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Paul BrownTides – Chartwork 2nd Class
Chartwork 2nd Class
Tides
(Adapted from RYA Shorebased slides)
Paul BrownTides – Chartwork 2nd Class
What Causes Tides?
Gravitational effects of the moon (and sun) which exert a pull on the water on the Earth's surface.
What terms have you heard relating to tides?
High
SlackEbb
Flood
Neap
Range
Stand
Low
Spring
Paul BrownTides – Chartwork 2nd Class
TIDES
SunEarth
Moon
Paul BrownTides – Chartwork 2nd Class
TIDES - SPRINGS
Earth
NewMoon
Sun
Paul BrownTides – Chartwork 2nd Class
TIDES - SPRINGS
Earth
FullMoon
Sun
Paul BrownTides – Chartwork 2nd Class
TIDES - NEAPS
Earth
First Quarter
Neaps
Neaps
Sun
Paul BrownTides – Chartwork 2nd Class
TIDES - NEAPS
Sun
Earth
Last Quarter
Neaps
Neaps
Paul BrownTides – Chartwork 2nd Class
TIDE TABLE
18TH
0456 5.8 m
1205 1.7 m
1727 5.9 m
HW
LW
Range4.1
metres
GMT
Paul BrownTides – Chartwork 2nd Class
TIDE TABLE
18TH
0556 5.8 m
1305 1.7 m
1827 5.9 m
Add an hour forBritish Summer Time
Paul BrownTides – Chartwork 2nd Class
TIDAL HEIGHTS - DEFINITIONS
Chart Datum
Charted depth(sounding)
MHWS
MLWS
MLWN
MHWN
Depth of water
Chartedheight
Drying height
Paul BrownTides – Chartwork 2nd Class
TIDAL DIAMONDS & DATUMS
Tidal streams referred to HW at PLYMOUTH
Paul BrownTides – Chartwork 2nd Class
TIDAL DIAMONDS & DATUMS
3 hours before HW
Stream setting towards 318(T)
Springs2.9 kn Neaps 1.5 kn
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
Look up time and height of HW Dartmouth and height of LWHW Dartmouth 1815 BST 4.8m LW 0.7mIs it Neaps or Springs? Close to Springs
Use curve to find:Height of tide at Dartmouth at 1415
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
LW height 0.7m entered here
HW height 4.8m entered here
HW Dartmouth 1815 BST 4.8m LW 0.7m
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
HW Dartmouth 1815 BST 4.8m LW 0.7m
Draw a line joining the points
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
HW Dartmouth 1815 BST 4.8m LW 0.7m
Write time of HW in box below
1815
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
HW Dartmouth 1815 BST 4.8m LW 0.7m
Write subsequent hours in boxes
1415 1515 1615 1715 1815
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
Draw vertical line from 1415
to spring curve
1415 1515 1615 1715 1815
HW Dartmouth 1815 BST 4.8m LW 0.7m
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
Draw horizontal line from curve to diagonal line
1415 1515 1615 1715 1815
HW Dartmouth 1815 BST 4.8m LW 0.7m
Paul BrownTides – Chartwork 2nd Class
TIDAL CURVE
Draw perpendicular to HW line
1415 1515 1615 1715 1815
Height of tide at 1415 = 2.9m
Paul BrownTides – Chartwork 2nd Class
RULE OF TWELFTHS
1st hour 1/12
2nd hour 2/12
3rd hour 3/12
4th hour 3/12
5th hour 2/12
6th hour 1/12HW +1h +2h +3h +4h +5h LW
Paul BrownTides – Chartwork 2nd Class
TIDAL STREAM ATLAS
Atlas gives
Direction & Rate
of tidal stream for each hour
4 hours after HW PORTSMOUTH
Paul BrownTides – Chartwork 2nd Class
TIDAL STREAM ATLAS
Thick and long arrows show
strong stream
Short and thin arrows show weak stream
4 hours after HW PORTSMOUTH
Paul BrownTides – Chartwork 2nd Class
TIDAL STREAM ATLAS
03,05
Rate of stream
0.3 kn at Neaps
0.5 kn at Springs
12,23
Rate of stream
1.2 kn at Neaps
2.3 kn at Springs
Stream
Slack