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If with the midship tanks unfilled, the trim exceeds 0.5°, it must be reduced to zero, since in the opposite case, with the midship tanks filled, it increases significantly.

As the midship tanks fill up, their ventilating system is closed immediately. If as the midship tanks fill up, the submarine acquires a significant negative buoyancy or a trim of 5-10° and more, a bubble must be introduced into the midship tanks and the required quantity of water pumped out of the auxiliary tank, then, removing the bubble from the midship tanks, continue trimming.

After trimming is completed, the main ballast tank vents are closed, after which the compartment heads report to the control room on the presence of personnel in the compartments and the quantity of water in the auxiliary ballast tanks. This information is recorded in the deck and trim logs.

If before trimming, the annular spaces of the torpedo tubes were not filled with water from the water-round torpedo tanks, then after trimming is completed the quantity of water in these tanks must at least equal the quantity required to fill the annular spaces.

Trimming under way. In a calm sea, a submarine can be trimmed at periscope depth, and in a rough sea at safe depth. Before diving, the command "Proceed to your stations, prepare to dive" is given. After the men have taken their stations in accordance with the diving procedure, the conning tower hatch is dogged down, the electric motors started and main ballast taken on. After ballast has been taken on, the order "Trim the submarine at a depth of so many meters, with such and such a way, with a trim of so many degrees by the head (or stern)" is given.

Main ballast is taken on the same as in trimming without a way on. The midship tank vents are closed immediately after the tanks are filled.

The indicated trimming depth is maintained by the way and trim. There is no need to develop a large trim in diving. The main ballast tank vents are closed immediately after the submarine attains the ordered depth, after changing the trim from the head to the stern.

If the submarine does not dive, water must be taken into the auxiliary tank through the kingston or the fine flooding valve. As soon as the depth gauge indicates a change in depth the water intake is shut off.

If after filling the midship tanks the submarine acquires negative buoyancy, the submarine must be trimmed by the stern by means of the rudders and way and, while maintaining the ordered depth, water must be simultaneously pumped out of the auxiliary tank.

If these measures are inadequate, a bubble is admitted to the midship tanks or they are blown, or the required amount of water is pumped out of the negative tank and then, removing the bubble from the midship tanks, trimming is continued. These measures are taken depending upon the rate of change in the depth of the submarine.

Air bubbles must be removed from the forward and after main ballast tanks and from the superstructure by alternately trimming the submarine by the head

and by the stern ("rocking" the submarine), after which the main ballast tank fore and aft vents are closed.

Through drainage or taking water into the auxiliary tank and by pumping the auxiliary ballast between the trimming tanks, the bow planes are adjusted to zero position and the stern planes with a slight deviation from the plane of the frame, and the submarine maintains its depth with a slight trim by the head. In this position the submarine is considered trimmed.

After the submarine is trimmed, the midship tank vents are opened to remove the residual air bubble, then these vents are closed. The submarine is maintained for awhile with a trim of zero degrees and the command "Trimming completed" is given. With this command, the compartments report to the control room on the presence of personnel in said compartments and the quantity of water in the auxiliary ballast tanks, and appropriate entries are made in the deck and trim logs.

4. Controlling the Diving Planes in Event of a Crash Dive

With the command "All hands below," all hands on the bridge (on the deck and in the superstructure) quickly go below.

With the "Crash dive" alarm, the deck watch quickly goes below (if the command "All hands below," has not been given), and the submarine crew simultaneously takes the following measures:

1) stops the diesels; disengages the forward clutches; dogs down the diesel air main induction inlets and other hull openings; opens the MBT pressure equalizing valves containing fuel, and also the buoyancy tank vent;

2) starts the electric motors;
3) fills the main ballast tanks;
4) controls the diving planes;

5) blows the negative tank and closes its kingstons;

6) closes vents in the midship tanks and main ballast tanks.

In crash diving, the midship tanks are filled after the conning tower hatch is dogged down and after the monitoring instrument on the control panel indicates that the conning tower hatch, the diesel main air induction and the ship and battery vents are closed.

In the initial stage of diving, the bow planes must be set for diving and the stern planes for surfacing. In this case, both pairs of diving planes create downward forces. The stern planes, which create a trimming moment by the stern, enable the submarine to remain on an even keel, equalizing the trimming moment which occurs when the negative tank is filled.

In attaining depth, when all of the main ballast tanks are filled, the planes must be set for diving, a trim of up to 10° (depending on the class of submarine) must be created, and must be maintained during diving.

If the submarine must remain at periscope depth, the negative tank is blown at half the periscope depth and, if need be, the submarine dives to a depth where it is safe from ramming-a depth not less than periscope depth.

In diving, the diving plane angles vary according to the amount of trim and the diving rate. In submerging, the command "Report on depth" may be given, and as soon as the planesman receive this command he reports the change in depth every five meters, or every one-fourth meter at periscope depth. As the ordered depth is approached, the trim is reduced and the planesman reports the diving depth reading on the depth gauge.

In crash diving, the submarine must be rigged for emergency blowing of the fore and aft main ballast tanks if the trim rapidly increases and exceeds the permissible. The midship tanks may have to be blown if there is a loss of buoyancy due to incorrect calculation of the weight of the submarine or spontaneous blowing of the negative tank.

5. Diving of a Submarine and Control of the

Diving Planes in Stormy Weather

Diving in heavy seas, like ordinary diving, commences with the command "Proceed to your stations, rig for diving."

In a large wave, the submarine must dive with the negative tank full and at high speeds, creating a considerable hydrodynamic force on the diving planes.

In the initial stage of diving, the bow planes must be set for diving and the stern planes for surfacing, thus permitting the submarine to remain on an even keel and also creating a downward force. After the submarine deck submerges, the stern planes must be reset for diving. Then the stern and bow planes will create a trim by the head, thus assuring rapid submergence of the submarine. The negative tank should be blown at a depth not less than periscope depth.

6. Handling a Submarine Snorkeling

A submarine begins snorkeling submerged when the "general quarters" alarm is sounded.

In rigging for snorkeling, the submarine crew takes the following measures: 1) rigs for snorkel propulsion (charging) the diesel and line shaft indicated by the Commanding Officer of the submarine (the electric motor operating in this case is on the same side as the diesel which will not be snorkeling);

the bilge;

2) rigs the intake and exhaust vent for snorkeling;

3)

raises the snorkel mast and drains it into one of the tanks or into

4) checks for water in the snorkel gas and air lines;

5) opens the snorkel air valve and starts the blower;

6) starts the engine at low speed by order of the Commanding Officer

of the submarine.

The command "Trim the submarine at a depth of so many meters" is given before the snorkeling submarine begins diesel operation. The transition to

snorkel operation is made upon completion of trimming, after which Condition No. 2 is sounded.

At the time the submarine begins snorkeling, additional hydrodynamic forces and moments arise, considerably altering the equilibrium of forces and moments while operating submerged, necessitating a corresponding adjustment of the diving planes in order to compensate for them.

The buoyancy of the submarine does not change in hoisting the masts, since the water they contain will constitute part of the underwater displacement of the submarine.

After the diesel engine is turned on, pressure is created throughout the entire engine gas exhaust system. As the indicated exhaust pressure is attained, the upper double-action snorkel valve is opened. After the submarine begins snorkeling, it acquires positive buoyancy due to removal of water from the exhaust lines. In this case, buoyancy is reduced to zero by taking an appropriate amount of ballast into the auxiliary tank.

The transition from small to large engine loads is accomplished gradually in order to prevent vapor formation on the surface of the sea near the exhaust nozzles.

Maintaining a submarine at the ordered depth while snorkeling is a primary task. Care must be taken to assure that the float valve is not submerged. In heavy seas and whenever the planesman is unable to maintain the submergence depth precisely, the snorkel air induction may take water. In this case the float valve is closed, producing a sharp pressure drop inside the submarine.

When a high vacuum develops, the diesel must be stopped and the submarine begins operating submerged on electric motors, rising to periscope depth. After the submarine stops snorkeling and the exhaust lines are filled with water, the submarine acquires negative buoyancy.

In the transition from snorkeling to operating submerged, residual buoyancy is reduced to zero by pumping an appropriate quantity of ballast from the auxiliary tank.

The shift from snorkeling occurs as follows. With the command "Crash Dive," personnel stop the operating diesels and disengage their clutches, shut off the ship ventilation system, close the exhaust lines, open the snorkel kingston and lower the snorkel mast, start the electric motors, dog down the bulkhead sluices, and rig the engine compartment for diving. Then, by means of the way and rudders, the submarine dives to the ordered depth. The negative tank is filled if the need arises.

7. Handling a Submerged Submarine

The diving depth of a submarine is varied by creating a trim, and through speed and buoyancy. A well trimmed submarine must be controlled entirely by the stern planes.

The bow planes are used:

1) in crash diving;

2) in turning the submarine;

3) in the presence of negative buoyancy;

4) to develop trim in varying the diving depth;

5) in propelling with electric motors at cruising speed.

In order to achieve a rapid change in diving depth, the bow planes must be set to full down (or up) and the stern planes used to maintain the necessary trim.

In proceeding to the ordered depth, the submarine must be controlled by the stern planes. The bow planes are set at zero or, if the need arises, are set to surface (or dive).

The negative tank should be filled to accelerate diving under extreme circumstances, for example, to avoid ramming or in event the submarine broaches due to a wave and is unable to submerge by headway.

A submarine in neutral trim making a turn assumes a trim by the stern. The greater the speed of the submarine in turning and the greater the angle of the diving plane, the less often this phenomenon occurs. The planesman must be informed whenever the vertical rudder is adjusted and eased.

Control of a submarine at periscope depth in heavy seas is complicated by the fact that the submarine tends to broach due to the wave. A submarine operating at periscope depth in fresh weather must:

1) have slight negative buoyancy;

2) proceed at least at moderate speed;

3) have a slight trim by the head.

It is recommended steering a course beam on to the sea.

Whenever due to a high sea it is impossible to maintain periscope depth, it is necessary to operate at a safe depth and to proceed at a speed at which the submarine can be maintained at periscope depth.

If a submarine broaches in a rough sea, it is submerged by filling the auxiliary tank and then blowing it.

When a submarine dives to considerable depth it acquires negative buoyancy due to compression of the hull. The creation of negative buoyancy is indicated by an increase in the trim by the stern and a corresponding need to increase the angle of adjustment of the diving planes for surfacing.

In diving under circumstances permitting the submarine to surface, with the creation of a large trim (immediately after filling the midship tank or tanks), and with a subsequent increase in this trim, the submarine should stop diving and surface.

For this purpose, the main ballast tank vents must be closed, the midship tanks blown and a bubble admitted to the end tanks according to the trim.

8. Counteracting the Loss of Buoyancy and Trim

The primary causes of buoyancy loss with a simultaneous increase in trim are as follows:

a)

When the submarine is diving:

1) penetration of water in the pressure hull;

2) inaccurate calculation and method of trimming;

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