u
Mekelweg 2, _ co Deift
NEW ENGLAND SECTION
THE SOCIETY.OF NAVAL' ARCHITECTS
AND'MARINE EÑGINEERS
JUNE, 1965
CONSTRUCTION OF AN. AXI.L-FLOW
PUMPJET PROPULSION uNIT
BY
JAMES HARVIE
JUDITH L. ROBINSON, EDITO
GENERAL DYNAMICS- ELECTRIC BOAT IVISION
NEW :ENGLßtD SECTION, SNAE
GROTON, CONNECTICUT .1 bnderafdelinq der( Scheepsbouwkun'e Technische .Hosd.c
Mkeweg 2
-PRICE 8 1.00This paper describes the construction of a pumpjet propulsion
unit to reduce propeller noise on the GLOVER (AGDE-l). Although
hydrodynamic design details are classified,
structural design is
described, and metallurgy, cutting, forming and welding of the bronze alloy used in the pumpjet are discussed, and the problems encountered are reviewed. TECHNISCHE UNIVERSITEIT
bmdum
Mekelweg 2, CD Deift TeI. 015- 780873 Fc 0150 73ß3ß ABSTRAÇTThe pumpjet installation on AGDE-1 is part of the U. S. Navy program to reducè underwater noise radiated from, combatant ships. With many weapons systems dependent on underwater sound for detection and tracking reduction of noise is essential to reduce the range at which the ship can be detected and to reduce interferénce to the ship's own detection and tracking equipment.
The propellèr is a major source of underwater noise, and a major part of propeller noise is caused by cavitatioñ. The pumpjet was developed as a thrust produr which will operate with a minimum of cavitation up to the full power of the ship. The pumpjet is an axial flow pump consisting of a multibladed propeller type impeller rotating in a fixed duct, or shroud, with small tip clearance. The shroud eliminates the tip vortices, accelerates the incoming flow,
and turns it to the axial direction. The shroud is contoured to avoid cavitation due to its own
motion through the water. The pumpjet is installed at the same location as the conventional propeller.
Pumpjets werê installed in 1956 on USS WITEK (DD848), a twin screw DD692 Class
destroyer, with good results. NOise was significantly reduced, propulsive efficiency was
good, and maneuverability, although impaired, was acceptable.
The Navy noise reduction program includes a number of approaches to thê elimination of noise and the transmission of noise. This program has resulted in the development of special requiremènts for equipment, foundations, resilient mounts, piping, and vibration damping, as well as for propellers. Some of the concepts can be tested on existing ships, and sorne must be built into the ship. The specifications for ships of the DE 1040 Class include many of the latest thoughts on low noise surface vessels. The Navy decided to equip AGDE-1, one of the ships of that class, with pumpjet propulsion as well. In so doing, the Navy seized the opportunity of fitting a ship already under construction with the latest development of the. pumpjet which had proven successful on the WITEK. On AGDE-1, however, a single unit with a larger rotor was used. The decisIon was implemented by a change order issued nearly a year after award of the basic contract.
*Assistaflt Hull Superintendent, Bath Iron Works Corporation
-1-CONSTRUCTION OF AN AXIAL-FLOW
PUMPJET PROPULSION UNIT
.-- By James Harviè, * Associate Member
r
I:INTRpQcTIoN
---- ( "
- The producnonof surface ships with minimum waterborne noise is vital to the
anti-súbnârhiewaifate j,t'ágrm of the U. S. Navy.
Reduction of waterborne noise permits greater sonar range, better passive listening by the surface ship, and less range of passive dètection by submarines. COnventional propellers have been recognized as serious noisemakers and consequently a prime target in the noise reduction program.A number of attempts have been made to develop quiet propulsion units to replace conventional propellers One approach which has shown promise is the pumpjet which is similar to an axial flow pump with an impeller or rotor turning within a fixed shroud. This paper describes the construction of a pumpjet propulsion unit for the GLOVER (AGDE-1). Because many aspects of the design are classified, this paper does not include a detailed dis-cussion of the design. Performance of the unit is not discussed inasmuch as GLOVER has not yet undergone sea trials.
III. DESIGN
Hydrodynamic Design
The Bureau of Ships solicited proposals for the hydrodynamic design of the pumpjet for AGDE-1 and tested models of each proposed design at the David Taylor Model Basin The design chosen for use on AGDE-1 includes a five-bladed rotor 11 feet 7 Inches diameter, a sevn-bladed stator aft of' the rotor, a shroud 16 feet long and 13 feet maximum diameter with
a canted inlet. Two struts connect the shroud to the hull of the ship. See, figure 1. The
Burau of. Ships furnished Bath Iron Works with offsets for the rôtor, stator and shell, and specified the contour of the struts. For a detailed discussion on pumpjet design, see
refrence 1.
To aid in testing and evaluation of the purnpjet, the preliminary design provided for the installation of hydrophones ànd accelerometers in the duct añd struts of the pumpjet and vie'ing ports in the hull of the ship.
Detailed Design
The detailed design of the pumpjet was developed by Gibbs & Cox, Inc. in close coU.aboration with Bath Iron Works.
An important consideration was the arrangement to permit assembly of the rotor on the ship and disassembly after the ship is in service. The rotor is installed on a stub shaft which has a bearing in the stator and a bolted coupling to the shafting forward of, it to permit
installation of the rotor Because the rotor diameter is greater than the diameter of the
mouth of the shroud, the lower forward section of the shroud was made portable The aforemost
section of the line shaft is installed after installation of thé rotor. See figure 1.
In the searchfor the material most suitable for the purnpjet, the following
character-istics were considered: .
Resistance to salt water corrosion and erosion. Resistance to fouling .both at rest and nderway.
Good physical properties including fatigue strength in salt water, impact resistance and resistance to stress corrosion cracking.
Adequate strength to meet design criteria.
Ease of fabrication and repair.; i. e., good casting, machining and welding properties.
A minimum galvanic couple with the steel hull and between elements of the pumpjet.
4S5EMBLY -EL(V4T/OAJ
-2-Many materials were considered for the application including stainless steels, chrome steels, nickel steels, nickel-maraging steels, Ni-resist steels, HY-80, monels, and various types of bronzes. The possibility of making the duct and the rotor of dissimilar materials was also considered. Although this might have substantially reduced or eliminated the problem of protecting the steel hull the difficulty of providing protection against electrolytic action between the duct and the rotor, if made of dissimilar materials, appeared to be too grea.t.
Due to the configuration of the design and weight limits, 'it Was determined that the shroud and strut arms should be hollOw. Because castings to the desired design details could not be produced, it was decided that the shroud and struts shOuld be fabricated as a weidment
made up of plate, with castings included at locations most suited for their use Therefore it
was considered essential to select a material which had goad weldability as well as satisfying as many of the characteristics listed àbove as possible.
Excépt for the various bronzes, all of the materials mentioned above failéd to meet all
of the désired criteria, or were eliminated due to insufficient service experience. Of the several
bronzes that might have been selected, it was considered that Superston 40 was most suitable from the standpoint of castability, weldability, high strength, corrosion and erosion resistance,
and service experience Superston 40 is a manganese-nickel-aluminum bronze alloy identified
as Alloy 2 of Specification MIL-B-21230A. The properties and metallurgy of this material are discussed later in this paper.
Information was available covering about 13 years of successful use of Superston 40 for propellers, as well as laboratory reports on the characteristics of the alloy prepared both here and abroad. Experience with welding repairs of propellers of this material has been excellent. There had been little experience with the wrought form of the alloy which is made by hot rolling annealed castings. However, the physical properties of thé wrought material are either equal to or better than those of the cast form of the alloy, and it was considered that the workability would be similar.
The choice of Superston 40 was recommended to and accepted by the Bureau of Ships. Subsequent to this decision it was learned that this alloy when exposed to stagnant fouling conditions was subject to dealuminization Addition of 0 5 percent tin was found to counteract this condition, and the Superston 40 used in the AGDE-'l pumpjet was modified by this addition. An effect of the modification was to increase the liquidity of the weld puddle, which made welding somewhat more difficult.
The scantlings of the pumpjet shroud and struts were developed from strain energy analyses of' the complete structure. Loadings' consist of weight, lift, drag, torque, sideload in
turns and shock. Since the precision with which some of these loads can be determined is low, the stress was limited to 12, 500 psi, about 20% of yield. Further, the shroud is designed to 'be sufficiently rigid to avoid rubbing of the rotor tips undèr shock loading. The minimum tip clearance is 5/8 'inch.
The shroud is constructed with an inner and outer skin separated by continuous circumferential webs and intercostal longtitudinal webs. Castings. are used at the nose, at the intersection of the struts with the shroud, and at the longitudinal bolting surfaces of the
portable section, since the configuration in these locations is more suitable for castings The
skin is generally 1-1/2" thick except in highly stressed areas such as in way of the strut castings
where it is 2-1/4" thick. The webs are generally 2-1/4" thick. The webs act as backing for
seams and butts of the plating. The outer skin was installed last and was plug welded to webs
where the lower connection efficiency was acceptable. Plate butts With open roots against the webs were provided where higher efficiency was required. See figure 2.
The struts are constructed with a 1/2" plate skin and 1/2" plate grid of webs. Flat bar is welded to the webs to act as backing for the butts and seams of the skin The struts are bolted to the hull through a 2-1/4" fàying flañge. See figure 2.
.5EC770N 77i'RU a' 5WROW
LGDE-J PL/MPJET
All butts and seams in the shell plating and framing and in' the castings required 100% efficient full penetration welds. Elsewhere welding was kept to a minimum consistent with strength. It was fQund, however, that the fillet welds connecting the webs to the skin of the shroud had to be increased over the minimum to avoid excessive cracking due to thermal
stresses.
A recess is provided in the. shroud in way of the rotor tips. The original concept was to install rubber or plastic liners in this recess to minimize damage to the rotor in the event that foreign material became wedged against it, and to quiet tip cavitation. However, difficulty
vith the liners on USS WITEK led to a decision to install a portable bronze liner on AGDE-l. This liner is heavily damped by a compound vulcanized on the side away from the rotor tips.
Septum damping is provided on the outside of the trailing edge of the shroud, flush with the contour, to damp singing of the thin edge. The voids in the shell are filled with poly-urethane foam.
IV. METALLURGICAL ASPECTS OF SUPERSTON4O MODIFIED
Superston 40 (modified) is a relatively new,. high strength, highly corrosion-resistant copper base alloy having a nominal analysis of 13. 5% manganese, 7. 8% aluminum, 3.0% iron, 2. 25% nickel, and 0. 5% tin. When cast it is principally an Alpha-Beta structure with about 60%. of the Alpha phase in a Beta matrix. Alpha is ductile, and Beta is hard and brittle. Dependent upon subsequent heat treatment and working, the balance between the two phases may be adjustèd and the grain refined in size to give a fairly wide range of physical properties.
A fine grained Alpha structure of 60% or over is desirable for good ductility, high strength and impact resistance, and this structure is obtained by annealing at 13000 F. and slowly cooling. Since this alloy work hardens rapidly, any appreciable amount of cold working must be inter-spersed with annealing to avoid cracking. Because the strength of the aiioy at 13000 drops to about 10% of its cold strength, hot forming is readily done, but annealing of large structures can result in distortion or can even cause them. to collapse under their own weight.
The metallurgy of a welded jointis complex. Due to the deposition of. liquid metal between two relatively cold surfaces and the melting of these srfaces, about every possible phase for this alloy exists in a welded joint. Hence the ductility varies considerably across the weld. This condition may be eliminated by annealing, but as noted above, annealing is not always feasible. The weld metal is stronger but less ductilethan the base material. Welds of less than 100% efficiency will crack under load before deformation of the base metal occurs, while welds of 100% efficiency will force the base metal. to yield first under load.
Reference 2 is a complete metallurgical discussion of Superston. V. FABRICATION
Supers ton
Bath Iron Works started to collect background information on Superston as soon as it was selected for use in the pumpjet. Representatiyes of the Superston Corporation, Phelps-Dodge Copper Products Company, Columbian Bronze Corporation, and American Brake Shoe Company visited the shipyard and released all of the available information on the properties and working characteristics of Superston. While there was considerable experience with castings, very little work has been done with the wrought form of the material, and welding data was non-existent. Therefore, the first goal was to obtain some of the metal and some welding wire in order to learn more about welding and forming it.
Welding Techniques
The first Work by the shipyard was done using scrap castings cut up into bars and samples of various electrodes, following procedures commonly used in welding bronzes. Development of a suitable MIG welding procedure for Superston 40 was completed jUst prior to the change to the tin-modified alloy, which required the development of new techniques and à new procedure qualification. Welding details used in the design of the pumpjet were developed experimentally. The development of welding procedures and joint designs led to the conclusion that welding must be done under favorable conditions and generally in the flat position. Welds
in the vertical position are possible, but must be done with smaller filler wire. The extreme fluidity of the metal requires small welding wire, very low welding amperage and voltage, and considerable skill to produce acceptâble welds in the overhead position.
Fabrication Procedure
The close finished tolerances required and the need for positioning for welding dictated the approach to assembly which was finally used in our construction procedure. The struts were assembled on the outboard shell plating set in mockups parallel to the floor, and the inboard shell plating was installed in small pieces as closing plates after all of the internal structure had been welded. Experience in building submarine pressure hull sections indicated that by building the shell around a system of internal spiders, very close dimensional control and nearly perfect circulaiity can be achieved. The stator and a number of internal
spiders were fitted to a large central tube approximating the propeller shaft. The inner shell and framing were assembled around the stator and spiders with the axis perpendicular to the floor. The unit was then. turned so that the axis tube was supported in the horizontal position by end bearings, permitting positioning of all joints, for proper welding and facilitating installation of the outer shell and the finishing operation.
Lofting
Templates were developed in the mold loft and were made to design dimensions plus a shrinkage allowance based upon the maximum allowable plus tolerance of the finished unit and the shrink properties of Superston castings. Templates and sets for plate fabrication and ternplates for the spiders and for checking the unit during construction were made. Patterns for the cast components were made from the laydown in the mold loft. Patterns for the rotor and the stator were made by the foundry.
Purchase of Material
Wröught Superston is produced by hot rolling cast slabs to the desired thickness. Plate size is limited by the maximum available size of mold in which to cast the slabs, as well
as final plate thickness plate proportions and edge losses For the purpose of this job
Phelps-Dodge started with cast slabs of about 4500 pounds, from which finished plates weighing not over 3500 pounds could be expected Using an assumed density of 477 pounds per cubic foot th maximum area available coúld be determined, and the desited proportions selected. Through cose collaboration with the design agent, it was possible to keep the designed sizes within the
range of available sizes. Plate widths were limited to 35 inches minimum and 72 inches
max-!rum, although widths up to 120 inches could be produced by cross-rolling at extra cost. Bécause it was expected that considerable material would be removed in fairing and polishing the surfaces of the duct, the. plates were rolled to the desired thickness with all tolerances applied in the plus direction. The plates were rolled by Lukens Steel Corporation for Phelps-1'odge. All plated were inspected by the shipyard with ultra-sonic appatatus to ensure that
they were sound. .
All castings including the rotor and stator were procured from Columbian Bronze. The castings were inspected by the shipyard with ultra-sonic apparatus and proven. sound before use,.
Welding electrodes for use in MIG welding equipment were.ordered from Ampco Metals, Inc. Most of the electrodes were . 0ó2 inch diameter, although some . 045 inch and .[o3o inch diameter wire was .used for special applications. Over 9000 pounds of welding wire vere used. An unexpected production bottleneck was caused by the necessity for many drawings
to reduce the wire to the desired size and. for annealing of the wire after each drawing operation. Cutting
The plasma-jet cutting process is the prime tool used for cutting Superston. Plasma putting employs an electric arc to partially ionize a mixture of argon and hydrogen or air; the
rc and the ionized gas, or plasma, produce a thin flamelike jet which will cut ferrous and non-ferrous metals. The plasma-jet torch generally was mounted on a standard crawler-type portable burning machine. With a little practice, plates .1 - 1/2 and 2-1/4 inches thick were cut very close to size, allowing for grinding to smooth the cut edge, to produce the exact outline desired, and to prepare the edge for welding.
Some excess stock was left on cuts made in heavy castings and all bevel cuts over 20 degrees to allow for the tendency of the plasma stream to wander.
Some of the straight-sided cuts such as the framing bars were planed after cutting to produce the desired finish and contour. Bevels were planed where possible, but most of the bevels were made by hand chipping and grinding.
Shaping
The rough castings were chipped and ground to the desired shape and the parting line castings were machined, drilled and bolted together befor. being assethbled into the unit. Plate rabbets were planed in the castings for the forward ad after edges of thé strut arms.
-6
The major shaping operation was forming the shell plates. Because, the shroud is a tube with a generally round transverse section and an airfoil shaped longitudinal section, all of the inner and outer shell plates of the shroud have compound curvature. In general, these plates were shaped cold or with only low heat in a press using a standard die. Because of the thickness,
strength, and work hardening properties of the material, in-process annealing of the plates was
required if the shape was not obtained wth relatïvely few blows. Experimental data developed during construction of the unit indicated that annealing of all material after forming is desirable because the material can be put into better physical condition. It was not practicable due to the
status of construction to anneal all material, but all of the outer shell plates were annealed after forming. The. frames were bent to single curvature in the press. After shaping, the plates were checked for accurate contour, and final beveling and welding preparation were accomplished.
A great deal of the credit for the successful dimensional outcome of the pumpjet unit and the ease with which it was assembled belongs to the bending floor personnel for their very accur-ate shaping of the placcur-ates.
Assembly
The shroud was assembled on its aft end with its axis perpendicular to the floor. A 24
inch diameter tube 20 feet long was set up as the center of a system of circular frames or
spiders which established the contour of the inside of the inner shell The inner shell plating, castings, and framing members were.assembled around the stator and the spiders and tacked, and some welds which were in an advantageous position were completed.
The complete inner shell and framing of the shroud with its supporting system of spiders was lifted and turned as one assembly so that its axis, the shaft centerline, was parallel to the floor. Two babbitted open bearings supported the ends of the axial tube and permitted the unit to be rotated to any desired position for welding.
The inner shell and framing of the shroud were welded as described later. Upon
completion of welding, inspection, thermal cycling, and repair of cracks, the surface in way of the outer shell was faired to provide the outer shell plating with a good surface on which to land. Conduit piping for instrumentation attached to the shell was installed. The outer shell plating was then fitted, tacked, and welded.
The struts were assembled on the outboard plating set in mockups parallel to the floor. The castings forming the forward and after edges of the strut arms and the internal framing members were assembled and welded. Piping for air and instrumentation of the pumpjet were
installed in the struts. The inboard platiñg was fitted in panels to.permit welding to the faying
bars at each frame. Several of the panels were left off to provide access to the internal piping.. The strut palms are heavy horizontal flanges to provide bolted connections between the Superston and the steel hull as showñ in figure 2. The palms and some heavy adjácent structure were
sub-assembled welded and straightened before incorporation into the main strut assemblies Both
struts were annealed in a furnace after assembly.
In order to facilitate erection and regulation of the completed unit on the ways, and to eliminate field machining, two portions of the steel structure of the ship, including the steel bolting flanges matching the strut palm and large sections of floors and bulkheads were
assembled separately from the ship as units. These units and the struts Were faced and drilled
in the machine shop to permit bolting the pumpjet to a portion of the steel structure of the ship. Then the steel assembly was regulated within the ship, making the final attachment of the pumpjet to the ship a welded connectjon.
The struts were positioned palms down on a level floor, . set to the required angle and
spacing, and tied together as a unit with rigid braces Offsets of the duct in way of the strut
connections were lifted by transit and transferred to the struts, and the struts were trimmed to the required shape as defined by the offsets. The two struts were then assembled With the completed shroud and welded just prior to erecting the complete pumpjet unit on the ship.
The major problêm in construction of the AGDE pumpjet was welding. As. mentioñed
earlier in this paper, no previous experience with large Superston weidments was available for gudance añd there was no infömation on welding tin-modlified Superston 40, hence suitable pro-ceiures and methods had to be developed and the problems had to be overcome as they arose. Experimentation by the several suppliers of material and Bath Iron Works continued from the time Superston was selected for use in the pumpjet until the assembly was nearly complete.
An evaluation of the welding tests indicated that defects in Superston material decrease thè ductility and impact properties and that the weld material has greater tensile strength and hardness than the base metal and less ductility. To reduce porosity, the commOn defect in the weld metal, to an absolute thinimuni, high preheat was indicated for welding, with all possible welding being done downhand and none overhead.
All tacking on the castings, inner shell, and framing Was done with 4000 preheat. Some of the tacks cracked and were removed and replaced.. All tack welds werê proven sound before starting production welding. The assembly was preheated using electric strip heaters
t 2250 and wélded using local preheat to 4000. Some cracks developed in stressed areas during elding when the welds were less than 100% efficient or not substantial enough to transmit the fabrication loads. All cracks were removed and rewelded and the entire assembly was checked for defects by the dye penetrant method. This assembly was made completely free of known craòks.
Upon tacking the first few outside shell plates to the framing using lOcal preheat to a major crack occurred in the fillet weld connecting the framing to the inside shell plate. After this crack was repaired, a large crack occured in the fillet on the other side of the rib. lt was decided to thermally cycle the assembly at 40O450o before attaching the outside shell plates. The intent of the thermal cycling was to mechanically exercise the weldment to work ¿ut cracks which were already in existence and to bring out any cracks which might develop in liighly stressed areas.
The assembly was thermally cycled three times undèr very strict controls and uniform ieat. At the end of each cycle a complete dye penetrant examination was made and a critical technical analysis was made to see what the next procedure should be in view of the resUlts and knowledge to date The observation of the results of the cycling indicated that most of the cracks Dccured in the fillet welds and the majority of these at the corner intersections. There were relatively few cracks in füll penetration welds. The cracks disclosed by dye penetrant inspection
vere repaired after each cycle The amount of cracking diminished with each cycle particularly
in the third cycle when all the corner intersections of fillet welds were isolated
Although the ductility of the. weidment would have been increased by annealing, because the strength of Superston is very low at this temperature, it was impractical to anneal the pumpjet since unacceptable distortion would have resulted. The struts were annealed as it was thought distortion could be kept Within acceptable limits.
During the time that these production problems were being encountered, the labor-atones of all the interested companies were making comprehensive metallurgical studies to give a better insight into the problem. The studies disclosed that Superston gradually becomes harder and less ductile when subjected to temperatures somewhat above 2000. Thermal cycling was stopped as the major benefits of this had been achieved. Further refinement of thé Welding
procedure for welds using 1250 preheat produced welds with satisfactory radiographs so welding preheat Was reduced to 1250 fr the outer shell and all subsequeñt Welds.
The outside shell was tacked and welded with 125° preheat. All accessible wilds of the
completed assembly were dye penetrant inspected and all cracks were repaired Few cracks
developed in the welding of the outside shell Cracks which developed in the struts were primarily in the heavy members and all were repaired and dye penetrant inspected
8
r--VII. FINISHING
Tolerances and Finish
The specified dimensional tolerances for the shroud are: Location of center of leading edge and exit nozzle: design radius ± 1/4" and design length ± 1/4". Radial location of inner shell in way of rotor: design radius ±1/8".
Thickness: design thickness ± 3/8".
The c ntours. of the leading and trailing edges and the. inner and outer shell 'ere. checked at fourteen radial planes with gages. to the following to1erances
(1). Leading and trailing edges:. no departure over 1/32" from gage.
Inside shell: no departure over 3/16" from four foot gage.
Outside shell: no depárture over 1/8" from four foot gage.
Fair between radial planes.
The entire surface of the shroud and struts was finished to a 63 micro-inch finish.
The dimensional restrictions were met by the method and care in construction. The
contour requirements, however, were met by means fa major hand grinding operation. Some
welding buildup was required to repair scars and to level low spots, but most of the fairing was done by removing metal. As stated earlier, the plates were ordered with all tolerances plus to provide for the removal of material in fairing without weakening the structure. When the sur-faces were, to the required contour., the desired smoothness was obtained with progressively
finer grit sanding discs. The 63 micro inch finish was produced with number 80 grit sanding
discs after the unit was erected aboard ship.
The unit was carefully measured and checked with gages to demonstrate that it was Within the required tMerances. The only departure from the design shape is in the vicinity of the parting ca.stings of the removable forward ]ower portion of the shroud. Radial
measure-ments at the forward end indicate that the unit has spread in way of the bolted connection on each side.
Other Finishing Operations
In the work of finishing the pumpjet unit prior to erection, a number of special operations were required.
All of the internai voids in the shroud and struts were filled with polyurethane foam. Holes were drilled in the plating and the voids were steam cleaned. The voids were filled with foam 'and plugs were tapped in the holes, welded over, and ground' smooth.
'Recesses for instrumentation - vibration pickups and hydrophones - were tapped and
fitted för the instruments. Plates were fitted to cover the bolt pockets in way of the portable
section.
Thin Superston liner plates wi'th damping material vulcanized on the back were fitted and installed with screws in the recess provided in way of the rotor tips. These liner plates were 'shaped by the shipyard in quarters, and B. F. Goodrich applied the dampingmaterial,
which was developed especially for this use. '
Installation of the septum damping on the after edge of the shroud was a very fussy job.. After the outer shell contour was ground to,the proper shape, a 118" recess two feet wide was, chipped all around the shroud Naval brass sheet 1/16 thick was formed to the compound
curvature of the shell and fitted in place over a sheet of asphalt impregnated felt and welded to the shell.
VIII.. ERECTION
The pumpjet unit was fully assembled and finished as much as practicable in a building near the ways. The 65 ton weight of the completed unit less shafting, rotor, and the forward lower removable, portion was just equal to the maximum availäble crane capacity of the shipyard,' so it was necessary to remove the spiders and the portable shell section before the unit could be moved. Cranes within the building loaded the unit onto a lowbed trailer which hauled it out of the building to, where. another pair of cranes could lift it and carry it to the roadway, at the head of the ways, where it was loaded ori the lowbed again and moved into position at thè' head of the ways on which AGDE- 1 was being built. Cranes carried the pumpjet unit over the ship.and landed it in a special cradle on. the groundways aft of the ship. The cradle was slid up the greased ways into positibn under the ship and secured. The steel bolting flange assemblies which had been removed from the struts and temporarily located in the ship were dropped down onto the strut palms and bolted. Then the purnpjet unit was moved up into position on the ship with jacks and chain falls, and it was regulated to preliminary shaft line 'targets and welded into the ship.
The structure and fairing plates around the struts were Installed, añd the cradle was removed Shaft sighting and boring operations proceeded in the conventional manner On completion of boring, the shafting, bearings, and rotor were installed.
Replacement of the removable portion of the shroud was a job of considerable propor-tions. Upon removal, it had sprung open somewhat with respect to the fixed upper portion of the shroud. A heavy framework was erected outboard of the parting line on each side of the
unit, and by jacking against the framework, the removable portion was restored to a shape matching the fixed portions and the sections were bolted together The tendency of the unit to
spread open in way of the bolted jólnt requited the use of shims to ensure metal-to-metal contact
in way of all of the bolts. . . .
IX. REVIEW OF THE PROJECT
A review of the operating results cannot 'be. presented evén in 'an unclassified form because the GLOVER has not yet undergone sea trials. 'and it is not kiown Whether or not the pumpjet installation has accomplished its mission of reducing propeller noise below the levels attained on the WITEK. However, it is possible to review the effects of the installation on other aspects of the ship. The placement of a large mass at the stern of a, ship designed fora conventional propeller installation resulted in structural modifications t- support the unit and a rearrangement of tanks and compartments to offset the trim by the stern, as well as a loss in fuel capacity to offset the added weight The main propulsion reduction gear and its foundation required mothfication to withstand the additional thrust developed by the pumpjet The rudder was moved and redesigned, resulting in arrangement of the steering gear room and the torpedo installation Study of the performance of the WITEK leads to the prediction that the GLOVER will probably suffer a loss in maneuverability and backing power and a slight loss in speed. Installation of the pumpjet has added to the cost of the' shi'p and delayed ship construction. The significance of the acceptance by the Navy of the cost, delay, and compromises is tò underscore the extreme i'mportánce' of upgrading the anti-submarine warfare capabilities of the fleet through the reduction in self nölse of ships.
-The scope of the project is apparjent upon considçration that the hipyard was directed to design, build, and install a large, complex, and highly stressed structural weidment out of an experimental alloy to function as the propulsion unit for a ship that was already under construction.
The challenge of integrating the pumpjet and its associated elements into the design and into the production schedule of the ship has been met. From the start of the pumpjet project until delivery of the ship, the demands of this pròjeát on the facilities, supervision, and skilled mechanics of the shipyard have been substantial. The development of materials and processes and the solution of problems has been a significant exercise fOr the designers, the suppliers, and the shipyard It is hoped that the effectiveness of the pumpiet in reducing propeller noise will be of equal significance.
ACKNOWLEDGMENTS:
The author wishes to express his thanks for the assistance rendered by G. F. Cary II, C. A. Mayo, Jr., B. B. Burbank, and F. M. Bradway in the preparation of this paper, and G. E. Stimpson, Jr. in the preparation of the figures.
REFERENCES:
"Recent Developments in the Propulsion of Surface. Shifls and Submarines by Means of Axial-Flow Pump-Jets", by W. D. Crater and F. D. Mikelson
"New High-Strength Copper-Manganese-Aluminum Alloys", by J. M. Langharn and A. W. O. Webb, paper presented at the International Foundry Congress, Detroit, Michigan, May, 1962.
