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18A2. Types of dives . Three types of dives are possible: 1) the quick dive, 2) the running dive, and 3) the stationary dive, the choice being dictated by existing conditions. In all dives the ship is placed in the condition of neutral or negative buoyancy; the use of negative buoyancy shortens the diving time.

A quick dive is made when the ship is underway on one or more main engines. The bow planers are placed on FULL DIVE and the forward speed results in a maximum downward thrust on the bow planes. As the submarine submerges, the upper surfaces of the hull and superstructure act as planing surfaces and increase the downward thrust. The quick dive is the fastest of the three types and is used in acceptance trials of new submarines, when it must be executed within 60 seconds from standard diving trim.

A running dive is performed in the same manner in a minimum time, the only difference being that surface propulsion, at the beginning of the dive, is by battery-powered main motors.

A stationary dive is made when the ship is dead in the water. The main ballast tanks are completely flooded and enough water is flooded into the variable ballast tanks to destroy the remaining positive buoyancy. Flooding and pumping may be alternated to maintain the ship on an even keel at any desired depth. This type of dive is sometimes used during builder's trials to test and inspect the hull at various submerged depths down to final test depth.

The control station includes the bow and stern planesmen's stations and is equipped as follows:

a. Depth gage, reading from 0 to 165 feet, indicates the keel depth,

b. Inclinometers indicate the angle of the vessel's longitudinal axis with the horizontal.

c. The plane angle indicators are miniature diving planes, the trailing edges of which range over degree scales and indicate the angle of rise or dive on the bow and stern planes.

d. A motor control contact-type switch. provides selection of direction of rotation of plane-tilting motor in those installations using electrically operated planes. Hydraulically operated planes are controlled by a two-way valve.

e. The selector switch provides a choice of motors on which the controller is to be used. The bow planes may be rigged or tilted according to the position of the switch handle. A similar device at the stern plane controller provides for use at the stern plane motor to operate the after capstan.

f. The hand-operated clutch, on electric drive, permits shifting from power to brand operation of planes. Hydraulically operated planes are controlled by a valve which, when placed in the neutral position, permits manual drive direct to the planes.

g. A depth gage reading from 0 to 600 feet, mounted at the center of the control panel, is visible both to planesmen and the diving officer.

i. The aneroid barometer indicates the air pressure in the ship.

j. The hull opening indicator light panel, commonly referred to as the Christmas tree (Figure 18-1), indicates the condition of hull openings, vents and flood valves. Electrical contacts at these various openings and valves operate red and green lights in the panel. A green board shows that all hull openings are closed.

18A4. Rig for dive . Before an actual dive is undertaken, the submarine must be fully prepared. Compensation must have been made for all changes in weight since the last dive, and all hull openings, except those necessary for the operation of the ship on the surface, must be closed. The hull openings not closed, and the reasons therefore, are as follows:

a. Conning tower hatch which provides passage to or from the bridge.

b. The hull ventilation supply valve which remains open to permit the circulation of fresh air.

d. The forward and after engine room induction hull flappers which admit air to both forward and after engine rooms.

The safety and negative tanks are flooded and the flood valves left open. All bulkhead watertight doors and bulkhead flappers are checked for free operation. Outboard battery ventilation exhaust valves, if installed, are closed and checked by sighting the valve disc and by checking the mechanical indicator. Sufficient high pressure air, at least 45 percent of total capacity, must be cut into the manifold. Rapid and efficient communication must be established between the diving officer and all compartments.

All of these details must be checked by one or more officers. When the diving officer is informed that all preparations are completed, he reports to the commanding officer, "Ship rigged for dive."

18A5. Diving procedure . Each ship has a diving procedure which has been established by careful consideration of its particular characteristics, and is recorded in the Ship's Organization Book of that submarine.

The diving signal is two short blasts on the diving alarm, the second blast being the signal to start the dive. Two blasts are used

When the diving alarm is given, the following procedure is observed (items marked with all asterisk are executed at once without further orders)

*a. Stop all engines, shift to battery, set annunciators on "All ahead standard," open engine room doors and air locks.

*b. Close outboard and inboard engine exhaust valves, close hull ventilation supply and exhaust valves, close inboard engine air induction flappers, and close conning tower hatch.

*c. Open bow buoyancy vents and all main ballast tank vents, except the group or tank designated to be kept closed until pressure in the ship indicates that all hull openings have been closed.

*d. Rig out bow planes and place on FULL DIVE. Use stern planes to control the angle on the ship.

f. The following operations are performed by direction of the diving officer, who is guided by the existing conditions:

1. At 45 feet, shut the vents and slow to 2/3 speed.

2. At 15 feet short of desired depth, blow negative tank, shut its flood valve, and vent the tank.

3. Level off at specified depth, slow to 1/3 speed, cycle the vents, and adjust fore-and-aft trim and over-all weight.

4. Diving officer reports to conning officer when trim is satisfactory.

When diving in a heavy sea, the maneuver is accomplished most expeditiously by diving with the sea abaft the beam.

Submerged operations are usually carried on with the submarine in the state of neutral buoyancy. Shortly before reaching the desired depth when diving, the negative tank is blown. This places the ship in the state of neutral buoyancy in which the downward force of gravity is exactly- balanced by the opposite force of buoyancy and the ship will maintain its depth unless acted upon by some unbalancing force. The state of exact neutral buoyancy is probably never attained, but the approximation is near enough to allow depth control to be exercised easily by the diving officer.

In all normal submerged operations, the submarine is underway at relatively slow

In Chapter 2, final trim is defined as the adjustment of ballast while submerged which maintains the submarine at the desired depth, on an even keel, at slow speed, with a minimum use of the diving planes. The diagram in Figure 18-2 represents a typical submarine submerged and in final trim. The forward moments due to gravity, FGM, are exactly equal to the opposing moments, FBM due to buoyancy. Also the after moments, AGM and ABM, are equal. To meet the conditions of stable equilibrium, the forward

When forward motion is imparted to the submarine, new forces, due to the unsymmetrical contour, come into play and disturb the static equilibrium. These forces are indicated in the diagram. The upsweep of the forward end presents a planing surface, the resultant effect increasing with the speed. The superstructure, conning tower fairwater, periscopes, masts, deck guns, and other objects present more or less vertical surface above the center of buoyancy. The tendency of these forces is to rotate the submarine about a center with the result that, as speed is increased, the submarine tends to assume a small up-angle and decrease its depth.

This rotational tendency is counteracted by the diving planes. Since the location of the planes is not symmetrical about the center of buoyancy nor about the longitudinal axis of the submarine, the effect of the bow planes on the movement of the vessel is quite different from that of the stern planes.

The location of the planes is shown in Figure 18-2. (The dimensions shown are approximate, and apply only to the submarine described herein.) As indicated, the bow planes tend to change the vertical position of the submarine on an even keel. There is a certain rotational moment, but it is counteracted to a great extent by the longer after body which acts somewhat as a stabilizing rudder, resisting angular displacement.

The stern planes are located at a greater distance from the center of buoyancy and, although they are smaller in area, their effect is much greater than that of the bow planes. Their effectiveness is increased by their location directly aft of the propellers. This combination of a long moment arm and location in the propeller wash results in a rotational movement. Thus the bow planes are normally used to control the depth, and the stern planes the angle of the ship.

From the time the dive is started until the submarine reaches the specified depth and

18B2. Trim analysis . To place the submarine in final trim the shortest possible time requires a swift, accurate analysis of the submarine's condition. This analysis may be made in two stages: first, the over-all condition is determined and corrected; then, the condition of fore-and-aft equilibrium is determined and the necessary adjustments made. When the fore-and-aft trim is very evident, the necessary corrections should be combined with the correction for over-all trim. When properly made, this analysis conveys a thorough understanding of the submarine's condition and indicates the corrective measures.

Certain terms have been established as standard phraseology in describing the trim of the submarine. These terms are factual statements of conditions and also indicate the procedure necessary to attain final trim.

a. Heavy over-all and heavy aft. The entire phrase is necessary to describe conditions. Heavy over-all indicates negative buoyancy and heavy aft indicates that the fore-and-aft moments are not in equilibrium and that there is too much weight aft. The remedy and order would be, "Pump from after trim to sea."

h. Light over-all and light forward. Light over-all indicates that the submarine has positive buoyancy and light forward indicates the remedy: "Flood forward trim from sea."

c. All right over-all and heavy aft. This indicates that the ship is in the condition of neutral buoyancy and that equilibrium should be established fore and aft by the adjustment of ballast between the trim and auxiliary tanks. This adjustment may be obtained by any one of three methods:

1. Pump from after trim to forward trim.

2. Pump from after trim to auxiliary.

3. Pump from auxiliary- to forward trim.

It may be noted that the above trim conditions might be expressed by different phrasing. For instance, "heavy over-all and heavy aft" might be described as "Heavy over-all and light forward" and "Light over-all and light forward" might be phrased, "Light over-all and heavy aft." However, the standard phrasing is preferred. "Heavy over-all and heavy aft" leaves no room for doubt as to the condition or the remedy. As the object of a standard phraseology is to convey information concisely and efficiently, it should be adhered to at all tines.

18B3. Initial trim. When the submarine leaves the surface it is heavy over-all and heavy forward, the negative tank having been flooded to give negative buoyancy and an initial down-angle. Nearing the specified depth, the negative tank is blown and the planesmen control the angle and depth of the ship. The diving officer now observes the angle of the submarine. If the submarine is heavy or light to such a degree that the planesmen cannot maintain the depth without the assistance of the inclined surfaces of the ship, the inclinometer indicates the corrective action. Should it be necessary to carry an up-angle in order to hold depth, the ship is heavy and ballast is pumped from the auxiliary tank to sea until the planesmen can hold depth on an even keel. In the case of a down-angle, the auxiliary tank is flooded from the sea.

During this first check, which is made immediately on reaching ordered depth, the boat is moving at the speed of submergence. As the effects of inclined surfaces are proportional to speed, this first correction may not be enough. The diving officer now orders two-thirds speed and the angle is checked again and corrected as before if necessary. The speed is then reduced to one-third and the check and correction repeated. This trimming operation is repeated until depth can be maintained at slow speed with a zero bubble.

18B4. Final trim . When the ship is on an

18B5. Summary. Over-all trim is the process of attaining neutral buoyancy; final trim is the establishment of fore-and-aft equilibrium with neutral buoyancy. The foregoing description divides the procedure into two distinct phases and these are detailed as a sequence of operations. The experienced diving officer will, however, recognize both conditions simultaneously, and combine the operations as dictated by his judgment. Thus he may, in a minimum time, return speed control to the commanding officer by his report, "Final trim," meaning "All right over-all and all right fore and aft."

18B6. Special conditions. When diving, if the submarine, is so badly out of trim that the stern planesman cannot control the angle, the diving officer must first correct the fore-and-aft trim, thus enabling the stern planesman to control the bubble, before attempting any trim analysis. In this extreme condition, it must be remembered that, for a given speed, the forces resulting from the angle of the submarine are greater than those resulting from the angle of the planes. Changes of depth with way on, and carrying an angle, do not necessarily indicate the over-all condition.

Consideration must be given to the forces resulting from the speed and angle of the submarine. Therefore, if the stern planesman cannot control the angle, and the depth is changing in a direction contrary to that desired, the most effective measure that may be employed is that of reducing speed. For example, if the submarine will not go down while carrying all up-angle that cannot be

If the submarine is going down while carrying a down-angle that cannot be removed by the stern planesman, it must slow down or stop. If the depth continues to increase, then it may be concluded that the ship is "heavy over-all and heavy forward." Variable ballast must be pumped from forward trim to sea until the stern planesman can control the angle. It is possible that the condition of trim was "all right over-all and heavy forward." The submarine was in a condition of neutral buoyancy and retained its initial downward motion after the force resulting from speed and angle had been re-

18B7. Effect of backing while submerged . When the submarine has an excessively large down-angle during submergence, and it is desired to stop its downward motion, it has been stated that part of the force that is driving it down may be removed by stopping the propellers. However, due to the slow rate of deceleration, the downward motion will continue for a time after the propellers are stopped. The quickest way of stopping downward motion is to "stop and back." The reversed propellers tend to force the stern down and the ship squats. This also tends to remove the down-angle. Hence, the procedure for checking downward motion and down-angle when the planes are ineffective is "stop, back, and blow." These measures are resorted to in that order, using one, two, or all, depending upon the emergency.

At the sounding of the signal, three blasts of the diving alarm, or the passing of the word "Surface, Surface, Surface," the various actions necessary are performed.

The bow planes are placed on ten degrees dive and rigged in automatically unless the conning officer gives other instructions. A report, "Bow planes rigged in," is made to the conning officer. Speed is increased to about 6 knots to give maximum lift. Due to the up-angle on the ship, the increased speed makes the inclined surface of the hull effective and the resultant lift raises the ship. The stern planes are used to limit the up-angle to about 5 degrees. The up-angle may be increased by blowing the bow buoyancy tank. Blowing the safety tank increases the

The main ballast tanks are partially blown to surface normally. After surfacing, the high-pressure air is secured and the blow is completed with the low-pressure blowers.

During submergence, certain tanks are vented inboard, and torpedoes may be fired. This causes a consequent rise of pressure within the ship. On occasion this may be a rise of several inches. It has been found by experience that release of the energy in the large volume of air within the pressure hull may result in injury to personnel, damage to hatch gaskets, or the loss of loose gear caught in the rush of escaping air through an open hatch.

Sealing the lower conning tower hatch permits immediate opening of the upper hatch since the relatively small volume of air in the conning tower can be released without danger. This procedure expedites the movement of personnel to the bridge.

When the decks are awash, the conning tower hatch is opened and the commanding officer goes to the bridge. In the meantime,

During this interval, the low-pressure blowers, using air from within the ship, are

a. "Rig ship for dive." The order to carry out the preparations for diving listed in Section 18A4.

b. "Ship rigged for dive," or "Ship rigged for dive except ------------- " A report indicating the accomplishment of the above order.

c. "Clear the bridge." A usual preliminary to the diving signal. All personnel, unless excepted, lay below on the double.

d. "Bleed air." An order to bleed air into the submarine.

e. "Pressure in the boat." The report indicating that the hull is sealed.

f. "Green board." The report meaning that all hull openings are closed, as indicated by the Christmas tree.

g. "Six, (five, etc.) feet." An order to the diving officer, or the bow planesman, giving the desired depth.

h. "Ease the bubble." "Zero bubble." "Five degrees down bubble." Orders to the stern planesman giving the angle desired on the ship.

i. "Shut bow buoyancy vent." "Shut the main vents." "Open negative flood." Orders governing the operation of the various flood valves and main vents.

j. "Vent safety." Open safety vent, then, after tank has vented, shut the vent

k. "Blow safety." "Blow negative." "Blow all main ballast." Orders to the air manifold watch to blow the designated tank or tanks.

l. "Secure the air." "Secure the air to bow buoyancy." The order to stop blowing all tanks, or the designated tank.

n. "Full rise on the bow planes." "Five degrees dive on the stern planes," Orders to the planesman, giving the angle desired on the diving planes.

o. "Pump from forward trim to after trim." "Flood auxiliary from sea." "Blow from forward trim to sea." "Pump from auxiliary to after trim five hundred pounds." "Secure the pumping." Orders to the trim and air manifold watches, used in shifting variable ballast.

p. "Start the low-pressure blower, blow all main ballast." "Secure the air to number one." "Secure the low-pressure blower." Orders governing the operation of the low-pressure blowers.

q. "Pressure equalized." The report that the air pressure inside the submarine is the same as that of the atmosphere.

r. "Take her down." Increase depth as rapidly as possible. Exact depth will be specified later.

s. "Rig for surface." The order to place the ship in the normal peacetime surface cruising condition.

t. "Open bulkhead flappers, and recirculate." Given after the dive has been made and conditions are satisfactory.

u. "Low-pressure blower secured, all main ballast tanks dry, safety and negative flooded, conning tower hatch and main induction open, depth eighteen feet." A typical report by the diving officer, giving the conditions upon completion of surfacing.