Inquiry by the commanding officer of the U. S. S. Montana, as to the sorts of duty that the various members of the classes of student torpedo officers have performed since their graduation from the Naval Academy, has shown that a remarkably small percentage of them have had experience as assistant to the navigator; and inasmuch as many of these officers, upon their graduation from the torpedo class, will be assigned to torpedo craft, where they will be required to perform navigating duty, it was considered desirable to give as many of them as practicable as much experience along navigating lines as the movements of the ship would permit, keeping in mind the fact that this navigating work will not interfere with the course of torpedo instruction, as the torpedo instruction is not carried on when the ship is making a passage.
A suitable equipment of nautical instruments, charts, sailing directions, light lists, nautical almanacs, etc., was procured from the Bureau of Navigation, for the exclusive use of these officers, and a course of practical work was laid out by the navigator.
Since this equipment was received, but one sea passage has been made, viz., from New York to Mordazo Anchorage, Gulf of Guacanayabo, Cuba, but it is believed that the practicability and desirability of this instruction have been fully demonstrated.
As was expected, errors were made, some showing lack of conception of the principles of the work involved, and others a lack of knowledge of how and where to obtain certain necessary and desirable knowledge, and for these reasons this paper is written.
It is not purposed to discuss in detail the art of navigation, for that would be too voluminous, but it is desired to touch briefly upon the most important points of practical navigation, in the belief that such points will assist the class in overcoming the faults shown during the last passage and that they may be of assistance to some officer starting his first navigator's cruise.
Portions of the art of navigation can be obtained from books, but a very important portion can be obtained only from experience, assisted by the experience of others. The sooner he ascertains just what must be acquired by experience, and then acquires it, the sooner will the new navigator become an efficient unit of the department organization of the ship.
While these notes may easily be adapted to the condition of a ship cruising with the fleet, for present purposes it is assumed that the ship is cruising singly, and the departure land falls and arrival may be timed as seen fit within the normal limits of the urgency of the ship's orders, and the speed that may be necessary or desirable. However, every navigator must be prepared to make sea passages, departing at times and at speeds over which he has no control, and in fact this should be practiced.
The purpose of this paper, involves only the duties of the navigator in:
1. (a) Preparing the navigation department for a sea passage, and (b) the information that must be acquired before going to sea.
2. Acquiring the information that the navigator must acquire while at sea, with a brief discussion of how and why.
1. (a) To prepare the navigation department for sea, the navigator must:
(1) See that the steering gear is in order.
(2) See that the lead lines are checked.
(3) Have the sounding machine set up, with the tubes at hand, for it is not always known, ahead of time, when the sounding machine will be wanted.
(4) Have the patent log and log line aft, and ready to put over and be sure that the port log line is not put over the starboard side, for if there is a percentage error, it would be applied to the wrong log reading. It is a good plan to have the rotator encased in a box, except when actually over the side, in order that the vanes cannot be bent by knocks when transporting it.
(5) Have the charts that will be used corrected to the latest notice to mariners. The navigator should correct the charts himself for two reasons: (1) accuracy and (2) conversance with the corrections that are made.
(6) Start the gyro compass, if there is one, two and one-half hours ahead of the hour set for getting underway, and check it when it is thoroughly settled, by azimuths of the sun. If the sun is not available, it may be checked by taking bearings of three charted objects, and plotting them on the chart. At least three observations, at from 10 to 15 minutes apart, should be taken to determine if there is an oscillation. The compass may, in an emergency, be started and settled within one degree of the meridian, in one hour's time, but this should not be practiced.
Even if there is a commissioned officer on board taking immediate charge of the compass, the navigator should study it and be thoroughly familiar with its wants and ills, for with intelligent care it seldom requires more than the application of mature common sense.
(7) See that the sextant and a stand-by sextant are in adjustment. Attempts should not be made to remove a small amount of index correction, for it will not affect the accuracy or the rapidity of the work.
(8) Do not hesitate to take a local pilot, if there is one to be had, if there is the slightest doubt about the need for one. He is a good accident insurance policy, and much may, probably, be learned from him, both about the channel and the local traffic. The navigator should telephone for the pilot, and give him plenty of time to get on board, so that sailing need not be delayed by waiting for him.
There are other details to be looked to before getting underway, but as they do not materially affect ship control or the movements of the ship, they do not come within the purpose of these notes.
1. (b) Before getting underway the navigator should acquire the following information:
(1) What charts will be used.
(2) What courses will be steered, and what distance will be made good on each course.
(3) Total distance to be run.
(4) The best time for departure, and the state of the tide.
(5) The speed of the ship, in revolutions per minute and knots, best suited for making land falls, and timely arrival at the port of destination.
(6) What land or aids to navigation will be sighted, and at what time each will be sighted.
(7) What particular dangers are to be avoided.
(8) Look up the characteristics of all land, light houses, light ships, lights, and fog signals.
(9) When, if at all, should the sounding machine be used.
(10) What observations should be taken and at what times.
(11) What stars will be available for morning and evening observations.
(12) What currents may be expected during the passage.
(13 What per cent error should be applied to patent log readings for dead reckoning purposes.
(14) State of tide at the port of destination at the time of arrival.
It may be stated that at least a portion of the above information may be acquired after getting underway, and sometimes due to urgent orders, it must be; but, the navigator who goes to sea with the above information in his note-book, on his charts, and in his mind, is absolutely prepared for the passage, and will be prepared to the best of his ability, for any contingency or emergency.
The acquiring of the above information requires considerable thought and study, and should ordinarily be taken up in the order given, and along general lines as follows:
(1) What charts will be used.
The list should include:
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- A general chart or the chart of the least extent covering the whole passage. This is desirable for the purpose of giving a perspective of the passage.
- Charts of a more moderate extent on which the actual work is carried.
- Charts of the largest scale, i. e., of the least extent on which the courses should be laid, for the purpose of searching out more thoroughly and carefully any dangers to navigation.
- The largest scale harbor approach charts.
- The harbor entrance charts showing the entire channel on one chart, this to be used for perspective only.
- The largest scale harbor entrance charts.
- The largest scale harbor charts,
- The anchorage chart.
Anchorage charts should never be used for navigating purposes. Good practice is to transfer the berths from the anchorage chart to the harbor chart in use, for then the navigator is ready for a berth assignment by the commander-in-chief or the senior officer present, in case the assignment is not made until shortly before anchoring.
Charts should be referred to as H.O. 942, C.S. 1108, B.A. 1138. The consecutive numbers should not, ordinarily, be used, their use being for convenience in filing only.
Prior to getting underway, the charts to be used, should be selected and broken out, the light circles drawn in with black and red water-proof ink. A good plan is to use black ink for white lights and red ink for red lights and red sectors of lights. The name of each chart should now be written on its outside margin, toward the front, as it lies in the portfolio, in order that when a particular chart is wanted, the selected ones may be run through and the chart desired picked out, without reference to the chart catalogue and without unfolding the charts. Now arrange them in the order in which they will be used. When the study of them has been completed, place them in a drawer, empty portfolio, or in fact any place where they will be out of the way but safe and accessible.
The Pilot Chart and Hydrographic Bulletin should be consulted for the latest information on obstructions and the various valuable information that they contain. All obstructions, derelicts, etc., that may have been reported near the course to be made good, or that may have been carried near the course, should be transferred to the charts that will be used. The pilot chart should also be consulted for lines of variation, for they generally differ from those shown on general charts and are usually more nearly correct.
(2) What courses will be steered, and what distance will be made good on each course.
The sailing directions should now be carefully studied, for in most cases they furnish information as to standard routes to be sailed, with the distances both for heavy draft and light draft ships. These courses and the distances on each course should be laid down on each chart to be used, and should be sailed closely, except where the presence of a wreck or other obstruction renders such procedure impracticable. In any case the sailing direction courses should be retained on each chart for reference. If desired, they may be drawn in with water-proof ink, and thus save work in preparing for a similar trip at some time in the future.
Sailing direction courses should always be drawn in with waterproof ink on harbor entrance charts.
(3) Total distance to be run.
This should be very accurately computed, for by combining it with the time of departure and the speed of the ship, the time of arrival may be obtained, the necessity for which is obvious. It is also obvious that the total distance should be the distance from anchorage to anchorage.
(4) The best time for departure and the state of the tide.
(5) The speed of the ship, in revolutions per minute of the engines and in knots, best suited for making land falls and for arrival at the port of destination.
(6) What land or aids to navigation will be sighted, and at what time will each be sighted.
The three are closely associated, particularly for a ship on independent duty. Sometimes the navigator will not be asked for information on this subject, but he must study and be prepared to give the information if it is required.
The state of the tide at the port of departure or destination need not, necessarily, have anything to do with the time of arrival or departure, except where the channel is narrow and tortuous and hence made dangerous by currents, or where the depth of the channel is such that it is necessary for the ship to make the passage at high water. However, the advantage of going in on the flood and out with the ebb is obvious.
In the back of the tide tables are diagrams and directions for their use, giving the navigator information as to how to get the most benefit from tidal currents at our principal ports. Information about tides is also found in the sailing directions indexed under "currents."
The limits of the time of arrival should now be determined. Frequently the port of destination may be entered at night as easily, or more so, than in the daytime, in which case there will be no limit as to time of arrival. Again, the port of destination cannot be entered at night without grave danger. Again, there may be a narrow, dangerous, badly lighted channel to be passed, making a daytime passage practically imperative. Therefore, combining this with a practical time for departure, a suitable ship speed may be computed that will conform to reasonable limits of economy of coal and personnel and the urgency of the service of the ship.
The times of sighting the aids to navigation, land, etc., should be estimated in advance of going to sea, for it must be done sooner or later; as a matter of fact it will be done again after getting to sea, nevertheless it will be checking the work rather than original study. The work at sea should be principally confined to "Where is the ship."
(7) What particular dangers are to be avoided. After the courses have been laid on the chart, scan the charts carefully and red pencil them, i. e., draw a red circle around every shoal or obstruction that lies within several miles on either side of the course. This is desirable, for after getting to sea a study of the chart will be unnecessary, a glance at it will suffice to locate dangers.
(8) Look up the characteristics of land and all aids to navigation that will be sighted, together with the fog signals of such aids.
The land characteristics should be looked up in the Sailing Directions or Coast Pilot. The characteristics of the aids to navigation should be looked up in the light list and all correction slips pasted in the light list should be checked. A convenient method is to have made, a type written copy of the day, night, and fog signal characteristics of every aid to be sighted. By this means the navigator may carry a copy in his pocket for ready reference. He may turn one over to the officer of the deck, and one should find its way to the captain for his reference, as well as for his convenience when he writes the night order book.
The characteristics given on the charts, are usually correct, but should never be depended on, unless they have been checked with the light list.
(9) When, if at all, should the sounding machine be used.
The sounding machine has its greatest use in cloudy or foggy weather, if the ship is on soundings; and it is also of great value when steaming in localities where strong currents are known to exist, as for example, the run from Cape Cod to Nantucket Shoals Light Vessel. The run from Cape Cod to Nantucket Shoals Light Vessel is not, however, a very good example of current sailing on the sounding machine, for the depths of water are not well known or are poorly charted; and also, when approaching the light vessel from the northeast more than one "fit" for the line of soundings can usually be found.
To run on the sounding machine, take soundings half hourly and plot them by dead reckoning on a piece of tracing cloth, using the last fix as a point of departure. Place the tracing cloth on the chart and see if the soundings obtained correspond with the depths by chart. If they correspond, try to find a second "fit." If they do not correspond, move the tracing cloth around in the effort to find a "fit." In many localities the currents can be more or less accurately computed from current charts in the sailing directions, and the soundings should now be plotted by dead reckoning on another piece of tracing cloth, making allowance for the computed current.
It is well to bear in mind that any near fix obtained by soundings should be used with great caution, except where the soundings by machine definitely establish the position, on account of marked changes in the depth of water, which depths could exist in no other place in the vicinity, as for example, the mud gorge in the approach to New York. The mud gorge is a narrow channel extending in a northwest and southeast direction with depths of 40 fathoms where the surrounding depths are not more than 30 fathoms.
On approaching soundings in thick weather, the sounding machine should be used constantly, for the distance off shore can thus be accurately determined, and frequently the first depth obtained, coupled with the dead reckoning, will give an absolute fix.
It is sometimes desirable to follow a curve of depths, as in the run by the inside route from Cape Hatteras to Florida. This can be done very handily by using the sounding machine.
(10) What observations of heavenly bodies should be taken and at what times.
For a day's work the following observations of heavenly bodies should be taken:
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- Star observations at morning twilight.
- Sun observation when the sun is on the prime vertical in the forenoon, or as soon as it has sufficient altitude.
- Sun observation in the forenoon when the sun bears 135°.
- Ex-meridian observation of the sun.
- Meridian altitude of the sun.
- Sun observation in the afternoon when the sun bears 225°.
- Sun observation in the afternoon when the sun is on the prime vertical, or at such time before as necessary for it to have sufficient altitude.
- Star observations at evening twilight.
The times of the forenoon and afternoon observations of the sun are noted above for the condition of the ship being in north latitude, and having the latitude greater than the declination of the sun if they are of the same name.
It must be borne in mind that under certain conditions of latitude and sun's declination, the sun will be practically in the prime vertical all day; again it will be north of the prime vertical all day; and again it will be south of the prime vertical all day.
The principal object to be attained in deciding when to take sun observations, is to find out when, if at all, the lines of position may be obtained for a longitude line direct; the noon line is of course a latitude line; and the mid-forenoon and mid-afternoon lines should be taken at such times as to make the greatest possible angle with the other two lines.
Frequently when making short passages no observations of heavenly bodies are necessary. On the other hand, if there are known to be currents in the vicinity, a safe land fall may be planned by arranging the time of departure in order that a fix may be obtained a short time before the land fall.
(11) What stars will be available for morning and evening observations.
The navigator should be thoroughly familiar with the constellations that contain the stars that are suitable for navigational purposes. Before going to sea, he should, if necessary, go on deck at evening twilight and at morning twilight and observe their locations in the heavens, in order that each can be recognized on sight.
For the purpose of studying the stars and ascertaining when each will be visible, a planisphere is desirable and is inexpensive.
(12) What currents may be expected during the passage.
The currents to be expected during the passage must be carefully looked up, for frequently when currents are strong and the sea room is limited, allowance must be made for them. If the currents are not allowed for, the estimate should nevertheless be made, in order that the probable set and drift will be known, for it may be necessary to make the entire passage on dead reckoning and soundings.
(13) What per cent error must be applied to patent log readings for dead reckoning purposes.
If the error of the patent log is not known, it should be ascertained as soon as possible, by checking it on a measured mile or by running from abeam of one landmark to abeam of the next in a locality where there is known to be little or no current. A comparison between the run by patent log and the run by chart will give a percentage error.
Many navigators do not use the patent log, they using revolutions entirely for working up the dead reckoning position; but unless the log interferes with the maneuvering of the ship, its use is advised for a check if for no other purpose.
A ship's speed will usually vary somewhat under the varying conditions of draft and trim. An example of this variation is shown by the Montana. With normal trim and draft, the Montana will make 13 knots for 65 revolutions per minute, but if the ship is down by the head two or three inches, she will make thirteen and four-tenths knots for 65 revolutions per minute.
(14) State of the tide, at the port of destination, at the time of arrival.
This must be known in advance for it may be necessary to regulate the time of the ship's arrival, on account of channel depths, or the fact that the channel may be too dangerous for the passage except at slack water.
If the harbor can be entered regardless of the state of the tide, the information is, nevertheless, desirable for ship control on entering and must be known if the anchorage is crowded or if the ship must be moored.
(2) Acquiring the information that a navigator must acquire while at sea, when off soundings.
The U. S. Navy regulations require that the navigator shall obtain and report to the captain, the position of the ship at 8.00 a. m., noon, and 8.00 p. m., and at such other times as the captain may require it.
The navigator in making a position report to the captain should include in that report the following:
(1) Latitude by dead reckoning.
(2) Longitude by dead reckoning.
(3) Latitude by observation.
(4) Longitude by observation.
(5) Courses made good per gyro compass and per standard compass; and the distance made good on each course, since noon or some other specifically stated time.
(6) The total distance made good since noon or since some other specifically stated time.
(7) The average knots made good since noon or since the last fix.
(8) The current experienced since noon or since the last fix.
(9) The percentage error of the patent log.
(10) The error of the gyro compass.
(11) The error of the standard magnetic compass.
(12) The assumed variation obtained from the chart.
(13) The resulting deviation of the standard magnetic compass.
(1) The latitude by dead reckoning.
(2) The longitude by dead reckoning.
For the purposes of establishing a position point by computing "A" by the Haversine Cosine Method, accurate dead reckoning work is not necessary; however, no opportunity should ever be neglected to obtain as accurate a dead reckoning position as possible.
Ships frequently have to make a complete passage by dead reckoning, and for this reason the navigator should at all times practice dead reckoning to the maximum extent, by studying and applying currents and estimating the over ground speed of the ship by every known method. Practice in this will be found to be of inestimable value, for in addition to all of its other advantages, it will teach the navigator that when relying on dead reckoning, extreme caution must be exercised in approaching land or dangers.
(3) The latitude by observation.
(4) The longitude by observation.
The latitude can be directly obtained only as follows:
(1) By observation of a heavenly body, when it is on the meridian.
(2) By observation of Polaris.
(3) By the reduction to the meridian of the sun or a star.
The longitude can be directly obtained only as follows:
(1) By observation of a heavenly body, when it is on the prime vertical.
Latitude and longitude both may be obtained from the intersection of two or more lines of position, which were obtained by observations of two or more heavenly bodies, the observations being taken as nearly simultaneously as possible, and the lines of position run up or back by dead reckoning to any one of these lines of position that may be selected.
An absolute fix can be obtained only at a. m. and p. m. twilight, when two or more stars are available for observation. All other positions involve dead reckoning, which may be more or less accurate, for obtaining either the latitude or the longitude, or both. Therefore it will be seen that the latitude and longitude by observations at 8.00 a. m., noon, and at 8.00 p. m. will, either or both, invariably involve dead reckoning.
To obtain a position by observation, the following work should be done.
(a) At morning twilight, at least three stars should be observed if they are available. One or more in addition should be observed, but to be held in reserve in case they are needed for establishing the fix.
Polaris should always be included in the list of stars observed, for it is the only one from which the latitude can always be computed, and the computation (Nautical Almanac Method) is very simple.
(b) Observe the sun in forenoon when it is on the prime vertical for a line of position, as the longitude will then be obtained direct.
In northern latitudes and in the winter, it is not possible to observe the sun when it is on the prime vertical, therefore it should be observed as soon as it is from 12 to 15 degrees high.
(c) Observe the sun in the forenoon at about 10.45 a.m. for a line of position if the time is available.
This line of position is of particular value when current sailing, for obtaining the noon position by observation.
(d) A few minutes before noon, take an ex-meridian observation of the sun for the noon latitude.
This observation is necessary when cruising with the fleet in order that the forenoon lines of position may be run up to noon and the latitude and longitude obtained in advance for the noon position signal.
At local apparent noon, observe the sun for the noon latitude.
This observation should be made to check the latitude obtained by the ex-meridian observation.
(f) Observe the sun for a line of position at about 1.15 p. m., if the time is available.
This observation should be made principally for running back to noon to check the noon longitude as well as for running up to the last sun line of position taken during the day.
(g) Observe the sun for a line of position when it is on the prime vertical or before it gets below from 12 to 15 degrees of latitude. The principal" use of this line of position is to combine it with the noon line or with the early afternoon line for running up to 8.00 p. m. in case there be no star observations at evening twilight.
(h) Observe stars at evening twilight similarly to the observations at morning twilight.
The perfect conditions and times for an observations are when the sun bears 900, 135°, 180°, 225°, and 2700.
Unless the navigator knows from experience that his observations are always accurate, he should take at least three, at such times that a check on the accuracy may be obtained by a comparison of the time differences and of the altitude differences.
Doubtful observations should never be computed unless a near line of position will partly serve the purpose, for they tend to destroy confidence in the previous work.
The index correction should be checked before every observation if the sextant is laid down or subjected to any possible jar.
Every observation should be computed by the "Haversine Cosine" method, except those of Polaris, and the ex-meridian and meridian altitude of the sun.
At least every time that the sun is observed for altitude it should be observed for compass error; for, having the watch time and local apparent time difference, the compass error may be computed without table entry or computation, other than the entry of the azimuth tables.
(5) Courses made good per gyro compass and per standard compass, and the distance made good on each course, since noon or some other specifically stated time.
(6) The total distance made good since noon or some other specifically stated time.
The information called for under these heads is usually of general interest only; although, at times, it becomes most important, and is necessary for a full and complete position report.
The total distance from the port of departure to noon and from noon to noon, and from noon to the anchorage should be obtained for entry in the columns of the log for convenience in making up the cruising report.
(7) The average knots made good since noon or since the last fix.
No opportunity should be overlooked for obtaining the average knots over ground, for a part of the information regarding currents is derived from this and above all, the information is necessary for the accurate running up or back of lines of position, and this should always be used in preference to the run by revolutions or by the patent log.
(8) The current experienced since noon or since the last fix.
The current experienced is of great importance, for it must be applied in running lines of position and if it is sufficiently strong, it will frequently require a change of course to compensate it.
(9) The percentage error of the patent log.
The percentage error of the patent log should be computed from fix to fix for comparison of the run by log with the run by revolutions; it is of immense value under various conditions.
(10) The error of the gyro compass.
The necessity for knowing the error of the gyro compass and if it is oscillating, is obvious.
(11) The error of the standard magnetic compass.
(12) The assumed variation obtained from the chart.
(13) The resulting deviation of the standard magnetic compass.
The standard magnetic compass and the gyro compass should be checked every 15 minutes to detect any relative change of ship's head, which would indicate, (1) an oscillation of the gyro compass (2) that the gyro had left the meridian due to heavy weather or other cause, or that the magnetic compass was being affected by some local magnetic disturbance.
As close information of the magnetic compasses as possible should be kept, for the navigator never knows when he goes to sea, but that he may have to use them during the passage. Errors should be obtained by observations of the sun or stars with the gyro compass repeater, and thus obtain the true head and then comparing the head by magnetic compasses with the true head to obtain the magnetic compass error. The resulting deviation should be checked with the table of deviations.
"Piloting"
Currents should be studied very carefully and applied or compared with the actual current encountered on every passage no matter how short, for the navigator who does this will be very much more competent when in a fog, snow, or heavy rain, than he otherwise would be. Above all he will know his limitations.
The sailing directions and tide tables give very accurate information of currents, and usually local tide tables can be purchased which give even more complete information for that particular locality.
Courses should always be laid, giving a reasonable margin of safety. Buoys should be regarded with caution for they are usually more or less out of position, and are always subject to being out of position, particularly in localities of strong currents.
Valuable information of local conditions in unfrequented localities can frequently be obtained from the masters of merchant ships.
When piloting, the ship's position can be fixed by the following methods:
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- Bearings of three navigational aids or prominent charted objects on shore or tangents of land.
- Bearings of two navigational aids or prominent charted objects on shore or tangents of land.
- A bearing of one navigational aid and a range-finder distance.
- Two or more bearings of the same navigational aid or charted object with the course and distance run between.
There are other methods that may be used for fixing the position of the ship, but of all the known methods, those mentioned above are the most commonly used, and are adequate, and should be used in the order in which they are given.
A fix by three bearings is not only an absolute fix, but the plotting is checked and the error of the compass is more or less accurately observed. This method should always be used if possible.
A fix by two bearings is good if the compass error is accurately known, but it does not give a check on the work nor the compass.
A fix by one bearing and a range-finder distance is good, provided the distance to be observed is within the range-finder limit of reliability. This method, however, frequently fails at night as the flashing characteristics of many lights make it impossible to obtain an accurate range-finder distance.
When it is impossible to obtain range-finder distances recourse must be had to bearings with the course and distance run between them. This method at best is only an approximation, for the distance run, or course made good is almost invariably influenced by currents.
If the ship be in a fog, heavy rain, or snow, and is approaching dangers when the position is not accurately known, a good plan is to determine the maximum limits of the possible position of the ship, draw a circle around it and then lay a safe course from the extreme nearest the approached danger. The position circle should be carried along and all parts of it protected from danger until such time as a fix, or sufficient information on which to reduce the limits of possibility and probability, can be obtained.
When piloting, the ship's position should always be carried along by accurate plotting. Particular care should be exercised in getting an accurate fix immediately before and after changing course. The ship's advance and transfer should be known and applied when changing course in confined waters, i. e., changes of course should be made on a bearing of a charted object located as nearly abeam as possible, and the bearing should be so selected that the advance will place the ship on the new course and in the position which was selected when the chart study was made.
When near land or shoals a fix should be obtained at least often enough so that the maximum attainable current in that locality could not drift the ship into danger without warning.
Every opportunity should be embraced to obtain and use a leading mark when passing through narrow channels, i.e., select a bearing of a charted object, which, if this bearing be maintained, will lead the ship past the dangers. This will give a constant check on the ship's safety without recourse to plotting. A bearing of an object astern serves the same purpose.
The danger bearing is of immense practical value and should be used whenever occasion permits.
When approaching land, buoys, light ships, or light houses that it is desired to sight, set the pelorus or azimuth circle for the bearing on which the object is expected to be sighted and thus confine the search to a small arc of the horizon.
When changing course near land the new course should be sighted with the azimuth circle or pelorus, as a precaution against error which might have been made in laying the course or of the officer of the deck in setting the course.
After each passage the navigation work of the passage should be back checked, for the purpose of noting unexpected conditions obtained and for noting any faults in the plan for the passage, for it is principally by this means that the navigator acquires the fund of information that he must possess to be a successful unit in the ship's organization.
In conclusion the navigator should always remember that:
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- He is the only officer on board ship who must do all of his own work and can rely on no one but himself.
- He must do all of his own work carefully and painstakingly, for a little carelessness may result in grave danger to the ship.
- He should never take an avoidable chance, for he has to take enough chances without doing so deliberately.