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The improved ship channels into the Mississippi River are through South Pass and Southwest Pass. The following minor passes can only be used by small boats.

Main Pass has a depth of about 4 feet (1.2 m) over the bar at the Gulf entrance and about 5 feet (1.5 m) over the sill at the river entrance which is at Cubits Gap, about 3 miles above the Head of the Passes. In 1935 the passage over the sill was along the west shore, between the shore and an old barge sunk on the sill. The Gulf entrance to Main Pass is marked by Cubits Gap-Main Pass Light. Cubits Gap Light is just south of the Mississippi River entrance. This pass is used considerably by fishing vessels operating in Chandeleur and Breton Sounds.

Pass a Loutre divides at 41⁄2 miles below Head of the Passes and flows onward in two streams, the northern one still bearing the same name, while the southern is called Southeast Pass. Pass a Loutre divides again when nearly to the Gulf and discharges through two mouths, of which the southern this time is called Pass a Loutre and the northern, North Pass. Southeast Pass also branches when near the Gulf, and its northern branch is named Northeast Pass. These passes are deep from the Head of the Passes to within a short distance of the Gulf, but the mouths of all of them are obstructed by bars. In 1935, it was reported that 6 feet (1.8 m) could be taken into North Pass and about 3 feet (0.9 m) into Southeast Pass. These passes are used occasionally by small local craft but should not be attempted by strangers.

Pass a Loutre Beacon is a black and white spirally banded tower (unused lighthouse) on the north side of the pass and 2 miles inside the entrance; it is 76 feet high (23.2 m).

Northeast Pass Beacon is the grayish white tower of an unused lighthouse; it is about half a mile north of the pass and 2 miles west of the entrance to the pass.

The marsh lands south of Main Pass are used extensively for hunting and there are oyster camps about Redfish Bay.

Landmarks. The discolored water discharged from the Mississippi River is one of the first intimations to mariners approaching the passes of the proximity of land. This, however, cannot be depended upon to indicate distance, for with high-river stages and northerly winds discolored water will be met in some directions 60 miles or more from land, and the water will at times appear broken from 15 to 20 miles from the passes. The land near the entrances to the passes is low marsh covered with tall, coarse grass and weeds.

Approaching either South Pass or Southwest Pass, the lighthouses are the most prominent and easily recognized marks. To the east of each light there is an elevated water tank which is the next object recognized. The smoke from steamers in the passes is also a guide.

The wreck of a steamer lies 212 miles 344° true from Southwest Pass East Jetty End Light. As it is north of the shoal area off the West Jetty, its masts should not be taken for a ship in the pass.

Mud lumps, unstable mounds of earth of considerable extent, forced up by pressure underneath to a height of 2 to 8 feet (0.6 to 2.4 m) above the surface of the water, are frequently found within about a mile of the mouth of each pass and are said to be most numerous on the right side of each channel. They generally rise in a few weeks' time and then gradually wear away, though sometimes they subside even more quickly than they rise.

(26) TIDES AND CURRENTS

219

A speed trial course has been established about 4 miles east of Southwest Pass. The course is marked by four white can buoys, 1 mile apart, and by shore ranges at the ends of a measured nautical mile. The course bears 40° true (NE. by E. mag.). The shore ranges are opposite the two center buoys.

Fogs. From December to June fog may be encountered anywhere from 60 miles off the passes to the city of New Orleans. Southerly and easterly winds bring it in, and northerly and westerly winds clear it away.

Currents, Gulf of Mexico (see also p. 42).-The currents are variable in direction and velocity, depending at some seasons of the year upon the direction and velocity of the wind and, near the entrance to the passes, upon the stage of the river.

During February, March, and April the current runs to the southeastward with considerable strength, especially near the Tortugas, and it will be directly against a vessel most of the way on the course from there to the Mississippi River. During the rest of the year a countercurrent sets a little to the northward for the first 50 miles west of Tortugas. Then for 150 miles the main current runs to the southward and southeastward. For the next 100 miles there is an area of little movement, and for the last 125 miles, before reaching the mouth of the river, it runs strong to the east-northeastward.

During a light southerly wind a northeasterly set of 21⁄44 knots has been observed 13 miles southeast of South Pass entrance, and at the same time there was an easterly set of one-half knot at the lighted whistle buoy off the entrance.

At Southwest Pass lighted buoy the current is due chiefly to the discharge of the river. Its direction is southwesterly, and the velocity varies from 0 to 4 knots, the average being 1.7 knots.

Tides and currents, Mississippi River.-In the passes there is generally but one high and one low water in 24 hours, the extreme range being less than 1/2 feet. At New Orleans the tide is not noticeable. The current due to the tide is not strong at any point, and for purposes of navigation it is rarely taken into account. High river stages, usually occurring from April to July, decrease the effect of the tide. The average date of high river stage occurs in April and of low river stage in October. At New Orleans the extreme difference between high and low stages of the river is 21 feet; the mean difference is about 14 feet. The following table gives the velocity of the current in the river for the different months of the

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The greatest velocity in a given section is generally about one and one-third times the cross-sectional velocity. The velocities in the narrower portions of the passes are probably a little greater than those at the steamboat wharf at New Orleans.

At several places in the lower part of the river, countercurrents or eddies, are often found near the banks, which, if taken advantage of, can greatly assist vessels bound up the river.

At South Pass the river current frequently has an easterly set. At Southwest Pass it sets straight out from between the jetties, thence spreading out fan-shaped, with slightly greater velocity to westward.

SOUTH PASS

(Chart 1272)

South Pass, is one of the two important commercial entrances to the Mississippi River from the Gulf of Mexico. It lies 425 miles northwestward of Dry Tortugas and 90 miles southwestward of Mobile Bay entrance. It has been improved by the construction of jetties on both sides of the entrance and by dredging, so that there is a usual depth of 30 feet (9.1 m) or more throughout the length of the pass from the Gulf to the Head of the Passes, a distance of about 12 miles. The width of the pass varies from 600 to 850 feet; the width in the clear between the jetties at their ends is about 670 feet. Immediately outside the entrance the depths are subject to considerable change, due to the large amounts of sediment brought down by the strong river currents; but at a distance of 14 miles out from the end of the jetties the depths are more dependable, and 10 fathoms (18.3 m) can be found in any easterly or southerly direction.

In March 1936 there was a controlling depth of 32 feet (9.8 m) on the entrance range at the south entrance to the pass.

Lying between one-quarter and one-half mile off the end of the jetties on the west side of the channel is a dangerous shoal, marked by West Bank Lighted Bell Buoy 1, with depths of 7 to 17 feet (2.1 to 5.2 m) on it. Except for changes during and after high river stages, the position of and depths on this shoal are rather constant. This shoal, coupled with the strong currents coming out from the iver, makes the navigation of South Pass difficult for strangers without the aid of a pilot. A bend in the channel near the Head of the Passes also adds to the difficulty of navigating South Pass.

The approach to the entrance is marked by South Pass Lighted Whistle Buoy (vertical striped) 11⁄2 miles southeastward of the end of the jetties and by West Bank Lighted Bell Buoy 1 marking the shoal ground to the southwestward.

Two lighted ranges, South Pass West Jetty Range and South Pass Range, mark respectively the channel approaching and the channel through the entrance between the jetties, and South Pass East Jetty Light is located near the outer end of the east jetty. There is an air diaphone fog signal and a radiobeacon at South Pass West Jetty Front Light and these signals have been synchronized for distance findings, see page 27; also see Light List and H. O. Publication No. 205. At South Pass East Jetty Light there is a fog bell; it is operated every night from November 1 to April 30 and at all other times during foggy weather.

(26) RULES AND REGULATIONS

221

At Port Eads, 2 miles inside the entrance, there is a United States Navy Radio Direction Finder Station; call letter NBX.

South Pass (Rear) Lighthouse (Lat. 29°00'.9; Long. 89°10'.0), on the west bank 214 miles above the end of the jetties, is a white skeleton structure enclosing a cylindrical stairway. The light is flashing white (flash 1.5 seconds, eclipse 3.5 seconds), 108 feet (33 m) above the water, visible 16 miles.

The Pilots Station is a small settlement on the west bank about onehalf mile above the end of the jetties. Rates for bar pilotage are given on page 229.

Port Eads, situated 214 miles above the end of the jetties on the east bank, is a post office and headquarters for the construction force employed in the maintenance of the pass.

At the north end, the entrance into the pass from the Mississippi River is marked by Head of Passes West Jetty Light and Head of Passes East Jetty Light, on the west and east points respectively at the entrance, and by Cypress Lighted Range marking the entrance channel. There is an electric siren fog signal at the West Jetty Light. There was a controlling depth of 35 feet (10.7 m) through the north entrance to the pass in June 1935.

The following Rules and Regulations for the Navigation of South Pass, Mississippi River, have been prescribed for the protection of the pass and the works for its improvement.

1. Vessels descending South Pass may enter the pass at full speed, but, after passing Depot Bend Light shall reduce their speed so as not to exceed 12 miles per hour over the ground or from point to point, without regard to the velocity of the current or run of the tide. The limiting speed for ascending vessels, similarly measured, shall be 10 miles per hour.

2. Steamers, with or without tows, passing Port Eads, or any dredge or other floating plant working in or anchored in the Pass, shall reduce their speed to not more than 5 miles per hour over the ground if ascending, or 8 miles per hour if descending. In all other respects navigation shall conform to the War Department rules and regulations governing the display of signals on, and the operation of, all craft and accessories working on wrecks, engaged in dredging, surveying, or other work of improvement, and the use and navigation of the waters in the vicinity, in the Great Lakes and their connecting and tributary waters as far east as Montreal, the Red River of the North, and the rivers whose waters flow into the Gulf of Mexico, and their tributaries.

3. Vessels anchoring in the Pass shall take positions near the eastern bank, above a point marked by a post, painted white, which is about one-half mile above South Pass Lighthouse; and below a point 1 mile below the Head of the Passes Lighthouse; and vessels so anchoring shall put out such extra moorings as may be necessary to prevent their being blown athwart the channel and thus endangering the navigation of the Pass.

4. No vessel, except a towboat without tow, shall enter the channel between jetties from the sea until after any descending vessel which has been approached within 1 mile of the outer end of the jetties shall have passed to sea; and likewise, no vessel descending the river shall enter the channel at the head of the Pass until after an ascending vessel which has reached the Franks Crossing Light on right bank below Depot Bend, shall have passed through the entrance at the head of the Pass; also, no such vessel ascending the Pass shall pass Franks Crossing Light until after a descending vessel which has entered the channel into the head of the Pass has passed Depot Bend Light. 5. No vessel having a speed less than 9 knots shall enter South Pass from the Gulf when the stage of the Mississippi River exceeds a 15-foot reading on the Carrollton gage at New Orleans. Such vessels shall use the Southwest Pass. This regulation shall not apply when the Southwest Pass is not clear for safe navigation.

6. Ashes, oil, or other refuse matter shall not be thrown, dumped, or discharged in the Pass, nor in the Gulf of Mexico within a distance of 5 miles from the sea ends of the jetties.

7. Seagoing sailing vessels shall not sail down the Pass after dark, or up the Pass farther than the anchorages designated in paragraph 3.

8. After dark no tow shall consist of more than one vessel of any kind, whether steamer, sailing vessel, barge, or other craft, and during daylight no tow shall consist of more than two vessels of any kind, whether steamers, sailing vessels, barges, or other craft. Tows may be in any formation except that when towing on hawsers, the hawsers shall not be more than 50 fathoms in length. Tows will not be permitted to change formation once they have entered the Pass. When rough weather is to be anticipated in the Gulf of Mexico, down-bound tows will be made up on hawsers in the river before entering the Pass. When coming to anchor at the authorized anchorages, tows will use caution to avoid blocking the Pass for approaching vessels.

9. These regulations shall take effect June 1, 1931, and shall supersede those prescribed August 8, 1929, and subsequent amendments thereof.

Directions for South Pass are given on page 235

SOUTHWEST PASS

(Chart 1272)

Southwest Pass, the westernmost of the passes of the Mississippi River, is 19 miles west-southwestward of South Pass entrance and 280 miles eastward of Galveston entrance. It has been improved by the construction of jetties on both sides at the entrance and by dredging, and a least depth of 35 feet (10.7 m) is generally maintained from the Gulf throughout the length of the pass, a distance of 17 miles. The width of the pass varies between 1,200 and 2,800 feet, averaging 2,000 feet; the width in the clear between the ends of the jetties is 1,400 feet. Dredging is done as necessary to maintain the project depth. Near the end of the jetties the depths are somewhat changeable, but at all times there seems to be deep water in the Gulf from nearly every direction up to within three-fourths mile of the entrance.

In March 1936 there was a controlling depth of 39 feet (11.9 m) through Southwest Pass; in February 1936 the controlling depth on range at the head of Southwest Pass (Head of the Passes) was 34 feet (10.4 m).

A shoal with depths of 13 to 16 feet (4.0 to 4.9 m) extends along the west side of the approach channel for about a mile beyond the end of the west jetty. As at South Pass, the position of and depths on this shoal are rather constant except for changes during and after high river stages in the spring.

The approach to Southwest Pass is marked by Southwest Pass Entrance Lighted Whistle Buoy, 14 miles southward from the ends of the jetties. From this buoy, to abreast of Southwest Pass East Jetty End Light, the channel is marked by a lighted range (Southwest Pass Entrance West Jetty Range) and two lighted buoys, one on either side of the channel. Thence for a short distance the channel between the ends of the jetties is marked by a second lighted range (Southwest Pass Inner Range), succeeding the first range. The end of the first dike (A) near the end of the east jetty is marked by a light which is near the second channel range. A series of dikes has been constructed channelward from along the inner bulkhead of the east jetty.

The fog signal at Southwest Pass East Jetty End Light, which is at the end of the east jetty, is an electric siren. A fog bell at South

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