GETTING ON SHORE-LEAKING
The student is referred for more detailed information on this subject to Qualtrough’s “Sailor’s Handy Book,” where it is treated with special reference to yachts and yacht sailing.
We shall confine our attention chiefly to the two principal types of fore-and-afters peculiar to the waters of the United States, viz.: the two masted schooner, Fig. 515, Plate 123, and the sloop.
The Schooner has a fore and aft foresail and mainsail, both usually laced to booms and gaffs and attached to hoops on their respective masts. It has also a fore and main gaff topsail, triangular in shape, the luff attached to the topmast by hoops; the sails furling aloft at the lower masthead.
The head sails of coasting schooners are variously named according to the position of the stays.
When the forestay goes to the bowsprit cap, or nearly to it, the first head sail from inboard is thejib, beyond which are the flying jib and outer jib.
But if the forestay sets up at or near the knightheads, the sail set upon it is called the fore staysail, and the others are the jib, flying jib, and outer jib.
An additional jib, on the fore topmast stay, is called a jib topsail. Its tack lashing may have a long drift to enable the sail to hoist above the other jibs.
It will be seen from the above that the jib of a schooner is that sail whose tack is nearest to the bowsprit cap.
In our description of manoeuvres, &c., we assume the inner head sail to be a fore staysail.
The staysail sheet and fore and main sheets have their lower blocks strapped to a thwartship traveller. This traveller for the main sheet is a short bar of iron, and for the other sheets extends across the deck, and for the staysail sheet may be a wooden spar. Stout tail ropes or clew-ropes for the staysail and foresail enable those sails to be held to windward, if necessary, in tacking.
The foresail may be a combination of “boom and lug,” in which case the forward part of the foot has the usual
|The offshore cable A is taken in through the offshore sheet hawse pipe.The offshore quarter mooring B is taken to the mooring shackle under the mizzen chains; C and D, the inshore moorings, are similarly secured. There may be also additional breast fasts, as at E and F.|
The ship is kept clear of the wharf, which is the side on which the moorings are usually the tautest, by means of spur shores as in the figure. These consist of heavy spars, the inshore end supported on trucks. The outboard end is made to bear against the ship’s side by a chain passing through a score in the heel of the shore, or better through the shore itself between the ship and the trucks, so that the chain will not foul the latter. The ends of the chain are secured to piles; a tackle may be clapped on one end of the chain.
The outboard end of the spur shore should take upon a saucer hung from the ship’s side. This outer end should
|have a bolt on top for a tackle, to hang the shore if the ship is forced from the wharf; also used to haul the spur shore into position. Hauling into a Dry Dock. The ship at A has her bow warp run to the head of the dock and|
|forward breast lines fast to piles. A tug has a line to A’s port quarter and is in the act of pointing her. This is done at or near slack water.At B the ship is nearly in the dock. Her bow warp, with which she is hauling in, is fast to a pile at the head of the dock.|
Forward and after breast lines or check lines are fast to piles. The vessel is kept in position by slacking these check lines from time to time. They are passed up the dock from pile to pile as the vessel advances.
Backing a Vessel into a Slip. Steamboat men acquire great skill in handling their boats about
|wharves, by availing themselves of the properties of the spring and the power of the engines. Let A represent a fixed point. By steaming ahead it is evident that the line AB will spring the ship’s head around in the direction of the dotted line.In the same manner, by backing, will AB1 spring her stern around the point A as a centre.|
Again, let it be required to back a steamer into a narrow slip. By the use of a quarter spring on starboard quarter, and backing the engines, the ship may be made to turn on her centre as in the above cut. A line from the starboard bow carefully tended prevents her from swinging off too much.
Should it be required to get the ship A to the wharf at B, back the engine, when the starboard bow line will bring the
|ship alongside the wharf, and by checking the line handsomely, she may be brought to the berth required.Taking a, Vessel in Tow, in Port. Tugs when towing in strong tideways or crowded harbors always make fast alongside the tow, and usually as far aft as possible.|
Before the tug comes alongside, make preparations on board the tow by getting out fenders, unshipping gangway ladders, tending braces, running in guns, and topping up boats as may be necessary. Have hands stationed to receive the heaving lines.
The lines used by the tug are the towline proper, or spring, from the bow of the tug to the quarter of the tow; the bow line, from the bow of the tug to a point well forward on the tow; also two breast fasts from the bow and quarter of the tug to points directly abreast on the tow. In backing, the bow line has a good lead to give the necessary sternboard to the tow. In giving a rank sheer with the helm, the bow, or quarter, breast fast (as the case may be) will keep the tug in position and prevent her sheering away from the tow.
If the screw of the tug is right-handed, she will make fast to the port side of the tow, circumstances permitting.
In this position the tug will make a much straighter sternboard if obliged to back, and in going ahead under port helm (the weak helm) she will control the tow more effectually than if on the starboard side.
In towing a vessel of the Trenton class in the East River a tug of the Catalpa size (200 tons) would use an 8-inch spring, 8-inch bow line, and 6-inch breast fasts. The same tug, towing the Galena, would not need larger lines than 6-inch for spring and bow line.
The method of towing alongside is not used at sea, unless in very smooth water. In attacks on fortified places it has been used to great advantage.
If it is desired to tow from ahead, the tow having been notified, will send her hauling lines aboard when you have taken up a position ahead. Steamers have bitts to make fast their tow ropes. The vessel towed will take them either to the bitts or capstan.
In taking a vessel in tow from an anchorage, the towing steamer may be forced to anchor ahead of the ship to be towed, and the latter will first heave up (the hawsers being secured), and then the towing steamer.
The latter when ahead should use a bridle. The bridle lessens sheering, which might result in carrying away the dolphin striker or head stays.
THE TURNING POWERS OF SHIPS.*
In a calm and in smooth water when a steamer is advancing on a straight course, with uniform speed, the action of a very small disturbing force will deflect her from that course. As soon as the helm is put over and an unbalanced pressure is developed on the rudder the vessel begins to turn.
Her angular motion is gradually accelerated as the helm angle is increased, and after the helm is hard over. After reaching its maximum the angular motion becomes uniform, and thereafter if the helm and revolutions of the engines remain unaltered the vessel continues to swing around through equal angles in equal times. Where there is powerful mechanical steering gear this condition of uniform
|circular motion is quickly reached, probably by the time a ship has swung through 360° or even a less angle from the original course.With manual power at the helm, similar uniformity of angular motion is not obtained until the ship has completed two or more circuits, the longer time in putting the helm over accounting for the difference.|
The curve traversed by a steamer in making a complete turn of 360° brings her somewhere within the true circle by a distance varying (other conditions being equal) with the amount of time required in putting the helm over.
In Fig. 1 the vessel has started to turn at P
* From “Lecture on the Turning Powers of Ships,” by W. H. White, R. N., and the discussion by Capt. Colomb, R. N., and others of the said lecture. Reprinted from the Journal of the Royal United Service Institution in Navy Scientific Papers, No. 7.
|PE is defined as the tactical diameter, or the distance between the two positions when the original course is reversed.At C, when a curve of 90° has been described, of which PG and GC are the coordinates:|
GC is the advance, or distance that the ship has moved in the direction of her original course.
PG is the transfer, or distance that the ship has moved in the direction due to the position of the helm.
Then, if O is the centre of the final circle, FD is the final diameter.
These are the elements of the curve so far as space is concerned, and what should be known for every ship is the advance, and the transfer up to 90° and the tactical diameter. The elements of time required are the time which it takes the ship to go from P to C, and to pass from C to D, and consequently the time from P to D.
The determination of the tactical diameter corresponding to various revolutions of the screw and various helm angles for individual ships is also of value. This is especially true where vessels of different sizes and types are assembled for combined movements under steam. In such a squadron, each vessel must know by experiment the number of revolutions which will give the same speed as a given number of revolutions of the flagship’s screw. In like manner, each ship must know the value of her helm angles, relative to the helm angles of the flagship, and of other vessels of the squadron.
Drift Angle. Fig. 1 assumes that when the centre of gravity of a ship has turned through a path of 90°, the line of keel has also altered 90° in direction. But as a matter of fact the centre of gravity will have turned 90° some time before it reaches C.
The drift angle, which represents this difference, is the angle between a tangent to the path of the ship’s centre of gravity and the keel line.
As the ship commences her turn, the drift angle will be an increasing quantity until uniform motion is reached.
In Fig. 2 the motion of rotation is assumed to have become uniform. The centre of gravity is then moving in a circle, and the keel line of the ship will make a constant angle with the tangent to that circle.
A represents the bow and B the stern of the ship. C shows the position of the centre of gravity on the keel line AB. O is the centre of the circular path in which C, A and B are moving. T T1 is the tangent to the path (G1, C, G2)
|of the centre of gravity and the angle ACT is the drift angle.The value of the drift angle varies considerably in different vessels and in the same vessel under different conditions of speed and helm angle. In the Thunderer, for example, with a constant helm angle but with varied speed, the angle was as follows:|
The drift angle increases:
(a.) With increase in speed when the helm angle and rudder area are constant.
(b.) With rudder area and helm angle, speed being constant.
In any given time the head of the ship must have turned through an angle from the original course which exceeds the angle turned through by the centre of gravity, by a quantity equal to the drift angle.
In Fig. 2, if P is the foot of a perpendicular from the centre 0 upon the middle line of the ship A B, then to an observer on board, P will appear to be the “pivot point” about which the angular motion of the ship is being performed; for the keel line A B coincides with the tangent to the path of the point P, which is not true of any other point on the keel line. Hence, at P, there is no drift angle.
In the case of the Thunderer, the pivot point P varied from 67 to 103 feet before the centre of gravity, or from 80 to 40 feet from the stern. As the speed and drift angle increased the pivot point moved forward.
To the drift angle is due the loss of speed sustained by a ship in turning. In several cases where this loss has been carefully measured, the speed of advance on the circular path has been only seven or eight tenths of the speed on the straight. The drag of the rudder has little to do with this loss of speed.
Glancing once more at Fig. 2, it will be evident that at each instant while the propelling force is delivered along or parallel to the keel line the actual motion of the vessel in turning is not directly ahead, but sideways.
In fact, the motion bears a considerable resemblance to that of a vessel sailing on a wind, and there is a considerable pressure developed on the side of the bow most distant
|from the centre O. This pressure not only checks the speed of the ship, but exercises a decided turning effect, assisting the pressure on the rudder. The importance of this assistance will appear more clearly when it is remembered that owing to the rotary motion of the vessel while turning, the flow of water at the stern is different, even in screw steamers, from that which would take place before the angular motion became marked. In fact, the effective helm angle becomes very much reduced from the angle RBD, Fig. 2, which the rudder makes with the keel line AB, produced. We have no exact data for estimating the amount of this reduction, but it approaches to equality with the drift angle for the rudder axis B. If OB is joined, and BQ drawn perpendicular to it, then the effective helm angle, according to this rule, should be taken as approximately equal to RBQ, and not to DBR, or a reduction of at least one-half from the angle made with the keel line, even in single-screw ships. Approximately the pressure on the rudder may be expressed as a function of the speed of the ship, and the sine of the effective angle of helm; so that the loss of rudder pressure consequent upon such a reduction in the effective angle as is asserted to take place will be very considerable. Apart from exact measures of the reduction, there can be no question as to the fact; and it is one of the matters upon which further experiments might well be made. With the assistance of a dynamometer to register the strains on the tiller end when the helm is first put over, and after the turning motion has become uniform, it would be an easy matter to discover the variations in the effective helm angle if the revolutions of the engines and speed of the ship were also observed.Heeling. The amount of heeling which accompanies turning is credited generally to the rudder pressure, whereas that effect may in most cases be neglected in comparison with the centrifugal force.|
A fair approximation to the angle of heel for a ship in turning is given by the following equation:
sin θ = 1/32 x d/m x v2/R
θ = angle of heel,
In the Thunderer, the centre of lateral resistance was found to be from .43 to .49 of the mean draught below the water line; probably a fair approximation for war ships of
|ordinary form would be from .45 to .5 of the mean draught. From the foregoing equation it will be seen that-The angle of heel varies:|
(1) Directly as the square of the speed of ship;
Hence it is obvious that ships of high speed, fitted with steam steering gear, capable of turning on circles of comparatively small diameter, are those in which heeling may be expected to be greatest. Moderate values of the meta-centric height further tend to increase the heeling. If the speed bedoubled, the angle of heel will be about quadrupled, if the radius of the circle turned and the metacentric height remain constant.
It is important to notice, that in taking observations of the angle of heel for a ship in turning, allowance must be made for the effect of the centrifugal force upon the indications of pendulums or clinometers. The error of indication is always in excess, and the correction is very easily made when the diameter of the circle and time of turning have been ascertained.
As the guns of a ship may be laid for simultaneous firing by director when the ship is on a straight course and on an even keel, and fired when the ship is under the influence of her helm, it may be of considerable importance to know what heel is to be expected for a given speed and_ helm angle, to adjust the director and lay the guns accordingly.
Helm Angles. Other things being equal, the rapidity with which a ship turns increases as the time of putting the helm over is diminished, and the diameter of the circle is also influenced. In the case of a British ship, where other conditions were almost unchanged, a steam steering gear was fitted, and the time in putting the helm hard over reduced from ninety seconds to twenty seconds. The time occupied in turning the circle was reduced from eight and one-half minutes to a little over seven minutes, and the diameter of the circle was reduced from 970 yards to 885 yards.
Before steam steering gear became common, equipoise rudders furnished the best means of putting a large rudder area over quickly to a great angle. But now that mechanical appliances are available, ordinary rudders hung at their forward edge are once more preferable, because they are less liable to derangement and more suitable for use in ships having sail as well as steam power,
Other things being equal, the turning effect of a rudder increases with an increase in the helm angle up to 40° or 45° with the keel line.
As illustrating the latter point, Admiral Sir Cowper Key found that the “Delight” gunboat behaved as recorded
|in the following table when the helm angle alone was varied: |
Lieutenant Coumes, of the French navy, gives the following results for the ironclad corvette Victorieuse, for an initial speed of about twelve and one-half knots:
Commander E. M. Shepard, of the U.S.S. Enterprise, reported the following for an initial speed of eight knots, being two-thirds power:
Tactical and Final Diameters. At present the published information of the ratio of tactical to final diameters is very limited, but for all practical purposes the determination of tactical diameters is the more important.
With manual power and ordinary rudders the tactical diameter for large ships has been found to vary between six and eight times the length of the ships.
For small vessels, where manual power suffices to put the helm over rapidly and the speed is low, the diameter falls to three or five times the length. For very long and swift torpedo boats, with manual power and small angles of helm, the diameter for full speed is as much as twelve times the length, and for half speed about four to six times the
|length. With manual power and balanced rudders the diameter for large ships has been reduced to four or five times the length; and nearly equal results have been obtained with ordinary rudders worked by steam or hydraulic steering gear. About three times the length is the minimum diameter ever obtained in large ships turning under the action of their rudders.*Effect of Twin Screws. Twin screws are now frequently adopted in the most powerful war ships, and their efficiency as propellers recognized. But they have the further advantage of enabling a vessel, by reversing one of her screws while the other drives her ahead, to turn in a very small circle, almost in her own length. The rate of turning is often slow under these circumstances, but the power of giving rotation to a ship practically destitute of headway and with a rudder possibly disabled, is of great value.|
With regard to the turning effect of twin screws when working in opposite directions, in deep-draft ships the time occupied in turning is usually greater than the time for turning the circle with both screws working ahead at full speed; whereas for shallow-draft ships the corresponding difference in time is small. For example, in the Captain, the time for circle at full speed ahead was five minutes twenty-four seconds; that for circle with screws working in opposite directions, six minutes fifty-two seconds. In the shallow-draft gunboats of the Medina class, on the other hand, the full-speed turning trial gave about three minutes six seconds for the circle, and with screws working in opposite directions the time was only three minutes thirteen seconds. It will be obvious that in the shallow-draft ships the ratio of the moment of resistance to rotation to the turning moment of the screws is much less than the corresponding ratio for deep-draft ships.
With ordinary rudders the use of twin screws does not appear to interfere with the efficient action of the rudder when both screws are working ahead, as compared with that in single-screw ships; experience has shown that equipoise rudders are not desirable features in twin-screw ships. With steam or mechanical steering gear the use of equipoise rudders is, on other grounds, not preferable; so that this feature in the use of twin screws is of comparatively small importance.
Exercises under Steam. Steering trials made during the service of a ship at sea enable officers to gauge the effective performance of their vessels under varied conditions of wind and weather, speed and helm angle. The
* The methods suggested for measuring the diameters of circles will be found in Appendix L, together with the results obtained for the “Tennessee,” “Quinnebaug,” and “Enterprise.”
|value of such knowledge cannot be over-estimated. On the subject of turning trials an eminent authority * is quoted as saying that a table of turning powers is no less necessary to a ram than a range table to a gun. But exercises in manoeuvering should not be confined to the describing of circles and determining of tactical diameters. In the Mediterranean squadron under Lord Clarence Paget, R. N., the vessels were exercised on convenient occasions in performing a figure of 8 evolution. This was done by placing buoys as shown in the diagram, and under the following conditions, viz.:A, B, C, D, are four buoys placed in the form of a parallelogram, of which the long side will be approximately four and one-half times, and the short side three times, the length of the ship.|
E, F are two buoys placed one length and a half of the ship apart, and at even distances from the centre of the parallelogram. The ship is to enter the parallelogram, either between B and D or between A and C, the exact time of her stern passing the dotted line between the two buoys being noted; she is then to perform a figure of 8 within the parallelogram by crossing, each time between the points E and F, as shown in the diagram, and she will then come out at the opposite end of the parallelogram from that at which she entered, the precise moment of her stern passing between the buoys on leaving the parallelogram being also noted.
No ship is to use more than half-boiler power, but she may aid herself in any manner by the use of sails or otherwise, as may be deemed expedient.
When once the ship is within the parallelogram, if any part of her should touch the dotted straight lines between the buoys, she will be supposed to have grounded, or should she touch either of the buoys E, F, she will be supposed to have fouled the ships which they are intended to represent. In either of these cases the manoeuvre must be presumed to have failed. The direction and force of the wind, the state of the sea, and the direction and strength of the current (if any) are to be noted during the experiment.
* Captain (now Admiral) Bourgois, French navy
|As to the results, the author of the pamphlet from which this description is taken,* states the following:”This exercise had the effect of teaching the officers what were the steering capabilities of their ships, not only whilst going ahead, but when moving astern; and I may add that after we had made the experiment twice, in which I am bound to say we did not quite succeed, I had much greater confidence in managing the vessel when moving in or out of confined harbors, or in close order with the squadron. Such practice as this must prove useful, and cannot fail to instil valuable instruction regarding the steering properties of a vessel, not only for the benefit of her commander, but also of the lieutenants and master.”|
One may be enabled, by practice of this kind, to tell, within a few yards, where any ordinary combination of tide, wind, and rudder will place the vessel. With readiness of resource and good judgment, an officer applying such knowledge in action is likely to prove a dangerous antagonist.
STEAM STEERING GEAR.
The importance of the use of steam as a motor for steering ships was recognized many years ago. At that time practical men noticed the idea only with derision, but of late years its application has been common in the merchant marine and in foreign navies. Its introduction on board our cruisers is recent. One form adopted in the service is that invented by Mr. Sickels, the designer also of the “Trenton” windlass, previously described.
Plate 124 shows the general form of the Sickels’ steam steering; the particular design being that adopted for the U.S.S. “Lancaster.”
The engines AA consist of two cylinders of the half trunk variety, placed at an angle of 90° to each other and acting on the same crank pin; the shaft is above the cylinders, and the frames are cast on.
The valves are of the kind known as piston valves, steam being admitted in the middle and exhausted at the ends and through the valves. These valves are made with excessive lap on the steam side, and have a triangular score cut in them, by which means steam is admitted, at first, the object being to avoid the jerking motion which would result from a sudden, free admission.
There is also a negative lap on the exhaust side for the purpose of readily freeing the cylinders of water.
Upon one end of the crank shaft is secured a deeply grooved conical drum D, for the reception of the tiller ropes.
* Admiral E. A. Inglefield, R. N. “Recent Experimental Cruising,” &c.
|This drum is so constructed that when the helm is hard over the relative leverage is double or treble that when it is amidships, thus increasing the leverage where the resistance is greatest. The cone is also so proportioned as to get the same effect, as regards uniform tightness of ropes, as a quadrant or sliding block on the tiller would give.On the opposite end of the shaft is a brake wheel, W, secured by a key and set screw.|
The brake is a wrought iron hoop which embraces three-fourths of the circumference of this brake wheel; it is lined with a strip of red cedar and is held in place by adjustable springs in the brake fastenings, S, S. The use of this brake is to steady the operation of the machine.
In the brake wheel on the side farthest from the drum is inserted a pin fitting snugly, but free to move, and held in place by a key on the opposite side. This pin is forged on an arm, at the other end of which is forged another pin, to which are connected the valve stems. The last pin has a cam yoke, the yoke, pins, and arm being in one forging.
When the valves of the engine are in a neutral position, the pin on the arm, which operates them, has its centre coincident with that of the crank shaft.,
In the same centre line as the main shaft is a small shaft, supported in a bearing B; the centre of this bearing is enlarged by a collar on which is cut a thread which operates an indicator I, for the purpose of showing the position of the tiller. On the end of this small shaft nearest to the crank shaft is forged a disk; to the after side of this disk is secured a cam which fits neatly into the cam yoke. The cam is of brass, with steel shod points and sufficient eccentricity to actuate the valves.
The disk has also attached to it a pulley of brass, P, with a grooved thread on it, designed to carry the cord from a similar pulley on the hand wheel, intended for steering, placed on the upper deck, bridge, or elsewhere.
The forward end of this independent shaft has a hand wheel, H, secured to the shaft by a set screw. This gives an apparatus for steering, situated with the engine, &c., entirely below the water line.
To operate the machine the hand wheel is moved in either direction desired, thus changing the position of the cam, which in turn changes that of the yoke and pin on the loose arm, thereby operating the valves and causing the engines to revolve their shaft in the same direction as that given to the hand wheel.
The hand wheel having ceased its motion and being independent of the engines, as soon as the latter move the crank shaft and drum through an equal distance, it has brought both shafts to the same relative positions as at starting, and consequently closed the steam valves. The engine shaft, therefore, follows in direction and moves
|through the same angle as the hand wheel shaft, and stopping the motion of the latter, stops that of the former.The steering wheel for the upper deck is usually a small brass wheel, V, mounted on a frame in such a manner as to be capable of an adjustment vertically of several inches, for the purpose of tightening up the steering cord, which is wound in a suitable groove cut upon its face.|
A thread on the shaft, cut with a pitch corresponding to the cord grooves in the pulley, allows the wheel a certain amount of fore-and-aft motion. This furnishes a tell-tale to ascertain the position of the tiller and keeps the steering cord constantly in a vertical position over its hole in the deck, obviating the use of the slot cut for ordinary steering ropes.
When there is no steam on, the steering wheel might be moved so far over as to reverse the position of the cam and make the engine work the tiller, when steam is introduced, in a direction opposite to that intended:
Stops have therefore been provided to prevent the cam from being thrown too far either way. These stops consist of pins on either side working against spiral springs inserted on the sides of the yoke, against which corresponding stops on the cord pulley strike.
Below the cord pulley on the cam shaft, is situated a brass piece sliding on a wrought iron guide, carrying on its upper side a tooth which fits into the grooved thread of the pulley. By this tooth the slide follows the groove until it brings up against a stop held by a heavy steel spring. The object is to prevent the hand wheel being moved beyond the distance necessary to put the helm hard over either way.
Any shocks to the helm resulting from the force of the waves against the rudder, or from striking ice, wreckage, &c., are taken up by the cushion of the steam against the cylinder pistons. Hence, when using this steering gear, there is no possibility of the wheel’s taking charge in spite of the helmsmen, as sometimes occurs with the hand apparatus.
This apparatus is at all times ready for use when steam is raised, for, from the peculiar arrangement of the valves it is not necessary to first free the machine from condensed water to prepare it for service as is necessary in an ordinary steam engine.
Steam and hand power steering. An important point with any steam steering apparatus is the ability to connect or disconnect it quickly, so that the use of the ordinary hand wheel may be substituted for the steam steering gear or vice versa. To effect this with the Sickel’s patent the wheel ropes are rove off on the bight. Instead of securing the ends to the tiller as usual (Fig. 517), they are passed over sheaves and brought forward to the cone drum on the
|steam apparatus (Fig. 518). All that is necessary in wishing to use either method of steering is tolock the other in its midship position, and the ends of the tiller rope on the locked apparatus become the standing parts. This locking is instantly accomplished by pushing a pin K through a hole in the wheel, or a flange, thus securing it to some stationary object sufficiently to prevent its turning. Figs. 517 and 518 show the lead of the wheel ropes from the tiller.The above described apparatus differs essentially from the forms observed on board foreign vessels. In these the machines work with gears or worm wheels, and instead of acting upon the valves by the hand motion, have them driven by eccentrics as in ordinary engines. A supplemental valve is commonly attached with its ports so arranged that when worked by hand, steam is admitted to the centre or ends of the main valve, according to the direction of the revolution required, an arrangement similar to the reversing valve for the Trenton’s windlass. The steerer above described is necessarily quicker in action, and is, moreover, noiseless.|
Manton’s Steering Apparatus (Plate 125). This machine, as supplied to the Miantonomoh for trial, consists of a pair of horizontal engines working into larger gear. Upon these shafts are worms, running into a gear upon the rudder head, as shown in the figure. The valve motion is similar to that of the foreign machines above referred to.
On board the Miantonomoh the valve stem is attached to a screw actuated by a nut connected to a small grooved pulley. This nut is held horizontally by an attachment to the rudder head. The pulley, can give it a rotary motion, and as it is held from advancing or receding by the tiller attachment, the valve is moved through a distance corresponding to the pitch of the thread. In the pilot house is a larger grooved wheel on the same shaft with an ordinary hand wheel.
To work the machine. By revolving the wheel in the pilot house the pulley at the engine is turned, thereby turning the nut and drawing or thrusting the valve. This gives steam to the engines and they will continue to work till the steam is cut off by the reversing (supplemental) valve being put in its neutral position again by the automatic attachment on rudder head readjusting the nut. On the worm shafts on each end of the worms are rubber buffers, or springs, to relieve the gearing from shock of the sea.
With this form of steering gear the wheel ropes for a hand wheel cannot be left connected with the tiller, for if they were the hand steering wheel would revolve with every stroke of the engines when operating the rudder by steam.
|Baird’s Steering Apparatus. Plate 126 shows this form of apparatus, of which the inventor, Passed. Assistant Engineer G. W. Baird, U.S.N., has kindly furnished the following description:”The wheel H is used to steer by hand when coupled to the drum D as shown, but if slipped forward on the line of its axis it disengages from its clutch and sliding upon the square end of the shaft S’, engages the steam gear only. When steering by steam, any motion given to the shaft S’ is transmitted to the valve V through the intervention of the gears G and g, the shaft t, nut n, and lever L.|
The valve V admits steam (or compressed air) to the engine E, which starts the drum in motion through geared wheels; but the drum D, which is prolonged into a threaded shaft S revolving within the nut N moves the lever L in a direction to shut the valve V and stop the engine. The arms of the lever and pitches of the screws are so proportioned as to cause the drum D to complete the same angular movement that has been applied to the wheel and to stop then automatically.”
This form of apparatus has advantages in the small number of parts, simplicity and accessibility for repairs.
The Value of Steam Steering Gear. In discussing the turning power of ships, attention has been drawn to the question of time occupied in putting the helm over, as a component of the resistance to quick turning. The time so occupied depends directly upon the efficiency of the steering gear.
On board the monitor Roanoke, with the usual hand gear it took two men two minutes to move the rudder from one extreme position to the other and required 19 turns of the wheel. With the steam steerer one man could easily move the helm from hard a port to hard a starboard in 5 seconds with 3 1/2 revolutions of the wheel.
The power which such a machine must exert to put a rudder over to 40° has been found by trial (Napier’s experiments) to be equal in statical moment to the product of the following factors:
Power in excess of the demand is of course necessary, the amount depending on the tonnage and the nature of the service, but no possible defect lies in the direction of too much helm power.
An ordinary rudder, moved by hand, might answer for cruising purposes, and yet be insufficient for rapid manoeuvres in action. But by introducing steam steerers we are able to provide and manage much larger rudders than could possibly be operated by hand.
|Auxiliary Steering Screws. This method of increasing the handiness of vessels has been proposed by a Hungarian engineer.* The feature of the plan is a secondary screw (as shown in the diagrams) which is connected by an universal joint, of simple construction, to a projection of the main shaft. The joint consists of two steel double-eyed forks; between these forks is inserted a block of phosphor bronze. Into the block screw four pins, coupling the forks to the block, and to each other. A locking pin is then screwed into the block and takes in a groove, concave in form, cut out of the inside ends of the other four pins, which keeps them from working loose. Any form of steam steerer may be used with this apparatus, to insure quick handling of the helm.The auxiliary screw may be mounted on the after-part of the rudder, as in Fig. 519, Plate 127, or in the rudder, as in Fig. 520. Figs. 521 and 522 show the universal joint, P being the locking pin and A, B, C, D the coupling pins.|
By making the secondary screw of coarser pitch than the main propeller, a certain increase of speed has been obtained, assumed to be due to the action of the smaller screw in picking up the slip of the larger.
The apparatus is being fitted for trial to the U. S. tug “Nina.”
Vessels which do much of their cruising under canvas, will find disadvantage in the increased drag due to the additional screw. This is probably offset by the value of the second screw to the same vessel when under steam alone. Tables given in Appendix L illustrate the performance of the steamer “Stratheden” (2,000 tons), with and without the attachment.
The most important advantage claimed for this apparatus is its immediate effect upon the ship’s head. As soon as the helm is moved, a decided turning effect commences, whether the engines are reversed or continued running in the same direction.
Whether improvement is to be in the direction of twin screws, steam steerers, or other agencies, it is certain that, handiness must increase greatly in modern men-of-war, if the ram and torpedo are to be elements in naval warfare. To profit to the fullest extent by such improvements, experience in handling vessels under steam alone must be an essential part of a young officer’s education.
It would be idle to deny the existence of a prejudice against the discussion of many questions which relate to manoeuvres under steam. Nor is such prejudice confined to our own service.
* Mr. J. J. Kunstädter.
|“How many naval officers,” says Fremantle,* “care to know the number of degrees of helm that can be given to their ships, the tending of the screw to turn the ship unassisted by the rudder, the effect of turning the engines ahead or astern when the ship has head or sternway, or what the reduction of speed by putting the helm hard over? These and other questions are simple points of seamanship; yet an officer who would consider himself disgraced if he could not answer at once as to the lead of the lower studding-sail halliards, which may not be supplied to the ship in which he is serving, will acknowledge without a blush that he does not know if the screw of the same ship is right or left-handed, or how many blades it has.”It would be more practical to realize that while the weather-gage and manoeuvres used in obtaining it have lost their importance, there are more urgent reasons now than ever existed in the old sailing days for good judgment on the part of the officers. Combined with accurate gun practice, the skilful handling of ships, which is seamanship, decides most naval actions. And this is as true when the results are achieved with propellers and steam steerers, as it was when they were obtained with braces, tacks and sheets. The motive power alone has changed-the principle remains.|
* “Naval Tactics on the Open Sea,” by Captain the Hon. E. R. Fremantle, R. N.
GETTING ON SHORE-LEAKING-HEAVING DOWN.
When a vessel strikes, the first step is to brace aback if on a wind; to clew up and furl everything if before the wind, and if under steam, to reverse the engine. It may be possible, if she has struck on a sand-spit or knoll, to force her over into deep water, otherwise she should be hove off as she went on. The navigator should be at once despatched to sound around the ship, and the boom-boats be hoisted out. Carry out the stream-anchor and bring the cable to the capstan. Have careful hands in the chains by the lead to watch if she moves. Heave round and try to get her off. If she does not start, move the guns and men as necessary to change her trim. If this fails, send out a bower anchor and chain. While the boats are carrying out the anchor, send down the upper yards and top-gallant masts, and prepare to start the water and provisions. If still impossible to move her, start water, heave overboard guns and shot (supposing there is no hope from higher tides), and all heavy weights. The guns should be carried clear of the ship and buoyed, with buoy-ropes strong enough to weigh them. Construct rafts out of spare spars, to carry provisions, water, &c. Of course, if small vessels can be procured they will be used. While lightening the ship a good strain must be kept on the cables by which the ship is to be hove off. This is very important, and every time the purchases are observed to slack up, they should be set well taut again. In case the anchor comes home, back it with the stream.
Do not commence to lighten the ship until an anchor has been planted and a good strain hove on the cable, lest she go further on.
If a vessel is aground forward, shears may be raised over the bows, the heels resting on the bottom and the legs long enough to reach well above the bows; the object being to lift her by means of a heavy shear-head purchase. This method was once successfully tried with the United States sloop-of-war “Vincennes,” but would not answer with any but the smaller class of ships.
Another instance is mentioned of a ship having run stem on very hard, and after unavailing efforts to get her off, hung on a rock abaft the foremast. All weights were run aft; balks of timber were placed athwartships forward of
|the place where the ship hung, and projecting through the ports; perpendicular shores were placed under these from the ground; slung to the balks, and wedges prepared for driving between their outer ends and the shore-heads. Opportunity was then taken of the first increase of water to set up the wedges, remove the after weights and heave in on the purchases at the same time. On this the ship started immediately; and, by a repetition of the same process of leverage, was completely cleared of the rock.Vessels draw much less water when hove keel out than when upright or heeling over. It is related that a certain vessel had been driven so far up on shore, in a heavy gale and unusually high tide, as to be considered irrecoverable, and was sold for the mere value of her timbers; the purchaser floated a scow alongside of her at high water, and hove the vessel keel out by her masts, and then warped the pair into deep water.|
If the tide commences to fall while the vessel is still aground, she must be shored up to prevent falling on her broadside. The spare fore and main topmasts may be used for this purpose. Weight their heels with kentledge, bend on guys to place them, and let their heads take beneath the fore and main chains. Should she rest too heavily on the spars, send out kedges to the opposite side, and bringing the hawsers to the mastheads, set them taut to steady her. * At the next high tide try her again. If a steamer can be procured, let her tow in the direction you are heaving. If a ship is at hand to assist, she may anchor near, and, taking a hawser from you, heave at the same time.
When the vessel first strikes, and the sails are hove aback, or the engine reversed, the officer of the deck should send men in the lower rigging to shake the ship, sally from side to side, or move the guns aft quickly. These means often suffice to get the ship off.
If a ship bilges, all further efforts to get her afloat are of course abandoned. The first step in this case is to get the boats out, and then to keep her upright, saving as much of her effects as possible.
Ships sometimes get hard and fast after grounding, from neglecting to lay anchors out beforelightening.
In some cases, the water close under the stern is too deep for anchoring.
It is reported that the bower anchors of an English man-of-war, that had grounded in the St. Lawrence, were transported over the decks; and, being let go from the quarters with a purchase on each, which was carried to the bows, the ship was hove off.
H. B. M. steamer “Gorgon,” of twelve hundred tons and three-hundred-and-twenty-horse-power, was driven on shore
* Unnecessary with a flat-floored ship.
|in a gale, near Montevideo, and imbedded in the sand to a, depth of nearly twelve feet. Camels were constructed on the spot, tanks made water-tight by introducing fearnaught and lead within their lids. Boilers were hoisted out and made water-tight, and these, with casks, &c., affording altogether a buoyancy equal to three hundred and sixty-seven tons, were secured under the ship by means of cables passed round the bottom. These appliances, together with screws, and heavy purchases leading to anchors planted astern, being duly pre pared, the ship, on the tide filling the dock that had been dug about her, was rescued from her perilous condition. “The whole operation presents a picture of united energy and skill to which maritime records afford no parallel.” The details of these operations have been narrated by one of the ‘Gorgon’s’ officers, not only as an account of the means used to restore the ship, but likewise to point out to the young officer to what advantages the qualities of perseverance and forethought may be applied, if duly cultivated in early life.”*The dimensions of one of the camels, whose buoyancy was equal to sixty-two tons, is as follows:|
The planking was three-inch fir, doubled at the edges, and nailed on over seven frames, each nine inches by five.
Cases have been related where officers have thoughtlessly given the order, on the ship grounding, to let go an anchor. The impropriety of this is obvious, for there is great danger of the ship striking on it and bilging. For the same reason when guns are thrown overboard, care should be taken that they be not placed where there is a possibility of the ship striking on them.
When a ship has touched lightly or run into soft mud, a moderate-sized anchor and hawser run out astern and hove taut, may suffice. Then all that is requisite is to loosen her in her bed. This may be done by running in the guns on one side, and sending all hands on the opposite side to list her; by letting the crew sally from side to side by the stroke of the bell, or, as has been successfully tried on board the practice-ships, by manning the lower rigging and causing the crew to shake together.
If badly ashore, be careful not to bring the heaving-off cables over the stern, so that they may have a tendency to bear it down and press her heel on the bottom. Should both bowers be planted astern, bring the cables to the quarters outside, where hang them; now lash to them your heaviest
* Recovery of the “Gorgon,” by Captain Key, R. N. This little work may be found in the Library of the Naval Academy, and is well worth reading.
|blocks, say the cat, and toggle the fish block to the forward main deck port, also outside; reeve a hawser for a fall, and bring the hauling part from the cat in through an after port each side, taking one to each capstan, or use one capstan and a deck tackle. This gives a better lead.|
SHIP ON SHORE. WEATHER FINE.
THERE BEING MUCH RISE AND FALL OF TIDE.
Out boats and plant stream in best direction. Hoist out spare spars, and commence shoring up as rapidly as possible, as she will be left high and dry at low water. As soon as well shored up and spars lashed and cleated, close all the ports and secure them.
Should it be a coral or rocky bottom, her safety will depend in a great measure on keeping her upright. Besides the spare spars take as many from aloft as possible; remove all weights from aloft, and run the guns in to a taut breeching. Get all weights from the side to the centre of the ship and lash them.
The finer the ship’s bottom the more the danger to be apprehended from her heeling, and consequently the more the care required in shoring up.
If a full-bottomed ship, and one with a great deal of dead-rise, were both to get on the same rugged shore, the latter, supposing both to be kept upright, would stand the better chance, as she would rest on her keel alone, while the former would rest on her floor; if the two ships were heeled over and striking hard, the full ship would be in danger of bilging, while the sharp ship’s lee side will be water-borne, and the ship striking on her keel.
Should both ships be left high and dry on “a hard” without shoring up, the full ship would be left nearly upright while the other would probably be lying on her beam ends. This is a critical position for a strong ship, and extremely dangerous for an old one.
In the matter of heaving off, the sharp ship, by taking the ground in fewer places and causing less friction, would give less trouble than one with a long, flat floor.
The foregoing remarks show the importance of officers being familiar with the model, or “lines” of their ship.
THE CASE OF THE “MONONGAHELA.”
The U. S. steam sloop Monongahela (2100 tons displacement) was thrown on shore by a tidal wave at Santa Cruz, W. I., November, 1867, and an expedition for the floating of that vessel was sent from New York, in the U. S. barque
|“Purveyor,” taking along all the necessary material and twenty-six picked men, mostly shipwrights and caulkers, under the direction of the late Thomas Davidson, Jr., Naval Constructor, U. S. N.The working party arrived at Santa Cruz (West End) Jan. 31st, 1868, and found the ship high and dry, broadside on, and heeled over at an angle of 15°. The rudder and steering post were broken, metal connection and main stern post gone below stern bearing, a considerable portion of the stern knee gone, after end of keel and garboard strakes gone for forty-five feet, the remaining keel badly chafed and in places broken to the bottom planking, the starboard bilge chafed nearly through the plank to the timbers in many places, twelve streaks of wall plank under the after pivot port on the port side broken, and the sheer line very much out of place on that side.|
The badly chafed places of the starboard bilge were trimmed out and white pine plank filled in, caulked, made tight, and sheathing copper put on this side and the keel. Before the keel could be repaired or the ways put under for launching, it was necessary to raise the ship bodily two feet or more. Not having the power to do that at once, the rolling process was resorted to. This was done by placing white pine timber under the ship, filling the space from the bottom plank to the coral in line with the keel, and about five feet out. Hydraulic jacks were then placed under the port bilge, and the ship rolled on her starboard bilge, to a sharp angle. The keel was then carefully blocked, and the ship rolled back on her port bilge to her original position, the timber increased in thickness, &c., &c. This operation was gone through with several times, or until the keel was raised twenty-six (26) inches. After which, new after keel and garboard strakes were put in, posts and rudder repaired, and timber run out on either side to take the place of metal connection and secure the steering post. The propeller was unshipped and four sets of launching ways put under, extending to the water. Owing to the heavy surf which rolled in continuously, it was found impossible to lay the ways from the bank to deep water singly; and it was decided to prepare them about one-half mile south of the ship and near where she first came on shore. A diagonally braced framework or platform was first made, and on this the ways were laid and secured, and the whole fabric launched and towed to the ship, and the four ways connected at the same time, extending out from the land two hundred and thirty-seven (237) feet, or to 14 feet 6 inches depth of water. After the ways were connected, a very difficult job was performed in getting the depth of water at the blocking spots, which were taken four feet asunder. These depths had to be taken several times and an average adopted to get a correct grade. From the great unevenness of the bottom this was hard
|to get correctly. After this, the blocking was secured and the whole mass sunk with kentledge. On the 4th of March an attempt was made to launch, but by the bursting of a 90 ton hydraulic jack the bow of the ship started too soon and had got ribband bound before the stern had got fairly started; when the stern did get started it went very fast, and before the bow could gather way again the stern had become ribband bound. It stopped between blocking, the ways broke, and the ship dropped in six feet of water aft and five feet forward. Fortunately, the packing remained in place, and the keel was kept clear of the bottom 18 to 20 inches. This gave the water a chance to breech through and prevented the sand from banking on the outside. All the material was picked up, new ways fitted and put under, the packing was removed by blasting. Anchors were laid out abreast the ship, and in the direction that she was to be hauled, broadside to; crabs put in place, tackles rove and shores made of white pine timber and plank strong enough. to support the pressure of a 90 ton jack. Six of these shores were made. Tackles, chains, &c., were on the seaward side to haul out; shores, jacks, &c., on the land side, to push out. A jack was placed between each shore and the ship’s side, to which both were hung by small tackles about three feet above the water, as also was a small stage on which the man stood that worked the jack.The other end of the shore was backed by the coral at first, and as fast as the ship moved out the space was filled in with kentledge until a man tending this end was up to his waist in water. The shore was then taken down and lengthened. This was done several times until the last shores made were one hundred and thirty-five feet long and over eight feet wide.|
After this manner the ship was pushed slowly out, broadside to, on her ways, until within one foot of floating draft, when the tackles relieved the jacks and in a short time the ship was afloat. The utmost care had to be taken with the tackles in order to preserve their effectiveness for the final effort, as the chains available were not of sufficient size to bear the capacity of the crabs, and were broken several times. They were of little assistance while the shoring out was in progress.
All the material was reshipped on the barque, the topside of the ship and the deck were caulked, and the broken walls planked over. The expedition reached New York on its return early in June, 1868.*
* The foregoing description is from information kindly supplied by Mr. W. F. Noyes, master carpenter at the Navy Yard, Portsmouth, N. H., who was a member of the expedition.
Water passes as the square root of its altitude; that is, if we suppose equal holes to be made in the bottom of a vessel at one foot, four feet, nine feet, and sixteen feet beneath the surface of the sea, the water will rush in the holes with a velocity equal to the square root of their respective depths. If for example, 1 represents the velocity with which it enters at the first hole, the numbers 2. 3, and 4, will represent the velocity with which it enters the others.
After the water has risen in a vessel, it will rush in all the covered holes with the same velocity, regardless of their depths, which velocity will be represented by the square root of the difference between the level of the water within and without the vessel.
Suppose a ship drawing twenty feet to spring a leak sixteen feet below the water line, or four feet from the bottom of the vessel. The velocity with which the water enters this leak is represented by 4; but when the water has risen in the vessel, say eleven feet, the water will then enter with a velocity = squareroot(20-11) = squareroot(9) = 3; when the water has risen sixteen feet, the velocity will be represented by squareroot(4) = 2, etc. Hence it will be seen that although the pumps may not gain on the leak at first, yet they may do so after the water has risen inside the vessel above the leak.
In order to discover the locality of a leak, it is recommended to steer in different ways. If the leak increases when going ahead at full speed, it is probably forward, otherwise it is abaft. If it neither increases nor diminishes, it may be on either side; which may be discovered by going on different tacks.
Upon springing a-leak the pumps are at once manned and kept going. The carpenter then endeavors to discover it, and on doing so will stop it if possible from the inside. The hold or fore-peak may have to be broken out for this purpose. Sometimes by listening attentively, the noise of the water rushing in will betray its locality.
If the leak cannot be got at in any other way, and is a dangerous one, a sail may be “thrummed” and placed over the hole from outside.
Sails are thrummed as in making a mat. They are got over the bows, and hauled close up over the opening by guys and tackles. The most expeditious way to thrum a sail is to pour on hot pitch, and then tread oakum over it.
Should the leak be on one side, and near the water line, the ship may be hove about or listed; when the carpenter may get at it and nail over sheet lead, or planking lined with fearnaught.
|It is of course advisable, whenever possible, to stop leaks from the outside. Many ingenious devices have been resorted to for this purpose, when the ordinary methods of thrummed sails, mats, etc., have been unavailing.The U. S. steamer “Proteus,” in one of the blockading squadrons, was fitted with a chute for discharging ashes through the bottom of the ship. This consisted of an iron cylinder with the lower end bolted to the bottom of the vessel and the upper end, a little above the water line, closed with a tightly-fitting plate when not in use; the plate moved in and out by a lever, as required.|
In a gale of wind the bottom fastenings of this cylinder commenced to work adrift, and a dangerous leak was developed at the lower end of the chute.
To stop the leak, the vessel was hove to, a wooden shot-plug was secured to the end of a rope, and just inside the shot-plug a small line with a deep-sea lead attached was connected to the same rope with a squilgee toggle, a line from the toggle being retained inboard. Shot-plug and lead were lowered through the chute, tending the tripping-line of the toggle. When enough rope had been paid out, the squilgee toggle was pulled out by its tripping-line. The lead went to the bottom, the shot-plug floated up alongside, was grappled from the surface and taken inboard. Using the rope as a marrying line, a heavier line was hauled through the chute, and when its outboard end reached the deck it was made fast to a suitable plug formed of mattresses, hammocks, etc. By manning the other end of the line the improvised plug was hauled under the ship and tightly jammed in the bottom of the ash-chute, stopping the leak and probably saving the ship from foundering.
It is obvious that the reason for not using the heaviest line at first was that the shot-plug would probably not have floated it.
On board a merchant ship an extensive leak in a seam was effectually stopped, from outboard, as follows: The vessel being hove to, a rough bag was formed out of a tarpaulin with a broad flap cut in one side, loosely stitched on and the edge connected with a tripping-line, led to the deck. The bag being filled with sawdust, the mouth was sewn up and the bag drawn by lines passing under the keel to the vicinity of the leak, with the flap side nearest the ship. The flap being torn open by the tripping-line, the sawdust worked out and, mingling with the water, effectually closed the seam.
This method was successfully applied on board the U.S.S. Independence at Mare Island in overcoming an annoying leak in the run of the vessel.
As an instance of closing serious leaks from inboard, the case of the “Worcester” may be mentioned here. This vessel, when flag-ship of the North Atlantic squadron,
|worked the Kingston valve entirely adrift from its fastenings during heavy weather, the result being that a solid stream of water nearly a foot in diameter commenced pouring in to the ship. Until some two or three feet of water were in the hold, all efforts to close the leak were unavailing, but finally a nine-inch shot (with its diameter suitably increased by wrapping in canvas) was rolled over the orifice of the leak by men up to their knees in the water. Assisted by the back pressure of the water in the vessel, two or three hands could keep the shot in place until it was secured there by a cross-piece of timber, one end of which was placed under one of the boilers, and the other end wedged down by a shore from under the berth-deck beams.Should a vessel be found to leak very badly, she may, if in the vicinity of land, be beached, as a last resort; or, if near a harbor, be run in and put aground to keep her from sinking in deep water.|
If in danger of going down, anchors, guns, &c., must be hove overboard, boats hoisted out, and rafts constructed for carrying men, provisions, and water.
No rules can be given for such cases. Much depends. upon the example of coolness and energy set by the officers, and the general state of discipline. Much, too, depends in all emergencies upon the professional abilities of officers, their practical knowledge and fertility of resource.
The student is referred for accounts of shipwrecks, for the various means of rescuing people from stranded ships, for constructing rafts, &c., &c., to the professional works with which the Naval Academy library is so generously supplied.
Heaving Down. When vessels have sustained injury in their bottom, and there are no opportunities for docking, recourse is then had to heaving down. Tackles are brought from the mastheads to the shore, or to another vessel, and these being hove on, turn the bottom up out of the water.
The following notes were taken at the heaving out of the United States frigate “Brandywine,” at the Navy Yard, Brooklyn.
The wedges of the fore and main masts were knocked out, and the masts got entirely over to the weather partners, the stays were also set up afresh, two extra pairs of shrouds were got over each masthead, and set up to dead eyes toggled with a long strap to the main deck ports. (These shrouds were taken forward of the masts so as to equalize the strain between the forward and after shrouds.) Two small chains were middled and eyes formed in the bights, which were well parcelled; one was put over the mainmast head, and the other over the fore; the ends were taken in through the air ports abreast the respective masts, and well set up to stout Spanish windlasses, which were rigged on
|the berth-deck in the securest manner possible; great care was taken that all the shrouds, extra shrouds, and chains, bore an equal strain.Strong shores were placed against the heel of each mast, with their other ends leading up to the junction of the berth-deck beams to the side, where they were well wedged; these were to windward, and were to counteract the tendency of the heel going out of the step to windward when the strain of the purchases was felt to leeward; other shores had their upper ends resting against that part of the under side of the berth-deck which is directly over the keelson; the lower ends rested on the skin of the hold to leeward about midway between the keelson and the ends of the berth-deck beams, where they were firmly wedged; these were to support the body of the ship when down on her side.|
Five bolts, three and a quarter inches in diameter at the large ends, and two and a quarter inches at the small ends, were driven through the side of the ship abreast of each mast, about one foot above the berth-deck, and well secured at their inner ends.
The camels or bolsters (being large frameworks of timber to protect the channels from the heels of the shores, and strong enough to bear the strain), were hoisted up by the pendant tackles and strung abreast the masts to windward. The shores were of white pine, seventy-five feet long, nineteen inches square at the heel, and thirteen and a half inches at the head, with a mortice cut through at each end; two were used for each mast, and they were got aloft by having a large three-fold block lashed at the masthead, and a purchase rove of a five and a half inch manilla fall; the lower block was lashed to the shore about one-quarter from the head, and thus each leg was hove up separately to windward; the masthead lashing was of new well-stretched four-inch rope, ten turns of which were passed through the mortice, round and round, and ten more crossed; the heels resting over the camels, were spread so that one might be as much forward as the other was abaft the mast, were gammoned to the bolts in the side with different sized white rope, after which the gammonings were well frapped together; three spare shores were lashed between the mast and each shore (making six for each mast), at equal distances, and belly lashings were hove on in the same places.
With so much weight on one side, the ship heeled considerably, to counterbalance which, water-casks were lashed on the opposite side, and filled, which brought her upright again.
A large and a small purchase were used for each mast; the large purchase-blocks were four and a half feet in. length, the small ones two and three-quarters; the upper
|blocks for the former were lashed to their respective mastheads, above the shores, with seven turns of a nine-inch manilla lashing, the upper blocks of the latter were lashed on with five turns of the same stuff; the lower blocks with their leaders strapped with a long and a short leg were toggled to the spar in the pits.Three crabs were placed for each mast, one for each purchase, the third as a backer for the large one; these crabs were secured to anchors planted in the ground, which were also assisted by pigs of iron.|
An anchor, to which the stream cable was bent, was planted in the water abreast the mainmast, the cable opposite the fore purchase was secured to a pile at a convenient distance abreast the foremast; both cables were taken under the keel through the spar-deck ports, and stout tackles clapped on them; the breast fasts were slacked and the ship hove off a sufficient distance by the cable, after which all was secured.
A pair of small but stout sheers, with a figure-of-eight head lashing and head guys, was raised near each pit and relieving tackles attached to the heads; a relieving tackle was also hooked to bolts in the wharf opposite to each mast and then to the gammoning bolts; the falls were rove, and the ship was steadied by them and the relieving tackles.
All the ballast was now got out and placed over the spar which ran through the pits, and to which the lower purchase blocks were toggled; the berth-deck was scuttled abreast the main hatchway, to leeward, and pumps rigged there; the ship was caulked thoroughly, the lee gun-deck ports closed in and caulked also, together with the air ports and scuppers.
All moveables were passed ashore, and the falls rove, the large falls were of eleven-inch manilla rope, the small one of eight-inch manilla rope; the purchases were three-fold; saddles, with rollers, were placed under the falls from the leaders to the crabs, and every precaution taken to prevent chafe; a spar-maker was stationed at the partners when heaving, to see when and how much the masts came over; the main came to within two inches of the lee partners, and the fore touched gently. As the mast-heads got below the sheer-heads on the wharf, the relieving tackles from the sheer-heads were hooked to stout straps around the mastheads; when keel out, the falls were well stoppered and bitted to the crabs, the relieving tackles hauled taut and shores put under the mastheads to assist the relieving tackles; the purchase falls were well covered with tarpaulins.
Every night the ship was righted, and on Saturday night the falls were unrove; previous to her being hove down the next day the frappings of the gammonings were always hove taut.
The starboard forward main swifter parted in heaving
|down the first time, which was the only accident which occurred.In cases where the vessel has been dismasted, or where it would be impossible to procure sufficient length of purchase falls, &c., the bottom is turned out of the water by means of spur derricks. H. M. S. “Success,” for instance, was thus repaired. The upper ends of the derricks were cleated on the ship’s side, the lower, to which the purchase blocks were lashed, were secured from rising by turns of the chain cable, that were passed under the bottom from the opposite side, being steadied by guys led from forward and aft.|
The after bearings of the “Croesus,” a screw ship of twenty-five hundred tons, were, in the absence of a dock, recently repaired by means of a caisson, which, when placed, enclosed the heel of the ship from the foremost stern post aft.
It was formed sloping at the fore part from the base to the top, and sufficiently open at that part to admit the heel, the dimensions being twenty-two feet at base, fifteen feet at top, twenty feet in depth, and nine feet in breadth. Displacement about one hundred tons. It was sunk by loading it with chain cable, which was removed when the caisson was drawn forward into position by guys. The caisson was kept free by constantly working two seven-inch pumps; the stern of the ship being raised in consequence nineteen inches.