Articles from Past Issues of The Ebb and Flow
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From the April 2000 Issue of Ebb and Flow
Rule of Twelve to Calculate Tide Movements
by Maryanne Tempest
Some of the islands around Florida are so close to shore at low tide
there may be only a foot or two of water. On extreme low tide you may
not have enough water to paddle back to the mainland. Therefore, itıs
important to know how to calculate how fast the water will raise and
fall as the tide changes.
The Rule of Twelve for a rising/falling tide:
1/12 of its total rise/fall in the first hour
2/12 in the second hour
3/12 in the third hour
3/12 in the fourth hour
2/12 in the fifth hour
1/12 in the sixth hour
When planning your trips check the tide times and calculate in advance
how much water will be flowing or ebbing. Remember paddling in waters
one foot deep you will use more energy than maintaining the same speed
in water 10 feet deep. If you are tried or at a low energy level,
arrange to paddle in deeper water so that you can safely reach your
destination.
Navigation
by Jim Greenhalgh
Determining what the tide will be doing at any given time and place is
a matter of consulting the tide tables.
Table 1 of the tide tables gives the predicted times and heights of
high and low water at a main reference station.
Table 2, Tidal differences and other constants gives a list of
corrections for thousands of subordinate stations.
As an example lets say that TBSK planned a trip to Egmont Key at 9am on
Saturday the 22nd of April.
The reference station is St. Petersburg and table 1 indicates that low
tide will occur at 9:58 am and will be 1.1 ft. above what is listed on
the chart. High tide will be at 4:06 pm and will be 2.3ft. above the
chart datum. The subordinate station on table 2 is Egmont Key which shows
a difference of -2:27 for high tide and -2:24 for low, with a ratio of
.91 for difference in depth.
According to these tables low tide at Egmont will occur at 7:34am and
high tide at 1:39pm. The depths on both tides will be above the charted
depth by 1ft. and 2.1ft. respectively. So, if our club leaves at 9am we
can expect to leave on an incoming tide (flood), we will reach high
tide (slack water) at 1:39pm and if we return after that time we will
proceed on an outflowing tide (ebb). At no time on the trip would we have
a problem with depth.
The same cannot be said for a trip to Weedon Island. Try going to
Weedon Island anytime past halfway though ebb tide and you had better plan
to bring your hiking boots with you.
As kayakers it is very beneficial to check the tides prior to a trip
and learn to use the tides to your advantage. Proper planning around the
tides can lead to a more enjoyable trip as opposed to fighting an
uphill battle.