People often contact Lavers with enquiries about various aspects of the tide tables they use, about tides in general or tides at particular locations. We always answer when we can but we do not have a telephone information service for tide times. So, in the hope that we can provide you with what you need right away, and to ease the burden of our much loved telephonists, here are some commonly asked questions.
WHY ARE SOME OF THE ENTRIES IN THE TIDE TABLES BLANK?
This is because the high water or low water turning points are slightly more than twelve hours apart. The exact time lapse varies with the cycles of the tides but it is always more than twelve hours. Thus, if a turning point (high or low) occurs, say, a few minutes before midnight the next one will be a few minutes after midday and the morning column will show a blank for that day. These are known as “crossovers” and they cause more confusion in the ISO format than they do in Lavers own.
WHY DOES THE READER HAVE TO ADD AN HOUR FOR SUMMERTIME?
Lavers tide tables show all times in Universal Time, formerly called Greenwich Mean Time. This is because many marine professionals depend on the tables for their work and U.T. is the accepted standard for time at sea. Also, British Summer Time dates have been known to change at short notice so standardising on U.T. (G.M.T.) means the tables are technically correct regardless of any bureaucratic rulings.
HOW COME LAVERS GOT THE DATES OF BRITISH SUMMER TIME WRONG IN 1999?
This information has always been supplied to Lavers by The Royal Greenwich Observatory. For 1999, the Home Office extended the duration of British Summer Time for a week beyond the dates supplied to us. Lavers, not unreasonably we feel, buys the calendar information from the R.G.O. up to three years in advance and pays a fee for permission to publish it. In the meantime the R.G.O. was re-organised from its labs in Cambridge. The scientists either left or were redeployed and the rest of the functions were transferred to the National Maritime Museum back at Greenwich. No one there was able to notify us that the information we had bought had been updated and so we published the dates as supplied. The last Calendarial Information Sheets we bought were supplied to us by a museum curator.
The consequences of this were in the main fairly trivial. The phone rang a lot and we were able to explain but we did hear from couple who, relying on Lavers reputation for accuracy, mistimed their arrival at a grandchild’s christening and missed it. We were devastated and very angry that we had not been informed of the changes.
WHAT IS MEANT BY LIVERPOOL (ALFRED)?
The predictions in Laver’s Liverpool Tide Table had until recently always been calculated using observed reference data collected many years ago at Princes Dock . The tide gauge was removed from Princes long ago and the main Mersey tide gauge is now at Alfred Dock, Birkenhead. Gradual changes in the global tidal regime, and to the river itself, have meant the old data no longer reflects actual conditions and so recordings from the new gauge must now be used.
Together these changes have resulted in an average +10 minute shift in the time and +0.2 metres in the height of high water predictions.
WHY NOT USE THE I.S.O. LAYOUT?
The International Standard layout for tide tables shows each turning point in chronological order for each day. The first entry for the day might be for high or low water depending on the stage of the cycle and there are usually four lines per day but with crossovers this might be three. When the system was first adopted Lavers tables were changed accordingly but the outcry from our regular readers was such that we reverted to the high water on the left and low water on the right scheme we still use today. This also means that we can more easily continue to show the metric heights converted to feet.
WHY CAN’T I FIND OUT THE DEPTH AS WELL AS THE TIME AT MY FAVOURITE SPOT?
The information in Lavers tables is actually quite specific and refers only to the tides at the particular place where the tide gauge is located. The main tidal stream flows around the British Isles in a clockwise direction so the time element in the tide can easily be extended or reduced to determine when a certain stage in the cycle will be reached a given point. CLICK HERE to see a chart. The depth of water will vary from place to place according to the topography of the sea bed and this can change dramatically within a very short distance, though the sea surface remains level, of course.
HOW FAR UP THE BEACH/CLIFF/WALL DOES HIGH TIDE COME AT A PARTICULAR LOCATION?
This again depends on the topgraphy of the sea bed locally but it is often shown on large scale Ordnance Survey maps. Enquiries concerning engineering work on the coast are too technical to be dealt with by a publisher and advice should be sought from qualified professionals.
HOW DO WE CALCULATE THE TIDES?
For the printed publications, we don’t, we buy the information from The Natural Environment Research Council scientists at Bidston. We also run tidal prediction software in house to produce TideFile.
WHAT CAUSES TIDES?
There is a detailed description of how tides are caused when you follow this link to Sun & Moon Wind & Tide.
WHAT IS THE MEANING OF “CHART DATUM” AND OTHER TECHNICAL TERMS?
There is a brief glossary of terms used when referring to tides and predictions when you follow this link to Glossary of Terms
HOW MUCH IS THIS YEAR’S EDITION?
Follow this link to the Price List.
WHEN DO THEY FIRST BECOME AVAILABLE?
This is shown on the Catalogue page for each publication.
WHO OWNS THE COPYRIGHT IN THE TIDE TABLES?
Lavers tide tables contain copyright material belonging to various agencies and may not be reproduced in any form without permission. We can deal with most enquiries for permission regarding distribution of the data and we can and do also deal with any serious infringements which come to our notice.