Navigation chart

“ Hence, it will be impossible for you to correctly plot your course and distance sailed unless you have a chart which shows on it the degrees of latitude in which you are. For instance, if your Mercator chart shows parallels of latitude from 30° to 40° that chart must be used when you are in one of those latitudes. When you move into 41° or 29°, you must be sure to change your plotting chart accordingly. In very high latitudes and near the North pole, the Mercator chart is worthless. How can you steer for the North pole when the meridians of your chart never come together at any pole? ”

“ The Baker navigating machine, with the chart, was on my knees. Not knowing what kind of weather was before us, I knelt on my seat and made haste to take observations on the sea, the horizon, and the sun, through intervals in the covering of clouds.
The navigation of aircraft, in its present [Pg 43] stage, is distinctly more difficult than the navigation of seacraft. The speed at which they travel and the influence of the wind introduce problems which are not easily solved. ”

“ The ocean was all right, and so was the patent log; as for speed, one saw it with his own eyes. Therefore the thing that was not all right was the figuring that refused to boost the Snark along over the chart. Not that this happened every day, but that it did happen. And it was perfectly proper and no more than was to be expected from a first attempt at applying a theory.
The acquisition of the knowledge of navigation has a strange effect on the minds of men. The average navigator speaks of navigation with deep respect. ”

“ The navigator in planning his course between two positions lays the parallel rulers on these positions on the chart and carries this direction to the nearest compass [Pg 96] rose. This may be a true rose, in which event he remembers his T. R. E. rule, reversing it in this case, and with the variation given on the chart secures the magnetic course. In an iron or steel vessel, the deviation for that course must be ascertained from the deviation card by trial or from a Napier Diagram direct and applied to the magnetic course in order to obtain the compass course. ”

“ I've heard of navigators, you must know, whose reckoning by account has landed them by four degrees of longitude inland—same thing may happen with some folks' sextants. My course is your course, and you'll please to stick to it."
"There's not even yet southing enough," said Mr. Wilson.
"Yes, there is," cried Captain Punch. "you don't want to teach me navigation, do 'ee?"
Captain Parfitt rushed into the cabin and returned with a chart, which he laid open on the deck at Captain Punch's feet. ”

“ Assign for Night Work the following articles in Bowditch: Arts. 161-162-163-164-165. [Pg 16]
THURSDAY LECTURE The Chart Aids to Navigation
A chart is a map of an ocean, bay, sound or other navigable water. It shows the character of the coast, heights of mountains, depths at low water, direction and velocity of tidal currents, location, character, height and radius of visibility of all beacon lights, location of rocks, shoals, buoys, and nature of the bottom wherever soundings can be obtained. ”

“ The Lead Line
SINCE the coming of the mariners’ compass many centuries ago, navigation has made steady headway. It is now an exact science, and vessels properly equipped with needed instruments and with men able to use them, can, no matter what the winds or seas, or how extended the voyage, be brought safely to their destination.
The instruments used in navigation are, the compass, by which ship’s courses are steered; the sextant by which observations of the sun, moon and stars are taken, and through which the latitude is ascertained ”

“ Noon at the ship is the pivotal point of the day's work at sea. It is then that the navigator must report to the commanding officer the latitude and longitude by dead reckoning, the latitude and longitude by observation, the course and distance made good, the deviation of the compass and the course and distance to destination. ”

“ The practical value of this science is best appreciated by the navigator, who sees in the sun and moon his clock, and in the stars and planets the ready means of learning his latitude and longitude. It is one of the first tasks of the midshipman to become familiar with the use of the sextant, by which he works out the problem of ascertaining the exact place of the ship upon the ocean. Navigation is helpless without the assistance of astronomy. ”

“ Now if the navigator will draw, or imagine to be drawn in any such district, twelve vertical columns for the twelve months, and then sixteen horizontal lines through the same for the sixteen points of the compass, i.e., for N., N.N.E., N.E., E.N.E., and so on, omitting the by-points, he will have before him a picture of the “Investigating Chart,” out of which the “Pilot Charts” are constructed. In this case, the alternate points of the compass only are used; because, when sailing free, the direction of the wind is seldom given for such points as N. by E., W. by S., &c. ”

“ In practical navigation a vessel commences her voyage and attempts to sail in a certain direction, but the well-known elements of compass error, variation and deviation, current, wind, seas and poor steering all divert the vessel from the projected course. In dead reckoning a navigator strives to keep track of his position by keeping a record of actual courses steered and distances run. ”

“ He will be able to take a meridian observation with fair accuracy, and from that observation, with ten minutes of figuring, work out his latitude and longitude. And, carrying neither freight nor passengers, being under no press to reach his destination, he can jog comfortably along, and if at any time he doubts his own navigation and fears an imminent landfall, he can heave to all night and proceed in the morning. ”

“ From the days when navigation first became a science, unceasing efforts have been made to provide such maps and charts for every known portion of the globe. Geographical surveys, with the aid of the method of triangulation, have been made along all coasts, and elaborate series of soundings taken for a long distance from the coast line, and there are now few regions into which a ship ordinarily sails, or is likely to be carried by accident, for which elaborate charts, both of coast lines and of soundings, have not been provided. ”

“ The methods of navigation employed by mariners are the result of centuries of research and [Pg 94] invention, but have not yet reached finality—witness the introduction within the last few years of the Gyroscopic Compass and the Directional Wireless Telegraph Apparatus, as well as of improved methods of calculation.
In short journeys over land by aëroplane or airship the duties of a navigator are light, so long as he can see the ground and check his progress towards the objective by observation and a suitable map. ”

“ The most essential requirement for navigation is charts, general charts of entire oceans, or parts of them and their shores, compiled by the hydrographer from existing data, and special charts of smaller areas, of harbors, roadsteads, etc., prepared from special surveys. ”

“ At the inception of the Coast and Geodetic Survey in the early years of the century, so little was known of the dangers attending navigation along our extensive seaboard, that those who engaged in commercial enterprises were constrained to rely upon local knowledge and the reports of the hardy navigators who might carry their ventures to success. ”

“ He then compares that position with his voyage plan, his operational commitments, and his predetermined “dead reckoning” position. A good navigator anticipates dangerous situations well before they arise, and always stays “ahead of the vessel.” He is ready for navigational emergencies at any time. He is increasingly a manager of a variety of resources--electronic, mechanical, and human. Navigation methods and techniques vary with the type of vessel, the conditions, and the navigator’s experience. ”

“ In planning out in advance a long ocean voyage the experienced navigator would first, by laying down the track from port to port on a great circle chart, ascertain the shortest route between them, remembering that the greatest saving in distance over other routes is when the ports are far apart in longitude and both in high latitudes of the same name. ”

“ THE SCIENCE OF NAVIGATION Navigation, I may be permitted to repeat, is the mathematical science of finding ships’ positions at sea and of laying down courses to be followed. For the designation of positions latitude and longitude are used, latitude being measured north and south from the equator to the north and south poles, the equator being zero degrees of latitude, the poles being ninety degrees north and ninety degrees south latitude. ”

“ It is well known to seamen and philosophers, that, after the numerous improvements produced by the extensive commerce of the later ages, the great defect in the art of sailing is ignorance of longitude, or of the distance to which the ship has passed eastward or westward, from any given meridian.
That navigation might be at length set free from this uncertainty, the legislative power of this kingdom incited the industry of searchers into nature, by a large reward proposed to him who should show a practicable method of finding the longitude at sea ”

“ The number of miles a ship makes East or West is called Departure, and it must be converted into degrees, minutes and seconds to find the difference of longitude.
A ship, however, seldom goes due North or South or due East or West. She usually steams a diagonal course. Suppose, for instance, a vessel in Latitude 40° 30' N, Longitude 70° 25' W, sails SSW 50 miles. What is the new latitude and longitude she arrives in? She sails a course like this:
Now suppose we draw a perpendicular line to represent a meridian of longitude and a horizontal one to represent a parallel of latitude. ”

“ And, perhaps, we may look forward to a time when, by the command of wind and wave given by the steamboat, and by our increased knowledge of "ocean topography," if we may use the phrase; a ship may make its way across the ocean without ever being out of a current; a result which would be obviously a most important accession, if not to the speed, at least to the security of navigation.
Those ocean traversers evidently belong to a system. Some are permanent, some are periodical, and some are casual. The permanent arise chiefly from the effect of the flow from the poles to the equator. ”

“ Sailing charts are the smallest scale charts used for planning, fixing position at sea, and for plotting while proceeding on a long voyage. The scale is generally smaller than 1:600,000. The shoreline and topography are generalized and only offshore soundings, the principal navigational lights, outer buoys, and landmarks visible at considerable distances are shown. General charts are intended for coastwise navigation outside of outlying reefs and shoals. The scales range from about 1:150,000 to 1:600,000. ”

“ The advantage of being able to ascertain the ship's place in longitude, by observations of the moon, will ever be satisfactory, but more particularly through so vast a tract of sea, in which the error of the log may considerably accumulate, when ships arrive upon that coast where the land lies so nearly in a north and south direction, there can be no difficulty in discovering what part of the coast they are upon, their latitude observed will always point that out, by applying to the general chart, given from the authority of that most correct and able navigator Captain Cook. ”

“ The Art And Science Of Navigation Marine navigation blends both science and art. A good navigator constantly thinks strategically, operationally, and tactically. He plans each voyage carefully. As it proceeds, he gathers navigational information from a variety of sources, evaluates this information, and determines his ship’s position. ”

“ Difficulties with early navigators.—Up to the close of the last century, the navigator guessed as much as he calculated the place of his ship; vessels from Europe to Boston frequently made New York, and thought the landfall by no means bad. Chronometers, now so accurate, were then an experiment. The Nautical Ephemeris itself was faulty, and gave tables which involved errors of thirty miles in the longitude. The instruments of navigation erred by degrees quite as much as they now do by minutes ”

“ The reason for this is that in both cases, either your Variation or Deviation may change and throw you off.
Practically all navigation in strange waters in sight of land and in all waters out of sight of land depends upon the determination of angles. The angle at which a lighthouse is seen from your ship will give you much information that may be absolutely necessary for your safety. The angular altitude of the sun, star or planet does the same. The very heart of Navigation is based upon dealing with angles of all kinds. ”

“ Having no sun, moon, nor stars, their navigation is all done by dead reckoning; but they have developed instruments of extreme delicacy that locate land at great distances, accurately indicating this distance and the direction; others that determine speed, mileage, and drift, as well as a depth gauge wherewith they may record soundings anywhere within a radius of a mile from the ship. ”

“ XXXIV. So, in a little while, there were more than a thousand navigators engaged day and night, and in all parts of the ocean, in making and recording observations according to a uniform plan, and in furthering this attempt to increase our knowledge as to the winds and currents of the sea, and other phenomena that relate to its safe navigation and physical geography. ”