of this table the predictions given for the reference ports are extended so as to enable one to obtain the predictions for each day for a large number of other stations. Table 3 enables the height of tide at any time to be computed. Table 4 gives the time of the rising and setting of the sun. Table 6 gives the time of the rising and setting of the moon at certain places.

The effect of strong winds, in combination with the regular tidal action, may at times cause the water to fall below the plane of reference of the chart, mean low water. The water may also rise about the same amount above mean high water due to similar causes.

Caution. In using the Tide Tables, slack water should not be confounded with high or low water. For ocean stations there is usually but little difference between the time of high or low water and the beginning of ebb or flood current; but for places in narrow channels, land-locked harbors, or on tidal rivers, the time of slack current may differ by several hours from the time of high- or low-water stand. The relation of the times of high and low water to the turning of the current depends upon a number of factors, so that no simple or general rule can be given. To obtain the times of slack water, reference should be made either to figures given for various places in this volume of the Coast Pilot or to the Current Tables.

Current Tables for the Atlantic Coast of the United States are published in advance annually by the United States Coast and Geodetic Survey. This volume includes the daily predicted times of slack water and the times and velocities of strength of flood and ebb for certain reference stations and a table of current differences and constants by means of which corresponding daily predictions may be readily obtained for numerous other places. Tables for the velocity of current at any time, duration of slack, and rotary tidal currents at certain offshore locations, together with data on the Gulf Stream and wind currents are included. There are also current diagrams for six bodies of water along the coast, which show in a graphical form the velocities of the flood and ebb currents and the times of slack and strength over a considerable stretch of the channel of these waterways. These tables are for sale by the Coast and Geodetic Survey, Washington, D. C., and by authorized sales agencies; price

10 cents.

Tidal Current Charts in four volumes at 25 cents per volume_are published by the United States Coast and Geodetic Survey for Boston and New York Harbors, San Francisco Bay, and Block Island and Long Island sounds. These current charts are good for any year and show the direction and velocity of the tidal current for each hour of the current. They present a comprehensive view of the tidal current movement of the area as a whole and also supply a means of readily determining the direction and velocity of the current at various localities throughout the area.

CURRENTS, SANDY HOOK TO CAPE HENRY

The following statements are deducted from current observations which have been made at the lightships along this section of the coast and from other sources:

Tidal currents. These are rotary in character, generally turning clockwise, with minimum velocities three hours after strength of

121767°-37-4

flood and ebb in a direction at right angles to that at the time of strength. When not influenced by the larger bays or rivers, such as Delaware River, Chesapeake Bay, and New York Bay, these tidal currents are weak, averaging about 0.2 knot at strength, the direction of the flood and ebb at strength being on and off shore, respectively. In the immediate vicinity of the larger bays or rivers, the direction of flood and ebb at strength is directly in and out, and the strength of the current is increased, depending on the proximity of the mouth. These three rivers and bays affect the direction of the tidal currents to a distance of about 20 miles from their entrances, but the strength of the offshore current is not affected until within a few miles of the mouth.

Wind currents (see also p. 45).-Moderate to heavy winds set up strong currents in a direction about 20° to the right of the wind, reversing or greatly accelerating the normal currents; in fact, the principal currents along this stretch of coast, when away from the larger bays, are the wind currents. Their strength and set depend on the direction, strength, and duration of the wind.

Offshore currents. Observations made offshore have developed the existence of weak tidal currents, veering around the compass, similar in character to those inshore, although of less strength. These are accompanied by a general drift in a southerly to southwesterly direction, amounting to about 1/4 of a knot; this extends from about the 20-fathom curve out nearly to the Gulf Stream.

The following is a more detailed statement of the observations made at several localities. The wind currents are of more importance than the tidal currents, and the two must be combined in making allowance for set. (See Current Tables, Atlantic Coast).

Ambrose Channel Lightship. The tidal currents have a mean velocity of about 14 knot at strength of flood or ebb, the flood setting in a westerly and the ebb in an easterly direction. The strength of flood occurs about 1 hour before time of high water at Sandy Hook, and the strength of ebb about 1 hour before time of low water at Sandy Hook. Wind velocities of 10 to 25 miles produce currents of about 0.5 to 1 knot, setting about 20° to the right of the wind. The greatest observed velocity of the current was about 1.4 knots during a gale.

Latitude 38°58′ N., longitude 74°31′ W. (off the entrance to Delaware Bay). The tidal currents have a mean velocity of 14 knot at strength of flood or ebb, the flood setting in a northwesterly and the ebb in a southeasterly direction. The strength of flood occurs about 134 hours earlier than the strength of flood at Overfalls Lightship (or about 234 hours earlier than the time of high water at Sandy Hook). The strength of ebb occurs about 1 hour earlier than the strength of ebb at Overfalls Lightship (or about 22 hours earlier than the time of low water at Sandy Hook). Wind velocities of 10 to 30 miles produce currents of about 0.5 to 0.9 knot, setting about 20° to the right of the wind. The wind current must be combined with the tidal current in making an allowance for set. The greatest observed velocity of the current was 1.2 knots during a 50-mile-an-hour gale. Overfalls Lightship. See currents, Delaware Bay (p. 80). Latitude 38°25' N., longitude 74°46′ W.-The tidal currents have a mean velocity of about 14 knot at strength of flood or ebb, the flood

setting in a northerly direction and the ebb in a southerly direction. The strength of flood occurs about 1/2 hour later than the strength of flood at Overfalls Lightship (or about 1/2 hour before the time of high water at Sandy Hook), and the strength of ebb occurs approximately at the same time as at Overfalls Lightship (or about 14 hours before the time of low water at Sandy Hook). Wind velocities of 10 to 30 miles produce currents of about 0.5 to 1 knot, setting about 20° to the right of the wind. This wind current must be combined with the tidal current in making an allowance for set. The greatest observed velocity of the current was 2 knots during a 60-mile-an-hour gale.

Winter Quarter Shoal Lightship. The tidal currents are weak and rotary, the normal velocity being about 0.1 knot throughout the day. Observations indicate a southerly set of about 0.1 knot. The greatest observed velocity of the current was about 2 knots during a northeast gale.

Gulf Stream. For data concerning this unique and important current see either United States Coast Pilot, Atlantic Coast, Section D, Cape Henry to Key West, 1936, pages 32 to 36 or United States Coast Pilot, Gulf Coast, Key West to Rio Grande, 1936, pages 45 to 49.

WIND CURRENTS

There are given below the results of recent investigations on the currents caused by local winds. These investigations are based on observations made on a number of the lightships along the Atlantic coast from Nantucket Shoals Lightship to Brunswick Lightship. The results, therefore, apply more directly along the route between lightships but are applicable also to the coastal sailing routes farther offshore.

Direction of current due to wind.-It is evident that a wind continuing for some time will give rise to a current, the velocity of which increases with an increase in the velocity of the wind; and the mariner has taken it for granted that this current brought about by the wind sets in the same direction as the wind. But the results of careful observations show that this is not the case. Instead of setting with the wind, the current on the Atlantic coast of North America produced by local winds sets on the average about 20° to the right of the wind.

For example, a wind blowing from north will, on the North Atlantic coast, bring about a current that sets not south but about 20° to the right of south, or 200°. Similarly a wind from south will produce a current setting 20° to the right of north, or 20°. It is to be noted that while the current due to the wind will, on the North Atlantic coast, set 20° to the right of the wind direction, the current which a vessel experiences at any time is the resultant of the combined action of the tidal current, the wind current, and any other currents, such as the Gulf Stream or currents due to river discharge. Velocity of current due to wind.-The velocity of the current brought about by winds of different velocities is given in the table below. It will be seen that on the Atlantic coast of the United States the velocity of the wind current is about 12 percent of the velocity of the wind.

Table of current velocity due to wind-North Atlantic coast

An easily remembered working rule to get the velocity of the current due to wind along the Atlantic coast is to multiply the velocity of the wind (in miles per hour) by 12 and point off two places. This will give the velocity of the current in knots. For example, to determine the current due to a 40-mile wind we have 40×112=60, and pointing off two decimal places gives 0.60, or six-tenths of a knot. The maximum velocities likely to occur during storms at the following offshore localities are Ambrose Channel lightship, 11⁄2 knots; Five-Fathom Bank North Lighted_Whistle buoy 2 FB, 112 knots; Overfalls lightship, 31⁄2 knots; Fenwick Island Shoal Lighted Whistle buoy 2, 2 knots; Winter Quarter Shoal Lightship, 2 knots; and Tail of the Horseshoe Lighted Whistle buoy TH, 3 knots.

INLAND WATERWAYS

The following data concerning the Intracoastal Waterway, from Boston to the Rio Grande, the Route across Florida, the New York Canal System, the Lakes to Gulf Waterway, and the other river channels tributary to the Mississippi are included for ready reference.

THE INTRACOASTAL WATERWAY

The Intracoastal Waterway affords a protected route, with the exception of various sections, for vessels between Boston, Mass., and the Rio Grande, a distance of approximately 3,100 miles. No toll is charged for passage as the waterway is under Federal jurisdiction. Navigation is restricted, however, by the limiting depths, and horizontal and vertical clearances in the various sections of the waterway. The minimum width for the entire route is 40 feet. The locks in the alternate route through the Dismal Swamp Canal have a width of 37 feet and a length of 225 feet. The height of the masts of vessels is restricted by an overhead power cable at Socastee, South Carolina, to 74 feet (22.6 m) at normal low water and 67 feet (20.4 m) during freshets, allowing 3 feet for a factor of safety against high voltage current with conditions of dampness or sleet.

Boston to New York Harbor.-Between Boston and Long Island Sound it is necessary to pass through comparatively exposed waters and no inland route exists except for the passage through the Cape Cod Canal and its approaches.

The Cape Cod Canal extends from Cape Cod Bay to Buzzards Bay and with its approach channels affords a sea-level waterway 12.6 miles in length. The controlling depth in December 1936 was 23 feet (7.0 m) and the minimum channel width was 205 feet. The vertical clearance through the canal is 135 feet (41 m).

From the canal, the route generally followed extends from Buzzards Bay to the Atlantic Ocean, thence through Block Island and Long Island Sounds and the East River to upper New York Bay,

thence through the more open waters to lower New York Bay. There are numerous harbors on both sides of Long Island Sound.

An inland waterway extends along a portion of the south side of Long Island and affords a protected route from Gardiners Bay to East Rockaway Inlet with a controlling depth of 4 feet (1.2 m). New York Harbor to Delaware Bay.-An outside run between New York Bay and Delaware Bay is now necessary. Vessels whose draft permits use of the New Jersey Inland Waterway (described in the Inside Route Pilot New York to Key West) may shorten the run outside. This waterway is entered at its northern end through Manasquan Inlet, 23 miles south of Sandy Hook, and extends for 99 nautical miles to Cape May Inlet at Cape May. The waterway is maintained by the State of New Jersey as a 6-foot (1.8 m) project, but the controlling depth in April 1936 was reported to be 4 feet (1.2 m). Vessels are obliged to run outside from Sandy Hook to Manasquan Inlet, and to round Cape May and cross the lower reaches of Delaware Bay to the Chesapeake and Delaware Canal.

The Intracoastal Waterway formerly extended from New York Bay through the Raritan River, the Delaware and Raritan Canal, and the Delaware River to Delaware Bay. The Delaware and Raritan Canal, now under the jurisdiction of the State of New Jersey, has not been open to navigation since 1933.

Delaware Bay to Norfolk.-The Chesapeake and Delaware Canal (see p. 309) is a sea-level route which extends for a distance of 19 miles, from Reedy Point on the Delaware River 40 miles below Philadelphia, Pa., to the junction of Back Creek and Elk River, about 4 miles west of Chesapeake City, Md. There are no locks. The vertical clearance is 140 feet (43 m). It was reported in 1936 that vessels with a draft up to 12 feet (3.7 m) could use the canal. Dredging is in progress to increase the depth to 27 feet (8.2 m). From the junction of the canal and Chesapeake Bay to Norfolk, a distance of 210 miles through Chesapeake Bay, depths in excess of 12 feet (3.6 m) obtain.

Norfolk to Beaufort, N. C.-A sea-level waterway, paralleling the Atlantic coast, with a tidal lock at Great Bridge, Va., is afforded by the route through the Albemarle and Chesapeake Canal, the Alligator River-Pungo River Canal, and the sounds of North Carolina. The project for this waterway provides a depth of 12 feet (3.6 m) at mean low water, but the controlling depth was 11 feet (3.4 m) in September 1936.

The alternate route to Albemarle Sound by way of the Dismal Swamp Canal, a lock canal, had a controlling depth of 7 feet (2.1 m) in September 1936.

Navigation is practicable throughout the year on both of the above-named routes.

Beaufort, N. C., to Winyah Bay.-In September 1936 there was a controlling depth of 12 feet (3.7 m) from Beaufort Harbor to the Cape Fear River, thence 8 feet (2.4 m) to Little River, and thence 6 feet (1.8 m) to Winyah Bay.

Winyah Bay to Charleston. The project depth is 10 feet (3.0 m). The controlling depth in November 1936 was about 7.8 feet (2.4 m) but dredging to remove shoaling was under way.

Charleston to the St. Johns River, through the rivers and sounds of South Carolina and Georgia.-The project depth through the main