페이지 이미지
PDF
ePub

storm of small diameter, and a gradual fall would indicate the contrary.

Fourth.—The following table, from Piddington's Sailors' Hornbook, page 252, may be of service in aiding the Navigator to decide how to act under peculiarly trying circumstances, where a risk has to be taken to save the ship, and when the question of distance from the center becomes the most important factor in the solution of the problem:

TABLE. Average fall of barometer

Distance in miles per hour:

from center:
From 0.02 in to 0.06 in

From 250 to 150
From 0.06 in to 0.08 in

From 150 to 100
From 0.08 in to 0.12 in

From 100 to 80
From 0.12 in to 0.15 in

From 80 to 50 APPEARANCE OF THE WEATHER.—The indications of the approach of a cyclone do not differ materially from those of the ordinary gale; but a few such, as a hard steel-gray sky, or having a greenish tint, a blood red or bright yellow sunset, a heavy swell unaccounted for in any other way, and a thick lurid appearance of the sky, may be regarded in connection with a general threatening appearance of the weather, and particularly with a restless state of the barometer, as significant signs of a more than ordinary gale, and, whether seen separately or together, ought not to be disregarded.

BEARING OF CENTER, NORTH LATITUDE.—Having reason to suppose, from the action of the barometer and from the general appearance of the weather, that a revolving storm is near at hand, determine at once the bearing of the center. To do this, look in the wind's eye.

Then, if the ship is in the north latitude, the center bears eight points to the right of the wind point, or on the right hand, because in the northern hemisphere the currents of air within the storm disc move from right to left; that is, from north to west to south, and over east to north, &c., left-handed (in nautical parlance, against the sun), or in the opposite direction to the hands of a watch, looking at its face; and hence, at the north point of the storm circle the wind is east and the center bears south; at the west point of the storm circle the wind is north and the center bears east, always 90° or eight points to the right of the wind point.

BEARING OF CENTER, SOUTH LATITUDE.—But if in south latitude, the center bears eight points to the left of the wind point, or on the left hand, because in the southern hemisphere the currents of air within the storm disc move from left to right; that is, from north to east to south, and over west to north, &c., righthandled (with the sun), or in the same direction as the hands of a watch, looking at its face. Hence, at the north point of the storm circle the wind is west and the center bears south; at the east point of the storm circle the wind is north and the center bears west, &c., always 90° or eight points to the left of the wind point.

SEMICIRCLES OF STORM Disc.-The storm disc is divided into two equal parts by the line of the axis of the storm track, and the portion lying on the right side of this line (looking in the direction of the storm track) is termed the right semicircle, while the other half, or that portion lying on the left of the line, is called the left semicircle.

In the right semicircle the change of wind will be to the right; that is, from north toward east, from east toward south, from south toward west, &c., and the first change of wind will therefore indicate that the ship is in the right semicircle. Then put the ship on the starboard tack.

In the left semicircle the change of wind will be to the left; that is, from north toward west, from west toward south, &c., which will in like manner indicate that the ship is in the left semicircle. Then put the ship on the port tack.

The rule for the determination of the semicircle and the tack to heave-to on applies equally to all parts of the world; and if it be remembered that the name of the semicircle, the direction of the change of the wind, and the tack to heave-to on, all three correspond to the same side of a given line, we may reduce all that is necessary to remember, in order to place the ship in a safe position in the storm disc, to six words. Doing which, we should have:

"Right"....(Semicircle). For Right Semicircle. "Right".... (Wind changes to the right).

“Starboard" (Tack to heave-to on).

“Left”. . (Semicircle). For Left Semicircle, { "Left”. (Wind changes to the left).

"Port". .. (Tack to heave-to on). ON THE STORM TRACK Run BEFORE THE WIND-A vessel directly on the track of the storm, or near it on either side would not experience any perceptible change of wind, but would have a falling barometer and rapidly-increasing severity of the weather, if in front of the storm; and a rising barometer, with a gradual moderation of the weather, if in rear of the storm center.

If the ship be put before the wind and steered in one direction for a few hours, she will, if the storm be a revolving storm, change the wind, and reveal by this change the semicircle of the storm into which she has run.

To ASCERTAIN THE DIRECTION OF THE STORM TRACK BY IN. SPECTION.-In Piddington's Sailors' Hornbook, charts are found upon which are projected the tracks of a number of storms in the Atlantic and Indian Oceans and the China Seas, including the Bay of Bengal and a portion of the Pacific. An inspection of these charts will show that storms in particular localities generally travel in the same direction, and, ordinarily, the probable course of a storm may be found by inspection from one of these charts, the approximate position of the ship being known. But, as there is no absolute certainty that every storm will pass over the beaten track, no opportunity to verify the tracks on the charts or to ascertain by observation the approximate course of the storm should be neglected.

To Ascertain the Direction of the Storm by Observation The approximate direction of the storm track may be found by plotting the positions of the ship and center on two or more consecutive bearings, using an estimated distance on the first bearing, and keeping an accurate account of the ship's way during the interval between the bearings. It follows here, as a matter of course, that the greater the angle between the bearings used the better the results obtained by this method.

To obtain satisfactory results from any of the foregoing methods of observation the ship should be hove-to. Having determined the position of the ship in the storm disc, and the approximate direction of the storm's forward movement on its track, the Navigator may intelligently so dispose his vessel as to incur the minimum amount of danger or reap the maximum attainable advantage, as the case may be.

If it be necessary to distance the center or to run out of the storm disc, the following rules should be observed:

NORTHERN HEMISPHERE. Right SEMICIRCLE.—Haul by the wind on the starboard tack and carry sail as long as possible; if obliged to heave-to, do so on starboard tack.

LEFT SEMICIRCLE.—Bring the wind on the starboard quarter. Note the direction of the ship's head and steer that course. If obliged to heave-to, do so on port tack.

ON THE STORM TRACK. IN FRONT OF THE CENTER.-Square away and run before it. Note the course and keep it, and trim the yards when the wind draws on the starboard quarter. If, however, obliged to heave-to, do so on port tack.

IN REAR OF THE CENTER.-Run out with wind on starboard quarter, or heave-to on starboard tack.

SOUTHERN HEMISPHERE. RIGHT SEMICIRCLE.-Bring wind on the port quarter. Note the course and keep it. If obliged to heave-to, do so on starboard tack.

LEFT SEMICIRCLE.-Haul by the wind on the port tack. Carry sail as long as possible, and if obliged to heave-to, do so on port tack.

ON THE STORM TRACK. IN FRONT OF THE CENTER.-Run before it. Note the course and keep it, and trim the yards as the wind gradually hauls on the port quarter. If obliged to heave-to, do so on the starboard tack.

IN REAR OF THE CENTER.—Run out with the wind on port quarter, or heave-to on port tack.

A rise in the barometer, improvement of the weather, and a gradual abatement of the force of the wind, will result from the above maneuvers; and the ship should in each case be kept on her course until by these signs it is made evident that she is out of danger.

All the above maneuvers depends, of course, on sea-room and the ability to carry sail. If sail can not be carried or land interferes the ship should be hove-to on the starboard tack in the Right Semicircle, and on the port tack in the Left Semicircle, and never otherwise.

A vessel lying-to on the port tack in the left semicircle in the Northern Hemisphere, and on the starboard tack in the right semicircle in the Southern Hemisphere, lies with her head toward the storm center, but there is no danger in this; as hoveto she will not head-reach to any great extent, and will therefore not approach the center so as to endanger the safety of the ship. A vessel so disposed comes up to the sea with every shift of wind and will ride out the gale safely, whereas if she is on the opposite tack she is headed off by every shift of wind and will eventually bring the sea on the beam and quarter, in which position, even if she does not founder, she is certainly likely to receive serious damage from the sea.

A vessel finding herself in a favorable place in the storm circle may safely run along with the storm in the following positions:

To Profit by the Storm.

NORTHERN HEMISPHERE. ist. In rear of center on the line of its axis. Wind on port beam.

2d. Anywhere in the right rear quadrant. Wind on port side abaft the beam.

3d. Abreast and to the right of the center. Wind aft.

SOUTHERN HEMISPHERE. Ist. In rear of center on the line of its axis. Wind on starboard beam.

2d. Anywhere in the left rear quadrant. Wind on starboard side abaft the beam.

3d. Abreast and to the left of center. Wind aft.

« 이전계속 »