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Tides

Tidal predictions with the Admiralty Tide Tables – and crossing a bar

NauticTools2 works out high and low water at a secondary port using the method of the Admiralty Tide Tables (ATT) and lays out the result like the tidal prediction form used in navigation exams. It then answers the classic question: how much water is there at a given time – or when can I cross a bar with my draught?

• Admiralty Tide Tables
• Tidal prediction form
• Secondary ports
• Seasonal changes
• Mean spring and neap curves
• Full working

What it calculates

• High and low water at the secondary port from the daily predictions for the standard port, using the time and height differences from ATT Part II.
• Springs, mean or neaps worked out automatically from the nearest new or full moon and the standard port's spring lag.
• Seasonal changes in mean level for the standard and the secondary port.
• Height of tide at a required time, or the time window for a minimum height – from when to when there is enough water over the bar – using the digitised mean spring and neap curves of the tide tables.
• Time on Board: optionally all times also in the zone time kept on board, e.g. UT+1 for BST.

Every calculation comes with its working in the order of the form: state of the tide, seasonal changes, interpolation of the time and height differences, the result at the secondary port and the reading from the tidal curve – so you can check your own paper calculation line by line.

Step by step: from the exam data to a finished prediction

NauticTools2 already contains the data from the Admiralty Tide Tables 2005 that the German SSS and SHS exams use: 12 standard ports, over 200 secondary ports, the seasonal changes and the tidal curves. They are only added on request, so everyone else starts with empty lists and enters ports from their own tide tables.

1. Open the standard port manager

   On the home screen, tap the ATT Standard Ports tile. It sits with the management tiles next to settings, waypoints and reference ports.

   

2. Add the exercise data

   Press Add SSS/SHS exercise data (ATT 2005). A message tells you how many entries were added. Your own entries stay untouched, the package can be added again at any time, and Remove SSS/SHS exercise data takes it out again.

   

   Tip: As long as no standard port exists, the Tides ATT tool offers this button itself.

3. Open Tides ATT and search for the port

   Back on the home screen, open the Tides ATT tile. Type the name or number of the port into the search field at the top, e.g. “St. Mary's” or “1”. A match selects the secondary port and its standard port in one go – including ports like Plymouth or Helgoland, which the tables split into several sections (I, II) with their own time headings.

   

4. Enter the daily predictions for the standard port

   Enter date, time and height of high and low water from the standard port's daily predictions – in the time zone printed above the table. The first date is copied into the other empty date fields. If you keep a different time on board, choose it under Time on Board.

5. Calculate the tidal prediction form

   Calculate fills in the form: the header with both ports, the state of the tide (springs, mean or neaps boxed), then the lines for the standard port, seasonal change, StP corrected, differences, secondary port and duration.

   

6. Crossing a bar

   Only now does the Crossing a Bar block appear – just as in the instructions of the tide tables, the prediction comes first, then the question about height or time. You can choose:

   • Height of tide at a required time: how much water is there at 14:30?
   • Time window for a minimum height: from when to when is there at least 2.90 m?

   The slider below the tidal curve moves the time or reads off a height on the curve.

   

7. Working, printing and saving

   The Calculation steps show every intermediate result. The printout contains the form, the tidal curve and the working on as few pages as possible. Save stores the ports, daily values and question as an input set that you can load again later.

See a complete example

The exercise data include the example “St. Mary's 2005 (Example I)” from the instructions of the tide tables. Choose it in Tides ATT under Load – all values are filled in, and you can compare the result directly with the book.

Your own ports from current tide tables

If you sail with a current edition of the Admiralty Tide Tables, add your ports in the standard port manager: the standard port with its time headings, levels (MHWS, MHWN, MLWN, MLWS) and spring lag, then the secondary ports with their differences exactly as printed. Leave fields marked § or ⊙ empty – NauticTools2 then does not calculate with 0 but tells you that the tables give no value.

Not for navigation: All tidal values are approximations for training, exam preparation and passage planning. Wind and air pressure change the actual tide further. For navigation, use the official tide tables.

Related tools

• Tides BSH – height of tide by the method of the German BSH tide tables
• My Sailing Area (BSH) – high and low waters taken automatically from an imported station
• Age of Tide – springs, mean or neaps for a date