Thursday, July 21, 2011

Tools of the Trade: Time and Tide

Though blue water is the love of every dyed-in-the-wool seaman, a ship has no choice but to come near land now and again. Most lubbers imagine that it is out in the open ocean where the old wooden ship and her salty crew were in the largest amount of danger. In point of fact, the closer to shore a ship comes the more likely her chances of accident, injury or total wreck. The tides in any given port play an enormous part in either the safety or the demise of ships going in and out. Knowing as much as possible about their habits and quirks can be the difference between finding safe harbor and never going home again.

General understanding and documentation of tidal patterns has been around since man went out to sea. The Egyptians, who were leery of the vast ocean – as they knew the Mediterranean – but very familiar with their beloved Nile, left enormous amounts of documentation not only on Nile floods but on ebbs and flows in the Delta as well. Neither the Greeks nor the Romans were particularly forthcoming about tidal patterns and those master mariners, the Vikings, were not keen on writing down things they seemed to consider common knowledge. Both in the east, particularly China, and in the west, documents regarding tidal fluctuations began to show up around 1200 CE.

The earliest extant tidal table was produced in 1250 at St. Albans Abbey in Britain. The listings are meager, giving fluctuations for London and the Thames only but it was a start. In 1802 the New American Practical Navigator was published in Boston. Its author, Nathaniel Bowditch, connected tidal flux with the phases of the moon in an almanac style that would influence future documents. By the 1830s, both the British Almanac and the American Almanac included predictions for high and low tides in major ports along the Atlantic coast and, in the case of the American Almanac, the Gulf coast as well.

There are no certainties when one is dealing with the sea, however, and sailors had to know the variations possible in documented tidal fluxes. This meant having knowledge of the factors that could alter the regular tides as documented. First and foremost, one must be clear that any tidal table was no more that an educated guess. Seamen know that in places with vast discrepancies between levels of water at the two high and low tides in any given day, the tables could not be trusted. Keeping an eye on the barometer was also advisable; higher tides than predicted were likely to occur when the atmospheric pressure was low and vice versa.

Strong winds, even those originating far out to sea or well inland, could affect high tides in particular. Wind coming in off the ocean might make a high tide much higher, while wind coming off land – particularly strong, warm winds like a Santa Ana or Mistral – could decrease the depth of a high tide. Heavy storms have the same affect with the added irritation of altering tide times by up to an hour.

There were places in the world that have extreme tidal fluxes, and by the late 18th century most mariners knew where the major ones were. The Sea of Okhotsk between Russia’s mainland and the Kamchatka Peninsula and the English Channel, for instance, are renowned for their very high tides. The most extreme tidal fluxes in the world are on the Atlantic coast of modern Canada, particularly the Bay of Fundy where tidal runs can range in height as much as forty-five feet. Some experts estimate that the mid-tide flow of water here is equivalent to that of all the rivers and streams on Earth.

The wonder of the tides is just another reason to stand in awe of the sea. Don’t stand too long, though; there’s work to be done and no one likes a gawpus.

Header: Fishing Boats on the Bay of Fundy by William Bradford c 1860


Editilla~New Orleans Ladder said...

I just so dig this blog.

You should write a book from these posts, a non-fiction.
But, I'd also like to see you write a fiction set in the present or close future that combines your Pirates and your HoodooQ <-- re the latter have you ever read Tim Power's "Last Call" trilogy?

Hmmmm what else... oh! And while you're out could you pick me up some pickled herring?
Thanks Love :)

Pauline said...

Thank you, brother; your encouragement is very, very much appreciated.

Good idea on the fiction, too. I'll look into Powers' books before summer is over; I need a good read.

Oh, and would you like beer with the herring? I mean, as long as I'm out :)

Timmy! said...

Ahoy, Pauline! We have some pretty big "bore tides" here in Cook Inlet too. But having been to the Bay of Fundy and seen the tide come in there I have to admit it is pretty awesomely impressive.

@ Editilla: Hear, hear! I agree with you on the blog book suggestion. As for fiction, I have been priviledged to read much of Pauline's (as yet unpublished) historical fiction and can only say that it is wonderful! Of course, I am just slightly biased...

Pauline said...

I imagine that tidal trends (if you can call them that) will change as climate does but, for now, the Bay of Fundy still tops them all for crazy high tides.