportes (Madrid) · 2021 · Convocatoria de julio · PY Test 1 · question 39 Official paper · Official answer key
• Ministerio de Transportes (Madrid) · 2021 · Convocatoria de julio · PY Test 2 · question 32 Official paper · Official answer key

Try it: Navigation calculations

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