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In order to be constantly ready to maintain watertight integrity, the pressure hull and technical gear of the submarine must always be in operating condition and ready for use.

The submarine duty-watch section must continuously monitor the condition of the bilges and sea openings, increased pressure in the tanks, and pressure in the high-pressure air groups. Under way in a surface or submerged condition, mandatory inspection of the submarine is performed by personnel every 30 minutes and by order of the watch officer, irrespective of time. The inspection results are reported to the control room.

When a submarine operates in a surface or submerged condition, the vent valves of the main ballast tanks must be closed and in hydraulic control position. When a submarine is at sea, the sea openings may be opened, the engines may be started up and the crew may go to the bridge only with permission of the watch officer.

2. Surface Watertight Integrity Table

In designing a submarine, possible combinations of flooding of compartments and tanks are considered. Of these combinations, the most probable flooding under navigation conditions is selected and recorded in the watertight integrity table.

For each type of major damage this table indicates the forward and after draft, displacement and residual reserve buoyancy, transverse and longitudinal stability, angles of heel and trim, trim and heeling moments per 1°, and also the methods for righting the submarine, listing the elements involved in event of major damage, but also taking into account the steps taken in righting.

The following conventional symbols have been derived to designate compartments flooded in event of major damage and tanks flooded in righting:

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The watertight integrity table can be used to determine the condition of the submarine in various instances of major damage; to right the submarine while maintaining its seaworthiness, to have a complete understanding of the seaworthiness of the submarine after righting; and, finally, to avoid steps adversely affecting the seaworthiness of the submarine.

3. Using the Watertight Integrity Table

Having determined the number of damaged compartments and tanks, we find a similar damage situation in the watertight integrity table and use it to

determine the forward and after draft, the new displacement, reserve buoyancy, and longitudinal and transverse stability of the submarine.

Having evaluated the situation, a decision is made whether the submarine must be righted: the tanks are flooded or blown; and sequence indicated in the watertight integrity table must be followed.

In righting a submarine by flooding the tanks, it should be remembered that this causes a further decrease in the reserve buoyancy of the submarine, thereby placing it in even more dire circumstances (both with respect to transverse and longitudinal stability) than it was prior to righting.

In the history of underwater navigation, instances have been recorded in which submarines, possessing a low reserve buoyancy, have lost their longitudinal stability, as a result of which they have unexpectedly passed from a surfaced to a submerged condition. In order to right a submarine, it is best to first increase the reserve buoyancy by blowing the tanks inside the pressure hull (trimming, compensating, torpedo-tube flooding, fresh water storage, oil, and tanks, fuel, etc.). By blowing these tanks, the reserve buoyancy may be increased, longitudinal and transverse stability improved, and the heel and trim of the submarine decreased.

4. Utilizing Speed in Maintaining Watertight
Integrity in Submerged Condition

With existing high-pressure air reserves aboard a submarine, and the considerable time required to blow the ballast tanks at great depths, utilization of speed and the diving planes is practically the only effective means of dealing with plunges and trims at submerged depths.

In all cases in which water has entered the pressure hull in a submerged condition, the speed of the submarine must be immediately increased to the maximum possible speed at which a maximum trim moment is quickly developed by the stern planes, the carrying power of the submarine increased, and time gained to blow the ballast tanks before the submarine plunges beyond maximum operating depths.

With a significant and continually increasing loss of buoyancy, backing is not recommended, even while simultaneously blowing the forward ballast tanks, since this can result in a sharp increase in submergence depth and trim. Backing is required if measures to cope with plunging and trims by the head are necessitated by jamming of the diving planes for dive.

In order to make sure the submarine will climb when any compartment is flooded, a trim by the stern must be developed, and held within limits assuring prolonged operation of the power plant.

An increase in trim to values assuring only temporary operation of the power plant can be permitted only with full assurance that the submarine manages to surface during this time.

In order to maintain and steer a submarine with a flooded compartment at a given submergence depth, it must be placed in one of the balanced operating

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

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The resultant of the forces R is divided into horizontal R1 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."

Rudder stock

R

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

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1. A submarine is proceeding at constant depth H const, with trim 0°; the stern planes lie in the plane of the frame 8, = 0, and the bow planes are set for diving 80 (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.

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2. The submarine is proceeding at constant depth H = const, with trim 0°; the bow planes lie in the plane of the frame 8 = 0, and the stern planes are set for diving 8,#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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