There are (2) quick and simple methods for determining slack water. The best way is through use of Current Tables and the second way is through the use of the Tide Tables and a simple "Rule-of-Thumb."
The simplest and most accurate way to determine the time of slack water at Hell Gate, is to simply check the NOAA Current Tables (or the tables of your choice) for the date in question and extract the information.
An excerpt from the NOAA Tidal Current Tables for "Hell Gate" for the dates from March 1st thru March 4th is provided below.
From looking at this table, you can see that on the 1st of March there are (4) slack waters at Hell Gate; occuring at 0318, 0924, 1548, and 2148.
Hell Gate (off Mill Rock) Tidal Current Tables | |
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Predicted Tidal Current | March 2018 |
Flood Direction, 050 True. | Ebb (-)Direction, 230 True. |
NOAA, National Ocean Service |
Maximum Current |
Slack Water |
Maximum Current |
Slack Water |
Maximum Current |
Slack Water |
Maximum Current |
Slack Water |
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Day | Time h.m. |
Vel. knots |
Time h.m. |
Time h.m. |
Vel. knots |
Time h.m. |
Time h.m. |
Vel. knots |
Time h.m. |
Time h.m. |
Vel. knots |
Time h.m. |
1 | 0318 | 0624 | +4.00 | 0924 | 1224 | -5.10 | 1548 | 1848 | +3.90 | 2148 | ||
2 | 0048 | -5.10 | 0412 | 0712 | +4.10 | 1018 | 1312 | -5.1 | 1636 | 1936 | +4.00 | 2236 |
3 | 0136 | -5.10 | 0500 | 0800 | +4.00 | 1106 | 1400 | -5.10 | 1724 | 2024 | +3.90 | 2324 |
4 | 0218 | -5.10 | 0548 | 0848 | +3.90 | 1154 | 1442 | -5.00 | 1812 | 2106 | +3.80 |
In the event that you do not have access to Current Tables, you can use the times of high and low water at "The Battery" in New York City with the following time offsets.
On average, slack water at Hell Gate occurs:
and
Adding these corrections to the times of high or low water will give you a close approximation of the times of next slack water at Hell Gate.
As a practical matter I use this system quite often, but to avoid having to remember 2 different time corrections, I simply use 01:45 for both high and low water.
The Battery @ New York City (Tide Tables) | |||||||||
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Predicted Tides | March 2018 | ||||||||
NOAA, National Ocean Service | |||||||||
Date | Day | Time | Height | Time | Height | Time | Height | Time | Height |
03/01/18 | Thursday | 0124 Local | -0.8 L | 0731 Local | 5.6 H | 1402 Local | -1.0 L | 2000 Local | 5.33 H |
03/02/18 | Friday | 0215 Local | -0.90 L | 0819 Local | 5.60 H | 1449 Local | -1.10 L | 2049 Local | 5.30 H |
03/03/18 | Saturday | 0304 Local | -0.90 L | 0907 Local | 5.40 H | 1534 Local | -0.90 L | 2137 Local | 5.30 H |
03/04/18 | Sunday | 0352 Local | -0.70 L | 0955 Local | 5.20 H | 1617 Local | -0.70 L | 2226 Local | 5.20 H |
As can be seen in the Tide Table excerpt above, the first high water of the day for March 1st is 0731. Adding the high water time correction of 01:46 to that, you get a time of slack water of 0917 which is within 7 minutes of the 0924 predicted time in the NOAA Current Tables above.
The same thing can be done with low water. The next low water occurs at 1402. Adding the low water time correction of 01:43 to that, you get a slack water time of 1545 which is within 3 minutes of the 1548 predicted time in the NOAA Current Tables.
As you can see this is not as accurate as the prefered method - "using the NOAA Tidal Current Tables." While accuracies of within 1 to 8 minutes of the published times might be considered the rule, differences of 20+ minutes have been noted. The bottom line is this method can provide you with sufficient enough accuracy to plan your passage in the event you do not have access to the published tidal current data.