8/8/2019 28 Tide Currents

1/39

Navigation

NAU 102

Lesson 28

8/8/2019 28 Tide Currents

2/39

Tidal Current

The periodic

horizontal flow ofwater accompanying

the rise and fall ofthe tide.

8/8/2019 28 Tide Currents

3/39

Tidal Current

Moon

8/8/2019 28 Tide Currents

4/39

Tidal Current

Two Types:

Rotary Currents

Reversing Currents

8/8/2019 28 Tide Currents

5/39

Rotary Currents

Occur offshore where direction of flow

is not restricted.

Coriolis Effect causes set to rotate

through all directions.

Clockwise in the Northern Hemisphere

Counterclockwise in the Southern Hemisphere.

8/8/2019 28 Tide Currents

6/39

Rotary Currents

Water flows continuously

but the speed and

direction changes

Two speed maximums in

opposite directions

Two speed minimums about

halfway between the

maximums

8/8/2019 28 Tide Currents

7/39

8/8/2019 28 Tide Currents

8/39

Reversing Currents

Occur where direction of water flow is

constricted:

Coastal areas

Rivers

Bays

Straits

8/8/2019 28 Tide Currents

9/39

Reversing Currents

Definitions

Flood the movement towards shore or

upstream.

Ebb the movement away from shore

or downstream.Slack the period when speed of the

current is zero.

8/8/2019 28 Tide Currents

10/39

Tidal Current

8/8/2019 28 Tide Currents

11/39

Current Predictions

We can predict set and drift of tidal

currents using:

Computer Programs

Tidal Current Tables

8/8/2019 28 Tide Currents

12/39

Tidal Currents

Horizontal movement of watercaused by the tides.

8/8/2019 28 Tide Currents

13/39

Tidal Current Tables

2 volumes bylocation

Data on tidal

currents

Published annually

by NOS

8/8/2019 28 Tide Currents

14/39

Tidal Current Tables

Table 1 - list of predicted times ofmaximum currents and slack water, with

the velocity of the maximum currents,

for a number of reference stations.

Arranged by Tables

8/8/2019 28 Tide Currents

15/39

Table 1

8/8/2019 28 Tide Currents

16/39

Tidal Current

Table 2 - gives differences, ratios, and other

information related to a relatively large number

of subordinate stations.

Index numbers of subordinate stations are

found in theIndex.

8/8/2019 28 Tide Currents

17/39

Table 2

8/8/2019 28 Tide Currents

18/39

Tidal Current Tables

Table 3 - enables determination of currents velocity at

any time between entries in tables 1 and 2.

8/8/2019 28 Tide Currents

19/39

8/8/2019 28 Tide Currents

20/39

Tidal Current Tables

The volumes also contain:

Wind-driven currents Combination currents

Gulf Stream currents for the east coast

Coastal currents on the west coast

8/8/2019 28 Tide Currents

21/39

Example Problem #1

Current at Reference Stations

What will be the time, speed anddirection of the maximum currents

and slack waters at Key West, Florida

on 19 November?

8/8/2019 28 Tide Currents

22/39

Example Problem #1

8/8/2019 28 Tide Currents

23/39

Example Problem #1

8/8/2019 28 Tide Currents

24/39

Example Problem #1

Time Speed Direction

0327 0 -

0619 1.5 020 T0922 0 -

1225 1.9 195 T

1604 0 -

1822 1.0 020 T

2054 0 -

8/8/2019 28 Tide Currents

25/39

Example Problem #2

Current at Subordinate Stations

What will be the time, speed and

direction of the first maximum

currents and slack waters at Grants

Tomb on 04 June (DST applies)?

8/8/2019 28 Tide Currents

26/39

Example Problem #2

8/8/2019 28 Tide Currents

27/39

Example Problem #2

8/8/2019 28 Tide Currents

28/39

8/8/2019 28 Tide Currents

29/39

Example Problem #2

8/8/2019 28 Tide Currents

30/39

Example Problem #2

MBF F MBE E F E

Narrows 23:31 01:45 04:52 08:24 1.3 1.7

Grants

Tomb

+1 59 +1 53 +1 45 +2 10 x 0.9 X 1.2

01:30 03:38 06:37 10:34 1.2 2.0

Flood 025 T

Ebb

8/8/2019 28 Tide Currents

31/39

Example Problem #3

Current at Any Time

What will be the speed and direction

of the tidal current at Grants Tomb

at 0430 on 04 June?

8/8/2019 28 Tide Currents

32/39

Example Problem #3

8/8/2019 28 Tide Currents

33/39

Example Problem #3

MBF F MBE E F E

Narrows 23:31 01:45 04:52 08:24 1.3 1.7

Grants

Tomb

+1 59 +1 53 +1 45 +2 10 x 0.9 X 1.2

01:30 03:38 06:37 10:34 1.2 2.0

Flood 025 T

Ebb

Time of SlackTime of

Maximum

8/8/2019 28 Tide Currents

34/39

Example Problem #3

Interval Between

Slack & Maximum

Current

06:37 (Slack)

-03:38 (M

ax)2h 59 min

Interval Between

Slack & Desired Time

06:37 (Slack)

-04:30 (D

esired)2h 07 min

8/8/2019 28 Tide Currents

35/39

8/8/2019 28 Tide Currents

36/39

Example Problem #3

MBF F MBE E F E

Narrows 23:31 01:45 04:52 08:24 1.3 1.7

Grants

Tomb

+1 59 +1 53 +1 45 +2 10 x 0.9 X 1.2

01:30 03:38 06:37 10:34 1.2 2.0

Flood 025 T

Ebb

Time of

Maximum

8/8/2019 28 Tide Currents

37/39

Example Problem #3

1.2 (speed of max current)

x 0.9 (factor from table 3)

= 1.1 knot flood

What will be the speed and direction

of the tidal current at Grants Tomb

at 0430 on 04 June?

8/8/2019 28 Tide Currents

38/39

Daylight Savings Time

Times in Table 1 are in Standard Time

If you are keeping Daylight Savings Time,Spring Forward

Add one hour to times from Table 1.

8/8/2019 28 Tide Currents

39/39

Introduction to Navigation

Questions?