RYA Yachtmaster Tidal Streams & Secondary Ports

Question 1

In a tidal stream atlas, the figures '08,15' alongside an arrow mean:

Accepted Answer

Mean neap rate 0.8 knots; mean spring rate 1.5 knots

Answer

8 metres depth; 15 minute duration

Answer

0.8 nm drift; 1.5 hour set

Answer

08:00 and 15:00 times of maximum flow

Question 2

Why does tidal range vary between springs and neaps on a fortnightly cycle?

Accepted Answer

The relative positions of the Sun, Earth, and Moon — at new and full Moon, solar and lunar tidal forces combine (springs); at quarter Moon they partially cancel (neaps)

Answer

Seasonal temperature changes affect sea level

Answer

The Earth's rotation accelerates at new Moon

Answer

Weather systems cause fortnightly pressure changes

Question 3

At a secondary port, HW time difference is +0h 45min and LW time difference is +1h 10min. Standard port HW = 0800, LW = 1400. What are the secondary port HW and LW times?

Accepted Answer

HW 0845, LW 1510

Answer

HW 0845, LW 1450

Answer

HW 0715, LW 1350

Answer

HW 0900, LW 1600

Question 4

The height of HW at a standard port is 5.8 m at springs and 4.2 m at neaps. Height difference for a secondary port is +0.3 m (springs) and +0.2 m (neaps). Today's HW height is between springs and neaps (range factor 0.6). What is the secondary port HW height (approx)?

Accepted Answer

4.2 + 0.6(5.8−4.2) + [0.2 + 0.6×0.1] ≈ 5.22 m

Answer

5.8 + 0.3 = 6.1 m

Answer

4.2 + 0.2 = 4.4 m

Answer

5.0 + 0.25 = 5.25 m

Question 5

A vessel needs to cross a bar with 1.8 m draft plus 0.5 m clearance. The charted depth at the bar is 0.4 m. The current tide height is 1.5 m. Can the vessel cross?

Accepted Answer

No — required depth = 2.3 m; available depth = 0.4 + 1.5 = 1.9 m — 0.4 m short

Answer

Yes — with 1.5 m tide there is enough water

Answer

Yes — the charted depth guarantees 1.8 m

Answer

No — the bar is permanently closed

Question 6

When using the Yachtmaster method to estimate arrival time at a tidal gate, which tidal atlas pages are used?

Accepted Answer

Pages referenced to hours before and after HW at the tidal atlas standard port for that area

Answer

Pages referenced to calendar date

Answer

Pages showing maximum spring rate only

Answer

Pages from the previous year's atlas