Nautical Charts

by G. R. Putnam

The standard three-arm protractor, or station pointer, as it is known to the English, should be a part of every navigational outfit because of its value in locating a position by the three-point problem. A recent American invention, Court's three-arm protractor, is an instrument made of celluloid for the same purpose. It should not be considered as a substitute for the standard metal instrument, but it is a simple, cheap, and handy supplement to it, as it may be readily used for small angles and short distances where there are mechanical difficulties in working with the metal three-arm protractor. Other protractors can be used for the three-point problem, as, for instance, Cust's protractor on celluloid, on which the angles are drawn in pencil and erased, and the tracing-paper protractor.

Degree of reliance on charts. The value of a chart must not be judged alone from its general appearance, as skill in preparation and publication may give a handsome appearance to an incomplete survey. On the other hand a thorough survey might through poor preparation result in a chart defective either in information or in utility.

FIG. 48. THREE-ARM PROTRACTOR IN USE ON A CHART, PLOTTING POSITION FROM TWO ANGLES.

The degree of completeness of the soundings, the character of the region, and the date of the survey should be taken into account in deciding as to the amount of reliance to be placed on the chart. Areas where the soundings are not distributed with fair uniformity may be assumed not to have been completely surveyed. Caution should be used in navigating on charts where the survey is not complete, and even where careful surveys exist care must be taken if the bottom is of very irregular nature with lumps near the navigable depth, as for instance on some of the coral reef coasts. Isolated soundings shoaler than the surrounding depths should be avoided, as there may be less water than shown. In such a region, unless the whole area is dragged, it is impossible to make it entirely certain that all obstructions are charted.

While an immense amount of faithful work has been put into the preparation of many charts, the user must constantly exercise his own judgment as to the reliance to be placed on them. A coast is not to be considered as clear unless it is shown to be; buoys may get adrift and be in a different position or be gone altogether; fog signals vary in distinctness owing to atmospheric conditions; extreme or unusual tides may fall below the plane of reference; owing to strong winds the actual tide may differ from the predicted tide. Errors sometimes creep in from various sources, such as those due to different reference longitudes or the use of a corrected longitude for a portion of the chart without changing other positions to which the same correction is applicable; clerical and printing errors may occur; there are sometimes omissions in surveys; a feature may get plotted in two different positions; tide rips are reported as breakers and floating objects as rocks or islands, and thus many dangers have gotten on the charts which cannot be found again, and false reports are sometimes made to shield some one from blame. Most of these classes of errors and uncertainties, however, disappear in the use of charts of a thoroughly surveyed coast.

Use the latest editions of charts. The latest edition of a chart should always be used and should be corrected for all notices since its issue. Carelessness or false economy in not providing the largest scale or the latest chart has been the cause of more than one marine disaster.

The British Board of Trade issue the following official notice to shipowners and agents: "The attention of the Board of Trade has frequently been called to cases in which British vessels have been endangered or wrecked through the masters' attempting to navigate them by means of antiquated or otherwise defective charts. The Board of Trade desires, therefore, to direct the especial attention of shipowners and their agents to the necessity of seeing that the charts taken or sent on board their ships are corrected to the time of sailing. Neglect to supply a ship with proper charts will be brought prominently before the Court of Inquiry in the event of a wreck occurring from that cause."

The following is a translation of a notice in the preface to the catalogue of charts published by the German government: "Owners and masters of vessels are apprised that cases of marine accidents in which the casualty was due to antiquated or erroneous charts, have frequently been before the admiralty courts. In consequence of this, the 'Instructions for the prevention of accidents to steamers and sailing vessels,' issued by the Seeberufsgenossenschaft have been amended by the following additional paragraph: 'It is obligatory upon every master, except when engaged in local coastwise navigation, to keep the Notices to Mariners regularly, and with the aid of them to carefully keep his charts up to date.'"