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 TideHigh 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 PatternIn 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 PatternMixed 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

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?

VANCOUVER

Day Time Feet Meters

5 0549 13.8 4.21101 7.2 2.2

SA 1727 14.1 4.3

6 0010 4.3 1.30636 14.1 4.3

SU 1218 8.9 2.41757 14.1 4.3

SECONDARY PORTS

VANCOUVERHIGHER HIGH WATER LOWER LOW WATER

TIMEMEAN TIDE LARGE TIDE TIME MEAN TIDE LARGE TIDE

DEEP COVE +0 30 +0.2 +0.5 -0 06 +0.1 +0.5

REFERENCE PORTS

TABLE 2HIGHER HIGH WATER LOWER LOW WATER

MEAN TIDE LARGE TIDE MEAN TIDE LARGE TIDE

VANCOUVER 14.4 16.5 3.6 -0.2

Reading Current Tables

.

REFERENCE SECONDARY CURRENT STATIONS

TABLE 4 (page 135)

TIME DIFFERENCES % REFERENCE RATE

TURN TO FLOOD

MAXIMUM FLOOD

TURN TO EBB

MAXIMUM EBB FLOOD EBB

FALSE NARROWS +0 10 +0 25 +0 25 -0 35 50 55

DODD NARROWS

OCTOBER 2013

TURNS MAXIMUMDAY TIME TIME KNOTS

19 0043 +7.8

0358 0703 -6.6

SA 1009 1251 +6.0

1544 1903 -7.0

2219

(page 97)

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.

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