Tides for Sea Kayakers
Overview
• What is a Tide?
• Types of Tides – Spring and Neap
• High and Low Tides
• Rule of Twelfths
• Calculation of Tides at Secondary Ports
• Calculation of Currents at Secondary
Stations
• Tide Races and Over falls
• Tidal flow direction
What is a Tide?
Tides are the vertical rise and fall of the ocean level due to
the gravitational and centrifugal forces between the earth
and the moon and to a lesser extent the sun.
High and Low Tide
High tide is when the water stops rising (Also known as High
Water).
Low tide is when the tide stops dropping is Low Water or low tide
Slack Water is when there is NO movement of water in either
direction.
Different Tidal Patterns
Diurnal Tide
Semi Diurnal Tide
Mixed Tide
Semi-diurnal Tidal Pattern
In general in most of the world, the tides go up and
down on a semi diurnal curve.
A Semi-diurnal tide has two high tides and two low
tides in a lunar day (24.8 hours).
Diurnal Tidal Pattern
A Diurnal tide is a tide with one low and one high tide
in a lunar day (24.8 hours).
Mixed Tidal Pattern
Mixed tides are a diurnal and a semi-diurnal tide within
the same geographic area.
Mixed Semi-Diurnal Tides have two different ranges in
tide levels
Tidal Patterns
For kayakers to remember:
A Diurnal Tide has a 24 hour 50 min cycle.
A Semi Diurnal Tide has a 12 hour 25 min
cycle.
Tidal Patterns Around the Earth
Cause of different Tidal Patterns
The Four Phases of the Moon
Rule of Twelfths
Consider the general rule of twelfths:
The flow of water between low and high tide is divided into a
6 hour period.
The first hour will move 1/12 of the total volume of the tide.
The second hour will move 2/12.
The third hour will move 3/12.
The fourth will move 3/12.
The fifth hour will move 2/12. And
The sixth hour will move 1/12.
As a result the middle two hours move roughly half of the
tidal volume.
TIDAL FLOW
Tidal flow can be augmented by a number of
factors:
• Shallow water
• Headlands
• Constrictions
• Wind direction
Tidal Races and Overfalls
Reading Tide Tables
SECONDARY PORTS
VANCOUVER
VANCOUVER
Day Time
Feet
Meters
5 0549 13.8 4.2
HIGHER HIGH WATER
TIME
DEEP COVE
+0 30
LOWER LOW WATER
MEAN TIDE
LARGE TIDE
TIME
MEAN TIDE
LARGE TIDE
+0.2
+0.5
-0 06
+0.1
+0.5
1101 7.2
2.2
SA 1727 14.1 4.3
6 0010
REFERENCE PORTS
4.3 1.3
TABLE 2
0636 14.1 4.3
SU 1218 8.9 2.4
1757 14.1 4.3
HIGHER HIGH WATER
VANCOUVER
LOWER LOW WATER
MEAN TIDE
LARGE TIDE
MEAN TIDE
LARGE TIDE
14.4
16.5
3.6
-0.2
If we were to plan a paddle up Indian Arm launching at Deep Cove on Saturday
October 5 when would it be a good time to launch?
Reading Current Tables
REFERENCE SECONDARY CURRENT
STATIONS
DODD NARROWS
TABLE 4 (page 135)
OCTOBER 2013
% REFERENCE
RATE
TIME DIFFERENCES
TURNS
TURN TO MAXIMUM TURN TO MAXIMUM
FLOOD
FLOOD
FLOOD
EBB
EBB
FALSE NARROWS
+0 10
+0 25
+0 25
-0 35
50
EBB
DAY
MAXIMUM
TIME
TIME
KNOTS
0043
+7.8
0358
0703
-6.6
1009
1251
+6.0
1544
1903
-7.0
55
19
You have to catch a Ferry back to the mainland
at Departure Bay on October 19th and have to
travel
North though False Narrows, when would
.
you attempt this in a kayak?
Hint: A Flood tide travels north through False
Narrows – from marine chart.
SA
2219
(page 97)
Tide Take-aways
• Know your tidal type (mixed, diurnal semi-diurnal)
• Know when high and low tide occur
• Know when neap and spring tides occur
• Know the rule of twelfths for peak flow
• Check the tidal tables before getting on the water
• Be aware of tidal races and where they occur
• Be aware of tidal directional flow and it’s variance
around land masses
THE END