Tides for Sea Kayakers - PowerPoint Presentation

Slide1

Tides for Sea KayakersSlide2

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 directionSlide3

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.Slide4

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.

Slide5

Different Tidal

Patterns

Diurnal

Tide

Semi

Diurnal Tide

Mixed TideSlide6

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).Slide7

Diurnal Tidal Pattern

A

Diurna

l tide is a tide with one low and one high tide in a lunar day (24.8 hours).Slide8

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

levelsSlide9

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

.Slide10

Tidal Patterns Around the EarthSlide11

Cause of different Tidal PatternsSlide12

The Four Phases of the MoonSlide13
Slide14

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. Slide15

TIDAL FLOW

Tidal flow can be augmented by a number of factors:

Shallow

water

Headlands

Constrictions

Wind

directionSlide16

Tidal Races and

OverfallsSlide17

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

4.2

1101

7.2

2.2

SA

1727

14.1

4.3

6

0010

4.3

1.3

0636

14.1

4.3

SU

1218

8.9

2.4

1757

14.1

4.3

SECONDARY PORTS

VANCOUVER

HIGHER HIGH WATER

LOWER LOW WATER

TIME

MEAN TIDE

LARGE TIDE

TIME

MEAN TIDELARGE TIDEDEEP COVE+0 30+0.2+0.5-0 06+0.1+0.5

REFERENCE PORTS

TABLE 2

HIGHER HIGH WATER

LOWER LOW WATER

MEAN TIDE

LARGE TIDE

MEAN TIDE

LARGE TIDE

VANCOUVER

14.4

16.5

3.6

-0.2Slide18

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

MAXIMUM

DAY

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 19

th

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. Slide19

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 massesSlide20

THE END