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OF COMPUTING THE TIMES OF
HIGH WATER AND LOW WATER
AS REQUIRED AT THE
AN EXAMINATION SPECIALTY
CAPT. R: M. PUGSLEY
(LATE MASTER U. S. TRANSPORT SERVICE)
“Mariner's Guide," "Current-Course Projector," "Course Protractor,"
17 South STREET
Copyright, 1916, by R. M. PUGSLEY
Books and Instruments
CAPT. R. M. PUGSLEY
POR SALE BY ALL DBALERS
CAPT. PUGSLEY'S GUIDE to the U. S. Local In
spectors Examination of Masters and Mates of Ocean-Going Steam and Sailing Ships, with complete-instructions and information for those who wish to learn navigation and save the expense of attending school by preparing themselves for
the examination. Price, $2.00. CAPT. PUGSLEY'S NEW YORK PILOT AND GUIDE
to the U. S. Local Inspectors Examination of Masters and Pilots for New York Bay and Harbor. Covers inland pilot examinations generally except
the sailing directions Price, $2.00. CAPT. PUGSLEY'S TIDES. A special work on com
putation of tides for use of applicants for U. S. Local Inspectors licenses. Contains 18 problems worked by two methods, covering every condition
with detailed explanation for each one. Price $2.00. CAPT. PUGSLEY'S LEARNER'S COMPASS CARD.
-For those who wish to learn the compass. Price, 50 Cents.
Any of the above books sent to any address
on receipt of price by
CAPT. R. M. PUASLEY 17 South Street, New York City
This volume is not intended to be a scientific treatise of the phenomena of tides; the object being to set forth in as clear and concise a manner as possible the standard methods used by practical navigators to compute the approximate time of high and low tides at a given port on any date, and particularly for those wishing to take the U. S. Local Inspectors examination for an ocean going license, as that is one of the problems given every applicant.
The lunitidal intervals used are taken from Bowditch and that of the high water differs a minute or so in some cases from that given in other works. The American Ephemeris and Nautical Almanac is used throughout as it is usually given applicants at examinations.
R. M. PUGSLEY.
In comparing the times of high water and low water found by the methods given here with those in the tide tables issued by the United States Coast & Geodetic Survey, a difference in most cases will be found and is due chiefly to the fact that the predictions given in the tables are the direct results of the proper scientific methods employed which takes into consideration every known element which may properly enter the calculation and are therefore to be accepted as the correct standard.
By the following methods only one element, the moon, is considered, the effect of the sun being entirely neglected, and while not exact the results are quite near enough for ordinary, practical use, and so much so that it is not necessary for the navigator to perform a long tedious calculation when a nearly correct result will meet the requirements.
When the sun's place differs from that of the moon ninety degrees the difference between these methods and the tide tables will be the maximum, and at the minimum when the sun's place and that of the moon are the same or one hundred and eighty degrees different.
In assuming a degree of dependence the nature of the port or place must be considered. Those into which streams of importance do not empty are subject to the influence of winds only, which do not affect the times of tidal occurrences to a marked extent. Large streams do, and together with the wind flood tide sometimes does not occur, the condition being low water without a change of height worth considering, except that perhaps which may be due to freshet.
Philadelphia is such a port. The flood tide under normal conditions runs about five hours and the ebb tide about seven hours, which is due to the emptying of the Delaware River. When the
country is quite dry and strong northwest winds blow for several days the tide may remain low. The other extreme would be abundant rains over the section drained by the stream and northeast winds when the tide would remain very high.
These facts are mentioned to illustrate the necessity of taking into consideration every local influence when the time of high water or low water is a factor of importance in the navigation of a ship.