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any gear not self holding, any shock on the rudder is transmitted to the hand wheels, and considerable power is required to hold

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the gear at any required angle.

FIG. 89.

To hold the hand wheels in such a gear a "Fayrer's brake" is fitted. This is a band brake bearing

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on a wheel on the hand-steering shaft. It can be tightened by standing on a foot-plate either side (Fig. 89).

In Harfield's gear an interesting clutch is fitted just abaft the hand wheels (Fig. 90). The wheels A and B are loose on the

shaft, and are provided with pawls at A and B, so that motion of A in a right-handed direction and motion of B in a left-handed direction (looking from the bulkhead) is impossible. The pinion, which gears with the spur wheel on the steering gear, moves endwise on the shaft by means of a thread, the shaft acting as a bolt and the pinion as the nut. If the hand wheels are rotated in either direction it will be noticed that the pinion is drawn along to the wheel A or B, which is free to rotate. If, however, the motion is reversed, i.e. the rudder becomes the motor in either direction, the pinion is drawn along to, and jams against, the wheel A or B, which is prevented from rotating, so that the rudder cannot react on the hand wheels.

Such a clutch or a Fayrer's brake is unnecessary when a worm and worm wheel is introduced into any portion of the gear, as this renders the gear non-reversible.

Spare Gear. With such an important fitting as the steering gear, a large margin of strength is provided in all the parts, and spare parts are provided for certain portions of the gear, so that these may be replaced in case of disablement. The following is the list of spare gear provided in a recent vessel fitted with screw gear. A similar list is provided for other gears.

One connecting rod, two bushes for same, two pins for same; one spur wheel 781 in. diameter; one spur wheel 451 in. diameter, one bush for same; two nuts for screw shaft keep plates; two sets of brasses for screw shaft; one gunmetal nut, right-handed; one gunmetal nut, left-handed; one set of brasses for guide rods, No. 4. All of these are tried in place and stowed.

In some gears a length of shafting in the shaft passage is made the weakest part of the gear, so that this would be the first to go, and so save the steering gear itself. A spare length of this shafting is carried to replace.

Clutches, etc.-All steering wheels are so arranged that the upper part of the wheel moves in the same direction as that of the ship's head. In a large ship the steam steering wheels take the rudder from hard-over to hard-over in eight complete turns, the hand wheels requiring twenty-four complete turns.

Clutches are fitted to enable the gear to be changed quickly from connection with one engine to the other, or from either engine to the hand wheels. In doing this it is necessary to hold the gear (unless this is self holding), by means of a brake, usually a friction brake. Indicators are provided in a prominent position,

showing the angle at which each engine, hand wheels, and the steering gear itself are situated. It is of the greatest importance that connection should only be made when the engine or hand wheels, as the case may be, indicates the same angle as the steering gear itself. For, suppose the engine at 5° port is coupled with the steering gear at 0°, then when the steamengine is taken over to hard-a-starboard the gear will bring up against the stops with the engine at full speed, and some part of the gear will be fractured. In recent ships the steam gear brings up at 35°, the gear itself at 37°, and the rudder at 38°. The clutches to the steering gear should be so arranged that it is not possible for the steam steering engines to become geared up together, or for either to be geared up to the hand wheels under any circumstances.

Auxiliary Steering Gear.-It was until recently the practice. to provide auxiliary means of steering, for use supposing the steamengines and hand wheels were disabled. This usually consisted of a set of blocks and tackles, which could be fastened to the gear to work it by hand. The gear provided entailed considerable weight, and was difficult to rig up in place. Ships which had the auxiliary provided never used it, and it has been removed from a number of ships. The present practice is simply to rely on the hand wheels as the alternative in case the steam-engines are not available. From this point of view, the use of twin screws is an alternative method of steering, and cases have occurred recently in which ships have had to go long and stormy voyages without a rudder at all, the steering all having been performed by the twin

screws.

CHAPTER IX.

PUMPING, FLOODING, AND DRAINAGE.

THE present chapter deals with the methods adopted in ships of the Royal Navy for clearing water out of the ship, which has entered through damage or has accumulated in the bilges under the ordinary conditions of working; and also the means for voluntarily admitting water into certain portions of the ship to preserve stability, or to keep the ship upright or on an even keel after damage, or to flood the magazines, etc., in case of fire.

By Drainage is meant the means of allowing water to pass from one compartment to another until it reaches a pump-suction by which it can be removed.

By Flooding is meant the deliberate admission of water into the ship through a sea-cock. This may be necessary to correct heel or trim after damage, or in the event of fire.

By Pumping is meant the general arrangements adopted to remove water from the ship by means of the fire and bilge pumps in the engine-rooms, or by the Downton pumps, worked by manual power.

Before dealing generally with the subject, it will be advisable to see how far the pumps fitted to a ship are able to deal with the inflow of water.

If A be the area of a hole in a ship's bottom in square feet, and d the distance of the centre of the hole below water, then the initial velocity of the water through the hole is given by 8 ft. per second, so that every second there would be 8A√ā cubic ft. of water entering, or about 14A√ tons per minute. If the hole is 16 ft. below the surface, about 56 tons will enter in a minute for every square foot of area.

The following is the specified capacity in tons per hour of the pumps available for dealing with such a leak in a recent large ship, viz.

Four centrifugal pumps (used ordinarily for circulating`
water through the condenser drawing from the sea),
which can draw from the engine-room bilge
Four fire and bilge pumps...

Four Downton pumps

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5600 tons

400 tons

100 tons

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6100 tons

That is about 102 tons per minute. But we have seen above that the water through 1 square ft. amounts to 56 tons a minute, so that a hole only 2 square ft. in area (19 in. diameter), 16 ft. below surface, is sufficient to overpower the whole pumping capacity of a large ship. Such a hole is small in comparison with what would result from a collision, and this illustrates the importance of efficient watertight subdivision, which has been dealt with in previous chapters. By this means the damaged compartments may be isolated, and a collision mat placed in position over the hole so that repairs of a temporary nature may be undertaken.

In recent ships the arrangements for pumping and drainage are considerably simpler than formerly adopted; it is proposed only to deal with the arrangements in a battle-ship of the Duncan class, as being typical of recent practice.

Main Drain.-Special arrangements are made for clearing the ship of large quantities of water for which the ordinary steam and hand pumps would be inadequate. For this purpose a main drain (Fig. 91) is worked above the inner bottom from the forward boilerroom, branching to either engine-room. This drain is 15 in. diameter in the middle boiler-room, and 20 in. x 15 in. in the after boiler-room. By means of this drain, water can be passed from either boiler-room into one or both engine-rooms. Sluice valves, with non-returns, are fitted as shown to control the flow of water to the engine-rooms; the non-return valves automatically prevent the passage of water from the engine-rooms or from one boiler-room to another. In each engine-room, suctions are taken down from the circulating pumps of the condensers, so that these pumps can be made to draw from the engine-room bilge if desired instead of from the sea. These circulating pumps work independently from the main engines, and their engines are placed as high in the engine-rooms as possible, in order that they may continue working even if the engine-room is flooded to a considerable depth. The sluice valves on the main drain are worked from below and also from the main deck.

In addition to the main drain, the forward compartments likely to have large quantities of water are drained into the forward

H

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