Lectures in Navigation Part 22

_10. Distance to Destination_

The same remarks as are made under (9) hold true here.

_11. Set and Drift of Current_

Find the difference between your D.R. position and your position by observation at noon, i.e., the course and distance from your D.R.

position to your position by observation. The course is the set of the current, the distance the amount of drift, all of which is easily calculated by Table 2, Bowditch. This difference between the two positions is seldom due to current. It is due to all errors of steering and the like. But these are all ascribed to current, for the sake of convenience. This calculation of the current is seldom used now, particularly when steaming in convoy.

It is obvious that a schedule, such as outlined above, cannot be adhered to in all kinds of weather or under all conditions. It is merely an outline of what might properly be included in a 24 hour day, the weather conditions of which will lend themselves at any time to taking the observations mentioned. The weather of each succeeding day may force you to adopt a different routine. Nevertheless, the closer you can keep to the above schedule the more exact will your various positions be.

_(c) On Entering Pilot Waters_

See that all charts of the locality you intend to enter are corrected to date.

Study these charts carefully, making notes, in detail, of the aids to navigation that you intend to pick up.

In noting lights give their distinctive appearance, range of visibility, approximate time of sighting them, and any other information that you think you may need. If you have this information with you when on the bridge it will save much time and trouble that you would otherwise have to spend, at possibly a critical time, in the chart room.

See that log lines, sounding machine, etc., are in order for instant use.

Remember that in entering pilot waters the safest landmarks are permanent ones. Buoys, cans, etc., may drag from their positions or be lost altogether. This can also happen to lights.h.i.+ps.

Become familiar with soundings, rise and fall of the tides, and the like, in the neighborhood in which you intend to anchor. If possible choose an anchorage that will enable you to get bearings from two or three fixed points on sh.o.r.e. As soon as possible after anchoring secure your bearings by pelorus and have them checked up by the quartermaster at regular intervals. This will determine how much, if any, dragging has taken place.

Lastly, always remember that no amount of advice can make up for your own carelessness. Hold yourself ready for any emergency, keep cool, keep patient and keep pleasant. Common sense is the best antidote in the world for strange situations. If you have that, and the knowledge you should have secured from these lectures, you cannot go far wrong.

While the day's work which follows does not include every sight in regular sequence as given in the above discussion, it will give a fair idea of the navigator's work during a day's run. Put it in your notebook. (Note to Instructor:--Spend the rest of the period in explaining carefully each step of this example.)

A DAY'S WORK AT SEA

Departure taken from noon position Jan. 25th, 1919, in Lat.i.tude 30 01'

N, Longitude 73 47' 20" W. Course p.s.c. NE 3/4 N. Deviation 2 E.

Variation 4 W. Log registered 20. s.h.i.+p continued on this course until about 6:30 P.M. when log registered 98 and observed alt.i.tude of Star Rigel, East of meridian, 39 36' 20". WT 6h 33m 19s P.M. C-W 4h 55m 04s.

CC 2m 16s slow. HE 37 ft. IE 0' 20" off arc.

Changed course to 40 (true) and steamed until 3 A.M. when log registered 198. At this time s.h.i.+p ran into heavy NE gale. Slowed down to 7 knots per hour until about 8:30 A.M. when observed (_) 18 25' 10"

and bearing by compa.s.s S 46 E. Variation 7 W. WT 8h 31m 16s A.M. C-W 4h 55m 04s. IE + 0' 10". Same HE, CC.

s.h.i.+p then steamed on true course of 39 at 7 knots per hour until noon when log registered 261 and observed meridian alt.i.tude (_) 37 59' S.

Same IE (+ 0' 10"), HE, CC. Required:--

1. Position by D. R. at noon.

2. Position by observation at noon (corrected for Longitude by a factor).

3. Deviation of compa.s.s at 8:30 A.M.

4. Watch Time of Local Apparent Noon.

(See Next Page)

At Sea, Jan. 25, 1919. Lat. in 30 01' N Lo. in 73 47' 20" W Steamed until 6:30 P.M.

========================================== Course | Dist. | D. Lat. | Dep. | D. Lo.

------------------------------------------ N 35 E | 78 | 63.9 | 44.7 | 51.5 ==========================================

Lat. Left 30 01' N Lo. Left 73 47' 20" W D. Lat. 1 03 54 N D. Lo. 51 30 E ------------ ------------ Lat. in 31 04' 54" N Lo. in 72 55' 50" W Mid Lat. 30 30' N

---------------------------------------------------------------- At 6:30 P.M. Obs. * Rigel.

Obs. Alt. * 39 36' 20" W.T. 6h 33m 19s Log hav "t" 8.92502 E + 00 20 C.W. 4 55 04 Log cos Lat. 9.93269 ------------- C.C. 2 16 Log cos. Dec. 9.99544 39 36' 40" ----------- -------- HE - 7 09 G.M.T. 11h 30m 39s Log hav S 8.85315 Nat hav S .07130 ------------- (.).R.A. 20 14 58 Nat hav L--D .11349 T.C.A. * 39 29' 31" (+).C.P. 1 53.3 ------ ------------- ----------- Nat hav ZD .18479 Dec. of * 8 17' 42"S G.S.T. 31h 47m 30.3s 50 55' 00" ZD Lat. 31 04 54 N --W.Lo. 4 51 43 -90 00 00 ------------- ----------- ------------ L.~D. 39 22' 36" L.S.T. 2h 55m 47.3s 39 05' 00" C.Alt.

------------- *R.A. 5 10 41 39 29 31 T.Alt ----------- ------------ "t" 2h 14m 54s 24' 31" Alt. Diff. Toward.

[Ill.u.s.tration: TZ N 135 E, S 45 E]

================================================ Course | Dist | D. Lat. | Dep. | D. Lo.

------------------------------------------------ S45 E | 24.5 | 17.3 | 17.3 | 20 ================================================

Lat. Left 31 04' 54" N Lo. Left 72 55' 50" W 17 18 S 20 E ------------- ------------- Lat. in 30 47' 36" N Lo. in 72 35' 50" W

Changed course to 40 (true)

=============================================== Course | Dist | D. Lat. | Dep. | D. Lo.

----------------------------------------------- N40 E | 138.5 | 106.1 | 89 | 105 ===============================================

Lat. Left 30 47' 36" N Lo. Left 72 35' 50" W 1 46 06 N 1 45 E ------------- ------------- Lat. in 32 33' 42" N Lo. in 70 50' 50" W 8.30 A.M.

(_) 18 25' 10" W.T 20h 31m 16s Log hav "t" 9.28284 IE + 10 C-W 4 55 04 Log cos Lat. 9.92573 ---------- C.C. 2 16 Log cos Dec. 9.97595 18 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 32' 54" ----------- ------ G.A.T. 1h 16m 04s 71 30' 00" ZD Nat hav ZD .34135 Dec. 18 53' 24" S -W.Lo. 4 43 51 -90 00 00 Lat. 32 33 42 N ----------- ----------- ------------ L.A.T.(t) 20h 32m 13s 18 30' 00" C.Alt.

L~D 51 27 06" 18 32 54 T.Alt.

----------- 2' 54" Toward

[Ill.u.s.tration: TZ N 128 E S 52E]

=========================================== Course | Dist. | D.Lat. | Dep. | D.Lo.

---------|-------|--------|--------|------- S 52 E | 3 | 1.8 | 2.4 | 3 ===========================================

Lat. Left 32 33' 42" N Lo. 70 50' 50" W 1 48 S 3 E ----------- ----------- Lat. in 32 31' 54" N Lo. in 70 47' 50" W Bearing of Sun by Compa.s.s S 46 E True Bearing of Sun S 52 E ------- Total Error 6 W Variation 7 W ----- Deviation 1 E

========================================== Course | Dist. | D. Lat | Dep. | D. Lo.

---------+-------+--------+------+-------- N 39 E | 24.5 | 19 | 15.4 | 18.4 ==========================================

Lat. Left 32 31' 54" N Lo. Left 70 47' 50" W 19 N 18 24 E ------------ ------------ Lat. in 32 50' 54" N Lo. in 70 29' 26" W