MECHANICAL ENGINEERING

ACKNOWLEDGMENT This article, b.r/ Joseph B. Walsh and Willium 0. Rainnie, Jr., of the Woods Hole Oceanographic Institute, appeared in the August 1964 issue of “Mechanical Engineering.” \

EXPLORATION, an activity that has intrigued man for centuries, has been extended in only the past few decades to the vast region beneath the sea. In spite of the attraction of the undersea world, until recently, technology (excepting the efforts of Bar- ton in the nineteen thirties) provided the means to bring man to depths less than perhaps 500 ft. below the surface. This depth seems shallow indeed when one realizes that pearl divers unaided by apparatus of any kind reach depths of nearly 200 ft. whereas the deepest parts of the Ocean lie more than 35,000 ft. deep.

Oceanographers interested in exploring the deep Ocean have lowered instruments on wires from sur- face ships. This method has the severe h i t a t i o n that the scientist cannot control his experiment or observation as closely as he would wish. Another drawback to doing deepsea research from surface ships is the great difficulty that the scientist has in making visual observations. Television and photog- raphy are valuable tools, but in some cases they provide an inadequate alternative for the scientist whose experiment requires him to see what he is doing.

The need for a manned submersible has been

apparent at the Woods Hoie Oceanographic Insti- tution (WHOI) where oceanographers from widely differing disciplines want a vehicle whch can be used as an underwater laboratory. The opportunity for constructing such a vehicle was provided in the Spring of 1962 when funds were made available by the US. Navy, Office of Naval Research. The prob- lem at WHOI then became that of deciding what type of submersible would best serve the needs of the Oceanographers. The specifications for Alvin, a two-man submarine capable of going to a depth of 6000 ft., emerged from discussions in which various possibilities were compared with oceanographc re- quirements, technical and financial reality, and, above all, the necessity for safe operation.

PERFORMANCE SPECIFICATIONS General

One of the primary considerations in drawing up the specifications was the desire to have a vehicle ready for use less than a year after the awarding of the contract. Thus, each specification was written so that it could be met using currently available ma- terials and techruques. Another charaderistic con- sidered essential was portability. The decision to

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ALVIN MECHANICAL ENGINEERING

have a submarine small enough to be carried on the deck of the WHOI research shps Atlantis I I or Chain required that the vehicle weight not exceed 22.000 lb. and that the overall length be about 20 f t . The t h r d condition, one that all designers face, was the limitation in funds available. These three condi- tions formed a framework which bounded the choice of the various operating charac te r i s t icdepth , speed, endurance, payload, and so on. The oceano- graphic worth of these mutually dependent char- acteristics dictated the values finally specified. Depth

An operating depth of 6000 ft. was chosen as the least possible value satisfying the needs of the WHOI scientists. This depth capability opens to exploration about one-sixth of the area of the bot- tom of the Oceans and neighboring seas, including the continental shelves, part of the continental and island slopes, and many sea mounts. This upper 6000 ft. layer of the ocean includes much of the life of the Ocean as well as the region where vari- ables such as current, temperature, and sound ve- locity, of interest to the physical oceanographer, are most active.

A collapse depth of 10,800 ft. was specified, re- sulting in a safety factor

Collapse depth Operating depth

of 1.8. This safety factor is generous when compared with the value usually used in military submarine construction. Muneiivern bi li t y

High speed was not required by any of the scien- tists planning to use the submarine. A continuous speed of 4 kt was found to be acceptable to most of the users. The ability to reach a higher speed for a short time by overloading the motors was felt to be a desirable safety feature. No intricate maneuver- ing abilities were requested. A diving rate of 200 fpm, a turning diameter of 100 ft., a stopping dis- tance of 100 ft., the ability to hover, and control of longitudinal and vertical pitch and yaw motions were the only characteristics WHOI required. Power

Whereas maximum speed fixes the size of the propulsion motor, the power required for propul- sion is determined by cruising speed and endurance time. The ability to maintain 2.5 kt for 10 hr. was deemed sufficient. In addition to the propulsion power requirement, the power supply was required to supply power for the hotel load for the 10-hr. period and to supply the scientific equipment with a load estimated to be 18 kwh.

Scientifi Requirements One of the primary functions of the oceanographc

submarine is to give the scientist the ability actually to see what he is doing. Accordingly, it was specified that there be five forward-viewing ports-one look-

ing directly forward, one downward, and one to each side-and one peephole looking dlrectly u p ward through the hatch for use when surfacing. A survey of the equipment required for scientific pur- poses, such as a mechanical arm, sonar, lights, cameras, scientific instruments, showed that a 1200- lb. scientific payload was required in addtion to a 500-lb. allowance for perSOMe1 and their equipment. A hatch diameter of at least 20 in. and a hull inside diameter of 6.5 ft. was needed for accommodating personnel and equipment inside the pressure hull.

The requirements in the foregoing which define the design problem were included in specifications accompanying the invitations for bids.

Specifications embodying the design features dis- cussed were sent out to companies which had dem- onstrated interest in the field of deep-diving sub- marines. In August, 1962, the contract was awarded to the General Mills Corporation which had entered the low bid of $575,000. Litton Industries subse- quently took over. The completed vehicle was dedi- cated on June 4, 1964.

GENERAL DESCRJPTION OF Alvin Figure I gives a three-view line drawing. Figure

2 presents a cross section of the general arrange- ment. Personnel and some navigational and scien- tific equipment are housed in the forward sphere. Although the forward sphere and forebody are posi- tively buoyant, additional buoyancy for power sup- ply, payload, and the like is provided by the stem spheres and plastic buoyancy material. The power supply and main propulsion equipment which are open to the pressure of the sea are housed aft of the pressure hull. A fiberglass fairing encloses the structure.

Pressure H u l l The pressure hull, fabricated from HY-100 steel.

has an inside diameter of 79.3 in. and a minimum nominal thickness of 1.33 in. The sphere is spup as two hemispheres from 2 5/l&in. plates and then heat-treated to at least 100,000 psi yield a t 0.2 per cent offset. with an elongation at fracture of 18 per cent, a reduction of area of 50 per cent, and a Charpy impact value of 30 ft.-lb. The hemispheres are machined inside to the finished dimension, welded together, and machned to dmension on the outside. Cutouts are made for the port and hatch ~nserts. The inserts, machined from forged stock, are then welded in place, and the assembled sphere is stress relieved at 1050 F for 3% hr. Three spheres were made in this way, one for AZvin, one for veri- fication of the collapse depth, and one extra.

Propulsion and Maneuvering Control There are several alternatives for the propulsion

of a submersible, the most common being the use of diesel motors for surface operation and battery- powered electric motors while submerged. WHO1

MECHANICAL ENGINEERING ALVIN

I- . .

o 0 a , . ~ ~ ~ . I I I I C Y L ~ - ~ I I V C I

Figure 1. The ALVIN vehicle for manned exploration of the ocean depths. It had to be so designed that it could be made with current materials and techniques, and it had to be portable-20 I t . in length and not more than 22,000 Ib. There was also a limitation in funds-and the vehicle had to be ready within a year.

decided in the interest of conserving weight to sac- rifice capabilities of Alvin and transfer this role to a mother ship. Although hydraulic power is known to be somewhat less efficient than some of the other means of underwater propulsion, it has the distinct advantage of versatility and fineness of control not available from the electric motor alone. Also, heavier motor and pump components can be located as re- quired to give a proper center-of-gravity and center- of-buoyancy relationship. In addition, this system makes it possible to tap the propulsion system to run underwater drills, and so on, during the times when propulsion would not normally be required. Therefore, the present system is composed of two d-c electric motors running in oil driving two hy- draulic pumps. One of these pumps is constant volume; the other is variable volume, giving an almost infinite variety of speed and power over the normal speed range and a t the same time sirnplify- ing the electric controls. Solenoid-operated valves are used to reverse the flow to the hydraulic motors, permitting the electric motors to run in one direc- tion a t virtually constant speed.

The two electric motors, each nominally rated at 11 hp at 4500 rpm can be overloaded up to 15 hp for short periods. The pumps drive the fixeddisplace- ment hydraulic motors turning three shrouded pro-

pellers-a 15-hp motor for the main stern drive and 7%-hp motors for the port and starboard propellers.

Alvin will spend a great deal of its time at slow speeds or completely stopped observing small seg- ments of the ocean and its bottom. Therefore, rud- ders and planes, which rely on lift generated by motion, are not suitable for maneuvering. To take the place of the rudder, the main propulsion motor can be rotated 1 5 0 deg. in azimuth by hydraulic rams. In addition, the two smaller motors are ro- tatable 300 deg. about an athwartships axis to pro- vide fore-and-aft or up-anddown thrust. The small motors, which can also be reversed hydraulically, are rotated about their axis by 1/5-hp electric mo- tors. Thus, dynamic forces can be used to position the vehicle in depth as well as to steer and propel it.

The overall efficiency of the propulsion system is computed to be 20 per cent. This permits speeds from 0 to 5.78 kt. Most cruising will be done at 2 kt. and below, but the “burst” speed of almost 6 kt. allows for rapid response in avoiding obstacles, chasing marine creatures, and operating in currents for short periods of time. Ballast and Trim Systems

Normal surface freeboard of 15 in. between the edge of the hatch and the waterline is provided by main ballast tanks enclosed within the fiber-glass

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ALVIN MECHANICAL ENGINEERING

Figure 2. Power supply and main propulsioa are open to the pressure of the sea. Hydraulic power d iem fineness of con- trol, and E M be tapped to run underwater drills.

body. The main ballast tanks, whch have floods and vents similar to those on conventional submarines, are blown on surfacing by compressed air. The blow valves and the vents are solenoid operated from within the sphere. The pressure in the air tanks is sufficient normally to provide some buoyancy even at maximum operating depths.

The fore-and-aft trimming system is a mercury system in which the relatively highdensity mer- cury is moved fore and aft rapidly by dsplacing it in a closed circuit by means of a hydraulic system pumping oil. Approximately 600 lb. of mercury is contained in this system. This trim system is ex- pected to be one of the most effective means of changing attitude of the submarine quickly for fol- lowing the contours of the Ocean bottom, as well as providing an up or down angle of at least 30 deg. during descent and ascent.

The overall trim of the boat is obtained by a sys- tem in which oil from trim tanks is used to displace seawater within the envelope of the submarine. To make the submarine light, oil is drawn from the trim tanks by a standard hydraulic pump. The oil in turn expels seawater from the interior of the afterbody near the center of gravity, thus providing buoyancy equal to the weight of the &placed water. The craft can be made light, heavy, or neutrally buoyant through the operating depth range. The oil

system was considered superior to a system in which seawater was pumped directly in spite of the weight penalty engendered by the weight of the oil, be- cause hydraulic pumps operating at these pressures (3000 psi) are more reliable, lighter in weight, and less expensive than similar seawater pumps.

Power Supplies The primary power supply consists of storage

batteries located in three oil-filled, pressure-com- pensated battery boxes aft of the pressure hull near the longitudinal center of gravity. Fuel cells, com- pact nuclear power plants, or other more exotic sources hold promise for vehicles of this h n d to lessen the dependence on the surface-support unit, but these simply were not available in time to con- tribute to this problem. On the basis of power/unit weight and cost/cycle of battery life, one cannot rationally choose othw than the lead-acid battery. “lus choice has a useful by-product in that if a par- ticular mission becomes critical, one can approxi- mately quadruple the stored energy for the same weight (but at about ten times the cost) by substi- tuting silver-zinc batteries.

The batteries were specified to be located outside of the pressure hull for several reasons, namely, the batteries provide some buoyancy since they weigh

MECHANICAL ENGINEERING ALVIN

2700 lb. in air but only 2000 lb. in seawater. They provide easily jettisonable emergency ballast. The personnel are not exposed to hazards from escaping hydrogen and chlorine, and valuable space in the pressure sphere is conserved. These advantages far outweighed the inconveniences in servicing, the necessity for remote-control circuits, and the partial or complete loss of power when the batteries are used as ballast.

Life-Support System The approximately 170 cu. ft. of space in the

pressure sphere must be supplied with oxygen and must have provision for removing the CO, and wa- ter vapor created by the two occupants. The system to do this is designed for an 8-hr. dive, with pro- vision for a 24-hr. dive for extended scientific ob- servation or emergency use.

Oxygen added to the atmosphere from gaseous oxygen bottles is circulated toward the front of the sphere by two small blowers. The air is then cir- culated past the occupants to the rear and drawn through CO, and H,O removal racks. The rate at which oxygen is added is automatically controlled by the decrease in cabin pressure as the CO, is ab- sorbed. Manual override of this feature is provided for emergency use. Instrumentation is installed to monitor the O2 and CO,.

Lithium hydroxide (LiOH), a commonly used CO, absorbent in military submarines, is used in this vehicle also. The water-vapor removal is ac- complished by sponges which have been soaked in a saturated solution of lithium chloride (LiC1) and dried in a vacuum oven. Approximately 0.6 lb. of water per lb. of desiccant (including carrier) is ab- sorbed with an exit humidity of approxmately 30 per cent by this method.

For emergency use in the case of fire and also for shallow-water escape, SCUBA gear will be carried at all times during diving operations.

Safety Features Safe operation under normal operating conditions

is a criterion which was applied for judging all the various components which make up the submarine. The safety factors used, navigational equipment, visibility, life-support system, and so on, all are very adequate for assuring safe operation in normal situations. All systems are designed such that fail- ure of a component will not result in disaster.

Caution on the part of the operator and observer should result in completely emergency-free opera- tion throughout Alvin’s life. However, provision must be made for the extraordinary occurrence. Additional buoyancy can be obtained in emergen- cies by dropping the batteries. The batteries are droppable by halves, each section providing about 1000 lb. of buoyancy. The mercury in the fore-and- aft trim tanks can be dropped as well for an addi- tional 600 lb. of buoyancy.

The vehicle was designed such that protuberances

which could become entangled with cables or the like were eluninated if possible. The mechanical arm, which by its very purpose is more likely to become entangled than other components, is detach- able from its foundation. The various measures for increasing buoyancy will be sufficient for freeing Alvin in many situations. As a last resort, the pres- sure sphere and forebody which is 400 lb. buoyant can be detached from the rest of the structure and float to the surface. The buoyancy of the sphere can be augmented by the main ballast system normally used to provide freeboard on the surface since the tanks and air supply are attached to the sphere. The sphere is detached from the hull mechanically from within the sphere. Pavload

WHO1 felt that at least 5 per cent of the total displacement should be devoted to the scientific in- struments which constitute Alvin’s payload. This 1200-lb. payload, which is composed of instruments exclusive of those needed for safety and navigation, includes:

Item

Scanning sonar . . . . . . . . . . . . . . . . . . . . Underwater TV . . . . . . . . . . . . . . . . . . . . . Underwater telephone . . . . . . . . . . . . . . Underwater mechanical arm . . . . . . . . Echo sounder ...................... Power conversion . . . . . . . . . . . . . . . . . . Precise navigation . . . . . . . . . . . . . . . . . . Cameras ........................... Lights .............................. Recorders and Miscellaneous . . . . . . .

Totals ............................

200 50 50 200 100 200 150 90 50

110 1200 -_

2000 400 200 500 lo00 5Ooo 1000 700

4000 5200

20,000 __

These devices, which are procured separately from the basic vehicles, are intended to be the basic instrument “suit.” They will be supplemented or replaced by the individual investigator who has a particular problem to solve. Many of these ad&- tional instruments can be designed to provide their OWTI buoyancy. Operations, Surface and Submerged

The submarine is completely dependent upon s u p port in the way of battery and air charging, life- support chemicals, and other necessities from either a mother ship or shore base. Although towing to the operating scene and charging whle in the water is possible, it is planned that most ships and all bases will have crane or other capacity available to lift out the vehicle after each dive.

Alvin will not do very much horizontal traveling on the surface. The mother ship will lower the sub- marine over the side at or near the diving site. The main ballast tanks located in the fiber-glass fore- body, whch are air filled on the surface, provide freeboard of approximately 15 in. from the water- h e to the top of the pressure sphere. Surface navi- gation will be done by telephone by the observer in the conning tower to the operator in the sphere.

.

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ALVIN MECHANICAL ENGINEERING

An estimate of the dwing trim will be made prior to each dive and the variable water ballast adjusted to this trim. Fore-and-aft trim changes will be com- pensated for by the mercury trim system. When ready to &ve in all respects, the solenoid-operated vents on the main ballast tanks will be opened and the vehicle will submerge. The use of propulsion or heavy overall trim to reach operating depth is op- tional.

When the vehicle reaches operating depth, the overall trim will be adjusted for neutral buoyancy under most conditions. If this craft has a “neutral angle,” this will be adjusted as well. If bottoming is desired, the overall trim system can be used to make the vehicle heavy, or the lift propellers used to force it down.

To surface, either propulsion can be used to drive the submarine up or the variable ballast can be pumped. Blowing of the main ballast tanks can begin as won as pressure in air tanks exceeds the ambient. On a normal surfacing operation, the main ballast tanks will be blown near the surface. Program

Although WHOI has ships sufficiently large to act as a mother ship for Alvin, these have not been fitted out with the necessary gear for lifting the sub- marine out of the water. The procedure for taking Alvin aboard must be carefully controlled since the fairing surrounding the structure is relatively light. Until this problem is solved, Alvin will probably be based at various ports on the east coast of the

nental slopes, and most of the Bermuda and Bahama area.

ACKNOWLEDGMENTS The Deep Sea Research Vehcle Project a t WHOI

is funded under a contract with the Office of Naval Research, Department of the Navy (Code 466) . The continuing encouragement and advice of Capt. C. B. Momsen and Lt. Cdr. F. Edwards were most im- portant.

Mr. Harold E. Froehlich, project engineer a t Gen- eral Mills, Incorporated, and hs colleagues are re- sponsible for changing Alvin from a design concept and set of specifications to a reality, and their efforts cannot be overestimated.

A set of manufacturing and safety provisions was supplied by the Bureau of Ships (Code 420, Cdr. R. Aroner) and these proved to be very valuable in the construction. Fruitful discussions with Commander Aroner’s group and personnel of the Naval Labora- tories, DTMB, NRL, NOL, MatLab) were held f r e - quently and contributed greatly to our knowledge.

A. C. Vine, J. W. Mavor, Jr., and Earl Hays, all of Woods Hole. with the two authors prepared the preliminary specifications and have followed the construction.

REFERENCES “Deep Submergence Research Conducted During the Period

November 1. 1961-October 31, 1962,” WHO1 Ref. No. 62-41, November, 1W.

H. E. Froehlich. “Deep Diving Fkseamh Submarine Tech- nical Report.” General Mills report, June, 1962.

“Specifications for the Design and Construction of a Re- search Submarine for Operation at 6ooo Feet,” WHO1 re- port, May, 1962.

“ S p i a l hovisions for the Design and Construction of a Research Submarine for Operation to a Depth of 6ooo Feet.” Bureau of Ships, Department of the Navy, August, 1962.

United States or neighboring islands and towed to , the diving site. Towing, although a stopgap meas- ure, still opens up to exploration that are currently of interest to oceanographers-the conti- nental shelf, the Blake Plateau, some of the conti-

The Convair division of General Dynamics has received a 3961,000 contract from the United States Navy Bureau of Ships to design, fabricate and test a hydrofoil stabilizing system.

The research and development program will ex- tend over the next two years.

The Convair set of subcavitating hydrofoil-struts will include a fail-safe, mechanical stabilization sys- tem. known as HYSTAD (Hydrofoil Stabilization Device). The Convair system will be designed for use on the U. S. Navy’s high-speed hydrofoil test craft, FRESH-1.

The function of HYSTAD, an all-mechanical con- trol mechanism, is to provide stability for fully- submerged hydrofoil craft, which are inherently un- stable and usually require electronic autopilots. The system would be employed as a back-up to an auto- pilot.

Feasibility of the HYSTAD has been established during a hydrofoil craft s t a b i h t i o n study per- formed by Convair for the Bureau of Ships under another contract. Thrs initial program was complet- ed late in 1961.

The current program will include operational

tests of the HYSTAD-equipped hydrofoil-strut sys- tems on the Navy’s FRESH-1 in early 1966, prob- ably in the h g e t Sound area.

A complete system for one ship will be fabricated. It will include a forward pair of struts and foils, an aft centerline strut, operator’s control, and instru- mentation display to record the depth of the foils. A portion of the fabrication work will be performed at Convair.

Convair’s marine sciences group will conduct hy- drodynamic model tests at the division’s towing basin. Data gathered during tank tests will be used to develop stability derivatives for analog simulation studies. These mathematical representations of forces acting on the craft in different sea state con- ditions will help determine final design of the hy- drofoil stabilization device.

After fabrication, the Convairdeveloped HY- STAD will undergo engineering tests at the San Diego plant to verify design before the system is installed on the Navy’s test craft for open water checkouts.

GeneraZ Dynamics Press Release