THE MILITARY ENGINEER

SALVAGE OF T m USS FRANK KNOX

ACKNOWLEDGMENT

This article bg Captain W . F . Searle, Jr., and Alex Rynecki is reprinted with permission of The Society of American Military Engineers from the March-April 1968 issue of The Military Engineer. Copyright 1968.

Fast on the coral of Ratas Beef, the radar-picket destroyer is buffeted by the sea as she awaits salvae.

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MILITARY ENGINEER KNOX SALVAGE

THE RADAR-PICKET destroyer Knox was hard aground! A prompt attempt to back off failed, and the ship rested entrenched on Pratas Reef, an atoll 180 miles southeast of Hong Kong. It was early morning July 18, 1965.

The forward tanks were ballasted down to pre- vent further grounding or broaching by the follow- ing seas. The situation, while serious, was well controlled. No one had been hurt. All boilers were steaming, and the ship’s engineering plant con- tinued to operate. Navy Salvage Ships (ARS) and Salvage Tugs (ATF) that were stationed in the Far East were immediately dispatched to help.

The Knox (3,460 tons loaded, 390 feet long) was aground from her forefoot to about 250 feet aft. The sonar dome had been ripped off, and the compart- ment above it was flooded. The crew, well trained in shipboard damage control, placed emergency pumps, shored bulkheads and decks, and began dewatering. Fortunately, the weather was mild and the seas were calm.

A Navy salvage tug towing several barges was diverted to the reef. She placed one of her empty barges alongside the destroyer, and 155 tons of fuel and ammunition were offloaded. The Knox pumped feed water over the side and shifted fuel aft. Calculations indicated that the ship was 210 tons aground on high tide.

The 3,000-hp Salvage Ship Grapple arrived on July 20 and quickly laid a pulling tackle (called beach gear by salvors) to seaward. With the Knox backing down and with one set of beach gear* and the pulling power of the Grapple, the stranded de- stroyer moved aft about 12 feet.

With more assistance on the way, the situation appeared promising at this point, but ’Typhoon GILDA started blowing, and the sea state increased to 1Zfoot swells. The barge alongside, which could not be removed, started pounding against the Knox. Continued winds and heavy seas forced the salvors to cease pulling operations. Once again, the Knox was ballasted down to prevent shoreward move- ment and pounding on the coral. During the night of the 20th, gale-force winds and seas battered the ship. She moved sideways about 40 feet. The pound- ing caused additional flooding and severe structural damage. At nearly all points in contact with the reef, rivets were loosened, leaks occurred, and dam- age was inflicted on longitudinal and transverse members. Lateral and vertical loads were trans- ferred through members of the ship’s structure to other decks and to other members. The damage was further increased by the continuous pounding of the barge. As the raging storm continued, progressive flood-

ing exceeded the capacity of the pumping equip- ment, and space after space was abandoned to the

*A system of an 8,000-pound “deadman” anchor, 1%-inch wire rope for pulling and a 9.1 fourfold pair of purchase blocks wlth an &ton winch,’ generally good for 50 tons of pull.

flooding waters. During the night, the Knox was forced some 75 ieet farther onto the reef and ad- ditional extensive structural damage occurred. Overnight a relatively controlled stranding situa- tion, with every indication of early extraction, had changed into an extensive, serious, and most diffi- cult offshore salvage job.

THE SITUATION

The entire forward half of the ship’s bottom was open to the sea. All forward tanks and compart- ments were bilged, as were the forward engine room and fireroom and the amidships fuel tanks, Minor leaks into the after fireroom were con- trollable, but the No. 3 boiler foundations were distorted, and the after feedwater tanks were con- taminated. But, worst of all, the keel beneath the forward engine room was broken or distorted and the main deck and sheer strakes were buckled.

The Knox and her brave crew who rode out the storm were fortunate still to be together after the storm passed. It was urgent that the salvage work be resumed. By this time, the smaller salvage ships were joined by a virtual armada of Navy ships, in- cluding an aircraft carrier, tanker, and a destroyer tender/repair ship. The carrier was particularly useful since the surf, pounding against the reef in the wake of the typhoon, prevented small boats from reaching the Knox. The carrier’s helicopters were used to transport salvage personnel and equip- ment to the stricken ship.

The first requirement was to prevent further flooding and to shore damaged holding bulkheads and decks. As the weather abated, divers went down into flooded spaces and later over the side to inspect the damage. It was almost a week before the seas quieted enough for patches to be placed on the hull.

Several sizes of special ship salvage pumps were transferred from the salvage ships to the Knox. These included large 10-inch and 6-inch gasoline- driven de-watering pumps; high-head, high-capacity &inch electric submeqible pumps; and all sorts of small gasoline, electric, and air-driven units.

While divers were inspecting the hull and me- chanics were plugging leaks and shoring bulkheads, other salvage crews set about trying to pump out the flooded compartments. It was soon evident from the holes in the hull that it could not be dewatered by pumping. Air compressors were sent from the salvage ships, and, after rigging manifolds and sealing off vents and other piping, attempts were made to force the flood water out with an “air bubble.”

In preparation for dragging the ship seaward, other divers went down to inspect the coral bottom. They found the ship impaled. Hugh chunks of the hard coral were sticking into holes and dented hull panels. The ship had ground herself into a coral bed. It appeared that the Knox would actually have

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KNOX SALVAGE MILITARY ENGINEER

to be pulled up and over a coral ridge which ran roughly under her mid-body. It was clear that the coefficient of friction between hull and coral was high. In order to attack this problem, divers began a lengthy program of placing powder points and blasting the coral. Also, large rubber tanks were assembled in the United States and airlifted to the scene. These tanks were to be snaked under the hull and used as pneumatic jacks in much the same way that wing jacks are used to raise aircraft whose landing gear has collapsed.

In the meantime, the salvage ships were laying new sets of beach gear-ight sets in all. A total of two A M , four ATF', and one Submarine Rescue Ship (ASR) were soon on the scene, too, which would provide a formidable pulling force. Each set of beach gear could develop between 40 and 50 tons of pull; each ARS, A", and ASR could pull 30 tons using the ship's power. In addition, the after engine room and No. 4 boiler of the Knox were still usable, and the vessel could back on her port propeller. Given favorable weather and the elimination of the impaling coral heads, this pulling force would be sufficient to extract the Knox from her stranded position.

SALVAGE METHOD ANALYSIS In the meantime, the effect of the flooded con-

dition of the ship and her damaged structure were being studied. A detailed analysis of all compart- ments was undertaken. The flooded compartments were sounded, and the status of liquid loading (fuel oil, diesel oil, lubricating oil, feed water, and potable water) was checked (Figure 1). Ammunition and stores remaining on board were inspected. The best possible data on the broken keel, ripped hull plates, and buckled main deck and sheer strake were re- corded. All these data were sent to the Navy Bureau of Ships in Washington and to the Pearl Harbor Naval Shipyard, where naval architects and struct- ural engineers analyzed them.

From the standpoint of stability it was calculated that, if the ship were pulled free in her flooded con-

dition, she would be sufficiently stable to be towed, in reasonably fair weather, to a safe haven. Her draft aft would be 15 feet, forward 22 feet, and metacentric height (GM) 1.5 feet. But the struct- ural engineers soon determined that, with her dam- aged hull g d e r and the extreme sagging condition caused by the total flooding of her forward engine room and fireroom, the Knox would break in two if she were extracted. It was estimated that she would break near the No. 2 boiler uptake, ripping diagonally into the forward engine room.

The architects then calculated the stability of the two pieces. Assuming that the holding bulkheads did not fail, it was decided that the stem half would be stable and could be towed stern first to port. It was questionable as to whether the turbines and re- duction gear in the wide-open forward engine room would cause such a load on the starboard shaft's bulkhead seal as to jeopardize the holding bulkhead. The forward half of the ship, with all its lower tanks and compartments bilged, would upend, float for awhile in a vertical cork-like fashion, and slowly sink from progressive flooding.

If a similar situation had prevailed with a tanker or merchantman or naval auxiliary, it is Likely that the hull would have been deliberately cut in two by explosives and the valuable stern half saved. In the case of the Knox, the principal value in the ship lay in the forward part. She had just recently completed a modernization overhaul. Being a radar-picket de- stroyer, she was equipped with an ultra-modem Combat Information Center (CIC) containing ex- pensive and scarce electronic gear. Her tripod for- ward mast carried rare and costly antennae. The damage done to her hull and forward machinery plant was not large compared to the total value of the ship. Even her keel-mounted sonar dome, which had been wiped off, was not significant since the vessel was equipped with two sonars: a variable depth (VDS) towed unit on her stem, and a small conventional unit forward. Thus, the problem was one of saving the whole ship. Action had to be taken to keep her from breaking in two. Urgent

SHEER STRAKE B U C K L E D 1 TO 1 / 2 FORWARD E N D OF STRUCTURAL TEE WELDED O N T H E PORT 6 S T A R B O A R D M A I N DECK AS A STIFFENER TO R E I N F O R C E T H E S H I P I N VIEW OF KEEL DAMAGE P R O F I L E @ e

FORWARD PART OF H U L L ENTRENCHED IN CORAL

LEGEND SONAR TORN OFF

AGROUND FORWARD a FLOODED C O M P A R T M E N T

CORAL REEF BELOW SHIP APPROXIMATE SHAPE WATER I N T A C T (STORED WATER) O F D A M A G E D B O T T O M

FUEL INTACT

FLOODED C O M P A R T M E N T H O L E D B U T POSSIBLE T O DE WATER W I T H COM- PRESSED AIR

Figure 1. Liquid Lopding and Flooding Prior to Salvage Operations

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MILITARY ENGINEER KNOX SALVAGE

instructions were dispatched from Washington di- recting that she not be extracted until the dangerous sagging condition was Corrected or the hull girder strengthened.

Several methods were considered to correct this condition. Repeated attempts to pump out the for- ward machinery spaces were unsuccessful. Access openings were few, and even the largest pumps could not lower the water more than a foot. Large structural H-beams were taken to the Knox from the Navy Ship Repair Facility at Subic Bay, Philip- pines. With much difiiculty and without cranes, these were placed on her deck. It was not possible to rig and weld beams outboard and against the sheer strake, so shipfitters and welders from the destroyer tender undertook to fit and weld the beams to the wrinkled main deck. This proved almost impossible on the exposed port side where water broke over the deck edge. The weather deck amidships on a destroyer is only 6 feet wide on each side, and it was soon evident that this arrange- ment could not adequately strengthen the hull girder to prevent the ship breaking in two.

FOAM-IN-SALVAGE

As a last resort-indeed, as a shot in the dark- the possible use of foam to displace the flood water was considered. Inquiries were made to the Super- visor of Salvage who was engaged in research and development on a Foam-in-Salvage (FIS) system whereby chemical foam could be generated under water. Such a system had been under consideration for a number of years, and several different chem- ical formulas had been tried.

One system employed polystyrene balls, gen- erated in hoppers on the deck of the salvage ship and forced or blown through air hoses to a diver who directed the flotation balls into a flooded com- partment. This is the “ping-pong-ball” system of salvaging ships. It is a practical technique for sal- vage in harbors and near the shore where the large quantities of material can be readily handled. The technique requires that the compartments be fairly well sealed, although not airtight, as the mass of balls has no shear strength, and the balls tend to escape. A further disadvantage of this system is that the mass of balls acts as an air bubble and migrates to the high side as the ship rolls. Thus, the center of the added buoyancy is not static.

The FIS system as used on the Knox, on the other hand, constitutes cast-in-place foam. Compared to the polystyrene system, there are several advan- tages. The raw materials are simple to handle and require a minimum of mixing equipment on the deck. The basic material is a resin which comes in drums. This resin is pumped through a hose directly to a “gun” which is handled by the diver. The gun is the mixer. A second hose, attached to the gun, carries a mixture of freon gas, a frothing agent and catalyst. When the diver pulls a single trigger, he

Diver Descending with Foam “Gun”

actuates two metering valves in the gun, thus in- troducting the two raw materials into a mixing chamber at the base of the gun’s nozzle from which the foam is emitted as a frothing mass similar to a sticky shaving cream. The diver directs the nozzle into the compartment to be foamed, and as long as there is an overhead against which the foam may accumulate, and openings in the bottom through which water may be displaced, the diver can fill the compartments.

To keep the gun from clogging with foam, there is a second and smaller trigger which the diver must pull for 30 to 40 seconds, after he releases the main trigger, to allow solvent from a third hose to flush the mixing chamber.

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KNOX SALVAGE MILITARY ENGINEER ~~ ~ ~~ ~ _ _ _ _ _ ~ ~ ~ _ _ _ _ _ _____

PART OF HULL N C H E D I N CORAL

IMATE SHAPE O F SONAR TORN O F F APPROXIMATE SHAPE OF CORAL REEF BELOW SHIP DAMAGED BOTTOM @

LEGEND

The foam as it ejects from the nozzle is still react- ing, but it becomes “solid” within a very short dis- tance (4 or 5 feet). It has a si&cant shear strength which makes it unnecessary for cracks, portholes, and small hatches to be closed. The foam will not spread or transport itself like fie-fighting foam, but must be directed by the diver into the various parts and various levels of a compartment in a manner similar to pouring concrete-only upside down.

In the machinery spaces on the Knox, foam was placed from the overhead down. First, the volume between the overhead and the water level was filled to give the water-displacing foam a “base” against which to work. It was first planned that a false overhead of wood would be constructed at the water level but, with so much piping and machinery, it was easier and faster to foam the abovewater space. In a case involving the cargo hold of a freighter or in cases where sufficient time and outside support are available, the false overhead would doubtless be used. In the Knox, access trunks were left so that divers could descend all the way to the lower levels. The foaming was then continued with the nozzle held only a few feet below the descending ceiling of foam. It was found that the texture (buoy- ancy) of the foam was better if the distance from the nozzle to the overhead was short.

In the flooded forward storerooms, a different foam application technique was used. Holes were drilled in the deck above, through which pipes were inserted at carefully varied lengths and spaces. The foam was inserted first in the shorter pipes and then in succeeding longer ones as the foam ceiling de- scended.

After the foam had been installed inside the machinery spaces and forward compartments, the divers worked outside the hull, finishing the job by applying foam through ruptures in the hull plates and holes drilled for this purpose.

BUOYANCY Compartments totaling 1,240 tons of floodwater

were foamed in the Knox, using some 76 tons of raw material. The basic foam density; under labora-

Typical Damage, Starboard Side Looking Forward

tory conditions, is approximately 2 pounds per cubic foot when generated at atmospheric pressure, and 3 to 3% pounds per cubic foot when generated at a depth of 33 feet of sea water. In terms of buoy- ancy, and under ideal conditions, the foam in the Knox would produce approximately 60 pounds of net buoyancy per pound of raw material. But in actual use, allowance must be made for variations in mixing and foam generation. Also, the foam does not seek out and completely fill all corners and areas which are difficult to reach, so a permeability factor (as high as 0.6 in machinery spaces) must be allowed. In making strength and stability calcu- lations for the Knox as foamed, a foam efficiency of 30 to 40 percent was used, depending upon the spaces involved. This efficiency estimate was con- sidered conservative and, in later operations, effi- ciency above 50 percent should k expected.

By August 21, all the foam had been placed. All water possible had been removed from the ship (Figure 2) and preparations were ready for the attempt to pull the Knox free. The ship was in its lightest possible condition, the tide was high, the spaces had been dewatered or foamed, and a chan-

FOAM IN A I R U S E D TO BRACE UNDERWATER F O A M

c] FOAM U S E D FOR WATER DISPLACEMENT

Figure 2. Urethane Foam Placement

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MILITARY ENGINEER KNOX SALVAGE

nel had been blasted through the coral reef. Finally, a “moving force” (such as waves or a ship’s wake) against the ship was needed to break the static friction. It was too much to expect all desired con- ditions to exist at once!

On the day for the big pull, the weather was too good; there was a flat calm. So, at 3.5-foot high tide, with a Navy destroyed steaming close by at 33 knots making waves, and with the pulling force of six sets of beach gear and one ARS tugging, the Knox floated free on August 24 at 5:30 a.m. She rode nicely, down a bit by the bow, but with no evidence of progressive bending amidships.

The Salvage Ship U S Conserver towed the Knox stern firsl in order to ease dynamic loading on the damaged bow section. Two days later, the vessel was delivered by the Conserver to Koahsiung, For- mosa.

With such severe keel damage and main deck buckling, a successful refloating and towing opera- tion could not have been made without the use of foam to reduce the sagging condition of the ship. Without foam in the forward fireroom and engine room and the other compartments forward, the ship would probably have broken in two, even if she had been pulled free by force and the use of ex- plosives for channel blasting.

The entire operation was successful because of a combination of several factors: the lightening of the Knox by weight removal; the beach gear hauling system and the pulling by salvage ships and tugs; the removal of coral sections impaling the ship, and the blasting of a channel to deep water; dewatering by pumping and with air; and the removal of water by displacement with FIS (Foam-in-Salvage) .

FOAM REMOVAL AND REHABILITATION

Although the significant advantage of cast-in- place foam, as compared to polystyrene ball sys- tems, is its shear strength, the material is in fact a solid mass. This advantage for the salvor presents a problem to the ship repair activity-removing the foam. The material is not acted upon by ordinary or nonacid solvents. It has been found that the only practical way of removing it is by mechanical means. It must be hacked, sawed, scraped, picked, and wire brushed, and then transported to disposal bins. In the case of the Knoz, the Japanese laborers at the United States Naval Ship Repair Facility, Y o b suka, Japan, spent 11,300 man-hours in removing and disposing of the foam. The work was done es- sentially by hand. Other techniques were tried. One

Parted Plate Showing Foam Material Filling Hole

was the use of an ultrahigh-pressure jet water blasting nozzle. This was very effective in cutting the foam, but the jet was so hazardous to the work- ers in its path and caused such a spray and fog in

GIBBS & COX, INC. NAVAL ARCHITECTS AND MARINE ENGINEERS

NEW YORK AND WASHINGTON, D.C.

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KNOX SALVAGE MILITARY ENGINEER

After removal of the foam from the Knor, a thorough survey of the ship was conducted, and a decision was made to rehabilitate her, The value of her undamaged CIC and mast installations was a chief reason for this decision. There followed twelve months of intensive work at Yokosuka, during which the hull was repaired and the flooded ma- chinery spaces were completely rebuilt. All the machinery in the forward engine room and fireroom was reworked and returned to service, The foam in no way injured the machinery, and it is possible that the foam protected it from oily waters and corrosion on the two occasions that the hull was dewatered and dry - docked before preservation

In the fall of 1966, the Knox returned to the Fleet, her hull sound and her valuable CIC still function- ing. Her continued service is a tribute to the salvage

who for Six weeks On 'ratas Reef labored to extract her, and to a new salvage twhniqu*Fm- in-Salvage-whch saved the ship from breaking in two when she was pulled free.

Hard Reminine in Comment after Extensive Removal

the closed compartments, that all other manual measures were taken. work had to be suspended. In Japan, it was thus found more expeditious and no more expensive to use a manual removal scheme.

disadvantage of foam is that it is mildly combustible. It will not support combustion, but if welding is done on a bulkhead opposite the foam, the foam will smoulder and produce noxious fumes.

THE INCREASING IMPORTANCE OF TAIWAN

Certainly for ships of up to about 100,000 tons d.w., 'Taiwan is bound to emerge as a shipbuilding nation of increasing stature. The old-established shipyard at Keelung, of the Taiwan Shipbuilding Corporation, capable of building ships of up to about 35,000 tons, but which has hitherto alternated a modest merchant shipbuilding program with naval construction, is in the midst of a US. $10 million development program with the technical advice of Ishikawayjima-Harima Heavy Industries, of Japan, to include a building dock suitable for the construction in two parts of tankers which will then be enlarged to take such ships,

The new building dock is scheduled to come into operation in January, 1969, following which, with con- struction on slipways, ship production will increase to about 200,OOO tons per year, in addition to about 1,750,000 tons of ship repairs annually.

Shiprepairing also will be the prelude to ship con- struction at the new shipyard due to commence opera- tions at Kao Hsiung, in Taiwan, an ambitious project by the National Chinese Government, Mitsubishi Heavy Industries, of Japan, and the C.Y. Tung Group, which is contributing to the operations the 50,000-ton lifting capacity floating dock purchased from the former naval dockyard at Malta and which at present is being oper- ated in Yokohama by Mitsubishi H.I. To be Tamed the Chung Hwa Shipbuilding Corp., this yard will have building berths and a 110,000-ton building dock.

However determined such companies may be to enter the fiercely competitive world of shipbuilding, consid- erable emphasis is placed on the more profitable ship- repair business.

In Singapore, for example, the Swan Hunter Group are taking the emphatic measure of sending their man- aging director, Mr. Reginald Ibison, to aid the impetus

in setting up the Port of Singapore Authority dockyard and the naval dockyards on an efficient commercial basis. The Royal Navy will be using the dockyard un- til the end of 1971, when Britain is scheduled to with- draw her forces from the Singapore and Malayan bases. In the meantime, steps towards the commercialization of the yard are under way.

Already in its first year of operation of the P.S.A. dockyard, the Swan Hunter Group point to a 17 per cent increase in production and, in profitability, of 61 per cent.

In the neighboring Jurong Shipyard, in which Japan's Ishikawajima-Harima Heavy Industries has an interest, a second drydock is building, to take, initially, tankers of 100,OOO tons, but the dock width is sufficient for tankers of 200,000 tons and plans exist for the extension of this dock a t a later date. This new dock should be in operation in April of next year. Although small commercial ships are built in Jurong, the feasibility of building larger ships is being studied at this moment.

Hong Kong watches all these developments closely, but does not appear unduly dismayed, despite the un- certain future of the Colony with the lease on the New Territories expiring in 1997, when nine-tenths of the Colony must be handed back to China. But Hong Kong's two main shipyards have in recent years in- vested a good deal in the streamlining of their facili- ties to improve further shiprepairing and budding of ships.

No one imagines that Japan will be ousted from her strength in shiprepairing, but what is evident is that immense resources are building up to offer a serious challenge, and certainly there will be some shift in re- pair work to the advantage of Taiwan and Singapore.

Motor Ship, July 1968

698 Naval Enqineen Journal, October 1968