Rendezvous Involving Station Keeping

Rendezvous Involving Station Keeping

Your vessel is engaged in the Ministry of Defence’s assigned duties. At 0400 GMT Your vessel has been ordered to come 2.5 miles to the port beam of an RFA Vessel to receive stores by helicopter. The RFA vessel is heading 350° T at 10 knots and is bearing 290 T from you at a distance of 22 miles. Your vessel’s maximum speed is 15 knots. Find the following by plotting:

• The course to steer to reach the advised station as early as possible
• The ETA at the station
• The distance that you expect to pass astern of the RFA vessel
• The CPA from the RFA

Rendezvous Involving Station Keeping

Choose a suitable scale. For the example, plot 1:2 has been used. Plot the course of the RFA vessel from the center of the sheet. Plot the bearing and distance between both vessels as line O-RFA, with O representing your vessel.

Since you are expected to position yourself at 2.5 miles to the port beam of the RFA vessel (270° R x 2.5′), measure the distance 2.5 miles to the port beam of the RFA vessel at point A’. Join OA’. This is the relative approach as seen on the radar of the RFA. Your vessel would be seen as moving along this line from the RFA.

The plotting interval used is 1 hour. At O, plot WO in direction of 350° T x 10′.

From W, mark 15′ along the line OA’ and identify it as A. Join WA. WA is the course to steer to reach 270° R x 2.5′ from the RFA. From the plot, the course is 323°.5 T.

For ETA: Time to station (A’) = (OA’ / OA) x Plotting interval
(24.2 / 7.5) x 1 = 3h 14m
ETA 0400+ 0314 = 0714 GMT

For distance astern: Draw a line reciprocal to the course of the RFA to meet the line OA’. Measure the distance of this line. From the plot, it is 1.3′.

For CPA: Draw a line from the center to be perpendicular to the OA’ and reach OA’. Measure the distance of this line. This is the CPA and is 1.1′.