Paul BrownTides – Chartwork 1st Class

Chartwork 1st Class

Tides

(Adapted from RYA Shorebased slides)

Paul BrownTides – Chartwork 1st 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 1st Class

TIDES

SunEarth

Moon

Paul BrownTides – Chartwork 1st Class

TIDES - SPRINGS

Earth

NewMoon

Sun

Paul BrownTides – Chartwork 1st Class

TIDES - SPRINGS

Earth

FullMoon

Sun

Paul BrownTides – Chartwork 1st Class

TIDES - NEAPS

Earth

First Quarter

Neaps

Neaps

Sun

Paul BrownTides – Chartwork 1st Class

TIDES - NEAPS

Sun

Earth

Last Quarter

Neaps

Neaps

Paul BrownTides – Chartwork 1st 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 1st 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 1st Class

TIDAL HEIGHTS - DEFINITIONS

Chart Datum

Charted depth(sounding)

MHWS

MLWS

MLWN

MHWN

Depth of water

Chartedheight

Drying height

Paul BrownTides – Chartwork 1st Class

TIDAL DIAMONDS & DATUMS

Tidal streams referred to HW at PLYMOUTH

Paul BrownTides – Chartwork 1st Class

TIDAL DIAMONDS & DATUMS

3 hours before HW

Stream setting towards 318(T)

Springs2.9 kn Neaps 1.5 kn

Paul BrownTides – Chartwork 1st Class

TIDAL CURVE

Paul BrownTides – Chartwork 1st 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 1st 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 1st Class

TIDAL CURVE

HW Dartmouth 1815 BST 4.8m LW 0.7m

Draw a line joining the points

Paul BrownTides – Chartwork 1st Class

TIDAL CURVE

HW Dartmouth 1815 BST 4.8m LW 0.7m

Write time of HW in box below

1815

Paul BrownTides – Chartwork 1st 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 1st 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 1st 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 1st Class

TIDAL CURVE

Draw perpendicular to HW line

1415 1515 1615 1715 1815

Height of tide at 1415 = 2.9m

Paul BrownTides – Chartwork 1st 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 1st Class

SECONDARY PORTS

National Standard Port

DOVER

Standard Port examplesPortsmouth

Plymouth (Devonport)

Secondary port examplesFoweyTorquay

DOVERPortsmouth

Flood

TidePlymouth

Torquay

Differences on Plymouth HW

Fowey = Plymouth minus 15mins

Torquay = Plymouth plus 45mins

Fowey

Paul BrownTides – Chartwork 1st Class

SECONDARY PORTS - TIMES & HEIGHTS

Standard Port PLYMOUTHTimes Heights in Metres

High Water Low Water MHWS MHWN MLWN MLWS 0000 0600 0000 0600 5.5 4.4 2.2 0.8 1200 1800 1200 1800Differences FOWEY- 0010 - 0015 - 0010 - 0005 - 0.1 - 0.1 - 0.2 - 0.2

Standard Port PLYMOUTH Times Heights in Metres

High Water Low Water MHWS MHWN MLWN MLWS 0100 0600 0100 0600 5.5 4.4 2.2 0.8 1300 1800 1300 1800

Differences TORQUAY

+ 0025 + 0045 + 0010 0000 - 0.6 - 0.7 - 0.2 - 0.1

Paul BrownTides – Chartwork 1st Class

INTERPRETING THE 'DIFFERENCES BLOCK'

0100 0200 0300 0400 0500 0600 0700 0800 0900 1000 1100 1200 1300TimeDiff

Standard Port PLYMOUTH Times Heights in Metres

High Water Low Water MHWS MHWN MLWN MLWS 0100 0600 0100 0600 5.5 4.4 2.2 0.8 1300 1800 1300 1800

Differences TORQUAY

+ 0025 + 0045 + 0010 0000 - 0.6 - 0.7 - 0.2 - 0.1

Paul BrownTides – Chartwork 1st Class

Standard Port PLYMOUTHTimes Heights in Metres

High Water Low Water MHWS MHWN MLWN MLWS0100 0600 0100 0600 5.5 4.4 2.2 0.81300 1800 1300 1800

Differences TORQUAY

+ 0025 + 0045 + 0010 0000 - 0.6 - 0.7 - 0.2 - 0.1

INTERPRETING THE 'DIFFERENCES BLOCK'

0100 0200 0300 0400 0500 0600 0700 0800 0900 1000 1100 1200 1300TimeDiff +25 +45 +25

Paul BrownTides – Chartwork 1st Class

Standard Port PLYMOUTHTimes Heights in Metres

High Water Low Water MHWS MHWN MLWN MLWS0100 0600 0100 0600 5.5 4.4 2.2 0.81300 1800 1300 1800

Differences TORQUAY

+ 0025 + 0045 + 0010 0000 - 0.6 - 0.7 - 0.2 - 0.1

INTERPRETING THE 'DIFFERENCES BLOCK'

0100 0200 0300 0400 0500 0600 0700 0800 0900 1000 1100 1200 1300TimeDiff +25 +29 +33 +37 +41 +45 +42 +39 +36 +34 +31 +28 +25

Paul BrownTides – Chartwork 1st Class

INTERPOLATION

Torquay 30th May When is HW in the morning?

Standard Port Plymouth (Devonport) HW 0320 UT

Difference approx +35 mins HW Torquay 0355

Time Differences (min) Torquay

+0025 +0030 +00450100

02000300

04000500

0600

+0035 +0040

Paul BrownTides – Chartwork 1st Class

TIDAL STREAM ATLAS

Atlas gives

Direction & Rate

of tidal stream for each hour

4 hours after HW PORTSMOUTH

Paul BrownTides – Chartwork 1st 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 1st 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