Chapter - 17

Piloting Instruments

LIST OF NAVIGATING INSTRUMENTS FOR SMALL BOATS

Compass
Celluloid Course Protractor Dividers (bronze)
Pelorus or Bearing Finder Patent Log and Log Line
Lead and Lead Line
Good Timepiece
Deviation Card
Log Book

Charts
Coast Pilot
Lake Survey Bulletin
Tide Table
Light List

The Lead And Lead Line

Of the instruments necessary for successful piloting, a motor boatman should be familiar with a few of the most common ones. Of these the lead line is probably the most useful. As is well known, the lead line is a device for determining the depth of water, and consists essentially of a suitably marked line having a piece of lead of a certain definite shape, somewhat similar to a window weight. For use on motor boats leads of various weights are used, ranging from five to fourteen pounds. A lead line of twenty-five fathoms is sufficient for all ordinary purposes. The deep sea lead weighs from 30 to 100 pounds, and a line of 100 fathoms or upwards is employed.

Marking The Lead Line

Lines are generally marked as follows:

2 fathoms from the lead, with 2 strips of leather.
3 fathoms from the lead, with 3 strips of leather.
5 fathoms from the lead, with a white rag.
7 fathoms from the lead, with a red rag.
10 fathoms from the lead, with leather having a hole in it.
13 fathoms from the lead, same as at 3 fathoms.
15 fathoms from the lead, same as at 5 fathoms.
17 fathoms from the lead, same as at 7 fathoms.
20 fathoms from the lead, with 2 knots.
25 fathoms from the lead, with 1 knot.
30 fathoms from the lead, with 3 knots.
35 fathoms from the lead, with 1 knot.
40 fathoms from the lead, with 4 knots.

And So On.

Fathoms which correspond with the depths marked are called "marks." The intermediate fathoms are called "deeps." The only fractions of a fathom used are the half and quarter. The length of lead lines should be checked up frequently while wet. The bottom of the lead is hollowed out, and the hole is filled with tallow or a like substance by means of which a sample of the bottom is brought up. The process of filling the lead with tallow is called "arming the lead."

The Patent Log

The log is a device for determining the distance which a boat has run through the water. There are three principal kinds of logs known as the patent log, chip log, and the ground log. Of these three, the patent log is the only one used to any extent today.

The patent log consists of a registering device, tow line, and a rotator. The registering device is generally made fast to some permanent position near the stern of the boat, and the length of tow line used must be sufficient to extend beyond the effect of the boat's wake. The rotator is attached to the outer end of the log line, and is a small spindle with a number of wings or blades extending radially in such a manner as to form a spiral, and when drawn through the water in the direction of its axis rotates about that axis after the manner of a screw propeller. The registering device is so calibrated that instead of registering the number of total turns of the rotator and log line, it will register in nautical miles.

Modern Logs

New types of logs and speedometers may be purchased today which are usually actuated by water pressure on a fitting installed on the bottom of the boat. It is a great convenience in piloting to have such an instrument permanently installed so that speed or mileage can be read directly from a calibrated arc on or near the engine instrument panel.

The Chronometer

The chronometer, the timepiece used on ships, differs from the clock or other timekeeping instruments in that it is constructed to perform its work with greater precision. Correct time, or regularity of a timepiece on shipboard is absolutely essential.

The Course Protractor

The course protractor has generally superseded the ancient parallel rulers for the purpose of transferring the direction of the line drawn on the chart to the compass rose on the chart, in order to determine its direction. In using the course protractor, its center should be placed on the chart exactly over the boat's position. The arm of the protractor is then swung around to the nearest compass rose on the chart, making the hair line down the center of the arm pass directly over the center of the compass rose.

Holding the protractor arm firmly in this position, the compass part of the protractor is then swung around until the hair line cuts the same compass point or degree on the protractor compass as it cuts upon the compass rose. The compass and the rose are now parallel, or, in other words, they have the same variations. Holding the protractor compass firmly against the chart, the protractor arm is moved until its center line cuts the point on the chart where it is desired to lay a course. The compass course either in points or degrees can then be read off directly.

Should the boat's compass have any deviation, the course can be easily corrected to take account of this error by simply turning the protractor compass around, while holding the arm against the chart— clockwise if the error is easterly, and counter-clockwise if the error is westerly.

The Pelorus Or Bearing Finder

In order to take observations and bearings of distant objects with any degree of accuracy, it will be necessary to have some form of bearing finder or pelorus. The pelorus as it is manufactured and sold today by the dealers in nautical instruments is so very expensive that for the little use which the motor boatman has for such an instrument it would hardly pay him to go to the expense of purchasing one. However, with a little care, a home-made bearing finder may be constructed which under ordinary conditions will be found to give fairly accurate results.

Government Publications

Sailing Directions and U. S. Coast Pilots. These publications contain the same type of information, but the former, published by the Hydrographic office, deals with foreign waters and coasts, while the latter, published by the Coast and Geodetic Survey, covers the United States and its possessions. In these publications are descriptions of coast lines and harbors, etc.

Light Lists. These are published by the Hydrographic Office in six volumes, covering foreign countries, and by the U. S. Coast Guard in six volumes for the United States, and its possessions, except for the Philippine Islands.

Tide tables. These are now issued in four volumes, as follows: Europe and West Coast of Africa (including Mediterranean Sea) ; East Coast, North and South America (including Greenland; West Coast, North and South America (including Hawaiian Islands) ; Central and Western Pacific Ocean and Indian Ocean. Together they contain daily predictions for 185 reference ports and differences and constants for about 5,000 stations.

Current Tables. These tables are issued in two volumes by the Coast and Geodetic Survey, Department of Commerce, entitled Current Tables, Atlantic Coast, North America and Current Tables, Pacific Coast, North America and Philippine Islands. They include the predicted times of slack water and the times and strength of current for each day in the year at a number of reference ports, and current differences and constants for numerous other places, as well as other useful current information.

Pilot Charts. Pilot charts prepared by the Hydrographic Office, U. S. Navy Department, are an extremely useful source of information to the navigator on hydrography, navigation, and meteorology.

Notice to Mariners. The Hydrographic Office issues weekly Notices to Mariners containing corrections to publications and charts. They are prepared jointly by the U. S. Coast Guard and the Hydro-graphic Office.

H. O. 205 and H. O. 206, Radio Aids to Navigation. This publication of two volumes contains a list of radio stations throughout the world, detailed and general information concerning such services and international and various national regulations on the subject.

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