tide ce year 3 phase i
DESCRIPTION
TRANSCRIPT
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TIDES
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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:
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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.
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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.
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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.
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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
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Earth- Moon System
Earth – Moon Barycentre – 1000 km inside Earth
Perigean tide – Closest to Earth
Apogean tide - Furthest to Earth
Difference – 15 to 20 %
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Earth- Moon System
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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 %
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Earth- Sun System
Perihelion
Aphelion
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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.
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Lunar Phases
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Phases of Moon
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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
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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
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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
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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
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TIDAL THEORY
Sublunar bulge
AntipodalBulge
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TIDAL THEORY
Sublunarpoint
AntipodalPoint
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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.
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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
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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
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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.
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TIDAL THEORY
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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
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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.
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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.
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Spring & Neap tide
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Spring & Neap tide
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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
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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
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Ports Classified into : -i. Standard Portsii. Secondary Ports
Classification based on :-a. Importanceb. Usability &c. Tidal characteristics
ADMIRALITY TIDE TABLES
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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
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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
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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
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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.
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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
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PROCEDURE FOR FINDING HOT
HOT2.1m
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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
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STD PORT – ATT Vol III
Find HOT at KARACHI (Entrance) at 0600 hrs on 01 Jul 01
0315 6.6
0930 0.8
1535 6.7
2155 0.0
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STD PORT – ATT Vol III
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
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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
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PROCEDURE FOR FINDING HOT
HOT2.1m
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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
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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
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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
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HWLW
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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
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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
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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
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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
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ASSIGNMENT
1. Find the tidal predictions at Galle on 02 Nov 2004.
2. Find the tidal predictions at Jaffna on 03 Nov 2004
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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
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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
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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
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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
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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
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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.
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CHART DATUM
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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
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GROUNDING.
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GROUNDING.
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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
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(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
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TOP CLEARANCE
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BOTTOM CLEARANCE
FOLLOWING EQUATIONS HOLD FOR BOTTOM CLEARANCE
CHARTED DEPTH + HOT = DRAUGHT + BOT. CLEARANCE
OR
HOT – DRY. HT. = DRAUGHT + BOT. CLEARANCE
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BOTTOM CLEARANCE
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BOTTOM CLEARANCE
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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.
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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.
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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
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NOTE
Pls get the following issued: -
• ATT Vol I 2001
• ATT Vol III 2001
• Std port & sec port tide prediction forms
• Graph sheets