Tide table

Tides bill is a term used in nautical navigation. With the help of Tidal bills attempting to make predictions about water levels in tidal waters. Typical calculations provide the high and low water times and heights of a given location. Further investigations to determine the water levels at time points between high and low water. Use the calculations usually tide tables. In Germany tide tables are published annually by the Federal Maritime and Hydrographic Agency ( BSH). From the British United Kingdom Hydrographic Office Admiralty Tide Tables are published. These include tide tables for a large number of locations worldwide. In tidal calculations using tide tables only the known gravitational influences of the moon and sun can be considered. Other influences such as the effect of the wind must be estimated by other models of computation.

In tests on specific sailing Seem like the sport coastal or the Sportseeschifferschein also tasks to tide invoice to be solved. For example, is the water depth to determine for a given location to a specific date and time. Another type of task asks for the earliest possible time at which a shoal on the flooding water can be crossed. This requires knowledge of the maps depth and draft of the vessel.

Definition of Terms

The two pictures illustrate some abbreviations and terms that are common in the tidal customer. The sinusoidal curve represents the waveform of the water level. The following table explains the abbreviations used.

The German tide tables using Lowest Astronomical Tide ( LAT) as Chart Datum ( SKN ). Other terms related to the ' age of the tide ' in conjunction. The age of the tide determines whether Spring, mid -, or neaps is on a specific date. The following table summarizes some of the abbreviations and terms are used together.

For example MSpHW is the average height over many periods of high water at spring.

German tide tables

The given out by the BSH tide tables distinguish between reference points, and connection locations. The high and low water data for the reference points can be read directly from the tables. Each connection location assigned to a reference location. The tabulated quantities are listed for port locations only as differences, which must then be added to the values ​​of each reference site. The tide tables consist of four parts: Part 1 provides detailed forecasts for the European reference points, while Part 2 lists tidal differences for the European connection places; Parts 3 and 4 contain auxiliary panels and tidal cards.

Reference points

In Part 1 of the tide tables can be found at each reference location, the geographical coordinates of the reference points as well as a small map showing the location of the place. In tabular form is then given for each day, the time at which high or low water occurs and with what amount. In these tables, information can be found on the respective phase of the moon. Furthermore, under the tables on which time zone the values ​​given refer. Finally, found in each reference point a chart showing the average time course of the water level describes each for Spring time and neaps. From these diagrams to water levels can be graphically determined at time points that lie between high and low tide time. The latter is true both for reference and for connecting places for the practice of reasonable accuracy.

Example: The following table shows a section of the Part 1 of the 2010 tide tables for the reference location Wilhelmshaven.

Accordingly, the afternoon high tide occurs on Tuesday, July 27, 2010, at 13.53 a clock with a height of 4.90 m. To be considered here is the time zone. Since the table values ​​(in the case Wilhelmshaven ) in Central European Time ( CET) are specified, the flood of Central European summer time occurs at 14.53 clock. The water levels indicated refer to LAT. These words must still be added the cards depth ( KT) to obtain the water depth (WT ).

Connection locations

The following table shows an entry from the Part 2 of the tide tables 2010.

Information on the relevant reference point are shown in bold. First, the geographical coordinates are specified for each connection location. The occurrence times of high and low water are listed as differences to the respective times of the reference location. Finally, in the table are still the height differences of high and low water. These differences to the heights of the reference location are dependent on the age of the tide. For Mitt time the respective average values ​​are to be used from the values ​​of Spring and neap.

In single port locations in addition further corrections to the HWZ and NWZ must be considered. In such cases, can be found in the column that is designated in the table above with ' Tf.5 ', an abbreviation. The additional corrections are dependent on the half-life or NWZ of the reference location and using a table in Part 3 of the tide tables determined.

Example: Using the above example, we calculate the afternoon high tide and the succeeding low tide on 27 July 2010 Wangerooge, Long Reef. First, the age of the tide must be determined. This purpose is served table 2 of Part 3 of the tide tables. The Spring delay is already accounted for in this table, so that Spring time for said date will result. The following table illustrates the calculation to be performed.

Again, the time zone must be taken into account, and also in this case, the heights are referenced to LAT.

Twelfth rule

The twelfth rule provides a simple method to estimate water levels at time points between high and low water and between low and high water. They can be applied with reasonable accuracy only for sinusoidal path of the tide. The twelfth - rule assumes that changes the water level in the first hour after low or high water by 1/ 12 of the tidal range. In the second, third, ..., the sixth hour, the change is then 2/12, 3/12, 3/12, 2/12 or 1/ 12 of the tidal range.

Example: In a place the low water occurs at 6.25 clock one with a height of 1.20 m. The ensuing flood has a height of 3.20 m. The tidal range is therefore 3.20 m - 1, 20 m = 2 m. With what level of tide is expected for 8.25 clock? As that time is two hours after low tide time, with a height difference of 1/12 2 / 12 = 1/ 4 of the tidal range ie with ( 1/4) · 2 m = 0.5 m expected. This difference in height must be added to the low-water level, so that a height of the tide of 1.20 m 0.50 m = 1.70 m at 8.25 clock results.