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modes. Each of these modes corresponds to specific angles of trim by the stern; if they are exceeded, the trim begins to sharply increase and the submarine becomes uncontrollable. The values of the angles of balance of the trim for cases involving flooding of each of the compartments are determined at the time the submarine is designed, and are entered in the ship's log and records.

When a submarine is operating with a trim, special observation must be made of all machinery, systems and units, the reliability and operating time of which are limited by the amount of trim.

5. Use of High-pressure Air in Maintaining Watertight

Integrity in Submerged Condition

High-pressure air is the basic means of compensation for negative buoyancy and trim moments arising when water enters the pressure hull of a submerged submarine.

In order to quickly overcome and reduce increasing trims in a submarine, with simultaneous compensation for loss of buoyancy when water enters the pressure hull in a submerged condition, high-pressure air must be used only to blow the appropriate main ballast tanks. High-pressure air may not be used to raise the water level in the bulkheads or create counterpressure in a flooded compartment before beginning to climb, or to overcome and reduce trim.

When there is no speed (or when a speed in excess of 4-5 knots cannot be developed), the damaged submarine with a flooded compartment begins to climb only after creation of sufficient positive buoyancy to stop the dive. In order to quickly acquire the maximum possible positive buoyancy, the midship and end ballast tanks at the trimmed end must be blown simultaneously.

With a speed in excess of 4-5 knots (or with the possibility of developing it gradually), a damaged submarine with a flooded compartmen begins to climb only after a trim by the stern is developed and maintained within the required limits. In order to rapidly acquire the maximum possible trim moment, only one end group of ballast tanks at the trimmed end must be blown.

Simultaneous emergency blowing of all ballast tanks is feasible only if a compartment in the midship section is flooded (creating a negligible trim moment).

If a compartment distant from midship is flooded, emergency blowing of all ballast tanks sharply increases the existing trim, lets off part of the air from the blown tanks, and increases the probability the damaged submarine will plunge.

Irrespective of whether the submarine is in port or at sea, it must possess an irreducible constant reserve of high-pressure air, according to established standards. The expended reserve of high-pressure air must be replenished at the first opportunity.

SECTION 8. AGILITY OF SUBMARINES

1. General Aspects

The agility of a submarine is its ability to change direction of movement in turning the helm.

A submarine possesses agility in a horizontal plane (turning the vertical rudder) and in a vertical plane while submerged (turning the diving planes).

Let us consider the agility of submarines in a vertical plane.

If we turn the diving planes on a submarine proceeding at speed V, then the stream of water approaching the rudder blade will exert pressure on the latter. The resultant of the hydrodynamic forces on the rudders R (Fig. 11), perpendicular to the rudder blade

R =

KSV2 sin 8 0.195 + 0.305 sin 8

[kg]

(19)

where k coefficient, equal to 20;

S area of the rudder blade, m2;
V speed of the submarine, m/sec;

- angle of the rudder blade, degrees.

The resultant of the forces R is divided into horizontal Rn and vertical R, components. The former will decelerate the submarine, while the latter will change the direction of its movement in the vertical plane.

The stern planes lie directly in the stream of water generated by the screws. Therefore, the speed of the free stream selected is somewhat greater than the speed of the submarine.

If the diving planes create a trim by the head, it is designated with a minus sign (“_”), and it is said that “the rudders are set for diving”; if the diving planes create a trim by the stern, it is designated with a plus sign (“+”), and it is said that "the rudders are set for climb.”

R

Rudder stock

V

Fig. 11. Action of a diving plane at the
angle of attack with the free stream.

If the vertical component R, tends to cause the submarine to climb, it is considered positive (+R,), and if the submarine dives, it is negative (-R,).

2. Various Uses of Diving Planes

1. A submarine is proceeding at constant depth H = const, with trimų 0°; the stern planes lie in the plane of the frame 8g = 0, and the bow planes are set for diving 8670 (Fig. 12).

The submarine is light and possesses an unbalanced trimming moment by the stern. In order to trim, the submarine must pump water from the after trim tank into the forward trim tank and take on ballast in the compensating tank.

2. The submarine is proceeding at constant depth H = const, with trim y = 0°; the bow planes lie in the plane of the frame 80 = 0, and the stern planes are set for diving &#0 (Fig. 13).

The submarine is heavy and possesses an unbalanced trimming moment by the stern. In order to trim the submarine, ballast must be pumped from the compensating tank and water from the after trim tank into the forward trim tank.

From the examples examined above, it is evident that water must be pumped between the trim tanks in the direction of the moment from the diving

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planes. Having begun to pump water, the diving planes must be eased, at the same time varying the quantity of water in the compensating tank.

3. Using the Diving Planes Together

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1. A submarine is proceeding at constant depth H = const, with trim y = 0; bow and stern planes in different directions at 8 g = 85 (Fig. 14).

The submarine is hea and possesses an unbalanced trimming moment by the stem. In order to trim the submarine, ballast must be pumped from the compensating tank and water pumped from the after trim tank into the forward trim tank. In beginning to pump water from the after trim tank into the forward trim tank, the bow planes must be eased, then ease the stern planes after they assume a neutral position, while simultaneously pumping water from the compensating tank.

2. The submarine is proceeding at constant depth H; = const, with trim y 3-4°, bow and stern planes are positioned in different directions at 86 = (Fig. 15).

The submarine is light and possesses an unbalanced moment at the stern. In order to balance the submarine, ballast must be taken into the compensating tank and water pumped from the after trim tank into the forward trim tank.

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Fig. 15. Submarine is light.

4. Hydrodynamic Force on the Hull

No matter how well trimmed a submarine is, trims develop when it moves. This proceeds from the fact that a submarine is unsymmetrical with respect to the horizontal plane. The resultant of the hydrodynamic forces of the hull R' acts at a certain angle y to the rate of linear displacement of the center of gravity. The point of application of the resultant of the hydrodynamic hull forces O is called the center of pressure and is forward of the center of gravity (Fig. 16).

Let us divide the hydrodynamic hull force into vertical and horizontal components. The horizontal component Rh will be compensated by the thrust of the propeller, while the vertical component R', creates a lifting force.

In order to determine the effect of the hydrodynamic force, we make the following constructions.

At the center of gravity of the submarine we apply the vertical component Ry, acting in the opposite direction. A hydrodynamic moment results, since the resultant applied at the center of pressure O does not coincide with the center of gravity G.

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When a submarine is operating with full buoyancy the following remain open:

1) the conning tower hatch;

2) the diesel main air induction, engine room kingston and diesel exhaust valves, only when the diesels are operating;

3) the cooling water discharge valve and the valve of the main electric propulsion motors;

4) the pressure compensation valves in the fuel tanks;

5) the ship and battery ventilating shafts, by order and only during ventilation;

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