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Situados el 4 de marzo de 2023 a Hrb 10:15 en posición 36° 05,6´N; 006° 09,0´W nos encontramos en zona de corriente de Rc=S45E e Ih=4 nudos, navegando al Ra=115°. El desvío es 3° (-), la declinación magnética será la del año en curso y nuestra velocidad de máquinas es de 6 nudos. Se pide el rumbo y velocidad efectivos más aproximados a Hrb 11:30, suponiendo que las condiciones de navegación se mantienen estables desde Hrb 10:15.On 4 March 2023 at 10:15 in 36° 05.6' N, 006° 09.0' W in a current setting S45E at 4 knots, you steer Ra = 115° (deviation –3°, variation for 2023) at 6 knots. Find your effective course and speed:
Show the answer
Correct answer: a) Ref = 121°; Vef = 9.9 knots.
Why it is correct
In 2023 charted variation is dm ≈ −0.7º; with deviation −3º, Ct ≈ −3.7º and Rv = 115º − 3.7º = 111.3º (speed 6 knots). Vector-adding the current (Rc = 135º, Ihc = 4 knots) gives Ref = 121º and Vef = 9.9 knots.
Why the others are not
- b) Does not match the vector resultant of (111.3º, 6 knots) and (135º, 4 knots).
- c) Does not match the vector resultant of (111.3º, 6 knots) and (135º, 4 knots).
- d) Does not match the vector resultant of (111.3º, 6 knots) and (135º, 4 knots).
How to work it out in the exam
- Compute Ct(2023) ≈ −3.7º and true course Rv = 115º − 3.7º = 111.3º.
- Vector-add the ship (111.3º, 6 knots) and the current (135º, 4 knots): Ref = 121º and Vef = 9.9 knots.
Where this question comes from
- Ministerio de Transportes (Madrid) · 2023 · Convocatoria de abril · PY Test 1 · question 33 Official paper · Official answer key
- Ministerio de Transportes (Madrid) · 2023 · Convocatoria de abril · PY Test 2 · question 35 Official paper · Official answer key
Try it: Navigation calculations
Pending instructor review. Machine translation, not reviewed.