CHAPTER XXXV.

HANDLING VESSELS UNDER STEAM;

OR STEAM AND SAIL.

IN previous chapters we have considered the handling of vessels under sail alone, and with reference to those cruisers whose form and disposition of canvas enable them to manoeuvre under sail like ordinary sailing vessels.

In applying what has been said to steam vessels of war, it must be borne in mind that steamers under canvas never fulfil all the conditions looked for in quick working ships. This is partly due to the steamer’s form, to a reduced sail area for a given amount of tonnage, to the mode of masting, the drag of the screw, the screw aperture, and other causes.

Vessels of a similar type may differ widely in their qualities under canvas for the same point of sailing, and it would be beyond the scope of a book of reference to enumerate, even for vessels of a single class, peculiarities which are best learned in handling them.

Getting Under Way.-In getting under way under steam, the square sails are not usually set, but the head sails and spanker should be cleared away for assistance in casting. The mast covers should be put on and the mainsail covered, if left bent. Generally the mainsail is unbent and the gear unrove, unless intending to proceed under sail after making an offing. Put on the cover of the main topsail, if used. Reeve off the cat and fish.

Having notified the senior engineer in good time to light or spread fires, when steam is reported ready, call:

UP ANCHOR!

Bring to, unbit, and heave around.

The time required from lighting fires until steam is up may be from one to two hours with anthracite coal. In using bituminous coal with forced draft and other favoring conditions, steam may be raised in much less time.

With good banked fires the time required to spread them and get up steam ought not to exceed twenty minutes.

If a long and heavy heave, give a few turns of the engine now and then slowly to assist the bars. Should the anchor prove difficult to break out, give her a turn ahead, sending

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As soon as the anchors are secure, pipe down, and set the watch to work clearing up the deck, cleaning the anchors and chains, and paying the latter below.

If the steamer had been riding to an ebb tide you may find some difficulty in turning; if practicable, start ahead, and when clear of everything give a sheer with the helm and run up the jibs to pay her round, or she may be backed astern against the helm, using the jibs and spanker whenever they will be of service.

In a small harbor, or a close berth, a propeller may be turned by putting the helm hard over, when at short stay, and going ahead slowly, the water thrown from the screw having effect on the rudder in the same direction as if the vessel were going ahead.

TURNING AGENCIES IN SCREW STEAMERS.

In single screw ships, the rudder, the screw, the wind and sea, and the pitching of the vessel influence the direction of the ship’s head. Each of these factors is variable in the extent of its influence, excepting where the results are due, as cited below, to the shape of the underwater body, or to the shape and size of the rudder.

I. The effect of the rudder depends upon the amount of the rudder angle, size and shape of the rudder, and form of the underwater body of the ship, especially of the run. The rudder effect depends further upon the speed, and finally upon the force and direction of the screw current.

Through the latter conditions, the rudder effect is made to depend upon

* Under recent orders limiting the employment of pilots, the navigator cannot usually be spared to look out for the ground tackle forward. His place there is taken by a watch officer.

All steam vessels would be more effectually managed, when under steam, if provided with a pilot house forward.

** Modifications of these will be found very useful; for example, one bell repeated, means slower; four bells repeated, full speed; two bells repeated, “done with steam” (after anchoring or making sail); and when under banked fires two bells means “spread fires”

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III. The effect of pitching on the ship’s head is indirectly through the effect of draft on screw and rudder, and directly through the heel imparted to the ship.

IV. The turning effects of wind and sea are due directly to the pressure they exert on the forward or after body, and indirectly to their influence on the ship’s speed and heel.

Each factor, then, affects the ship’s head, in part directly, and in part indirectly, in connection with one or more of the other causes mentioned.

Assuming that there is neither wind nor sea, the features in single screw ships which produce turning effects are the screw and rudder. We shall consider these causes separately, and the effects of the screw in particular.

We note first that the screw may be either right or left-handed.

A right-handed screw is one which, viewed from aft, turns with the sun to drive the ship ahead. This is the screw in common use on American vessels, and is the one discussed throughout this chapter.*

Fig. 1 shows a vessel fitted with a right-handed screw, an elevation of the screw itself being given below the plan of the ship.

* The effects of a left-handed screw are precisely contrary to those of a right-handed screw.

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DIRECT TURNING EFFECTS OF THE SCREW.

The direct turning effects of the screw are due:

(a.) To the difference in resistance of the water to the upper and lower blades; (b.) To the pressure of the screw current upon the after body when the engine is reversed; (c.) To the lateral pressure of the screw stream upon the rudder-post and rudder when the vessel is going ahead.

(a.) Difference in Resistance to the Upper and Lower Blades. When the vessel starts slowly ahead, the water acted upon by the blade A, Fig. 1, presents a certain resistance to that blade. The water acted upon by the ascending blade D is of gradually decreasing density, while the lower blade C works in the most dense and least disturbed medium, and the descending blade B is gradually meeting an increased resistance. The resistance to the lower blades being greater than that experienced by the upper blades, the centre of shaft being the centre of effort, will incline to move in the direction of least resistance (the direction of the upper blades, shown by the arrows, Fig. 1), and as the stern of the ship holds this centre of effort, it must tend in the same direction, to the right (tostarboard), so that the vessel’s bow goes to the left (to port).

Moreover, when pushed aside by the lower blade, the denser strata of water experience a speedier inflow than water disturbed by the upper blades; partly owing to the greater density itself and partly on account of the sharper lines of the lower part of the run which permit such quicker inflow. This is an additional reason why the lower blades should experience the greatest resistance, and it therefore increases the tendency of the stern to go to starboard, bow to port.

If the ship is backing, contrary effects obtain, the stern going to port, bow to starboard, on account of the differences of pressure above described.

The wake current, occasioned by adhesion and friction when the ship is moving ahead, dams up the upper surface of the screw current, checking its motion to the rear. In many vessels, this surface indraught astern is very noticeable when the vessel is going at full speed. Its effect is to increase materially the resistance experienced by the upper blades. The “wake” current, therefore, acts in opposition to the effects due to greater density of the lower water strata.

The resultant of the unequal pressures on the upper and lower blades, and hence that part of the direct turning effect of the screw, depends upon the form and sharpness of the run, the draft, the number of revolutions, and the immersion of the screw.

When the water is just being set in motion, i.e., when

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(c.) Pressure of Screw Current on Rudder-post and Rudder. When the engine is working ahead, the blade moving to starboard and downward directs its stream against the lower starboard side of the rudder-post and rudder; the blades moving to port and upward, send their stream against the upper port side of the rudder and rudder post. As the rudder is usually broader at the bottom than at the top, and as the stream from the upward moving blades meets with the least resistance and distributes itself with the least effect, it follows that the current from the blades moving downward has greater influence than the stream from the upward moving blades.

The effect will be greater or less, according as the rudder happens to be turned toward the blade moving downward and inward, or toward the blade moving upward and outward.

With the helm amidships, the effect of the screw current on the rudder-post and rudder, ship moving ahead, is to turn the stern to port, bow to starboard. This effect is therefore opposed to the results due to the moving of the screw blades in media of different density, while it unites with and increases the effects due to the wake current.

The greater the width of the lower half of the rudder in proportion to the upper half, and the more the after portions

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II.-INDIRECT TURNING EFFECTS OF THE SCREW.

These effects are due to the influence of the screw upon the steering powers of the rudder:

(a.) By causing the speed of the ship and consequent way current with its pressure on the rudder; (b.) By causing the pressure of the screw current upon the rudder when the ship is moving ahead; (c.) By suspending the rudder effect when the ship is moving ahead with the engine working astern, the way current being thrust aside by the screw current.

Of the cause and effect in the first case (a), it need only be said that the ship’s speed itself is affected in turn by the rudder, speed decreasing as rudder angle increases. There is therefore here, within certain limits, a reciprocal action.

Under (b) may be noted that the screw current increases the effect of the way current on the rudder when the ship is moving ahead. Both screw and way current are strengthened by increase in the number of revolutions.

The effect of the number of revolutions on the turning power of the rudder, as expressed by the time and diameter of turning in a circle, has been investigated with the German corvette “Hertha,” with the following results:

In regard to the time of turning.-Change in the number of revolutions with different rudder-angles, had great influence on the time of turning:

Change in the number of revolutions when the engine is moving slowly is of greater proportionate influence on the time than an equal increase in number of revolutions when moving at great speed.

In regard to the diameter of the circle.-Change in the number of revolutions has but slight effect on the diameter.

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66 : 62 : 46 : 30 : 18 = 1.21 : 1.17 : 1.63 : 0.97 : 1.

Hence the time of turning varies inversely as the speed, and the diameter varies directly as the speed. The greater the number of revolutions the less the time and the greater the diameter of the circle.

Under (c) it may be said that in vessels moving ahead the suspension of the regular rudder effect due to a reversal of the engines will be more or less complete according to the relative value of the opposing forces. The screw stream being thrown forward, tends to push aside and away from the rudder the way current coming from forward, due to the ship’s onward motion. The regular steering effect of the rudder decreases, while the turning effects of the screw become, in most cases, the controlling force.

Apart from influences due to wind, sea; and pitching; the greater the rudder surface and angle, the less the diameter of the screw, the smaller the number of revolutions, and the sharper the upper immersed part of the run-the greater will be the steering effect of the rudder. Under reverse conditions, the greater will be the turning effect of the screw.

To summarize the results due to the screw alone, we may say

1st. That the screw has its greatest effect upon the ship’s head in backing.

2d. That the screw has its least effect upon the ship’s direction when going ahead, and that effect decreases as the vessel gathers headway. See also note, p. 544.

3rd. That these effects are greatest when the ship’s draft is light, the screw being, however, immersed.

Racing. What is said throughout this chapter of the screw effect presupposes that the screw is properly immersed. If this is not the case the effects may be precisely contrary to those described. No data obtained for a given ship at her normal draft can be relied upon when the vessel is badly out of trim or very light.

Chief-Engineer Isherwood, U. S. Navy, observes that inasmuch as the screw current is due to the slip, its strength and effects will depend entirely upon the amount of said slip.

The same authority points out the increase in the screw current, and its consequent effect on the rudder when the vessel is in very shoal water.

One can scarcely fail to notice the different effect of the screw motion on the wake when in shoal water, as compared with the appearance of the water astern when off soundings.

It is to be noted also that the effect of the screw upon the rudder depends very much upon the distance of the

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Turning Effect of the Rudder Alone. The rudder, considered apart from the screw, exercises its usual effect upon the ship’s head, the bow turning to starboard with a port helm when going ahead (Fig. 2), and to port with the same helm when making a sternboard, the effect of the rudder being greatest when the ship has headway.

Conclusions. Recorded experiments with the Bellerophon, Lord Warden,* Friedrich der Grosse (See Appendix L), and other vessels of great draft, high speed, and moderate sized rudders, show that such vessels, when moving at full speed ahead, have a tendency to fall off in the opposite direction to that taken when they are just starting or moving slowly ahead. This is due chiefly to increased resistance to the upper blades.

Such vessels, when backing, usually take an immediate and decided sheer, due to the screw effect, but increased perceptibly by a favoring helm. If, while backing, the helm is laid to counteract the screw tendency, it must be done quickly, for when the ship has once taken the sheer due to the screw, she may respond but slowly or not at all to the intended action of the rudder.

In vessels of medium size and speed, sharp in the upper part of the run, and with fair sized rudders, the results to be expected may be expressed in tabular form, as follows:

* In the essay, ” Few Years Experience with the Screw Propeller,” by A. J. Maginnis-Navy Scientific Papers, No. 12-the writer states, as a general rule, that the resistance to the upper blades becomes greater than the resistance to the lower blades at high speed, requiring starboard helm to correct the tendency of the screw when going ahead. This extreme deduction is not borne out by any known American data, but it is verified in the case of the deep-draft British iron clad “Lord Warden,” which carries at a speed of nine knots one-half to three-quarters of a turn of port helm, her screw being left-handed. (See “Naval Tactics on the Open Sea,” by Capt. the Hon. E. R. Fremantle, R. N.)

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EFFECT OF RIGHT-HANDED SCREWS ON THE STEERING

OF STEAMERS OF MEDIUM DRAFT AND SPEED.

In such right-handed screw ships the port helm may then be called the weak helm, and it is so regarded.

For vessels of medium size, draft, and speed, it seems to be admitted that-

1st. When the screw is reversed, the rudder will act as if the vessel were going astern, even though she have headway.

2d. When the screw is going ahead the rudder will act as if the vessel were going ahead, even though she have sternway.

3rd. The faster the vessel is moving in the opposite direction to that in which the screw is acting, the less powerful will be the action of the rudder.

Figs. 2 and 3 are designed to illustrate the reverse effect in the first case; Fig. 2 showing the ship’s head affected by the helm alone, Fig. 3 the result of reversing the engines.

Figs. 4 and 5 are from the reports of trials made by Professor Reynolds on the steamer Melrose in 1877 and published in the Engineering. The ship going ahead full speed, her engine being suddenly reversed and helm put hard a port, the vessel’s head turned twenty-eight degrees to port before the ship came to a standstill. Repeating the experiment, but putting the helm a starboard, the ship’s head turned forty degrees to starboard before the headway ceased. The courses taken in both cases being directly opposite to that which the rudder would have steered the ship under ordinary circumstances. Compare also Hankow experiments, Appendix L.
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Comparative Effects of Rudder and Screw. The greatest effect on the ship’s head is that of the rudder when the ship is going full speed ahead; next in importance is that of the rudder when the ship is moving at full speed astern. Of the effects produced when the engine is working in one way and the ship moving in the opposite direction, the most important is obtained when the screw is backing. But even at its greatest, the reverse effect of the rudder due to the screw is often feeble, differing in different ships, and even in the same ship. under varied conditions of draft.

Should there be wind and sea, when a danger has to be avoided, a ship bringing herself to a standstill by reversal of her engines should be regarded as partly at the mercy of influences which would be easily controlled by the rudder if the ship and screw were moving in the same direction. During the interval before coming to a standstill, screw, rudder, wind, and tide may balance, and the ship move in a straight line till stopped, or any one may pre-. dominate, and perhaps cause the ship to fall off in the very opposite direction from that which is desired. *

The “reverse effect” of the rudder as described here, is a general result observed in certain classes of vessels under stated conditions. To rely upon that effect under all circumstances would therefore be as unreasonable as to attempt to tack ship by the same means, whether under double-reefed topsails in a seaway, or under plain sail to royals in smooth water. Details of absolute accuracy for even one type of vessel under varying conditions of wind and weather have yet to be recorded.

Avoiding Dangers. With a right-handed screw great caution should be observed in stopping and backing, to avoid immediate danger ahead and to starboard. When

* The auxiliary steering screw described in the latter part of this chapter is claimed to reduce this “danger interval” to a minimum.

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Were the danger ahead and to port, by porting, reversing the engine to full speed astern, and quickly shifting the helm to hard a starboard by the time the engine begins to back, screw and helm would combine in their action to carry the ship’s head to starboard, and would probably do so sufficiently to avoid the danger.

In passing dangerously close by another ship or other obstacle, remember that when the helm is put over to prevent collision, it is the stern that moves, and that while the bow may be thus saved from touching, the stern may be fouled; but that if the helm be quickly shifted when the bow is just clear, the stern will be thrown out. Many a “touch-and-go shave” has been thus effected by judgment and nerve. This is a good practical hint, and one worth remembering.

Effect of the Wind and Sea on Steamers. The bow of a screw steamer having no headway, will fall off from the wind. If on an even keel, and the exposed surface is about equal fore and aft, she will lie with the wind abeam. If by the stern she will bring the wind abaft the beam.

If the engines of a screw steamer be reversed when head to wind she will in a short time turn stern to it.

If the engines of a screw steamer be reversed when in the trough of a sea she will, sooner or later, bring her stern to the sea.

Stopping. The distance required by a screw steamer to bring herself to a standstill from full speed, by the reversal of her screw, is said to be between four and six times the vessel’s length. The same authority * states that this distance is independent of the power of the vessel’s engines, or nearly so, depending upon the size and build of the ship. The statement is probably incomplete. Given two sister ships cruising in company at the full speed of the slowest ship; one vessel having very much better engines than the other, and able to steam several knots faster. If both suddenly reverse and back at their utmost speed, it would seem that the ship which can move the fastest astern will come to a stand sooner than the other.

Casting under Steam. An officer knowing

* Report of Professor Osborne Reynolds and the Committee of the British Association “To investigate the effects of propellers on the steering of vessels.”

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It would be very difficult under the above conditions to make the turn to the left without the help of sails or dropping an anchor under foot, for the angle gained while going ahead would be, at least partially, lost in backing.

STEAM AND SAIL.*

When a steamer goes ahead fast, the vanes are very deceptive, the wind appearing more ahead than it really is. When in doubt, set the flying-jib as a “wind feeler,” steady aft the trysail sheet or haul out the spanker. Should the latter stand well give the order-

Clear away the fore-and-aft sails!

Man the sheets and halliards! and when all ready, Haul taut! HOIST AWAY! HAUL AFT! Hoist the jibs taut up and trim down the sheets. Hoist the staysails and trim aft

* One effect of the combination of sail with steam power in propelling a ship, is to increase the efficiency of the screw; for as it then has a part, instead of the whole of the resistance of the water to overcome its slip is diminished.–RANKINE.

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To Tack a Steamer. Under canvas and steam, should it be required to tack ship, proceed as if under sail alone; if going very fast, slow down before luffing around, otherwise the sails as they fetch aback may bring too great a strain on the fore-and-aft stays. When you “let go and haul,” ring to go ahead fast.

To Reduce Sail. If ordered to furl sail and proceed under steam, send down to the engineer to get up steam,* raise the smoke stack and lower the propeller, haul up and furl the mainsail, and put the cover on or unbend it. Fill the fire-buckets aloft. When steam is up, call, SHORTEN SAIL! take in and furl everything, put the covers on and ring to go ahead.

When under steam be particularly cautious not to allow ropes to tow overboard, and in heaving the lead, care must be taken that the line does not foul the propeller. Send the light yards on deck, point the other yards to the wind or brace them sharp up. The topsail yards will soon take against the lee rigging, therefore sway them up about one-third and clap jiggers on the lifts; haul all the rigging taut.

To Make Sail on a Steamer. If ordered to let the steam go down and make sail, send the necessary directions to the engineer, and set all the drawing sail, including the mainsail, as soon as the smoke stack is out of the way.

Weather Helm. A screw ship under canvas is said to carry more weather helm than a sailing vessel, because the water passes along aft, on the lee side, and finding the screw aperture, passes through it; and thus offering less resistance permits the after part of the vessel to sag to leeward, and the forward part to approach the wind, a tendency which the weather helm is called upon to check; furthermore, it is not only the water which actually impinges upon the rudder which turns the ship; the check received by the water from the rudder is communicated to the water before

* Or ring two bells to “spread fires.”

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DIFFICULTY OF TACKING A SCREW-SHIP UNDER SAIL.

In tacking, as long as a sailing ship has headway, the water coming along the weather side of the bottom strikes the rudder and assists to turn the ship; but, in a vessel with a screw aperture, the water meets a constant current coming from the lee side through the screw hole caused by the lee way the ship is making, and the side movement of the stern, and is consequently carried off with it at a considerable angle from the line of keel without touching the rudder at all.

In tacking steamers under sail alone, in addition to checking head braces, flowing head sheets, or even hauling down head sails, it is a very common practice to brace around the crossjack yards when the vessel is within a point or two of the wind, before hauling the main yard. The object is to throw the stern in the direction to be taken in paying off on the new tack, and thereby bring the wind on the (new) weather bow. Such counterbracing is of course adopted only when it is taken for granted that the vessel cannot be brought around without a sternboard.

EMERGENCY SIGNAL TO ENGINE-ROOM.

As a rule, when steaming ahead at full speed the signal made to the engine-room, when it is desired to stop the engine, is first to “slow” (one bell), and then to “stop” (two bells).

Similarly when the engine is reversed, to go ahead the signal will be first made to stop (two bells) followed by one bell to go ahead.

In case of an accident, however, the required final signal is made at once, without intermediate signals, and as this should never be done excepting under such circumstances, the very fact of making “stop” from “full speed” constitutes a signal of emergency and it should be obeyed with the least possible delay.

Man Overboard. Under steam. Stop and back. Lower boat when in best position to rescue man.

Under steam and sail. Hard down the helm. Stop and back. Take in light sails if necessary, trim yards to assist in backing towards the man; lower boat in best position for rescue.

In both cases, observe the usual precautions about lowering a boat when making sternway.

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Bad Weather under Steam. If in a steamer of sufficient power, heave to head to sea with no sail set, using a sea anchor if desirable. Some steamers, notably long merchant steamers of recent construction, heave to with the wind on the quarter, engines going ahead slowly. But it would be unsafe, probably, for shorter steamers to do so.

A full powered steamer should be able to run before any sea.

Steamers hove to under sail alone, will vary greatly as to the amount of canvas spread and its disposition, but the conditions to be fulfilled are usually the same in all cases, viz.:

First, To show enough canvas, if possible, to ensure steerage way.

Second, To dispose it so as to counteract too great a tendency to fall off.

Modern steamers are often undersparred, so. that any one sail is comparatively small when the immersed longitudinal section is considered. Moreover, the steamer has greater proportionate length than the old fashioned sailing vessel, and a greater tendency to fall off.

The inference is that steamers will heave to under canvas with a greater number of sails and with more after sail than a sailing vessel of older model.

Hence we find many steam men-of-war heaving to under close reefed main topsail, main trysail, and storm mizzen or reefed spanker; the fore storm staysail being bent, but not always set. Others will hold on to the close reefed fore topsail as long as possible, in addition to the above canvas, to ensure the necessary steerage way.

Sending down the light yards and masts, whether under steam or sail, will greatly relieve the ship in heavy weather.

TAKING IN TOW AT SEA.

(a) There is a fresh breeze blowing, and A is wholly disabled, or nearly so. B steams along the weather side and throws a heaving line, if prudent, then puts helm hard a starboard, and stops when she can maintain her position

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(b) It is blowing a moderate gale. A is totally disabled, and in the trough of the sea. B dare not lower a boat, but slings a water-tight empty cask to the end of the deep sea lead line. She steams up on A’s weather quarter at a safe distance, veering or hauling in line to bring the cask alongside of A. B then puts his helm hard a starboard, and holds his position till the towline is fast on board of A.

(c) There is a heavy sea, and A is under control. B

steams ahead at a safe distance, head to wind. A barrel, full of holes, is slung, and the rope paid out until alongside of A. The barrel being full of holes will sink to the water’s edge and will not be affected by the wind. A cork fender and grate bar may be used instead of the barrel.

(d) Calm and smooth sea. A is disabled. B steams along her port side and throws a heaving line, puts helm hard a starboard, stops and hauls hawser on board.

(e) In a seaway. A has rudder disabled, but motive power is good. B wishes to help her into port. B takes hawsers from A’s quarters. A tows

and B steers. By this disposition, both steamers being large full powered vessels, B can steam at least at half speed, thus relieving A of that much work. If A were being towed, she would take rank sheers at short intervals, obliging B to slow

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Chasing. The chaser will steer a course slightly converging to that steered by the chase; taking the bearing by compass and measuring the angle subtended by the masts. By constantly keeping the chase on the same compass bearing, the chaser will attain the chase in the shortest time possible, and by the shortest route.

If the course steered by the chase is more advantageous than that steered by the chaser, the latter can steer a parallel course to take the same advantage, until he arrives as near as possible (that is, abreast of him), and then steer a course to cut him off. Make sail when it will draw.

The vessel chased should employ every means to retard the time of being overtaken. A few cables’ lengths more may suffice to save the chase; because a fog, an injury to the chaser, or night coming on, may enable him to escape.

Should the chaser be a sailing vessel, the chase will steam directly to windward. *

Collision. On a collision in steaming, upright the screw. In that case gear dragging overboard will not foul it, otherwise it will.

On a collision taking place when on soundings, it is generally best for the weathermost ship to anchor.

When two ships are becalmed near each other, either send the boats of both to tow the lighter, or of the one that lies in the most favorable position (with reference to swell) for being moved; or else, run warps out from the quarter of one to the bow of the other, or vice versa, and both may thus be sprung ahead and steered clear of each other.

To Anchor a Steamer. Ordinarily this is accomplished as follows: Steam in, “slow down” in good time, and, when near the berth determined on, stop the engine; as soon as headway ceases, and she commences going astern, let go the anchor and veer to the proper scope. With an ebb tide, anchor “head on,” and the tide will carry the vessel astern fast enough to take her chain. If a flood tide, the vessel should be sheered with the helm, and the anchor dropped so that she may not overrun her chain. When there is not enough wind or tide, reverse the engines, let go the anchor, and back till the required scope is laid out straight.

“Fifteen or twenty minutes before coming to anchor, the chief engineer should be informed of the fact, so that the fires can be allowed to burn down, and the pressure of steam to fall to such an extent that the necessity of blowing

* For Ship’s Papers, see Appendix N.

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On entering a narrow channel with the flood tide, a steamer could not “round to,” but would have to anchor “end on,” and swing to the tide; but if waiting for high water, intending to pursue her way up, she would have to anchor by the stern to keep pointed fair.

If after entering a narrow channel a steamer should find herself compelled, by the discovery of heavy batteries, or the appearance of the enemy in superior force, to go out again, the quickest way to wind the vessel would be by dropping and swinging to an anchor; then, as soon as pointed, heave up or slip, making all preparation beforehand.

Should the ebb tide be running, make use of a kedge, and anchor by the stern, giving the vessel a sheer with the helm, that the tide may catch her on the bow and sweep her around. On the flood, let the kedge go from forward to wind her, availing yourself of the helm, jib, spanker, and engine, as circumstances admit.

When ascending rivers where the turns are short, the engine should be slowed down,” or stopped, just before coming to a bend, to prevent reaching over to the further shore; and when going up against a strong ebb tide, in such a river, for example, as the Piscataqua, N. H., the engine must be stopped, and should that prove insufficient, an anchor must be let go in the bend to permit the vessel’s head to swing to the new course. When pointed right, weigh and stand on. This is an extreme case, however.

Young officers are liable to forget the great use of the jib and spanker in turning a steamer; they are often indispensable.

Mooring to a Buoy. Steam up to moorings slowly, keeping steerage way. If there is no wind, keep the buoy a little on the starboard bow, and when the engines are reversed the bow will fall off, bringing the buoy ahead. ** If the wind is on the port side, the buoy should be brought more off the starboard bow, as she will swing off more rapidly when the engines are reversed.

* Practical Notes on the Steam Engine, by J. W. King, Chief Engineer, U. S. N.

** References are exclusively to right-handed screws.

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In approaching moorings from to leeward, and with wind and tide so strong as to make it difficult for the boat to pull to windward with a whole warp aboard, the boat may be lowered in good season and given time to reach the buoy. Boat to carry a short towline and a heaving line. Having secured one end of the warp to the buoy and bent the heaving line to the other end, the boat awaits the arrival of the steamer, and at the proper moment pulls for her, tossing the heaving line when within range.

Large steamers frequently find it very difficult to get clear of their moorings in a crowded harbor. When the wind serves, the jib will be of great assistance; otherwise, the slip rope may be veered out as far as practicable and a broad sheer given with the helm or propeller.

The slip rope should be rove from forward aft, and the end secured well abaft the hauling part, so that when cast off it will fall clear. A steamer’s bow may be brought back to the buoy under very embarrassing circumstances by the end of the slip rope overriding the hauling part.

If the vessel overrides the buoy and there is a probability of fouling the propeller, the engine should be stopped at once. There will be a possibility of its going clear, and if not, there will be a fair chance of no damage resulting. If the vessel is head to tide, or wind, there is still a chance of clearing when she gets a sternboard in the act of swinging. If this fails, a strong hawser from the bow made fast to the buoy and taken to the capstan would probably clear it, particularly if there were not much tide.

Mooring at a Wharf: To make a successful landing at a wharf it is necessary to know the action of the tide or current. If by chance there should be neither tide, current, nor wind, it becomes a comparatively simple matter.

To moor at a wharf, slack water and calm. There is an advantage in approaching a wharf on the port hand, for if the bow should be pointing too much for the wharf a few turns back on the engine would swing her off, whereas were it on the starboard side the bow would be carried still more towards it. As soon as the wharf is approached, heaving lines are thrown ashore and bow and stern lines run to piles. If the vessel does not come up to the wharf promptly, make the stern line fast and give the engines a turn ahead, taking

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A wharf should be approached with a head tide when practicable. The bow fast would then be run out and the vessel dropped alongside. If the tide be weak a turn of the screw will assist. The stern fast and springs may then be passed out.

If there be a fair tide, the stern fast should be got out first and a turn taken, when the vessel will drop alongside.

If there be an eddy setting in the opposite direction to the current it must be allowed for.

The most dangerous eddy is one setting directly toward the wharf. In this case as little drift as practicable should be allowed, as there is danger of bringing up with great force against the wharf.

The most vexatious eddy is that which sets directly out from the wharf. In this case the vessel must reach her position under good headway, the engines be reversed promptly and headway stopped. The fasts must be gotten out as quickly as possible, and the vessel gradually sprung alongside by going ahead and astern alternately and taking in the slack of lines.

When the propeller cannot be worked it is frequently the custom to veer the bow fast well out and haul the stern to the wharf, the bow fast is then hove in by the capstan or windlass and the bow brought to the wharf. It is easiest to get the ship alongside in this way, there being less resistance (owing to the lesser draft) forward, and the capstan is handy for heaving the bow in.

To moor at an exposed wharf, where there is a heavy swell, making it unsafe to lie alongside. In such cases mooring buoys are commonly placed in position broad off the wharf. Run in between the buoys a n d the wharf, and run one

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Men-of-war having been hauled alongside a Navy Yard wharf generally use the fixed moorings prepared for the berth at which they lie, as shown in the figure.

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

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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

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

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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.

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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

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.
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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)

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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

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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

where:

θ = angle of heel,
v = speed of ship in feet per second,
R = radius of circle turned (in feet),
m “metacentric height”-height of transverse metacentric above centre of gravity,
d distance of centre of gravity above centre of lateral resistance.

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

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(1) Directly as the square of the speed of ship;
(2) Inversely with the metacentric height;
(3) Inversely with the radius of the circle.

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

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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

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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.”

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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

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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.

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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

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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

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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.

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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.

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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.

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* “Naval Tactics on the Open Sea,” by Captain the Hon. E. R. Fremantle, R. N.