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gradient decreases under the crest of a wave, and increases under the trough of the wave. This increase is greater than the decrease under the crest.
This results in heels and trims, hindering control with the diving planes. In individual cases an increase in trim by the stern increases the submergence depth of the submarine or will cause it to broach.
A negative buoyancy of 3-5 tons (depending on the class of submarine), which can be compensated for by operating the diving planes and increasing the speed, must be imparted in order to avoid broaching. Periscope depth must be maintained with a trim of 1-2° by the head, making it possible to use the vertical component of the hydrodynamic forces on the hull (which in this case will be downward) to control the submarine.
If, despite measures taken, the submarine cannot be maintained at periscope depth and displays a tendency to rise with a trim by the stern, the speed must be increased immediately and the negative tank filled. The latter is blown under high pressure upon reaching a depth somewhat greater than periscope depth, thus making it possible to maintain the submarine at the ordered depth. In rising from this depth to periscope depth, precautionary measures must be strictly observed.
10. Handling a Submerged Submarine in a Turn
When a submarine moves in its turning circle there is complex flow of water around its hull. In this case a significant longitudinal hydrodynamic moment and a downward hydrodynamic force arise.
Ordinarily in a turn a submarine is maintained with a slight trim by the stern. It is not practical to adjust the trim by pumping water between trim tanks, since the turn is of short duration.
In order to maintain the ordered depth in turning, both sets of diving planes must be set for diving before beginning it. The bow planes must be set at a larger angle than the stern planes.
If however the submarine begins to rise, the speed must be increased and the negative tank filled. The latter is blown as soon as the submarine begins to dive.
As the speed is increased the maximum trim angles should be decreased.
11. Handling a Submarine When the
Diving Planes Break Down
When the bow planes break down, it is possible to handle the submarine with the stern planes, which merely require resetting to a larger angle. Whenever the diving planes break down, the trim must be adjusted from a calculation of the ordered speed.
If the bow planes are jammed in surfacing position, the positive vertical component must be compensated by taking sea water into the forward trim tank and continuing handling with the stern planes. If the bow planes are jammed in diving position, part of the water must be pumped out of the forward trim tank. If the stern planes are jammed, control must be maintained with the bow planes. In order to compensate for the lift force and trim created by the stern planes, the trim must be adjusted.
If the stern planes are jammed in diving position, part of the sea water must be taken into the after trim tank. If they are jammed in surfacing position, water must be pumped overboard from the stern.
If both the stern and bow planes are out of commission, the submarine is maintained at the ordered depth by varying buoyancy or speed, or by using a depth stabilizer.
In order to create positive buoyancy and stabilize the submarine with a rapid increase in trim, the main ballast tanks (fore or aft, as the case may be) and midship tanks must be blown.
Moreover, with an increase in trim by the head, the submarine goes at full speed astern and, with trim by the stern, full speed ahead.
If in a submarine the trim by the stern increases in running ahead, then in event of a rapid rise the negative tank must be filled.
12. Handling a Submarine Bottoming and
Rising From the Bottom
Bottoming of a submarine may occur under way and while dead in the water at depths ranging from a safe depth to operating depth. The bottoming site is selected according to the nature of the bottom. Bottoming on solid rock or a rocky surface is not permitted, in order to avoid damaging the tanks or kingstons. The log is shipped and the fathometer housed before bottoming.
Bottoming without a way on. After personnel proceed to their stations with the command “Proceed to your stations, bottom,” a slight negative buoyancy is created, the submarine is trimmed up to 2° by the head, and the electric motors shut off. The submarine should submerge slowly. If diving stops, sea water must be taken into the negative tank (200-250 liters).
The moment of contact with the bottom is determined from the depth gauge needle, fathometer readings and a decrease in trim by the stern.
In bottoming at great depths, a submarine acquires additional negative buoyancy from compression of the hull, with a resulting increase in diving rate. Therefore, in order to decrease the diving rate, in some cases some of the water must be pumped out of the negative tank.
Bottoming with a way on. After the command is given and personnel proceed to their stations, a slight negative buoyancy is created, the submarine is trimmed up to 2° by the head and runs at slow speed. About 10-15 m above the bottom the electric motors are turned off and the submarine, with a trim by the head of approximately zero, should dive slowly under the sole influence of its slight negative buoyancy.
The moment at which bottoming occurs is determined from little bumps or scrapes on the bottom, from readings on the fathometer and depth gauge, and also from the decrease in trim by the stern.
In order to keep the submarine stable on the bottom, water must be taken into the negative tank and this fact recorded in the rough deck log.
Bottoming of a submarine on a thermal layer can occur while dead in the water or with a way on, both at periscope depth and at depths ranging from safe depth to operating depth.
Bottoming without a way on. Upon entering an area with a liquid bottom, the engines are stopped and slight negative buoyancy created, so that the submarine dives slowly. When a liquid bottom is penetrated the depth gauge needle stops and there is a reduction in trim.
Bottoming with a way on is done if the location and depth of a layer of liquid bottom are unknown. In bottoming, it is necessary to proceed at slow speed, create a slight trim by the head (or stern) and carefully observe the depth gauge. Entry of a submarine into a liquid bottom layer is indicated by the following: in diving, a cessation of diving and a reduction in trim; in surfacing, an acceleration in surfacing and an increase in trim. When the submarine enters a layer of liquid bottom, it must be stopped and must wait until a constant depth is established.
As a rule, passage through a thermal layer should be made with a way on and with a trim.
While lying on a liquid bottom, the depth gauge needle and trim of the submarine must be carefully observed in order to make sure that the submarine may get under way at any time and maintain depth.
In order to rise from a liquid bottom, it is necessary to proceed at slow speed, develop a slight trim by the stern (or head) with the diving planes and rise to the ordered depth.
14. Handling a Submarine In Anchoring and
Weighing Anchor Under Water
A submarine may anchor under water either with a way on or lying dead in the water. The following measures must be taken to anchor dead in the water:
1) select an anchorage site;
3) let out the anchor chain with an electric motor to a depth equal to the difference between the depth of the sea and the depth of the anchorage;
4) develop a slight negative buoyancy by taking water into the negative tank so that the submarine gradually submerges.
As soon as the anchor lies on the bottom, there is a decrease in trim by the stern and the submarine acquires positive buoyancy. In order to eliminate pa of this positive buoyancy, sea water must be taken into the forward trim tank in
order to stabilize the trim somewhat and to avoid creating negative buoyancy.
The depth of the anchorage should be changed by taking in or letting out the anchor cable. The trim should not exceed several degrees. In anchoring with a way on, the following steps must be taken:
1) dive to a depth exceeding the anchorage depth by 5-10 m;
2) adjust the trim of the submarine so that at a speed of 2-3 knots and zero trim it will maintain the ordered depth;
3) let out the anchor with an electric motor as the submarine reaches the anchorage site;
4) stop the engines when the distance between the anchor and the bottom is about 10 m, with the submarine diving slowly under inertia.
As soon as the anchor bottoms, the trim of the submarine increases by the head due to inertia, and if there is no inertia it increases by the stem. Subsequent steps are similar to those taken when the submarine anchors without a way on.
In weighing anchor, a slight trim by the stern should be developed and while simultaneously pumping water overboard from the forward trim tank, take in the anchor, preventing large trims by the head. As the anchor is weighed, there should be a trim by the head.
After at least 1/3 of the anchor cable has been taken in, the submarine must get under way in order to maintain the ordered depth.
15. Handling a Surfacing Submarine
The following orders are given before surfacing: to the sonar men-make a careful 360° listening sweep with the sonar; to the engine room personnel-rig one of the diesels to blow the ballast, either with a way on or while dead in the water.
After receiving reports indicating that the aforementioned orders have been carried out by the crew, with the command “Rise so many meters with a trim of so many degrees,” the planesman begins surfacing.
As periscope depth is reached, the trim is reduced to zero, the submarine proceeds at low speed, the periscope raised and the Commanding Officer of the submarine quickly observes the horizon.
Then, if the situation permits, the periscopes are lowered and the submarine rises to diving trim.
During surfacing, the submarine is brought to a slight trim by the stern and the submarine, by adjustment of the speed and planes, rises to half of periscope depth. At this depth the midship tanks are blown and their kingstons closed.
After these measures have been taken, making certain from the depth gauge that the midship tanks have been completely blown, the kingstons closed and the fore and aft superstructures are above water, the Commanding Officer of the submarine dogs down the upper conning tower hatch and goes to the bridge, from which vantage point he examines the position of the submarine and sizes up the situation.
In heavy seas, it is recommended that a bubble be admitted to the forward main ballast tank and the stern planes be reset for surfacing.
Later, with the command from the bridge “Blow the ballast,” the diesel main air induction is opened and the diesel turned on to blow the ballast. The main ballast is blown in accordance with diving and surfacing instructions.
The head of the engineering department supervises blowing of the main ballast tanks, which is done from time to time, since it is not evident to the Commanding Officer of a submarine under way which tanks have been blown.
In the process of blowing, heel must be carefully observed, making sure it does not increase. The heel is corrected by opening or closing valves for the two sides on the low-pressure air manifold.
As blowing of the main ballast is begun the negative tank is filled.
After blowing the ballast the Executive Officer of the submarine indicates the condition of readiness and the number of the oncoming watch section. The command “Secure from general quarters" is given after the oncoming watch relieves.
Under the supervision of the officer of the watch, personnel may go to the bridge after surfacing with permission of the Commanding Officer of the submarine, in accordance with regulations he has established. No one is authorized to descend from the bridge to the deck without special permission of the Commanding Officer or his Executive Officer.
16. Emergency Surfacing of a Submarine
Emergency surfacing is resorted to in event of a significant loss of buoyancy, resulting primarily from entry of water into the submarine and into tanks situated in the pressure hull, and with an increase in defective trim.
Emergency surfacing is achieved by blowing the ballast with high-pressure air when the command “Blow the main ballast” is given.
If the buoyancy loss is not accompanied by an increase in trim, the midship tanks must be blown while simultaneously attempting to maintain depth by means of speed and trim. In order to do this, the speed must be increased to full speed and the diving planes set for surfacing. If these measures are inadequate, the fore and aft main ballast tanks must be blown.
If the buoyancy loss is accompanied by a rapid increase in trim, it is necessary to admit a bubble into the midship and appropriate end tanks. In this case, there is an increase in trim by the head, the submarine must go full speed astern, and if there is an increase in trim by the stern, the submarine must proceed full speed ahead.
In addition to the aforementioned measures, whenever there is a buoyancy loss, water in the negative tank and water entering the submarine must be pumped out using the drainage system and pumps.