CHAPTER 6. TIDES, WEATHER AND YOU

Sailing conditions on the European side of the ocean are not exactly the same as the American side, so here are some pointers to help you. You may find that in your new sailing life you have to work more with tides and manage with fog than you ever did in the past.

TIDES

Tides in Europe vary hugely, from the 40-foot tides on the Brittany coast and in the Bristol Channel to the barely noticeable tides of the Baltic and Mediterranean. The significance of tides to a sailing boat changes as you move
around the European coast. In the Baltic and Mediterranean the negligible rise and fall of tides allows the Mediterranean style of mooring. The massive tides of western Britain and France means that in many harbors you will adjust your lines as the boat rises or falls and get used to drying out and taking
the ground at low water. In the North Sea working the tides is vital to your pilotage yet on the Netherlands side of the North Sea, where the flows from the north and south meet, the tides are neutral. In the English Channel you can really only sail along the coast and in or out of harbors according to the tides.

You will need a tidal atlas showing the flows and heights for any tide at any state of tide in any area of the Channel or North Sea. You should also learn to use the tidal diamonds on British Admiralty charts. At the very least you need a tide timetable for the areas you are sailing and become familiar with the use of primary and secondary ports to work out local tide times and heights. You can usually find this in a nautical almanac or cruising pilot of the sort I am sure you will be carrying.

The last few years have seen a number of computer programs that replicate the data from official tide tables but in a more convenient form. A good source is the British Admiralty Hydrographic Office website at www.ukho.gov.uk. This
has a generous definition of Europe, ranging from the Arctic to ports in the Western Sahara. Some commercial sites for navigation and tidal software are:

www.marinecomputing.com—European and World versions; www.neptune-navigation.com—UK and Europe versions; www.tideplotter.co.uk—UK and Europe versions.

Make your own observations of tides as a way of amending the published data. Tidal predictions are made years in advance from a set of standard mathematical calculations and cannot take account of the wind that has been blowing
all week or today’s barometric pressure. Your observations might make the difference between a quiet night at anchor or bumping the bottom at midnight. Keep a log of when tides turn, log the depth at anchor or when entering a river and compare this with the pilot book or chart to see:

• how cautious your pilot book author has been

• whether dredging or silting has changed the channel depth since the book or chart was prepared

• what a chart datum of lowest astronomical depth really means.

Also, keep an eye on the moon. It is your best, most visible indicator of the ticking tidal clock. The pull of the sun and moon on the earth is the main cause of tides but the moon has roughly double the influence of the sun.Tides are simply the oceans washing back and forth in their basins, like water in a bowl. The moon pulls water into a bulge on the side of the earth facing it and the earth’s spin causes a balancing bulge of water on the opposite side.

At full and new moon the earth, moon and sun are in a single straight line, producing the greatest pull on the earth and the most bulging tides. Spring tides, when high water is highest, low water is lowest and the greatest range occurs, come a few days after full and new moon. Neap tides, when tidal range is least, come at the first and third quarters of the moon, when the sun and moon pull at right angles to one another. The tides work on a daily cycle of about 13 hours and a lunar cycle of 28 days. The biggest spring tides occur in spring and fall, around the equinox, and since the moon’s orbit also varies on a 20 plus yearly cycle there is probably a 20 plus yearly variation in tides as well. But let’s not worry about that.

Tides are a mystery, whatever else people will tell you. Always seek local advice about what might or might not happen today and tomorrow if you have a particular trip that is tide-dependent. Think in terms of tidal gates, harbor bars, rules of twelfths, springs and neaps and barometric and wind effect on tidal height. There is much more to tides than the obvious one of being on a magic carpet either going with you or against you. Beating into the wind with the tide against you will be slamming into short sharp seas, with water breaking at the bows and running on deck. Even at the top end of a Force 4 or into a Force 5 you may need to reef, just to be comfortable.

• See Atlantic Crossings in our catalog.
  
  
• Back to main Excerpts page.