IE + 10 C-W 4 55 04 Log cos Lat. 9.92573
---------- C.C. 2 16 Log cos Dec. 9.97595
18 deg. 25' 20" ----------- -------
HE + 7 34 G.M.T. 1h 28m 36s Log hav S 9.18452 Nat hav S .15294
---------- Eq.T - 12 32 Nat hav L~D .18841
-()- 18 deg. 32' 54" ----------- ------
G.A.T. 1h 16m 04s 71 deg. 30' 00" ZD Nat hav ZD .34135
Dec. 18 deg. 53' 24" S -W.Lo. 4 43 51 -90 00 00
Lat. 32 deg. 33 42 N ----------- -----------
------------ L.A.T.(t) 20h 32m 13s 18 deg. 30' 00" C.Alt.
L~D 51 deg. 27 06" 18 32 54 T.Alt.
-----------
2' 54" Toward
[Illustration: TZ N 128 deg. E S 52 deg.E]
===========================================
Course | Dist. | D.Lat. | Dep. | D.Lo.
---------|-------|--------|--------|-------
S 52 deg. E | 3 | 1.8 | 2.4 | 3
===========================================
Lat. Left 32 deg. 33' 42" N Lo. 70 deg. 50' 50" W
1 48 S 3 E
----------- -----------
Lat. in 32 deg. 31' 54" N Lo. in 70 deg. 47' 50" W
Bearing of Sun by Compass S 46 deg. E
True Bearing of Sun S 52 deg. E
-------
Total Error 6 deg. W
Variation 7 deg. W
-----
Deviation 1 deg. E
==========================================
Course | Dist. | D. Lat | Dep. | D. Lo.
---------+-------+--------+------+--------
N 39 deg. E | 24.5 | 19 | 15.4 | 18.4
==========================================
Lat. Left 32 deg. 31' 54" N Lo. Left 70 deg. 47' 50" W
19 N 18 24 E
------------ ------------
Lat. in 32 deg. 50' 54" N Lo. in 70 deg. 29' 26" W
_At Noon._ L.A.T. 00h 00m 00s
(_) 37 deg. 59' S + W. Lo. 4 41 58
-----------
IE + 10 G.A.T. 4h 41m 58s
------------ E.T. (sign reversed) + 12 34
37 deg. 59' 10" -----------
HE 8 55 G.M.T. 4h 54m 32s
17
----------
-(-)- 38 deg. 08' 22" S
51 deg. 51' 38" N (ZD)
18 51 12 S (Dec.)
----------
33 deg. 00' 26" N. Lat. in at Noon.
Lo. Factor = .93 Lat. by Obs. 33 deg. 00' 26" N
Lat. Diff. 9.5 Lat. by D.R. 32 deg. 50' 54" N
------ ------------
Diff. Lo. 8.83 Lat. Diff. 9' 32"
Since Obs. Lat. is East of D.R. Lat. on Line of Pos.
Lo. Diff. is applied East.
/ Lo. by D.R. 70 deg. 29' 26" W
/ Lo. Diff. 8 50 E
Obs. Lat. * ------------
/ Lo. in at Noon 70 deg. 20' 36" W
D.R. Lat. *
/
/
_By Dead Reckoning from Noon to Noon_
===========================================================
Course | Dist. | D. Lat. | Dep. | D. Lo.
----------+---------+-----------+--------+-----------------
N 35 deg. E | 78 | 63.9 | 44.7 | 176' or 2 deg. 56'
N 40 deg. E | 138.5 | 106.1 | 89. |
N 39 deg. E | 24.5 | 19. | 15.4 |
| | ----- | ---- |
| | 189. | 149.1 |
===========================================================
Lat. left. 30 deg. 01' N Lo. left 73 deg. 47' 20" W
3 09 N 2 56 E
--------- -------------
Lat. in 33 deg. 10' N Lo. in 70 deg. 51' 20" W
Min. Lat. 31 deg. 35'
The Watch Time of Local Apparent Noon
Date--Jan. 26, 1919
G.A.T. of A.M. Sight 1h 16m 04s
Lo. in T. of A.M. sight 4 43 12
-----------
L.A.T. 20h 32m 52s
Total Time to Noon 3h 27m 08s
Course to Noon -- 39 deg.
Change in Lo. per hr. -- 5.2', 21s
3600s + 21s = 3621s
3 X 60 = 180
27
-----
207
60
------
12,420
08
--------
3621 ) 12,428 (3.43 hrs
10,863
------
15,650
14,484
------
11,660
10,863
------
3.43 hrs = 3h 25m 48s
W.T. of A.M. sight 8 31 16 A.M.
----------
W.T. of L.A.N. 11h 57m 04s A.M.
ANSWER.
_By D.R._
Lat. 33 deg. 10' N Lo. 70 deg. 51' 20" W
_By Observation_
Lat. 33 deg. 00' 26" N Lo. 70 deg. 20' 36" W
_Dev. at 8:30 A.M._
1 deg. E
_W.T. of L.A.N._ 11h 57m 04s A.M.
FRIDAY LECTURE
DAY'S WORK
At sea, November 28th, 1918. Departure taken at noon in Latitude 20 deg. 50'
N, Longitude 73 deg. 15' 20" W. Log at noon registered 34. Sailed on course
p.s.c. 73 deg., Deviation 3 deg. E, Variation 1 deg. W until twilight when log
registered 152.
Changed course to E 3/4 N p.s.c. and observed altitude of Star
Aldebaran, East of meridian 37 deg. 10' 10" and bearing by compass N 89 deg. E,
Variation 2 deg. W. WT 8h 10m 16s. C-W 4h. 51m 30s. CC 4m 08s slow. IE 1'
10" off the arc. HE 38 ft.
Ship steamed on this course, in heavy fog and rain, until 2:30 A.M. when
log registered 200. Ship changed course to E 1/2 N (true) and steamed at
8 knots per hour until 6:30 A.M. when weather cleared and observed
altitude Star Polaris 21 deg. 04' 20" N. WT 6h 35m 47s A.M. C-W 4h 51m 30s.
Same IE, HE and CC.
Ship continued on same course and speed until about 9:30 A.M. when
observed altitude of (_) 38 deg. 45' 20". WT 9h 39m 10s A.M. C-W 4h 51m 30s.
Same IE, HE and CC.
Ship then steamed a true course of 93 deg. at a rate of 10 knots per hour
until noon when log registered 294 and observed meridian altitude (_)
46 deg. 49' 30". Same IE, HE and CC.
Required 1. D. R. position at noon.
2. Position by observation at noon (corrected for Longitude by a
factor).
3. Deviation at 8:10 P.M.
4. Watch Time of Local Apparent Noon.
SATURDAY LECTURE
DAY'S WORK
At sea, April 21st, 1918. Departure taken from noon position in Latitude
31 deg. 50' N, Longitude 76 deg. 30' 31" W. Log registered 128 at noon.
Course p.s.c. until about 4:30 P.M. was N 10 deg. E. Deviation 1 deg. W.
Variation 3 deg. W. At about 4:30 P.M. observed altitude of sun's lower limb
25 deg. 13' 10" and bearing by compass N 87 deg. W. WT 4h 26m 46s. C-W 5h 04m
52s. CC 1m 03s slow. IE 0' 10" off arc. HE 29 ft. Log registered at this
time 188.
Course was then changed to NE x N (true). Weather cloudy. At about
twilight clouds broke away and observed altitude of Star Procyon West of
meridian 40 deg. 01' 00". CT 1h 37m 28s A.M. CC 1m 03s slow. IE 0' 10" off
arc. HE 29 ft. Log registered 236. Continued on same course until
midnight, at which time log registered 290. At midnight ship ran into
dense fog and slowed down to 8 knots until about 6:30 A.M., when fog
blew away and observed altitude of Star Polaris 35 deg. 29' 10" N. WT 6h 32m
14s A.M. C-W 4h 59m 02s. IE 0' 10" off arc. CC 1m 03s slow. HE 29 ft.
From 6:30 A.M. ship steamed a true course of N 32 deg. E until noon at a
rate of 15 knots per hour, at which time a meridian altitude of the (_)
was observed 65 deg. 37' 10" S. Log registered 424. HE 29 ft. IE 0' 10" off
arc. CC 1m 03s slow.
Required 1. D. R. position at noon.
2. Position by observation at noon (corrected for Longitude by a
factor).
3. Deviation of Compass at 4:30 P. M. sight.
4. Watch Time of Local Apparent Noon.
WEEK VIII--NAVIGATION
MONDAY LECTURE
DAY'S WORK
At sea, Nov. 12th, 1918. Departure taken from noon position in Latitude
39 deg. 40' N, Longitude 33 deg. 20' 04" W. Log registered at noon 1. Course
p.s.c. was 294 deg. until about 3:30 P.M., Deviation 1 deg. W, Variation 24 deg. W,
at which time observed altitude (_) 13 deg. 55' 10" and bearing by pelorus S
79 deg. W. WT 3h 22m 18s. C-W 2h 13m 20S. CC + 1m 10s. IE 1' 10" off arc. HE
32 ft. Log registered 46.
Course was then changed to 290 deg. p.s.c. until about 6:30 P.M. when
observed altitude Star Polaris 40 deg. 15' 40" N. WT 6h 32m 18s. C-W 2h 13m
20s. Same HE, IE, CC. Log registered 90.
Ship steamed on same course until 1:30 A.M. when log registered 196. At
1:30 A.M. sighted sub. on port bow. Ordered full speed ahead and made 17
knots per hour until 8 A.M. when observed altitude (_) 8 deg. 40' 00". WT 8h
01m 30s A.M. C-W 2h 13m 20s. Same HE, IE, CC.
Ship then steamed a true course of 272 deg. at a rate of 15 knots per hour
until noon, at which time observed meridian altitude (_) 32 deg. 35' 40" S.
Same HE, IE, CC. Log registered 362.
Required 1. D. R. position at noon.
2. Position by observation at noon (corrected for Longitude by a
factor).
3. Deviation of Compass at 3:30 P.M.
4. Watch Time of Local Apparent Noon.
TUESDAY LECTURE
DAY'S WORK
At sea, Dec. 10th, 1918. Departure taken from Latitude 19 deg. 50' N,
Longitude 20 deg. 01' 20" W. Noon position. Log registered 20. Course p.s.c.
N 16 deg. E. Deviation 2 deg. E, Variation 18 deg. W. Ship steamed on this course
until 8 P.M. when changed course to N 18 deg. E p.s.c. and observed altitude
Star Polaris 22 deg. 33' 14" N. WT 8h 09m 10s. C-W 1h 20m 05s. CC 2m 00s
fast. IE none. HE 39 ft. Log registered 104. Ship then steamed at 14
knots per hour until midnight. At midnight changed course to N 14 deg. E
p.s.c. and steamed at 12 knots per hour until 4 A.M. At 4 A.M. slowed
down to 9 knots per hour and steamed at that rate until 8:30 A.M. when
course p.s.c. was changed to N 17 deg. E and observed altitude (_) 22 deg. 40'
30". WT 8h 34m 16s A.M. C-W 1h 20m 05s. Same IE, HE, CC. Sun bore by
compass S 65 deg. E, Variation 18 deg. W. Continued on this course p.s.c. for
two hours, speed 12 knots. Thence steamed a true course of 4 deg. at same
speed to noon when observed meridian altitude (_) 42 deg. 36' 50" S. Same
IE, HE, CC.
Required 1. D. R. position at noon.
2. Position by observation at noon (corrected for Longitude
by a factor).
3. Deviation of Compass at 8:30 A.M.
4. Log reading at noon.
WEDNESDAY LECTURE
DAY'S WORK
At sea, July 19th, 1918. Departure taken from Latitude 40 deg. 30' N,
Longitude 45 deg. 00' 10" W. Noon position. Log registered at noon 68.
Steamed until 2:30 P.M. on a course p.s.c. 115 deg.. Deviation 1 deg. W.
Variation 25 deg. W. Log registered 125. Changed course to 118 deg. p.s.c. (Same
Variation and Deviation) and steamed until about 5 P.M. At about 5 P.M.
observed altitude (.) 22 deg. 40' 20" and bearing by pelorus N 55 deg. W. WT 5h
01m 16s. C-W 3h 00m 02s. IE 2' 20" on arc. CC 3m 32s slow. HE 32 ft. Log
registered 168. Course p.s.c. was then changed to 113 deg. until about 8
P.M. when observed meridian altitude of Star Vega 88 deg. 15' 10" S. WT 8h
02m 26s. C-W 3h 00m 02s. Same HE, IE, CC. Log registered 210. Continued
on same course p.s.c. until about 2 A.M. when observed altitude of Star
Vega 47 deg. 19' 20" West of meridian. WT 2h 04m 24s A.M. C-W 3h 00m 02s.
Same IE, HE, CC. Log registered 299. TZ of Star N 86 deg. W. Continued on
same course until 4 A.M. when log registered 329.
At 4 A.M. heavy fog and rain forced ship to slow down to 5 knots per
hour until about 9 A.M. when weather cleared and observed altitude (_)
51 deg. 52' 40". WT 9h 03m 18s A.M. C-W 3h 00m 02s. Same HE, IE, CC. Thence
ship steamed a true course of 88 deg. at a rate of 13 knots per hour to
noon, when log registered 394 and observed meridian altitude (_) 69 deg. 52'
20" S. Same IE, HE, CC.
Required 1. D. R. position at noon.
2. Position by observation at noon (corrected for Longitude by
a factor).
3. Deviation of Compass at 5 P.M.
4. Watch Time of Local Apparent Noon.
THURSDAY LECTURE
DAY'S WORK
At sea, Nov. 25th, 1918. Departure taken at noon from Latitude 25 deg. 05'
N, Longitude 37 deg. 10' 40" W. Log registered at noon 32. Course p.s.c. was
119 deg., Deviation 2 deg. E, Variation 19 deg. W until twilight when log registered
110 and observed altitude Star Polaris 25 deg. 30' 40" N. IE 1' 10" off arc.
HE 28 ft. WT 5h 40m 18s. C-W 2h 28m 11s. CC 4m 15s slow. Changed course
to SE x E 3/4 E, same Variation and Deviation, and steamed on this
course until about 8:30 P.M. when observed altitude of Star Markab,
West of meridian, 59 deg. 48' 10". Log registered 157. WT 8h 34m 48s. C-W 2h
28m 11s. Same HE, IE, CC. Steamed on same course until midnight when log
registered 210. Changed course to 110 deg. p.s.c. (same Variation and
Deviation), and steamed at 12 knots speed until about 8 A.M. when
observed altitude (_) 23 deg. 05' 10" and bearing by compass S 33 deg. E.
Variation 19 deg. W. WT 8h 04m 10s, A.M. C-W 2h 28m 11s. Same HE, IE, CC.
Continued on same course p.s.c. at a speed of 15 knots per hour until
noon when observed meridian altitude (_) 44" 30' 50" S. Same IE, HE, CC.
Log registered 366.
Required 1. D. R. position at noon.
2. Position by observation at noon (corrected for Longitude by a
factor).
3. Deviation of compass at 8:04 A.M.
4. Watch Time of Local Apparent Noon.
ADDITIONAL LECTURE
COMPASS ADJUSTMENT
The aim of this lecture is to give you a very few facts about magnetism
in general and compass adjustment in particular. The reason for
including the lecture in this book is because of repeated requests on
the part of graduates who have been consulted about the adjustment of
the compass on their ships and who have realized that their advice might
have been more helpful if they had learned more about the matter while
at this school.
The earth is a huge magnet. It is the effect of the magnetism in the
earth upon the compass needle which causes the compass error and makes
it necessary to correct it. How can it be corrected? To know that we
must first know the fundamental law of magnetism, namely, that opposite
poles of two magnets attract each other and similar poles repel each
other. From which it follows that if we decide to color red, for
instance, that end of a magnetic needle which points to North, the
magnetism of that part of the earth must be considered blue, i.e., of
opposite magnetism to the north-seeking end of the red magnetic needle.
Now, there are various kinds of magnetism which affect a ship's compass.
One is from the earth, another from the iron in the ship, etc. To
discuss them and, the theoretical cause of them in detail is beyond the
scope of this lecture. To correct them, four sets of magnets are
necessary, two of which are usually found in the binnacle of the compass
itself. One is a fore and aft magnet or set of magnets, the other an
athwartship magnet or set of magnets. The third set consists of the two
globes of cast iron placed on either side of the compass bowl (called
Quadrantal Correctors). The fourth magnet, or set of magnets, is to
correct the compass in case of severe heeling by the ship.
If you are ordered to adjust the compass the first thing to do is to
choose a fine day with smooth water. Take your ship to a certain spot,
the exact location of which you have found from the chart, and where
you are certain you will have plenty of sea-way in which to swing. Set
your watch to local apparent time (which you have calculated before
coming out). Take from the Azimuth Tables the sun's true bearing for
every four minutes of the time during which you will be occupied
adjusting, and convert it into the magnetic bearing by applying the
variation at the place selected (secured from the chart). Write down in
a small book these times and corresponding magnetic bearings.
Now go to your compass and see that its lubber line is exactly fore and
aft and in the keel line of the ship. Have another officer who is
thoroughly familiar with the pelorus stand by it as the ship is swung.
All being ready, secure the lubber's point of the pelorus at North and
clamp the sight vane to the sun's magnetic bearing at the time you have
figured to take the first heading. Starboard or port your helm until at
the time calculated the reflection of the sight vane on the pelorus dial
cuts on the proper magnetic bearing. The vessel's head will then be
pointing to magnetic North. If, now, the compass were correct it would
agree with the pelorus in showing the ship's head to be North. If it
does not do so, there is Deviation in the compass and its amount is the
amount of Deviation on that particular course. Suppose the Deviation
were to starboard, i.e., Easterly, and were due to magnetism in the
ship's starboard side. Then, if the magnetism in the North end of the
needle be considered red, the magnetism in the starboard side of the
vessel, in order to attract the red end of the needle, would be
considered blue and the ship's magnetism, with the compass needle
included, would look like this:
[Illustration]
To counteract this blue attractive force on the starboard side, screw up
the athwartship magnet in the binnacle toward the compass dial. Its
magnetism, if it were laid on the deck, would look like this:
[Illustration]
In other words, as this magnet is moved nearer the compass needle, by
the law of magnetism just given, the red end of the magnet repels the
red end of the compass needle from the starboard side and the blue end
of the magnet attracts the red end of the compass needle toward the port
side. When the compass needle points to North, as shown by the correct
pelorus bearing, the Deviation on this heading (i.e., North) is
corrected.
Now turn the lubber line of the pelorus to East. Steady the ship on this
heading until the shadow from the pelorus vane at the proper L.A.T. cuts
the circumference of the pelorus dial at the proper magnetic bearing.
The ship's compass should then show the ship's head pointing to East.
Suppose that it does not (as will usually be the case) but points to the
right of East. Then the ship's magnetism and compass would look like
this:
[Illustration]
To bring the compass needle back to North it would be necessary to move
up nearer the compass dial the fore-and-aft magnet (shown below), whose
magnetism would act on the compass needle on this heading of the ship
exactly as the athwartship magnet acted on the compass needle when the
ship was headed North:
[Illustration]
Now the ship's compass has been corrected for the North and East
headings respectively. The next correction is for the heading half way
between, i.e., North-east. If there is any Deviation on this heading,
adjust the cast iron cylinders (called Quadrantal Correctors), which are
on each side of the compass bowl, by moving them toward or away from the
compass until the ship's head by compass is North-east at the proper
time and bearing by pelorus.
The ship's compass has now been corrected for one whole quadrant,
namely, from North to East, and this will suffice for all four quadrants
since the relationships of the magnets themselves and the magnetism of
the compass needle is the same for any of the other three quadrants as
for the first. Compass adjustment, however, can never be absolutely
accurate. For that reason, it is wise to steam the ship completely
around, steadying on every fifteen degrees by pelorus to determine and
keep a record of remaining errors.
There is one more correction to make, i.e., for the heeling error. This
correction is necessary in case the ship is yawing in a sea-way so much
that the relationship of the ship's magnetism to the compass needle is
decidedly different from what it is when the ship is on a comparatively
even keel. It is compensated by a vertical magnet directly underneath
(or over) the binnacle, details in regard to which can be secured from
Bowditch Art. 125, p. 53.
It must be borne in mind that compass adjustment is not an exact
science, that an adjustment for one latitude is not correct for another,
that anyone of a hundred different causes can affect the magnetism of
the ship or of the compass needle, which in turn directly affects the
Deviation. In this connection, it would be well to read Bowditch Art.
129, p. 55. You should also read Arts. 119-130 in which are given, more
fully and in more scientific language, the contents of this lecture.
End of Project Gutenberg's Lectures in Navigation, by Ernest Gallaudet Draper