MCA CoC Navigation and Chartwork

Question 1

When plotting a position fix using two position lines on a nautical chart, the most reliable fix is obtained when the angle of intersection between the position lines is closest to which value?

Accepted Answer

90 degrees

Answer

A 90-degree angle of intersection between two position lines produces the most reliable fix because it minimises the area of uncertainty. As the angle decreases from 90 degrees, the 'cocked hat' or area of possible position increases, reducing accuracy.

Question 2

A vessel's GPS shows a position of 51°30.0'N 001°20.0'W. The chart datum is WGS84. What correction, if any, should be applied to plot this position on the chart?

Accepted Answer

No correction is needed as both use the same datum

Answer

When the GPS datum (WGS84) matches the chart datum (WGS84), no correction is required. Corrections are only necessary when the chart uses a different horizontal datum, such as OSGB36 or European 1950, in which case the datum shift noted on the chart must be applied.

Question 3

A vessel is steering 045°(T) at 12 knots in a current setting 135°(T) at 3 knots. What is the approximate course made good?

Accepted Answer

055°(T)

Answer

The current is setting roughly at right angles to the vessel's heading from the starboard quarter. Using the triangle of velocities, the current pushes the vessel to starboard of its heading, resulting in a course made good of approximately 055°(T). The exact value depends on vector resolution.

Question 4

Which publication issued by the UKHO provides information on tidal streams for UK waters, including rates and directions at hourly intervals relative to High Water at a standard port?

Accepted Answer

Admiralty Tidal Stream Atlas

Answer

The Admiralty Tidal Stream Atlas provides chartlets showing tidal stream direction and rate for each hour before and after High Water at the relevant standard port. These are essential for passage planning in UK waters where tidal streams can be significant.

Question 5

On an ECDIS, what does the term 'safety contour' refer to?

Accepted Answer

The depth contour selected by the mariner below which the seabed is highlighted as dangerous

Answer

The safety contour on an ECDIS is the depth contour chosen by the navigator to define the boundary between safe and unsafe water for that particular vessel. Areas shallower than the safety contour are highlighted, typically in a darker blue, to alert the navigator.

MCA CoC Practice Test

MCA CoC Practice Test

MCA CoC Navigation and Chartwork