RYA Day Skipper Tidal Calculations

Question 1

The Rule of Twelfths is used to estimate the rise or fall of the tide. In the 3rd hour of a 6-hour tide cycle, what fraction of the range rises?

Accepted Answer

3/12 of the range

Answer

1/12 of the range

Answer

2/12 of the range

Answer

4/12 of the range

Question 2

The tidal range at springs is 5.0 m and at neaps is 2.0 m. The range today is 3.5 m. What does this suggest?

Accepted Answer

The tide is between neaps and springs, closer to springs

Answer

The tide is at neaps

Answer

The tide is at springs

Answer

The range is abnormally small

Question 3

A tidal atlas shows an arrow with '15,28' for an hourly position. What do these numbers mean?

Accepted Answer

Neap rate = 1.5 knots; spring rate = 2.8 knots

Answer

15 degrees set; 2.8 knots rate

Answer

1.5 NM drift; 28 minutes duration

Answer

Neap set = 15°; spring set = 28°

Question 4

To find the height of tide at an intermediate time using Admiralty tables, a mariner uses:

Accepted Answer

The tidal curve for that port (springs or neaps curve as appropriate)

Answer

Only the Rule of Twelfths

Answer

A GPS receiver

Answer

The barometric pressure

Question 5

Chart datum is 0.5 m below MLWS at a particular port. The charted depth at a rock is 1.2 m. The height of tide is currently 0.8 m. What is the actual depth over the rock?

Accepted Answer

2.0 m

Answer

1.2 m

Answer

0.8 m

Answer

1.7 m

Question 6

A vessel draws 2.0 m. She needs 0.5 m clearance. The charted depth at the approach is 1.0 m. What minimum height of tide does she need?

Accepted Answer

1.5 m

Answer

2.5 m

Answer

0.5 m

Answer

3.0 m