HANDLING VESSELS UNDER STEAM
|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.