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Fig. 7. Graph depicting change in the position of the center of gravity Go, center of buoyancy Co and metacenter Mo with submergence of a submarine; 1) Distance from the baseline; 2) Draft.
Fig. 8. Position of the center of gravity Go and center of buoyancy Co when the submerged submarine possesses negative stability.
The righting moment in the submerged condition
= Da sin ,
buoyancy force, equal to the weight of the submarine;
5. Change in Transverse Stability in
Grounding and Docking
In full buoyancy condition, a submarine possesses waterline Wolo. In grounding, part of its volume of displacement emerges from the water, and a new waterline W,21 (Fig. 10) appears. In this case, the following forces will act on the submarine:
P - weight of the submarine, applied at the center of gravity Go;
When the submarine is inclined at angle 0, two pairs of forces will be created: P, D and R, P1.
The moment of the pair of forces P and D is the righting moment:
The moment of the pair of forces R and P, is the heeling moment of the submarine:
Fig. 10. Condition of a submarine in
grounding or docking.
The resultant moment is equal to the algebraic sum of the moments
It is evident from this expression that the initial metacentric height of the
P1 submarine p a decreases by the amount AH, numerically equal to the amount of displacement of the center of gravity of the submarine with displacement of load P, along the vertical from the point of tangency of the keel to the center of gravity of the volume WoloW L, emerging from the water.
When a submarine docks, a phenomenon similar to grounding occurs, i.e., in this case the metacentric height likewise decreases by the same amount.
SECTION 7. WATERTIGHT INTEGRITY OF SUBMARINES
1. Surface Watertight Integrity
For submarines, watertight integrity is classified as surface or submerged. Surface watertight integrity is the ability of a submarine to remain afloat with positive stability when the airtightness of the pressure and false hulls is disturbed due to partial loss of reserve buoyancy.
Submerged watertight integrity is the ability of a submarine to remain at depths not exceeding the maximum operating depth, shipping water into the pressure hull, to navigate submerged and rise to the surface of the sea.
Surface watertight integrity of a submarine is usually maintained with flooding of one compartment from the adjoining main ballast tanks from one side, and, in rare instances, with flooding of two adjoining compartments.
Flooding of one compartment of the pressure hull and adjoining side tanks while the submarine is operating in a surface condition is tantamount to taking on cargo from one side (at the bow or stern, on the port or starboard side), the only difference being that in event of heavy damage large masses of water are shipped, and, as a rule, with large trim and heeling moments. This complicates determination of the stability, trim, heel and forward and aft draft of the submarine.
With a small reserve buoyancy and with trim, the actual waterline undergoes significant changes, expressed by a decrease in transverse and longitudinal stability.
The primary means for maintenance of watertight integrity are:
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:
compensating tank. 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 sea. worthiness 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