Question 1

A tidal diamond on a chart is marked 'C'. You look up diamond C in the table. It shows for 1 hour before HW Dover: 205°T 2.6kn (springs) 1.3kn (neaps). What does this tell you?

Accepted Answer

At diamond C, one hour before HW Dover, the stream flows towards 205°T at 2.6 knots (springs) or 1.3 knots (neaps).. TIDAL DIAMOND tables: the direction (205°T) is the direction the stream is FLOWING TOWARD (set). The rate is 2.6kt at springs, 1.3kt at neaps. The table is referenced to HW at the standard port (Dover in this case). To use: find time relative to HW Dover → read off set and rate → interpolate between springs/neaps based on actual tidal range → apply to course-to-steer calculation.

Question 2

The tidal stream is described as 'setting 270°T at 2 knots'. What does 'setting 270°T' mean?

Accepted Answer

The stream is flowing towards the west, on a true bearing of 270°.. TIDAL STREAM terminology: SET = the direction the stream is flowing TOWARD. DRIFT = rate (speed) of the stream. A stream setting 270°T is flowing toward the WEST. This is opposite to wind convention, winds are named by where they come FROM (a westerly wind comes from the west); tidal streams are named by where they go TO. A tidal stream setting 090°T flows eastward.

Question 3

A passage of 30nm with a fair tidal stream of 2kt for 3 hours then a foul stream of 2kt for 3 hours. Boat speed 6kt throughout. What is the approximate total time for the passage?

Accepted Answer

4 hours 30 minutes. With the fair stream first: SOG 8 kn x 3 h = 24 nm. Remaining 6 nm at 4 kn = 1.5 h. Total 4 h 30 min. The streams do not cancel, because you spend less time in the foul stream.

Tidal Streams, questions and explanations

A tidal diamond on a chart is marked 'C'. You look up diamond C in the table. It shows for 1 hour before HW Dover: 205°T 2.6kn (springs) 1.3kn (neaps). What does this tell you?

The tidal stream is described as 'setting 270°T at 2 knots'. What does 'setting 270°T' mean?

A passage of 30nm with a fair tidal stream of 2kt for 3 hours then a foul stream of 2kt for 3 hours. Boat speed 6kt throughout. What is the approximate total time for the passage?

Practise this properly

Tidal Streams, questions and explanations

Questions

A tidal diamond on a chart is marked 'C'. You look up diamond C in the table. It shows for 1 hour before HW Dover: 205°T 2.6kn (springs) 1.3kn (neaps). What does this tell you?

The tidal stream is described as 'setting 270°T at 2 knots'. What does 'setting 270°T' mean?

A passage of 30nm with a fair tidal stream of 2kt for 3 hours then a foul stream of 2kt for 3 hours. Boat speed 6kt throughout. What is the approximate total time for the passage?

Practise this properly