Chapt - 26.pdf - po ang - Januszek66

CHAPTER 26

EMERGENCY NAVIGATION

BASIC TECHNIQUES OF EMERGENCY NAVIGATION

2600. Planning for Emergencies

The modern ship’s regular suite of navigation gear

consists of many complex electronic systems. Though they

may possess a limited backup power supply, most depend

on an uninterrupted supply of ship’s electrical power. The

failure of that power due to breakdown, fire, or hostile

action can instantly render the unprepared navigator

helpless. This discussion is intended to provide the

navigator with the information needed to navigate a vessel

in the absence of the regular suite of navigational gear.

Training and preparation for a navigational emergency are

essential. This should consist of regular practice in the

techniques discussed herein while the regular navigation

routine is in effect in order to establish confidence in

emergency procedures.

Increasing reliance on electronic navigation and

communication systems has dramatically changed the

perspective of emergency navigation. While emergency

navigation once concentrated on long-distance lifeboat

navigation, today it is far more likely that a navigator will

suffer failure of his ship’s primary electronic navigation

systems than that he will be forced to navigate a lifeboat. In

the unlikely event that he must abandon ship, his best

course of action is to remain as close to the scene as

possible, for this is where rescuers will concentrate their

search efforts. Leaving the scene of a disaster radically

decreases the chance of rescue, and there is little excuse for

failure to notify rescue authorities with worldwide

communications and maritime safety systems available at

little cost. See Chapter 28 for further discussion of these

systems.

In the event of failure or destruction of electronic

systems when the vessel itself is not in danger, navigational

equipment and methods may need to be improvised. This is

especially true with ECDIS and electronic charts. The

navigator of a paperless ship, whose primary method of

navigation is ECDIS, must assemble enough backup paper

charts, equipment, and knowledge to complete his voyage

in the event of a major computer system failure. A

navigator who keeps a couple of dozen paper charts and a

spare handheld GPS receiver under his bunk will be a hero

in such an event. If he has a sextant and celestial calculator

or tables and the knowledge to use them, so much the better.

No navigator should ever become completely

dependent on electronic methods. The navigator who

regularly navigates by blindly pushing buttons and reading

the coordinates from “black boxes” will not be prepared to

use basic principles to improvise solutions in an

emergency.

For offshore voyaging, the professional navigator

should become thoroughly familiar with the theory of

celestial navigation. He should be able to identify the most

useful stars and know how to solve various types of sights.

He should be able to construct a plotting sheet with a

protractor and improvise a sextant. He should know how to

solve sights using tables or a navigational calculator. For

the navigator prepared with such knowledge the situation is

never hopeless. Some method of navigation is always

available to one who understands certain basic principles.

2601. Emergency Navigation Kit

The navigator should assemble a kit containing

equipment for emergency navigation. This kit should

contain:

1. At least one proven and personally tested hand-

held GPS receiver with waypoints and routes

entered, and with plenty of spare batteries.

2. A small, magnetic hand-bearing compass such as is

used in small craft navigation, to be used if all other

compasses fail.

3. A minimal set of paper charts for the voyage at

hand, ranging from small-scale to coastal to

approach and perhaps harbor, for the most likely

scenarios. A pilot chart for the ocean basin in

question makes a good small scale chart for

offshore use.

4. A notebook or journal suitable for use as a deck log

and for computations, plus maneuvering boards,

graph paper, and position plotting sheets.

5. Pencils, erasers, a straightedge, protractor or

plotter, dividers and compasses, and a knife or

pencil sharpener.

6. A timepiece. The optimum timepiece is a quartz

crystal chronometer, but any high-quality digital

wristwatch will suffice if it is synchronized with the

ship’s chronometer. A portable radio capable of

receiving time signals, together with a good

wristwatch, will also suffice.

7. A marine sextant. (An inexpensive plastic sextant will

373

374

EMERGENCY NAVIGATION

suffice.) Several types are available commercially.

The emergency sextant should be used periodically so

its limitations and capabilities are fully understood.

8. A celestial navigation calculator and spare

batteries, or a current Nautical Almanac and this

book or a similar text. Another year’s almanac can

be used for stars and the Sun without serious error

by emergency standards. Some form of long-term

almanac might be copied or pasted in the notebook.

9. Tables. Some form of table might be needed for

reducing celestial observations if the celestial

calculator fails. The Nautical Almanac produced

by the U.S. Naval Observatory contains detailed

procedures for calculator sight reduction and a

compact sight reduction table .

10. Flashlight. Check the batteries periodically and

include extra batteries and bulbs in the kit.

11. Portable radio. A handheld VHF transceiver

approved by the Federal Communications

Commission for emergency use can establish

communications with rescue authorities. A small

portable radio may be used as a radio direction

finder or for receiving time signals.

12. An Emergency Position Indicating Radiobeacon

(EPIRB) and a Search and Rescue Transponder

(SART) are absolutely essential. (See Chapter 28).

sheet can be constructed through either of two alternative

methods based upon a graphical solution of the secant of the

latitude, which approximates the expansion of latitude.

First method ( Figure 2603a):

, etc.

Step two: Draw and label a horizontal line

through the center of the sheet to

represent the parallel of the mid-latitude

of the area.

Step three: Through any convenient point, such

as the intersection of the central meridian

and the parallel of the mid-latitude, draw

a line making an angle with the

horizontal equal to the mid-latitude. In

Figure 2603a this angle is 35

Step four: Draw in and label additional parallels.

The length of the oblique line between

meridians is the perpendicular distance

between parallels, as shown by the

broken arc. The number of minutes of arc

between parallels is the same as that

between the meridians.

Step five: Graduate the oblique line into

convenient units. If 1' is selected, this

scale serves as both a latitude and mile

scale. It can also be used as a longitude

scale by measuring horizontally from a

meridian instead of obliquely along the

line.

2602. Most Probable Position

In the event of failure of primary electronic navigation

systems, the navigator may need to establish the most

probable position (MPP) of the vessel. Usually there is

little doubt as to the position. The most recent fix updated

with a DR position will be adequate. But when conflicting

information or information of questionable reliability is

received, the navigator must determine the MPP.

When complete positional information is lacking, or

when the available information is questionable, the most

probable position might be determined from the

intersection of a single line of position and a DR, from a

line of soundings, from lines of position which are

somewhat inconsistent, or from a dead reckoning position

with a correction for set and drift. Continue a dead

reckoning plot from one fix to another because the DR plot

often provides the best estimate of the MPP.

A series of estimated positions may not be consistent

because of the continual revision of the estimate as

additional information is received. However, it is good

practice to plot all MPP’s, and sometimes to maintain a

separate EP plot based upon the best estimate of track and

speed made good. This could indicate whether the present

course is a safe one (See Chapter 23).

The meridians may be shown at the desired interval

and the mid-parallel may be printed and graduated in units

of longitude. In using the sheet it is necessary only to label

the meridians and draw the oblique line. From it determine

the interval used to draw in and label additional parallels. If

the central meridian is graduated, the oblique line need not

be.

Second method (F igure 2603b):

(or any other

convenient unit) of latitude at the desired

scale. If a sheet with a compass rose is

available, as in Figure 2603b , the

compass rose can be used as the circle and

will prove useful for measuring

directions. It need not limit the scale of

the chart, as an additional concentric

circle can be drawn, and desired

graduations extended to it.

2603. Plotting Sheets

If plotting sheets are not available, a Mercator plotting

Step one: Draw a series of equally spaced vertical

lines at any spacing desired. These are

the meridians; label them at any desired

interval, such as 1', 2', 5', 10', 30', 1

Step one: At the center of the sheet draw a circle

with a radius equal to 1

EMERGENCY NAVIGATION

375

Figure 2603a. Small area plotting sheet with selected longitude scale.

, 30', etc.).

Step three: From the center of the circle draw a

line making an angle with the horizontal

equal to the mid-latitude. In Figure

2603b this angle is 40

and from it determine the interval and draw in and label

additional meridians. If the central meridian is graduated,

as shown in Figure 2603b, the oblique line need not be.

The same result is produced by either method. The first

method, starting with the selection of the longitude scale, is

particularly useful when the longitude limits of the plotting

sheet determine the scale. When the latitude coverage is

more important, the second method may be preferable. In

either method a simple compass rose might be printed.

Both methods use a constant relationship of latitude to

longitude over the entire sheet and both fail to allow for the

ellipticity of the Earth. For practical navigation these are

not important considerations.

Step four: Draw in and label the meridians. The

first is a vertical line through the center of

the circle. The second is a vertical line

through the intersection of the oblique

line and the circle. Additional meridians

are drawn the same distance apart as the

first two.

Step five: Graduate the oblique line into

convenient units. If 1' is selected, this

scale serves as a latitude and mile scale.

It can also be used as a longitude scale by

measuring horizontally from a meridian,

instead of obliquely along the line.

2604. Dead Reckoning

Of the various types of navigation, dead reckoning alone is

always available in some form. In an emergency it is of more

than average importance. With electronic systems out of service,

keep a close check on speed, direction, and distance made good.

Carefully evaluate the effects of wind and current. Long voyag-

es with accurate landfalls have been successfully completed by

this method alone. This is not meant to minimize the importance

of other methods of determining position. However, a good

dead reckoning position may actually be more accurate than one

determined from several inexact LOP’s. If the means of deter-

mining direction and distance (the elements of dead reckoning)

In the second method, the parallels may be shown at

the desired interval, and the central meridian may be printed

and graduated in units of latitude. In using the sheet it is

necessary only to label the parallels, draw the oblique line,

Step two: Draw horizontal lines through the

center of the circle and tangent at the top

and bottom. These are parallels of

latitude; label them accordingly, at the

selected interval (as every 1

376

EMERGENCY NAVIGATION

Figure 2603b. Small area plotting sheet with selected latitude scale.

Angle 0

Factor

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

Table 2604. Simplified traverse table.

are accurate, it may be best to adjust the dead reckoning only af-

ter a confident fix.

Plotting can be done directly on a pilot chart or plotting

sheet. If this proves too difficult, or if an independent check is

desired, some form of mathematical reckoning may be useful.

Table 2604 , a simplified traverse table, can be used for this

purpose. To find the difference or change of latitude in minutes,

enter the table with course angle, reckoned from north or south

toward the east or west. Multiply the distance run in miles by the

factor. To find the departure in miles, enter the table with the

complement of the course angle. Multiply the distance run in

miles by the factor. To convert departure to difference of

longitude in minutes, enter the table with mid-latitude and divide

the departure by the factor.

0.4 = 10 NM. Since the course is in the

southwestern quadrant in the Northern Hemisphere, the

latitude of the point of arrival is 41

44'N -23' = 41

21'N. The

factor corresponding to the mid-latitude 41

32'N is 0.7. The

difference of longitude is 10

0.7 = 14'. The longitude of the

point of arrival is 56

21'W + 14 = 56

35'W.

Answer: Lat. 41

21'N, Long. 56

35'W.

2605. Deck Log

At the onset of a navigational emergency, a navigation

log should be started if a deck log is not already being

maintained. The date and time of the casualty should be the

first entry, followed by navigational information such as

ship’s position, status of all navigation systems, the

decisions made, and the reasons for them.

The best determination of the position of the casualty

should be recorded, followed by a full account of courses,

distances, positions, winds, currents, and leeway. No

important navigational information should be left to

memory.

Example: A vessel travels 26 miles on course 205

from Lat. 41

21'W.

Required: Latitude and longitude of the point of arrival.

Solution: The course angle is 205

44'N, Long. 56

- 180

= S25

W, and

. The factors corresponding

to these angles are 0.9 and 0.4, respectively. The difference of

latitude is 26

-25

=65

0.9 = 23' (to the nearest minute) and the

departure is 26

the complement is 90

EMERGENCY NAVIGATION

377

2606. Direction

S and can be considered on the

celestial equator. For an observer near the equator, such a

body is always nearly east or west. Because of refraction

and dip, the azimuth should be noted when the center of the

Sun or a star is a little more than one Sun diameter (half a

degree) above the horizon. The Moon should be observed

when its upper limb is on the horizon.

Body at Rising or Setting: Except for the Moon, the

azimuth angle of a body is almost the same at rising as at

setting, except that the former is toward the east and the latter

toward the west. If the azimuth is measured both at rising and

setting, true south (or north) is midway between the two

observed values, and the difference between this value and

180

Direction is one of the elements of dead reckoning. A

deviation table for each compass, including any lifeboat

compasses, should already have been determined. In the

event of destruction or failure of the gyrocompass and

bridge magnetic compass, lifeboat compasses can be used.

If an almanac, accurate Greenwich time, and the

necessary tables are available, the azimuth of any celestial

body can be computed and this value compared with an

azimuth measured by the compass. If it is difficult to observe

the compass azimuth, select a body dead ahead and note the

compass heading. The difference between the computed and

observed azimuths is compass error on that heading. This is of

more immediate value than deviation, but if the latter is

desired, it can be determined by applying variation to the

compass error.

Several unique astronomical situations occur,

permitting determination of azimuth without computation:

Polaris: Polaris is always within 2

) is the compass error. Thus, if the compass

azimuth of a body is 073

(or 000

at rising, and 277

at setting, true

south (180

) is

-----------------------------

277

1 7 5

by compass, and the

E. This method may be in error if the

vessel is moving rapidly in a northerly or southerly direction.

If the declination and latitude are known, the true azimuth of

any body at rising or setting can be determined by means of

a diagram on the plane of the celestial meridian or by

computation. For this purpose, the body (except the Moon)

should be considered as rising or setting when its center is a

little more than one Sun diameter (half a degree) above the

horizon, because of refraction and dip.

Finding direction by the relationship of the Sun to the hands

of a watch is sometimes advocated, but the limitations of this

method prevent its practical use at sea.

A simple technique can be used for determining

deviation. Find an object that is easily visible and that

floats, but will not drift too fast in the wind. A life

preserver, or several tied together, will suffice. Throw this

marker overboard, and steer the vessel steadily in the exact

opposite direction to the chosen course. At a distance of

perhaps half a mile, or more if the marker is still clearly in

view, execute a Williamson turn, or turn the vessel 180

of true north for

observers between the equator and about 60

North. When

Polaris is directly above or below the celestial pole, its

azimuth is true north at any latitude. This occurs when the

trailing star of either Cassiopeia or the Big Dipper is

directly above or below Polaris. When these two stars form

a horizontal line with Polaris, the maximum correction

applies. Below about 50

latitude, this correction is 1

°,

and

. If Cassiopeia is to the right of

Polaris, the azimuth is 001

and 65

,itis2

), and if

Cassiopeia is to the left of Polaris, the azimuth is 359

(002

above 50

°N

(358

The south celestial pole is located approximately at the

intersection of a line through the longer axis of the Southern

Cross with a line from the northernmost star of Triangulum

Australe, perpendicular to the line joining the other two stars

of the triangle. No conspicuous star marks this spot.

Meridian Transit: Any celestial body bears due north

or south at meridian transit, either upper or lower. This is

the moment of maximum (or minimum) altitude of the

body. However, since the altitude at this time is nearly

constant during a considerable change of azimuth, the

instant of meridian transit may be difficult to determine. If

time and an almanac are available, and the longitude is

known, the time of transit can be computed. It can also be

graphed as a curve on graph paper and the time of meridian

transit determined with sufficient accuracy for emergency

purposes.

Body on Prime Vertical: If any method is available

for determining when a body is on the prime vertical (due

east or west), the compass azimuth at this time can be

observed. Table 20, Meridian Angle and Altitude of a Body

on the Prime Vertical Circle provides this information. Any

body on the celestial equator (declination 0

°N

the smallest practical radius, and head back toward the

marker. The magnetic course will be midway between the

course toward the object and the reciprocal of the course

away from the object. Thus, if the boat is on compass

course 151

while returning, the magnetic course is midway between

337

while heading away from the object, and 337

and 151

+ 180

= 331

, or

------------------------------ 334

331

° .

Since 334

magnetic is the same as 337

by compass, the

If a compass is not available, any celestial body can be used

to steer by, if its diurnal apparent motion is considered. A

reasonably straight course can be steered by noting the direction

of the wind, the movement of the clouds, the direction of the

waves, or by watching the wake of the vessel. The angle

between the centerline and the wake is an indication of the

amount of leeway.

)isonthe

prime vertical at the time of rising or setting. For the Sun

this occurs at the time of the equinoxes. The star Mintaka (

Orionis), the leading star of Orion’s belt, has a declination

of approximately 0.3

073

compass error is 5

between 50

above 50

337

deviation on this heading is 3

Chapt - 26.pdf

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: