Imágenes de páginas
PDF
EPUB

approaching the point if traveling with the current, or after passing the point if traveling against the current. But it is difficult to conceive of any agency which could redeflect that current to the eastward after it had passed a point which had already caused it to swing off to the west, although such conditions would undoubtedly cause a local eddy current of considerable extent.

There are, however, some reasons for believing that the phenomena which have been observed are caused by currents which originate well offshore and flowing in strike the coast and are deflected to the north or south. This theory would explain the fact, already noted, that currents are so frequently encountered in relatively calm weather. It would also explain the fact that vessels have frequently experienced a considerable set directly inshore caused by currents acting so squarely across the track that they had no effect on the speed made good. Sets of this character appear to be particularly frequent between Heceta Bank and Cape Arago, between Trinidad and Cape Mendocino, and off Monterey Bay.

Under the conditions above described, it is absolutely necessary to take soundings for safe navigation on this coast in thick weather. It is the method which has been relied upon by the men who have navigated the coast in safety for years; its neglect has contributed directly to the great majority of the strandings which have occurred. In modern practice, the continuous chain of soundings obtained by a vessel, equipped with a reliable echosounding apparatus, will be found most useful in laying down on the chart the track made good by the vessel. (See Appendix, p. 339, under paragraph "Soundings.") Radio bearings (see p. 12) greatly reduce the dangers incident to navigation but the use of these should not lead the navigator to neglect sounding.

The master must assume the possible existence of a current which is setting his ship into danger, and take his precautions accordingly. The vessel's progress should be verified by an occasional sounding on each course where the depths permit, and in approaching each important danger or turning point soundings should be taken frequently for some time both before and after the change of course, unless in the meantime a reliable fix has been obtained. The soundings after the change are of the greatest value as revealing any error in the reckoning on which the change of course is based, and it may conservatively be stated that had such soundings been taken the great majority of the past disasters would have been prevented.

Navigation by means of soundings renders imperative a careful study of the chart. The navigator must learn what, for any given locality, are the critical characteristic features revealed by his lead which insure his safety or indicate the proximity to danger. What depths to follow and what to avoid; localities where soundings may be taken to advantage to obtain a check on the position; information revealed by the character of the bottom; and perhaps most important of all, as being the condition most likely to cause trouble even for the careful navigator, certain areas which duplicate the critical depths of the track, so that if the former were mistaken for the latter the result might be most serious; all these are items of the utmost importance.

Since the safety of all concerned must frequently depend on the soundings alone, it is essential that to the operation should be devoted a degree of skill and care commensurate with its importance. It is usually impossible for the master to give his personal attention to the task, but he should see that the man to whom he intrusts it is so carefully trained and so impressed with the importance of his duty that a mistake is next to impossible.

There is a method in common use on the coast of sounding without using pressure tubes, the depth being estimated from the amount of wire out. Such a method is perhaps justified for every other cast while feeling for the bottom as the vessel approaches soundings from deep water, but once the bottom has been picked up it should never be trusted. There are too many factors to be considered, and all of them uncertain and variable; the speed of the ship, the smoothness with which the reel is working, and, above all, the "personal equation" of the operator. He will be too much influenced by the depths which he thinks he should find. If he expects bottom in 30 fathoms (55 m) he will pay out the wire so slowly that he probably will not find the bottom in a depth of 60 or 70 fathoms (110 or 128 m). If he expects 80 to 100 fathoms (146 to 183 m) he may get bottom in 25 or 30 fathoms (46 or 55 m) and never know it. The records clearly show that this method of sounding has resulted in the loss of vessels through mistakes which could not have gone undetected if a tube had been used.

So, for every wire sounding taken while the ship is underway, a pressure tube should be used, and the lead should be armed to bring up a sample of the bottom. The amount of wire out should, of course, be reported, for that does give a general idea of the depth some moments before the tube can be reeled in. But this estimated depth should be verified by the tube and the sample of bottom obtained should be compared with that shown on the chart.

Finally, it is important to realize that under certain conditions pressure tubes are subject to considerable errors, with which the navigator should be familiar if he is to get full value for them.

The introduction of radio direction finder stations ashore, and of radio-compasses on board ship, have given the navigator additional ways of determining his position with a fair degree of accuracy, but sounding should never be neglected. A vessel equipped with an echo-sounding apparatus, may depend largely upon continuous soundings to furnish accurate information as to the vessel's position. Due to the fact that there are certain conditions under which radio bearings may be subjected to grave error, the additional check of sounding in critical places should be carried out. One of the worst disasters of recent years on the Pacific coast was due in part to the erroneous interpretation of a radio bearing received from a shore station.

The Coast Highway extends close along the shore in numerous places along the entire length of the Pacific coast. The navigator should take care not to confuse headlights of automobiles with aids to navigation.

[blocks in formation]
[blocks in formation]
[blocks in formation]

1, 027 1, 163 1, 2091, 1951, 217 1, 189 1, 2241, 2441, 273 87 175 284 369 566 615 674 729 744 761 793 849 899 942 1, 078 1, 124 1, 1101, 132 1, 1041, 139 1, 1591, 188 532 591 646 661 678 710 766 816 902 846 859 995 1, 041 1, 0271, 0491, 0211, 056 1, 076 1, 105 452 511 566 581 598 630 686 736 822 766 779 915 961 947 969 941 976 996 1, 025 96 293 342 4011 456 471 488 520 576 626 712 656 669 805 851 837 859 831 866 886 915 232 281 340 395 410 427 459] 515 565 651 5951 608 7441 790 63 124 180 195 212 244 300 350 436 380 393 529 67 124 139 156 188 244 294 380

[blocks in formation]
[blocks in formation]
[blocks in formation]
[blocks in formation]
[graphic]

1 Via Deception Pass.

2 Via Admiralty Inlet.

3 Cape Flattery to Balboa, Canal Zone, 3,908 miles.

DESCRIPTIONS AND SAILING DIRECTIONS

DIRECTIONS, SAN DIEGO TO THE STRAITS OF FUCA

Vessels may use the following directions, which give approximately the track followed by the high-powered steamers plying regularly between San Diego, Los Angeles, San Francisco, Columbia River, and Puget Sound ports. These courses are used by such vessels in preference to others farther off shore by reason of the fact that they lead well within range of the various fog signals and insofar as possible over depths where the lead may be used to obtain a check on the position.

Low-powered local steamers usually keep close inshore, following, in general, the curves of the land, in order to escape the full effect of wind and sea. In clear weather strangers may readily follow this inshore track by means of the chart; in thick weather they are advised not to use it, as the fog signals are few and far apart, and the currents variable and uncertain, making detailed local knowledge essential to safety. For that reason no directions for this track are given.

A detailed description of the coast, including landmarks, dangers, etc., follows these directions, beginning on page 33.

SAN DIEGO TO LOS ANGELES AND TO SAN FRANCISCO

Courses and distances

(Abbrevations: Pt., Point; Lt., Light; Id., Island; t., true; dist., distant) No. 1. San Diego to San Francisco (charts 5101, 5102, 5302, 5402)

[merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

SAN DIEGO TO LOS ANGELES AND TO SAN FRANCISCO-Continued

Courses and distances-Continued

No. 2. San Diego to Los Angeles (charts 5101, 5102)

[merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

No. 3. Los Angeles to San Francisco (charts 5202, 5302, 5402)

[blocks in formation]

The following brief summary of the methods actually employed in thick weather, by the ablest masters on the coast, indicates the methods and precautions by which safety is assured.

Northbound. From San Diego to Los Angeles (see table No. 2, above) the conditions are seldom such as to cause any deviation from the track. If uncertain of the position in approaching San Pedro Bay, steer so as to make sure of being to the eastward of the Point Fermin breakwater. Continue to a depth of 10 fathoms (18.3 m), and then haul to the westward in that depth, and the fog signal (siren) will be made without difficulty. There is a detached breakwater extension under construction eastward of the Point Fermin breakwater. The bell buoys set in 8 fathoms (14.6 m) and marking the ends of the detached breakwater may be heard in approaching the entrance.

Bound for San Francisco, the departure is taken from Los Angeles Lighthouse, and the buoy at Point Fermin and Point Vicente Light are made close-to. Crossing toward Anacapa Island, the possibility of a northerly current setting into Santa Monica Bay should be borne in mind. There is a diaphone fog signal at Anacapa Lighthouse.

Having made Anacapa Lighthouse, there are no dangers until approaching Point Conception. Here sounding should be relied upon to guard against an inshore set, and the depths should not be shoaled to less than 50 fathoms (91 m). From Point Conception, Point Arguello will readily be made.

The track from Point Arguello to Point Sur is a long one, on which currents of considerable velocity are frequently encountered, and to the southward of Point Sur depths of over 100 fathoms

« AnteriorContinuar »