Tides

Question 1

What causes tide

Answer 1

Tides are the periodic rise and fall of the surface of the sea due principally to the gravitational pull of the sun and moon.

Question 2

Explain Spring and Neaps tides

Answer 2

Spring and Neap tides
Spring Tides; A tide of relatively large range occurring near the times of new and full moon. This is where the range of tide is greater and higher highs and lower lows will be experienced. Caused by the earth, moon, and sun lying approximately on the same line.
Neap tides is the opposite where the sun and Moon are 90 degrees out from each other. The results are tides called neap tides, whose ranges are less than average. Higher lows and lower Highs!

Question 3

The relationship between Chart Datum, LATS, MHWS

Answer 3

Chart Datum (CD) is the lowest level of water ever expected (excluding meteorological conditions), taken from the lowest astonomical tide.

MHWS represents the highest levels that tides typically reach during spring tides.

Question 4

• What is a Tidal stream atlas

Answer 4

Major tidal streams for selected waters of northwest Europe. Direction and rate of tidal streams at hourly intervals.

Question 5

Explain how to do a tide height calculation for a primary and secondary port

Answer 5

nstructions for Secondary ports
• Use Fred’s Pro forma.
• Enter times and heights at Standard Port.
• Calculate range at Standard Port Difference between heights.
• Enter Seasonal Change at Standard Port with sign changed.
• Calculate Differences Interpolate/extrapolate.
• Enter Seasonal Change at Secondary port.
• Calculate times and heights at secondary port. •
TO FIND HEIGHT AT GIVEN TIME
• Complete as above.
• On appropriate Standard Port Curve diagram.
• plot heights of HW and LW occurring either side of required time and join by sloping
line.
• Enter HW time and sufficient others to embrace required time.
• From required time proceed vertically to curves using Range at Standard Port to
interpolate between Springs and Neaps. Do NOT extrapolate. (See below).
• Proceed horizontally to sloping line and then vertically to Height scale. Read off
height above Chart Datum.
TO FIND TIME FOR A GIVEN HEIGHT ABOVE CHART DATUM
• Complete as above.
• On appropriate Standard Port Curve diagram, plot heights of HW and LW occurring
either side of required event and join by sloping line.
• Enter HW time and those for half-tidal cycle covering required event.
• From required height, proceed vertically to sloping line, then horizontally to curves,
using Range at Standard Port interpolate between Springs and Neaps. Do NOT
extrapolate. (See Below).
• Proceed vertically to Time scale. Read off time.