8_5 Secondary Current Stations

Section 8 Tidal Waters

8.5

Secondary Current Stations

Current predictions are available for secondary stations and are found by using a table to correct data from a reference station.

Table 4

Table 4 is used to correct the daily current predictions for secondary stations. This table shows which reference station is used, as well as time and rate of flow corrections for the secondary station. The direction of the flood current is also provided if it differs from the reference station.

Practice Table 4
Use this table for the Test Yourself exercises in this section.

Finding Current Predictions for a Secondary Station

There are five steps to finding current predictions for secondary stations. Steps 1 through 5 below answer the question:

During the daylight hours of July 16th, what time will the ebb current at Baynes Channel reach its maximum rate of flow? What will be the rate and direction of the current?

Step 1

Baynes Channel is a secondary station. Table 4 shows that its reference station is Race Passage, because it's listed among the other secondary stations under "on/sur Race Passage".

Make a note of the reference station:

Station

Race Passage

Step 2

The current table for Race Passage shows that on July 16, the only ebb current during daylight hours begins at 1425 and reaches its maximum at 1710. The rate is shown as -2.4 knots.

Station
Time
Rate

Race Passage
1710

-2.4

Step 3

Now return to Table 4 to find the corrections for Baynes Channel. The time difference for the maximum ebb is -0 15, or minus 0 hours 15 minutes. The difference in rate is given as a percentage of the rate at the reference station. In this case the rate of the ebb current is 75 per cent of the Race Passage rate.

These figures are entered in the appropriate columns of the working table.

Port
Time
Rate

Race Passage
1710

-2.4

Baynes Channel
-0 15

75%

Step 4

Now apply the corrections and change the time to Daylight Saving Time.

The time difference of 15 minutes is subtracted from the time at Race Passage and converted to Daylight Saving Time by adding one hour. The time of maximum ebb at Baynes Channel during daylight hours is 1755 PDST. To get the rate, calculate 0.75 x 2.4 knots = 1.8 knots. This is the maximum rate of flow.

*Port*	*Time*	*Rate*
Race Passage	1710	-2.4
Baynes Channel	-0 15	75%
	1655	-1.8
	+100
PDST	1755

Step 5

The last step is to find the direction of the current. The direction of the flood current appears in the third column of Table 4. Unless stated otherwise, the direction of the ebb current can be taken as the reciprocal of the flood. At Baynes Channel this is 220°.

Ebb Direction:
(Flood) 040°

+ 180°
= 220°

A Review of the 5 Steps

1.	Use Table 4* to identify the reference station.*
2.	See the reference station's Current Table* to find the time and rate of the current for a specific day.*
3.	Use Table 4* to find the time and rate corrections for flood or ebb current, at the turn or maximum. Find the flood direction.*
4.	Apply the corrections to the current time and rate at the reference station, convert to Daylight Saving Time if appropriate.
5.	Calculate the direction of the current.

Section 8

Tidal Waters