Section 7: Tides, Waves and Routeing (Challenge Questions)

Question 1

Describe the non-astronomical component of sea level.

Answer 1

Storm surges

Temporary rises in sea level caused by strong winds and low atmospheric pressure associated with storms or hurricanes. Storm surges can raise water levels by several meters for a few days.

Question 2

With the help of a neat and labelled diagram, define the various tidal definitions such as MHWS, MLWS, MHWN, MLWN, drying height etc.

Answer 2

MHWS
MLWS
MHWN
MLWN
Drying Height
CD
HAT

Question 3

Explain what chart datum is and what its significance is.

Answer 3

• Lowest astronimical tides
• Most of the charts details are measure from the CD.

Question 4

Describe the four principal harmonic constituents are tabulated in the Tide Tables.

Answer 4

M2:
- Principal semi-diurnal constituent
- 2x per day the waves are high caused by the Moon’s gravitational pull.

S2:
- Principal semi-diurnal constituent
- 2x per day the waves are high caused by the Sun’s gravitational pull.

K1:
- Principal diurnal constituent
- 1x per day caused by the combination of the Sun’s and Moon’s declination.

O1:
- Principal diurnal constituent
- 1x per day caused by the orbit of the Moon.

Question 5

With the help of a neat and labelled diagram, explain what is ‘significant wave height’.

Answer 5

• The average of the 1/3 of the waves in a given sea state.
• 2x the height, 3x per day.

Question 6

What are the factors which affect wave height and direction?

Question 7

What is meant by optimum ship routeing?

Answer 7

When passage planning combines weather date, ship specifications, and operational objectives to determine the safest and most efficient route.

Question 8

What are the advantages of optimum ship routeing?

Answer 8

• Improved fuel efficiency.
• Improved safety
• Improved ETA
• Improved Emissions

Question 9

What is meant by a ship’s performance with respect to weather routeing?

Answer 9

Ship’s speed and fuel consumption efficiency.

Question 10

What are the various resources available onboard to the Master to assist in weather routeing?