tide ce year 3 phase i

1.PREDICTION OF TIDE LEVELS FOR SHIPPING (I.E. CALCULATING

TIDE TABLES)

2.NAVIGATION THROUGH INTRACOASTAL WATERWAYS, AND

WITHIN ESTUARIES, BAYS, AND HARBOURS;

3. WORK ON HARBOUR ENGINEERING PROJECTS, SUCH AS THE

CONSTRUCTION OF BRIDGES, DOCKS, BREAKWATERS, AND DEEP-

WATER CHANNELS

WHY LEARN TIDE?

THERE ARE SEVERAL REASONS WHY WE SHOULD WANT ACCURATE KNOWLEDGE OF TIDAL CHANGES IN SEA LEVELS:

WHY LEARN TIDE?

4. PROVISION OF INFORMATION NECESSARY FOR UNDERWATER

DEMOLITION ACTIVITIES AND OTHER MILITARY ENGINEERING

USES; AND THE FURNISHING OF DATA INDISPENSABLE TO

FISHING, BOATING, SURFING, AND A CONSIDERABLE VARIETY OF

RELATED WATER SPORT ACTIVITIES

5. THE ESTABLISHMENT OF STANDARD CHART DATUM FOR

HYDROGRAPHY.

WHY LEARN TIDE?

6. KNOWLEDGE OF TIDAL EXTREMES FOR COASTAL DEFENCE

AND FLOOD PROTECTION.

7. KNOWLEDGE OF TIDAL CHANGES THAT DRIVE

CORRESPONDING BIOLOGICAL, CHEMICAL, AND GEOLOGICAL

CYCLES IN THE MARINE ENVIRONMENT.

8. OBSERVING GLOBAL CHANGE IN SEA LEVEL.

BASIC DEFINITIONS

TidesPeriodic vertical oscillation of the sea surface in response to the tide raising forces of Moon and the Sun.

Tidal StreamPeriodic Horizontal oscillation of the sea surface under the effect of same tide raising forces of Moon and the Sun.

TIDAL THEORY

THE ANCIENT GREEKS RECOGNISED RELATION

WITH THE MOON

ISAAC NEWTON'S PUBLICATION OF PRINCIPIA (1687)

TIDES DEVELOP AS A RESULT OF THE

GRAVITATIONAL PULL OF THE MOON

MOON’S GRAVITATIONAL PULL APPROXIMATELY 2.25

TIMES GREATER THAN THE SUN’S

Earth- Moon System

Earth – Moon Barycentre – 1000 km inside Earth

Perigean tide – Closest to Earth

Apogean tide - Furthest to Earth

Difference – 15 to 20 %

Earth- Moon System

Earth- Sun SystemEarth rotates around Sun – every 365 ½ days

Earth – Sun Barycentre – inside Sun.

Perihelion tide – Closest to Earth

Aphelion tide - Furthest to Earth

Difference – 3 %

Earth- Sun System

Perihelion

Aphelion

Phases of Moon

The appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth.

One half of the lunar surface is always

illuminated by the Sun (except during lunar eclipses), and is hence bright, but the portion of the illuminated hemisphere that is visible to an observer can vary from 100% (full moon) to 0% (new moon).

The boundary between the illuminated and unilluminated hemispheres is called the terminator.

Lunar Phases

Phases of Moon

Waxing - the amount of illuminated surface as seen from Earth is increasing

Waning - the amount of illuminated surface as seen from Earth is decreasing

Crescent Moon

Gibbous Moon

Earth- Moon System

The time between two full moons is about 29.53 days (29 days, 12 hours, 44 minutes) on average.

This month is longer than the time it takes the Moon to make one orbit about the Earth with respect to the fixed stars (the sidereal month), which is about 27.32 days.

Earth- Moon System

This difference is caused by the fact that the Earth-Moon system is orbiting about the Sun at the same time the Moon is orbiting about the Earth.

The actual time between two is variable because the orbit of the Moon is elliptic and subject to various periodic perturbations, which change the velocity of the Moon.

Earth- Moon System

TIDAL THEORY

Assumption - a static ocean completely covers a smooth

earth.

It considers - Gravitational attraction of sun and moon

combine with centrifugal forces resulting from the revolution of

the moon and earth – result in unbalanced forces which produce

tides.

The result of the unbalanced forces is a distorted ocean

with two bulges

TIDAL THEORY

Sublunar bulge

AntipodalBulge

TIDAL THEORY

Sublunarpoint

AntipodalPoint

TIDAL THEORY

Sub lunar bulge :

The gravitation force exerted by the moon

creates tidal 'bulges' of water on the planetary

surface

Ocean water is drawn toward the gravitational

force of the moon and away from the gravitational

centre of the earth.

TIDAL THEORY

Antipodal bulge :

develops on the side of the earth directly opposite

the gravitation force exerted by the moon.

Position of the moon (relative to the earth) changes

only slightly in a single day, and the tidal bulges

remain fixed and the earth essentially rotates

'through' the tidal bulges

TIDAL FORCES

Force of gravity is proportional to

The product of the masses of two objects (The earth-

moon or earth-sun systems) and

Inversely proportional to the square of the distance

between the two objects,

or total gravity = G (m1x m2) / r2

TIDAL FORCE

When this force is resolved into components in x axis

and y axis

The resultant components are vertical and horizontal

component acting in y and x axis respectively

The vertical component is only a very small portion of

the earth’s gravity and hence actual lifting of the water

against gravity is infinitesimal.

TIDAL THEORY

TIDAL FORCE

Horizontal component which produce the tides by

causing the water to move across the earth and pile

up at the sublunar and antipodal points until and

equilibrium position is reached.

This horizontal component of the differential

gravitational force is known as tractive force and is

expressed as:

F h = 3/2 *(m2 r sin2 )/ d3

Spring TidesTwice every lunar month, the moon and the sun are

in line with each other and with the Earth.Net result is maximum tide raising forceHigher high waters and lower low waters than usual

experienced.

Neap Tides

Twice every lunar month, the moon and the sun are at right angles to each other.

Net result is minimum tide raising force

Lower high waters and Higher low waters than usual experienced.

Spring & Neap tide

Priming & Lagging

Effect of Sun and Moon taken together – the intervals b/w successive high and low waters is altered.

Priming- Moon b/w new and first quarter and b/w full and last quarter : high tide occurs before the moon’s transit of the meridian

Lagging- Moon b/w first quarter and full and b/w last quarter and new : high tide occurs after the moon’s transit of the meridian

ADMIRALITY TIDE TABLES

Vol I – UK & Ireland

Vol II – Europe, Mediterranean Sea & Atlantic Ocean

Vol III – Indian Ocean & South China Sea

Vol IV – Pacific Ocean

Ports Classified into : -i. Standard Portsii. Secondary Ports

Classification based on :-a. Importanceb. Usability &c. Tidal characteristics

ADMIRALITY TIDE TABLES

Standard Ports

The times and heights of high and low water are tabulated for every day of the year. The zone time used for the predicted times is the Standard Time for the Port and is indicated at the top of each page.The heights are shown in metres referred to the Chart Datum of the port concerned.E.g. Mumbai, Kochi, Chennai

Secondary Ports The times of high and low water are obtained by

applying the time differences tabulated in the Secondary Ports Table to the daily predictions for the designated Standard Port.

A negative time difference will give an earlier time than that for the Standard Port and a positive one a later time.

The times obtained by applying these corrections are in the time zone shown next above the Secondary Port, irrespective of the zone time used for the Standard Port predictions.

E.g. Quilon, Kakinada, Karwar, Jaigarh

NOTE

i. This method is only suitable when the duration of rise and fall is between 5 and 7 hours and

ii. when there is no shallow water correction.

STEPS FOR CALCULATING HOT

STEPS FOR CALCULATING HOT

i. Plot heights of HW and LW occuring either side of required time and join by sloping line.

ii. Enter HW time and sufficient others to embrace required time.

iii. From required time, proceed vertically to curve for duration, interpolating as necessary between curves on diagram.

iv. Proceed horizontally to sloping line, vertically to height scale. Read of height.

PROBLEM

Find HOT at KOCHI at 1200 hrs on 01 Jul 2001

0017 0.9

0823 3.2

1438 1.4

1950 0.7

DURATION = 0615

PROCEDURE FOR FINDING HOT

HOT2.1m

STD PORT – ATT Vol III

Find HOT at COLUMBO at 1000 hrs on 01 Jul 01

0017 4.4

0723 0.9

1324 4.5

1950 0.7


Find HOT at KARACHI (Entrance) at 0600 hrs on 01 Jul 01

0315 6.6

0930 0.8

1535 6.7

2155 0.0


Find HOT at DAR ES SALAM at 1000 hrs on 31 Mar 01

0112 0.8

0654 13.2

1340 0.7

1917 13.3

PROBLEM

Calculate the time of tide when HOT falls to 0.6 mtrs in the morning of 28 Feb 2001 at KOCHI

0217 0.9

0823 3.2

1438 1.4

1950 0.7

PROCEDURE FOR FINDING HOT

HOT2.1m

SECONDARY PORTS

Find the tidal predictions at Minicoy on 06 Jul 2004.

Step I: Obtain the geographical index number of the sec.port from the table(4401)

Step II: Find the data corresponds to the sec.port in Part II

Step III: Identify the STD PORT(COCHIN-4393)

Step IV: Fill up the table for secondary port predictions

EXTRACT OF PART II

No. Place Time Diff Ht Diff

MHW MLW MHWS MHWN MLWS MLWN

4393 COCHIN (see page 69) 0.9 0.8 0.6 0.3

4401 Minicoy +0006 +0011 +0.5 +0.4 +0.3 +0.2

Seasonal Changes: July 1

4393 - COCHIN = 0.0

4401- Minicoy = 0.0

Tidal Predictions at COCHIN on 06 Jul 2000

0250 0.7

0838 0.1

1604 0.9

2207 0.3

16

15141312

1111

10987

66

4321

LWHWLWHW

HEIGHTTIME

STD PORT

Seasonal Changes

DIFFERENCES

Seasonal Changes

SEC PORT

Std Port

Sec. Port

STANDARD PORT—COCHIN(4393) TIME/HT RQD-

SECONDARY PORT—MINICOY(4401) DATE 06 Jul TIME ZONE- -0530

0250

1604

0838

2207

0.7

0.9

0.1

0.3

+0006 +0011

0256

1610

0849

2218

0.0 0.0

0.00.0

+0.30

+0.50

+0.12

+0.20

(-)

(+)

1.0

1.40

0.22

0.50

EXTRACT OF PART II

No. Place Time Diff Ht Diff

MHW MLW MHWS MHWN MLWN MLWS

4428 COLOMBO (see page 72) 0.7 0.5 0.3 0.1

4430 Galle +0012 +0012 -0.1 -0.1 0.0 0.0

Seasonal Changes: Nov. 1

4428-COLOMBO = 0.0

4430- Galle = 0.0

Tidal Predictions at COLOMBO on 02 Nov 2000

0433 0.7

1045 0.2

1635 0.5

2228 0.2

16

15141312

1111

10987

66

4321

LWHWLWHW

HEIGHTTIME

STD PORT

Seasonal Changes

DIFFERENCES

Seasonal Changes

SEC PORT

Std Port __

Sec. Port

STANDARD PORT--COLOMBO--- TIME/HT RQD---------------------

SECONDARY PORT--Galle---------- DATE 02 Nov -TIME ZONE----

0433

1635

1045

2228

0.7

0.5

0.2

0.2

+0012 +0012

0445

1647

1057

2240

0.0 0.0

0.00.0

-0.1

-0.1

0.0

0.0

(-)

(+)

0.6

0.4

0.2

0.2

EXTRACT OF PART II No. Place Time Diff Ht Diff

MHW MLW MHWS MHWN MLWN MLWS

4437 TRINCOMALLE (see page 72) 0.7 0.5 0.3 0.1

4440 Jaffna +0654 +0654 -0.1 0.0 0.0 +0.1Seasonal Changes: Nov .14437 TRINCOMALLE = +0.14440- Jaffna =+ 0.1

Tidal Predictions at TRINCOMALLE on 02-03 Nov 2000

02 Nov 1721 0.3

03 Nov 0100 0.7

0751 0.4

1341 0.5

1816 0.4

16

15141312

1111

10987

66

4321

LWHWLWHW

HEIGHTTIME

STD PORT

Seasonal Changes

DIFFERENCES

Seasonal Changes

SEC PORT

Std Port __

Sec. Port

STANDARD PORT--TRINCOMALLE--- TIME/HT RQD---------------------

SECONDARY PORT--Jaffna---------- DATE 03 Nov -TIME ZONE----

0100

1341

1721/02

0751

0.7

0.5

0.3

0.4

+0654 +0654

0754

2035

0015

1445

+0.1 +0.1

+0.1+0.1

-0.1

0.0

0.0

- 0.05

(-)

(+)

0.6

0.5

0.3

0.35

ASSIGNMENT

1. Find the tidal predictions at Galle on 02 Nov 2004.

2. Find the tidal predictions at Jaffna on 03 Nov 2004

SECONDARY PORTS – ATT Vol I & II

EXAMPLE: Find the tidal predictions after 1600 H at Hastings on 05 Nov 99.

Step I: Obtain the geographical index number of the sec.port from the table(85)

Step II: Find the data corresponds to the sec.port in Part II

Step III: Identify the STD PORT and its index no.

Step IV: Fill up the table for secondary port predictions

PROBLEM

1. Find the tidal predictions at Alleppey on 31 Oct 2004.

No.Place Time Diff Ht Diff MHW MLW MHWS MHWN MLWS MLWN

4393 COCHIN (see page 69) 0.9 0.8 0.6 0.3

4394 Alleppey +0000 -0003 0.0 -0.1 -0.2 -0.2

Seasonal Changes: Oct 14393 - COCHIN = -0.14394 - Alleppey = -0.1

Tidal Predictions at COCHIN on 31 Oct 2004

0250 0.5

0829 1.8

1452 0.5

2007 1.3

PROBLEM

1.Find the tidal predictions at Visakhapatnam on 11 Nov 2004.

No. Place Time Diff Ht Diff MHW MLW MHWS MHWN MLWS

MLWN4393 BRE (see page 69) 1.9 1.7 0.5 0.2

4394 Vizag +0013 -0023 -0.2 -0.1 -0.2 -0.2Seasonal Changes: Nov 4393 - COCHIN = -0.14394 - Alleppey = 0.2Tidal Predictions at BASSEIN RIVER ENTRANCE on 11 Nov 2004

0115 1.5

0928 0.8

1705 1.3

2204 0.3

CHART DATUM

THE DATUM OR THE PLANE OF REFERENCE TO WHICH ALL

CHARTED DEPTHS AND DRYING HEIGHTS ARE RELATED.

IT IS A LEVEL SO LOW THAT THE TIDE WILL NOT

FREQUENTLY FALL BELOW IT.

THE LIST OF DATUMS USED BY VARIOUS COUNTRIES ARE

LISTED IN RESPECTIVE TIDE TABLES

FOLLOWING ARE MEASURED FROM CHART DATUM:- (I) HEIGHT OF TIDE AT ANY INSTANT. (II) HEIGHTS OF LEVELS AND DATUM LIKE MSL, ORDNANCE DATUM, HAT, LAT, MHWS, MLWS, MHWN, MLWN ETC. (III) CHARTED DEPTHS OF FEATURES PERMANENTLY COVERED BY THE SEA. (IV) HEIGHTS OF FEATURE PERIODICALLY COVERED AND UNCOVERED BY THE SEA DURING HIGH AND LOW TIDES RESPECTIVELY.(DRYING HEIGHT)

CHART DATUM

CHARTED HEIGHT / ELEVATION

ALL FEATURES SHOWN ON THE CHART PERMANENTLY ABOVE WATER LEVEL HAVE THEIR HEIGHTS MEASURED ABOVE MHWS. JETTIES, TOWERS. LIGHT AND SUCH PERMANENT STRUCTURE ARE GIVEN CHARTED HEIGHTS ABOVE MHWS.

THE HEIGHTS OF NAVIGATIONAL LIGHTS LIKE THOSE OF THE LIGHT HOUSE ARE TERMED AS CHARTED ELEVATION. OF LATE, THE PRACTICE OF REFERRING THESE HEIGHTS ABOVE MEAN SEA LEVEL HAS BEEN NOTICED.

THE DATUM FOR HEIGHTS IS PROMINENTLY SHOWN ON ALL CHARTS, BE IT MHWS OR MSL. SOMETIMES MEAN HIGHER HIGH WATER IS USED IN LIEU OF MHWS AS THE DATUM FOR HEIGHTS.

CHART DATUM

DATUM PROBLEMS

GROUNDING. A SHIP WILL RUN AGROUND IF SUFFICIENT

WATER RELATED TO HER DRAUGHT IS NOT AVAILABLE. THE TIME,

WHEN THE KEEL FIRST TIME TOUCHES BOTTOM, IS CONSIDERED

AS THE TIME OF GROUNDING.

HOT + CHARTED DEPTH = DRAUGHT OF SHIP

OR

HEIGHT OF TIDE - DRYING HEIGHT = DRAUGHT OF SHIP

GROUNDING.

REFLOATING

DRAUGHT REMAINS UNCHANGED. A SHIP EXPECTS TO

REFLOAT ON THE FOLLOWING RISING TIDE WHEN THE HEIGHT OF

TIDE REACHES THE SAME LEVEL AS IT WAS AT THE TIME OF

GROUNDING. THUS,

HT OF TIDE FOR REFLOATING = HT OF TIDE AT THE

TIME OF GROUNDING

(b)

IF CHARTED HEIGHT IS GREATER THAN REQUIRED HEIGHT

ABOVE WATER, SHIP CAN PASS THE BRIDGE AT ANY TIME.

IF CHARTED HEIGHT IS LESS THAN REQUIRED HEIGHT, SHIP

MAY NOT BE ABLE TO PASS BENEATH. TIDAL CALCULATIONS ARE

NEEDED TO DETERMINE THE TIME FOR SAFE PASSAGE.

CHARTED HT OF BRIDGE ABOVE MHWS + HT OF MHWS ABOVE

CHART DATUM = HT OF MAST (ABOVE KEEL) + (H.O.T~ DRAUGHT ) +

TOP CLEARANCE.

TOP CLEARANCE

TOP CLEARANCE

BOTTOM CLEARANCE

FOLLOWING EQUATIONS HOLD FOR BOTTOM CLEARANCE

CHARTED DEPTH + HOT = DRAUGHT + BOT. CLEARANCE

OR

HOT – DRY. HT. = DRAUGHT + BOT. CLEARANCE

BOTTOM CLEARANCE

EXAMPLE

A ship with masthead height of 40 m above keel has to pass under a bridge. The charted ht of the bridge above MHWS is 30 m. The ht of MHWS is 9 m above chart datum. HOT at that instant is 4m.

(a) Find the draught of the ship if 1.0 m top clearance is required.

(b) When 1.0 m top clearance is given, the bottom clearance is found to be 3 m . What is the charted depth of the place.

EXAMPLE

A ship drawing 5 m ran aground in the morning hours on 01 Nov 2000 at CHITTAGONG. The place of grounding had a charted depth of 3m. The tidal predictions from ATT Vol III are:-0408 4.11050 0.81635 3.62242 0.9

(a) Find the time of grounding.(b) Find the expected time for the ship to re-float.

A ship drawing 4.0 m is required to cross a shallow patch off Bombay on 17 Jul 07. If the charted depth of the place is 2.0 m and a bottom clearance of 1.0 m is required then calculate the time when she can do so earliest on this day. Use ITT method. The tidal predictions are as follows :-

Time HtH M M05 59 3.611 10 0.9

16 18 16 3.823 52 1.2

06 18 3.617 11 47 1.0

18 58 3.523 55 1.1

EXAMPLE

NOTE

Pls get the following issued: -

• ATT Vol I 2001

• ATT Vol III 2001

• Std port & sec port tide prediction forms

• Graph sheets

tide ce year 3 phase i

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