This document provides examples of tide and tidal calculations. Example 1 calculates limiting danger line depth based on vessel draught and predicted tide height. Example 2 calculates required tide height for a vessel deck to be level with a jetty. Further examples calculate predicted tide heights and times at various locations based on tide tables and charts. Examples also cover sunset/twilight times based on latitude/longitude and gyro error calculation from observed sunset bearing. The document demonstrates various tidal calculations and concepts.

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Tides &Tides &
AstroAstro
ConsolidatioConsolidatio
nn
A series of miscellaneousA series of miscellaneous
examplesexamples
A brief by Lance GrindleyA brief by Lance Grindley

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Example 1Example 1
 Your ship will be entering PLYMOUTHYour ship will be entering PLYMOUTH
when the predicted height of tide iswhen the predicted height of tide is
4.5 metres. If the draught of your4.5 metres. If the draught of your
vessel is 7.2 metres, at what depthvessel is 7.2 metres, at what depth
should the limiting danger line (LDL)should the limiting danger line (LDL)
be drawn?be drawn?

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Example 1 (Answer)Example 1 (Answer)
7.2m
2.0m
Chart Datum
4.5m
7.2m + 2.0m - 4.5m = 4.7m
Charted Depth

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Example 2Example 2
 Lying alongside in GREENOCK, ifLying alongside in GREENOCK, if
your maindeck is at a height 3.6your maindeck is at a height 3.6
metres above the waterline, whatmetres above the waterline, what
height of tide would be required toheight of tide would be required to
make the deck level with the jetty,make the deck level with the jetty,
having a charted height of 2.5 metres?having a charted height of 2.5 metres?

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Example 2 (Answer)Example 2 (Answer)
Jetty Deck
3.6m
Chart DatumChart Datum
HeightHeight
of Tideof Tide
MHWSMHWS
2.5m
3.4m3.4m
2.5m + 3.4m - 3.6m = 2.3m

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Example 3Example 3
 What is the predicted height of tide inWhat is the predicted height of tide in
PORTSMOUTH at 1200A onPORTSMOUTH at 1200A on
Wednesday 5 August, 1998?Wednesday 5 August, 1998?

HWHW LWLW HWHW LWLW RangeRange
09090909 14361436 4.1m4.1m 1.6m1.6m 2.5m2.5m
HW 1009AHW 1009A 30%sp30%sp

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Example 3Example 3
(Answer)(Answer)
HW +1 +2 +3 +4 +5-1-2-3-4-5-6
0 2 43 51
0 21 3
MEAN RANGES
Springs 3.9m
Neaps 1.9m
PORTSMOUTH
1009A
HW 4.1m
1200ALW 1.6m
3.7m

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Example 4Example 4
 What time will the predicted height ofWhat time will the predicted height of
tide rise to 7.0 metres during thetide rise to 7.0 metres during the
morning on Tuesday 23 June, 1998, inmorning on Tuesday 23 June, 1998, in
BRISTOL (AVONMOUTH)?BRISTOL (AVONMOUTH)?
HWHW LWLW HWHW LWLW RangeRange
06100610 12581258 12.9m12.9m 1.0m1.0m 11.9m11.9m
HW 0710AHW 0710A 95%sp95%sp

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Example 4Example 4
(Answer)(Answer)
+1 +2 +3 +4 +5 +6HW-1-2-3-4-5
0 4 862
0 42 6
MEAN RANGES
Springs 12.2m
Neaps 6.0m
AVONMOUTH
10 12 14
0710A0410A

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Example 5Example 5
 What is the predicted height of tide inWhat is the predicted height of tide in
SAINT JOHN, NB at 0900(+3) onSAINT JOHN, NB at 0900(+3) on
Tuesday 22 September, 1998?Tuesday 22 September, 1998?
HWHW LWLW HWHW LWLW RangeRange
12451245 06400640 7.6m7.6m 1.0m1.0m 6.6m6.6m
6hr 05min6hr 05min

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Example 5 (Answer)Example 5 (Answer)
+1 +2 +3 +4 +5 +6HW-1-2-3-4-5
0
0
4
2
8
4
6
3
2
1
0
0
2
4
1
2
3
6
+7-6-7
10
5
12
6
14
7
1345(+3)1.8m

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Example 6Example 6
 What time will the predicted height ofWhat time will the predicted height of
tide fall to 2.0 metres during thetide fall to 2.0 metres during the
afternoon of Thursday 29 January,afternoon of Thursday 29 January,
1998, in KARACHI? Give your answer1998, in KARACHI? Give your answer
in legal time.in legal time.
HWHW LWLW HWHW LWLW RangeRange
11141114 17271727 2.6m2.6m -0.2m-0.2m 2.8m2.8m
6hr 13min6hr 13min

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Example 6 (Answer)Example 6 (Answer)
+1 +2 +3 +4 +5 +6HW-1-2-3-4-5
0
0
4
2
8
4
6
3
2
1
0
0
2
4
1
2
3
6
+7-6-7
10
5
12
6
14
7
1114(-5)1315(-5)

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Example 7Example 7
 What is the predicted height of tide inWhat is the predicted height of tide in
CARDIFF(514) at 1600A on ThursdayCARDIFF(514) at 1600A on Thursday
18 June, 1998?18 June, 1998?

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Example 7 - TidalExample 7 - Tidal
Prediction FormPrediction Form
STANDARD PORT……………………TIME/HEIGHT REQUIRED…………
SECONDARY PORT…………………..DATE…..……….TIME ZONE……...
STANDARD PORT
TIMES HEIGHTS
HW LW HW LW RANGE
Seasonal Change
Seasonal Change
SECONDARY PORT
Duration/DST
Standard Port -
Secondary Port +
Cardiff
Avonmouth 1600
18 Jun A
1311 11.0m1931 2.9m 8.1m
34%Sp
-0015 -0033 -0.7m +0.1m
1256 1858 10.3m 3.0m
HW 1356A

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Example 7Example 7
(Answer)(Answer)
+1 +2 +3 +4 +5 +6HW-1-2-3-4-5
0 4 862
0 42 6
MEAN RANGES
Springs 12.2m
Neaps 6.0m
AVONMOUTH
10 12 14
1356A
8.0m

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Example 8Example 8
 What time should you sail fromWhat time should you sail from
PORTSMOUTH to arrive in HALIFAX,PORTSMOUTH to arrive in HALIFAX,
Nova Scotia, at 0900(+3) on Friday 26Nova Scotia, at 0900(+3) on Friday 26
June, if the overall distance isJune, if the overall distance is
2,562nm using an overall passage2,562nm using an overall passage
speed of 14 knots. Give your ETD inspeed of 14 knots. Give your ETD in
local time and allow time in hand (TIH)local time and allow time in hand (TIH)
of one hour per day or part of a day.of one hour per day or part of a day.

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Example 8 (Answer)Example 8 (Answer)
Distance 2562 at 14 knots = 183h = 7 days 15 hours
Time in hand 8 hours
Total time on passage 7 days 23 hours
ETA Halifax 260900(+3)
261200Z
Passage Time 072300
ETD Portsmouth 181300Z JUN
DST Zone (-1) +0100
ETD Portsmouth 181400(-1) JUN

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Example 9Example 9
 Ship’s time is zone (+3). How shouldShip’s time is zone (+3). How should
you adjust your clocks to legal timeyou adjust your clocks to legal time
before entering ST JOHNS,before entering ST JOHNS,
Newfoundland, when DST is not beingNewfoundland, when DST is not being
kept?kept?
 Clocks initially 3 hours behind UTClocks initially 3 hours behind UT
 Newfoundland (+3½) or 3½ behind UTNewfoundland (+3½) or 3½ behind UT
 ThereforeTherefore retardretard clocks by 30 minutesclocks by 30 minutes

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Rising & SettingRising & Setting
 Example 10.Example 10. What time will sunsetWhat time will sunset
occur on 5 February, 1997, in positionoccur on 5 February, 1997, in position
47º 00’N, 041º 15’W? Give your47º 00’N, 041º 15’W? Give your
answer in Zone Time (+3).answer in Zone Time (+3).
 Example 11.Example 11. What time is eveningWhat time is evening
nautical twilight (ENT) on 6 February,nautical twilight (ENT) on 6 February,
1997, in position 42º 00’S, 031º 30’E?1997, in position 42º 00’S, 031º 30’E?
Give your answer in Zone Time (-2).Give your answer in Zone Time (-2).

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Example 10Example 10
Port……..……… Date…………..
DR Lat…..….. DR Long…….... Zone....
Higher Lat.
Lower Lat.
Latitude Increment
Daily Change/Long Corrn
Local Mean Time (LMT)
Arc to Time (Longitude)
Universal Time (UT/GMT)
Zone ( )(Change sign)
Zone Time
Diff.
Daily Change
Time Diff.
5 Feb 87
47o
00N 41o
15W +3
50o
N
45o
N
1659
1712
-13
-0005 1716 +4/3
+0001
1708
+0245
1953
-0300
1653

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Example 11Example 11
Port……..……… Date…………..
DR Lat…..….. DR Long…….... Zone....
Higher Lat.
Lower Lat.
Latitude Increment
Daily Change/Long Corrn
Local Mean Time (LMT)
Arc to Time (Longitude)
Universal Time (UT/GMT)
Zone ( )(Change sign)
Zone Time
Diff.
Daily Change
Time Diff.
6 Feb 87
42o
00S 31o
30E -2
45o
S
40o
S
2034
2016
+18
+0007 2020 +4/3
+0001
2024
-0206
1818
+0200
2018

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Example 12Example 12
 You carry out a gyro check at aboutYou carry out a gyro check at about
1710(+2) just before sunset, when the1710(+2) just before sunset, when the
sun’s lower limb appears to lie a semi-sun’s lower limb appears to lie a semi-
diameter above the visible horizondiameter above the visible horizon
(True Sunset) on 6 February, 1997.(True Sunset) on 6 February, 1997.
Your DR position is 47º 00’N, 035ºYour DR position is 47º 00’N, 035º
00’W and the gyro bearing was 248º.00’W and the gyro bearing was 248º.
What was the gyro error?What was the gyro error?

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Example 12 (Answer)Example 12 (Answer)
Time 1710(+2) is 1910Z
Declination at 1900Z S15º 25.3’ or 15.4º
Latitude 47º
Amplitude 22.9º or W
23ºS
True bearing 270º - 23º = 247º
Gyro bearing 248º Error is 1º HIGH

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Questions?Questions?
????