US2361404A - Apparatus for excavating subaqueous material - Google Patents

Description

J. KALIX Oct. 3'1, 1944.

APPARATUS FOR EXCAVATING SUBAQUEOUS MATERIAL Filed Oct. 26, 1943 4 Sheets-Sheet 1 S11/umm wmv,

JOHN KALJX J. KALIX Oct. 3l, 1944. v

APPARATUS FOR EXCAVA'TING SUBAQUEOUS MATERIAL Filed Oct. o, 1945 4 Sheets-Sheet 2 J'OHN KAL/X J. KALlX Oct. 31, 1944.

APPARATUS FOR EXCAVATING SUBAQUEOUS MATERIAL 4 sheets-sheet 3 Filed oct. ze.l 194s IJ-@HN KA LI/x Oct. 3l, 1944. J. KALlx 2,361,404

APPARATUS FOR EXCAVATING SUBAQUEOUS MATERIAL Filed oct. 26, 194s 4 sheets-sheet 4 rfi/3.15

vPatented oct. 31, 1944 APPARATUS FOR. EXCAVATING"SUB- AQUEOUS MATERIAL John naux, Dayton, ohio Application October 26, 1943, Serial No. 507,663

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) y 6 Claims.

The invention described herein maybe manufactured and used by or for the Government for 4governmental purposes, without payment to me 'of any royalty thereon.

This invention relates to the art of dredging and more particularly it is directed to a submarine excavator for removing said, gravel, mud, silt or the like from canals, lakes, rivers and other bodies of water.

l One of the objects of the invention is toprovide a submarine excavator for removing subaqueous material from canals, harbors, or the like, also to restore the storage capacity of silted ood control dams and to make inlets into dry landfrom waterways.

Another object of the invention is to provide an improvement in the art of hydraulicdredging `.wherein means are providedfor producing a continuous oneway excavation of subaqueous material from canals or other waterways and'deposit ing the excavated material at an exceedinglyy rapid rate into collapsible sectional forms for building up embankments, walls,A abutments, dikes, and levees or the like to a predetermined level.

Another object of the invention is toprovideta method of excavating `subaolueous material'from bodies ofwater for deepening purposes-andthe like, which consists of loosening and'breaking'up the subaqueous material, creating a suction at the suction mouth yof a suction pipe, causing the broken subaqueous material to be sucked through the suction mouth and drawn througha Venturi opening in the suction pipe, pumping the subaqueous material through the suction pipe to .a discharge pipelineycreating a suction inthe discharge -pipeline and depositing the excavated'subaqueous material -for building up, adding vto or strengthening a shore, levee and the like.

Another object of the inventionis to provide a hydraulic dredge including dual suction pipes, swivelly mounted at one end of eachto one end of a delivery pipeline and having a suction pump and a motor for operating the pump'mounted Within one of each of the other ends of the suction pipes and cutterheads mounted to be rotated by the suctionpumps whereby subaqueous material may be broken up by the cutterheads,-sucked up through the suction pipes by the suctionl pumps and discharged through the delivery pipelineto any place desired.

Another objectief the invention is to provide a hydraulic dredge including a'suction pipe having a Venturi opening formed therein adjacent .to a suction mouth at one end thereof, a delivery `pipeline connected tothe .other end of :the suction pipe, an impeller driven motor. mounted within thesuctionpipe at the Venturi opening, a cutterhead mounted at the suction mouth oi the suction pipe and meansfor automatically transferring the torquesfrom the motor to between they impeller and cutterhead whereby subaqueous material .may ybe broken up by the cutterhead,

sucked through the suction 'mouth and pumped through the Venturi opening and sucton pipe into the delivery` pipeline. by the impeller for discharge toy any place desired When the cutterhead is working: in hard material or the like.

Another object of the invention is to provide a hydraulic dredge including dual suction pipes, each. swivellyijoined at one endto one end of a :delivery pipeline, said dual suction pipes and .delivery pipeline suspendedbeneath the dredge by means .of a vertically adjustable rack, motor driven suction pumps, one of each of which motor driven suction pumps being mounted Within one of .each of the suction pipes adjacent to the other free ends thereof, cutterheads mounted at the free endsof` the suction. pipes and connected to lbe actuated by said motor driven suction pumps, a pipe connecting the .free ends of the suctionpipes and holding them in spaced relation .with each other and means connected to actuate said suction pipes upwardly and downwardly or in a horizontal arc'about their swivel connection With the delivery pipeline whereby the cutterheads may be directed.y at any portion of subaque- .ous :material vin canals ,or other body of 4water for excavating thematerial.

In hydraulic :dredges of the suction -type for excavating subaqueousmaterial at presentin use, a main suction pump is provided on thedredge to create a suction in a suction pipe, whereby the subaqueous material is drawn up through the suction pipe and discharged bythe main suction pump to a delivery pipeline. The main suction .pump is limited in itsoperation by certain nat- .ural laws such'asso-called entrance lossesand. in .creating any-necessary lift of the subaqueous material from thebottom ofza bodyfof water tothe main suction pump.

lIt is therefore the aimvand purpose of this-.invention to eliminate vthe-necessityof using. a main suction pump on the vdredge by providingasuc- ,tion pump and amotor for driving y,the pump `Within a Venturi openingsformed in a suction pipe adjacent the suction mouth .thereof andcausing subaqueous material ,to :be drawn .into .the suc- .tion mouth and forced 'bylthe fmotor .driven suctionpump through the Venturi openingandsuction pipe into .a .discharge :pipeline having a j booster pump mounted therein for creating a suction within the discharge pipeline, whereby a con tinuous uninterrupted one-way excavation of the subaqueous material from bodies of water is provided,I which subaqueous material may be deposited into collapsible forms provided on a shore for producing an embankment or the like.

With the above and other objects and advantages in view, the invention consists of certain features of construction and operation of parts which will hereinafter be: described and shown in the accompanying drawings, in which:

Fig. 1 is a fragmentary side elevation of a dredge having the improved dredging apparatus mounted thereon;

Fig. 2 is an end view of the same;

Fig. 3 is a top plan view thereof;

Fig. 4 is a fragmentary llongitudinal sectional view of one end of a suction pipehaving a motor driven suction pump mounted therein, with a cutterhead directly driven by the suction pump;

Fig. 5 is a front end view of a modification of the same; Y

Fig. 6 is a'fragmentary longitudinal sectional View taken on the line 6--6 of Fig. 5;

Fig. '7 is an enlarged sectional view of a portion of a discharge pipeline having a suction booster mountedtherein used in carrying out the invention;

Fig. 8 is a front end view of dual suction pipes having the improved motor driven suction pumps mounted therein and supported by a pipe frame including a transversely extending 'pipe having additional pipes rotatably mounted thereon;

Fig. 9 is an enlarged fragmentary detail sectional view partly in elevation' illustrating the manner of rotatably mounting the additional pipes on the transversely extending pipe of the pipe frame;

Fig. Vl() is a fragmentary top view of the front ends of the dual suction pipes and supporting frame;

Fig. 11 is a vertical sectional view of a collapsible settling basin which may be used in carrying out the invention;

Fig. l2 is an enlargedfragmentary detail sectional view, partly in elevation, illustrating `the manner of swivelly connecting one end of a single suction pipe to a discharge pipeline;

Fig. 14 is an enlarged view of a pair of oating y members and their connected parts used in carrying out the invention;

Fig. 15 is a fragmentary longitudinal sectional view of the end of a suction pipe having a motor driven suction pump mounted therein, with a cutterhead removed therefrom.

Referring to Fig. 1, A designates a river, canal, or other body of water from which subaqueous material is to be excavated and B is a dredge on the body of water adjacent to a bank or shore C. The dredge B is propelled forwardly or rearwardly by means of an anchor I which enga-ges the shore C and from which a` chain 2 passes over apulley 3 on the front end of the deck 4 of the dredge and thence to any suitable type of actuating device 5 which engages the chain. From the actuating device Sthe chain 2 passes lover apulley 6, Fig. 3, mounted on the rear material may comprise a single suction pipe 1,

Fig. 12, swivelly connected by a universal joint 1', at one end to one end of an elongated discharge or delivery pipeline 8, Figs, 1 and 3, and having a suction pump 9 as illustrated Figs. 4 and 15 or a modification 9 thereof, Figs. 5 and 6, mounted in an inlet end thereof, but the' apparatus preferably comprises dual suction pipes IIl, each swivelly connected at one end to a Y-shaped end II of the discharge pipeline 8 by universal joints II', Fig. 13. The discharge pipeline 8 is made of a plurality of sections 8', Fig. 3, having their ends swivelly joined together at I2 and submerged in the body of water A. The pipe sections 8 arecarried by pairs of airtight floats I3 in the form of barrels arranged on opposite sides of the discharge pipeline 8. The pairs of floats I3 are mounted on opposite ends of transversely extending supporting bars I4 threadedly mounted on vertically extending rods`l5 anchored at their lower ends to the universal joints I2 of the pipe sections 8 shown in detail in Fig. 14. A crank I6 vis threadedly -mounted on the upper end of one of each of the rods I5 for a purpose which will hereinafter appear.

A vertically extending rack I1 is slidably mounted in brackets I8 mounted on the rear end of the deck 4 of the dredge, which rack I1 is connected at its lower end to the Y-shaped .end' II of the discharge pipeline 8, Fig. 13. A

pinion I9 mounted on a crank 20, rotatably supported on the deck 4 of the dredge engages the upper end of the rack I1, whereby upon turning -the crank 23 the dual suction pipes Ill may be raised or lowered under the dredge as the work of excavation proceeds.

The outer free ends 2I ofthe dual suction pipes I0 are held in spaced relation to each other by means of a transversely extending pipe 22 made of a pair of sections 22' joined together at one.

end of each by a T-shaped coupling 23 and nipples 24 joined to the other ends of the sections 22 by T-shaped couplings 25, which nipples 24 extend through the free ends 2| of the dual suction pipes into the suction pumps, Figs. 8, 9 and IIJ. The couplings 23 and 25 are rotatably mounted on the pipe 22, with the couplings 25 being closely adjacent to the free ends 2| of the suction pipes I0 and the coupling 23 being in the middle of the pipe 22. A supporting conduit 26 and a pair of air conduits 21 are mounted on the couplings 23 and 25 respectively, with the vsupporting conduit 26 having a clevis 28 mounted thereon adjacent to its upper end. The air conduits 21 are bent inwardly with their upper ends open to the atmosphere and held in abutting engagement with the clevis 28 on the upper vend of the supporting conduit 26 by a retaining clamp 29 or the like, Figs. 2 and 8.

The clevis 28 on the upper end of the supporting conduit 25 is engaged by a hook 30 on one end of a rope 3| which passes through a sheave 32 mounted on the upper end of a boom'33 on the deck 4 of the dredge and thence to a winch or drum 34 mounted on the boom 33. The lower end of the boom 33 is pivotally connected to a fpipes I is 'formed with a portion 43 of least "cross-section having-a bell-shaped suction mouth f44mountedlonan outer end thereof and a frusto-conical shaped section45 mounted on its inner end whereby a substantially Venturi-shaped pasf lsage-46 isprovided in lwhich the suction pump 9, Figs. 4 and 15,1or the suction pump 9,', Figs. 45.and Ei, may be mounted. The suction pump 9 is preferably of the propeller type including an impeller 41 :having blades 48 mounted thereon operable within the suction mouth 44 and directly driven by any suitable type of electric motor 49 centrally mounted on ribs 50 within the YVenturi-shaped passage 46.

A cutterhead v5| having blades '52 removably mounted thereon is operable in front of the bell- `shaped'suction mouth `44 and is directly connected to the-motor driven impeller 41 by arms .53.and'a central r0d^54 mounted on a bracket 55 secured lto Ythe outer end of the impeller, whereby the kcutterhead 5| is driven 'at the same speed Aand in thesame'direction as the motor driven impeller. The electric motor 49 has a rearwardlyextending streamline portion 49 and the elec- .tric motor in the free end of the single suction pipe '1 or Athe free ends l2| of the dual suction pipes Hl" are connected by electric conductors 56, the conductors for the electric motors in the .dual suction pipes extend through the transversely extending pipe 52 and up through the supporting conduit 26 where they are adapted to be connected to a suitable source of electric supply (not shown) mounted on the dredge B. In order to regulate the speed of operation of the electric motors, a rheostat 51, Fig. 4, may be connected in circuit with the conductors 56.

In Figs. 5 and', the cutterhead 5| is driven indirectly by the suction pump 9 in order to obtain greater efficiency and larger torque from the electric motor 49. The outer end 58 of the impeller41' `is elongated and provided with a circular groove 59 engaged by a belt 60 therein, which drives a pulleyl mounted on one end of a shaft 162 for a pinion 63 which shaft 62 is rotatably mounted in bearings 64 formed in a housing 65 mounted on the free end 2|v of a suction pipe |0 and adjacent to a bell-shaped suction mouth 44. The pinion 63 drives a ring vgear 66 rotatably mounted within the suction mouth 44. The blades 52 of the cutterhead 5| are connected to the ring gear 66 by means of varms 61 and the inner end of the central'rod'54 is rotatably mounted onr the outer end of impeller 41' by ball bearings 69 or the like. blades 48 of the impeller 41, Figs. 4 and 15, or the blades 48 of the impeller 41', Figs. 5 and 6, maybe adjustably mounted to provide a variable pitch by any suitable conventional means.

In Fig. 15 isL shown the suction pump 9 having the cutterhead 5| removed therefrom. It will v.be understood that the cutterhead 5| may be individually rotated in front of the suction mouth of the suction pipe by any of the conventional drivingmeans if desired- In order .to provide a suction in the long discharge pipeline 8 for transporting material such as oil or `sludge to a shore or other'place desired, a suction booster pumpv 10, illustrated in detail in Fig. '7, is mounted in an enlarged pipe section1l provi-ded in the discharge or delivery pipeline 8. The booster Apump'lll comprisesvan electric motor 10 mounted on ribs 12 and adapted to drivean impeller 13 having blades 14. The motor 19' andimpeller 13 extend longitudinally within :the 'center of the-'enlarged pipe section The vvsource of electricalfsupply (not shown) .which may ybe on vthe dredge B. Itfwill be readily un` derstood that ,an-y Vsuitable number .of -Ybooster pumps 10 may be provided in the discharge pipeline18. y

The excavated subaqueous-material from the dredge maybe directed by the dischargepipeline 8 intoasettling basin-11 providedon the shore or leveeC for forminga boundary wall by which ythe rsubaqueous material is confined to permit a separationof the water from the solid particles contained Yin the subaqueous material whereby the shore orlevee C maybe builtup, addedto or strengthened. Thesettling basin l1'|,.Fig. 11, is made inthe form of a knockdown or collapsible frame structure having a main conduit 18 containing a valve 19 and extending from one of the walls '89 ofthe settling basin, which walls-80 are mounted at their lower endsin the shore Cand held in place by upper and lower separator rods 8| and 8|', respectively. The Water in 4the subaqueous material'contained inthe settling basin 11 is adapted to enterv additional conduits 82 lead- Aing from .the'settling basin at different heights and having valves 83 provided thereon. The water in the conduits 82 feeds into a common conduit 84 extending at its upper end into the settling basin adjacent to the upper end thereof and connected to the main conduit 18, whereby upon opening-the valves 19 and 83 'the water in the settling basin is adapted to flow fromthe settling lbasin through the main conduit 18 and to ow back into the body of water A. After the water has been withdrawn fromv` the subaqueous material and the settled residue has reached a predeterminedheight, the settling basin is knocked downv with the bottom separator'rod 8| left in place. AAdditional settling basins (not shown) may be erected on the shore C while the water is being withdrawn from the settling basin 11.

The electric motors employed for driving the impellers are now available for normal operation under Water and adequate protection of equipment and personnel from the effects of possible short circuits can Vbe provided. By submerging the electric motors, the water hasa cooling effect thereon and in order to provide an additional cooling thereof the air conduits 21 are openedv at their upper ends to the atmosphere whereby air may enter the conduits 21 and pass through the conduit 22 tothe nipples 24 and thence to the electric motors 49.

In operation, assuming that the dual suction pipes IU have been lowered until the free ends 2|l thereof have engaged the subaqueous material within the body of water A and that the electric motors 49 have been connected to a suitable source of electric supply (not shown); upon actuating f the rheostat 51 the electric motors 49 may be rotated at any speed desired thus driving the impeller 41, Fig. 4, or the impeller 41', Figs. 5 and 6. In using the form of suction pump 9 shown in Fig. 4, the cutterhead 5| directly connected to the impeller 41 and driven at the same speed loosens the subaqueous material While the blades 52 of the cutterhead and the blades 48 of the impeller break up the subaqueous material into smaller pieces, thereby increasing the carrying capacity of the water in the subaqueous material. The broken subaqueous material is then sucked up throughthe suction mouth 44 .by the. suction AcrecaVated. 'By winding the rope :ated by the impellery 41 which pumps the .subaqueous material through the Venturi opening 46 and the suction pipes into the discharge pipeline 8. The suction booster pump 1|), by creating a suction in the discharge pipeline 8, draws the Vsubaqueous material therethrough and pumps it to any place desired such as into the settling basin 11, Fig. 11.

In the form of construction illustrated in Figs. 5 and 6, the cutterhead 5| is rotatedat a slower speed than the high velocity motor driven impeller 41' and the reaction of the cutterhead 5| to- `Iection tothe motor driven impeller 41' whereby the reaction of the cutterhead to the subaqueous material is counteracted, which results in less vibration. In homogeneous material the available motor torque is divided or split between thecutterhead 5| and the blades 48 of the impeller 41', whereby when a hard layer of subaqueous material is met and more power is necessary the electric motor 49 will take up the additional load, particularly when a series wound motor is used.

Upon the cutterhead 5| being stopped by a boulder or other large object, the belt 6U driven by the motordriven impeller 41 will slide on the pulley lil, whereby the motor 49 may continue to rotate vthe impeller 41 without damage thereto.

By winding the rope 3| on the drum 34on'the boom 33, the free ends 2| of the dual suction pipes I may be either raised or lowered in a vertical direction and directed onto the material to be ex- 39 on the winch 42 the boom may be raised or lowered to also move the free ends 2| of the suction pipes |l| having the suction pumps therein to any vertical position and, by winding the rope 36 from the winch 31 onto the winch 38, or from the winch 38 to the winch 31 the turn-table 35 may be rotated to move the boom 33 to thus move the free ends 2| of the suction pipes |0 in a horizontal arc.

When crank :in is turned pinion lil is rotated so that the rack |1 may be actuated to either raise or lower the suction pipes Il] including the end of the discharge pipeline 3 swivelly connected thereto away from or toward the bottom of the dredge I8 when desired. .Shouldy it become .necessary to repair any damage to the discharge pipeline 8, the cranks i6, Figs. 1 and 14, are rotated on ythe threaded rods l in a clockwise direction whereby the rods are moved upwardly on the bars I4 pulling the portion of the discharge pipeline 8 to be repaired upwardly with it toward' the oats |3 until the discharge pipeline is clear of the top of the body oi water A. After the repairs to the discharge pipeline 8 have been made, the cranks IS are rotated in a counter-clockwise direction on the rods i5 thereby causing the repaired discharge pipeline to be pushed down into the bodyl of water away from the floats |3.

' The apparatus has been particularly shown and described as including the dual suction pipes Il), but it will be readily understood that the single suction pipe 1, Fig. 12, having ythe excavating devices illustratedin Figs.,4 and or the device illustrated in Figs. 5 and 6, may be moved upwardly, downwardly, or in a horizontal arc about its swivel connection with the discharge pipeline 8 by the same tackle used in actuating the free ends' 2 'of the dual suction pipes l0. i

It will thus be seen that there is herein provided a novel and efficient form of dredging appa- Y ratus which is well adapted for all the puposes indicated. Even though there has herein been `shown certain features of construction and operation of parts, it is nevertheless to be understood that various changes may be made therein if the changes do not depart from the spirit or scope of the claims. l

Having thus described my invention, what I claim as new and wish to secure by Letters Patent 1. The combination with a hydraulic dredge including dual suction pipes having a suction mouth at one end of each and a delivery pipeline swivelly connected at their other ends, a suction pump operatively positioned within one of each of the suction mouth ends of the suction pipes, electric motors, one of each of the electric motors driving'one of each of the suction pumps and operatively mounted within the suction pipes, a transversely extending pipe including nipples holding the suction mouth .ends of the suction pipes in spaced relation with each other, a supporting conduit and air conduits connected in communication at one end each each with the transversely extending pipe, said air conduits opened to the atmosphere at their other ends and said nipples extending into the suction pipes and to the interior of the electric motors whereby air may enter said air conduits, pass through the transversely extending pipe andnipples and enter the electric motors for cooling the same, and means-for swingingthe suction pipes upwardly or downwardly or in a horizontal arc about their swivel connection with'the delivery pipe.

2. The combination with a hydraulic dredg including dual suction pipes having a suction mouth at one end of each and a delivery pipeline swivellyconneoted at their other ends, a suction pump operatively positioned within one of each of the suction mouth ends of the suction pipes, electric motors, one of each oi the electric motors driving one of each oiy the suction pumps and operatively mounted within the suction pipes,

crtterheads connected to be actuated byv said 4siction pumps, a transversely extending pipe ing opened to the atmosphere at their other ends and said nipples extending into the suction pipes and to the' interior of said motors whereby air may enter said last-mentioned conduits, pass through the transversely extending pipe and nipples and enter the motors for cooling the same and means for swinging the suction pipes upwardly or downwardly or in a horizontal arc about their swivel connection with the delivery pipeline.

3. The combinationY with a hydraulic dredge including dual suction pipes having a suction mouth at one end of each and a delivery pipeline swivelly connected at their other ends, a suction. pump operatively positioned within one of each of the suction pipes, electrick motors, one of each of the electric motors driving one of each of the suction pumps, a suction booster operatively mounted in said deliverypipeline, a transversely extending Vpipe including nipples holding the suction mouth ends of the suction pipes in spaced relation with each other, a supporting conduit and air conduit connected in communication at one end of each with the transversely extending pipe, said air conduits opened to the atmosphere at their other ends and said nipples extending into the suction pipes and to the interior of said motors, whereby air may enter `said last-mentioned conduits, pass through the transversely extending pipe and nipples and enter the motors for cooling the same and means for swinging the suction pipes upwardly or downwardly or in a horizontal arc about their swivel connection with the delivery pipeline. l

4. The combination with a hydraulic dredge including dual suction pipes having a suction mouth at one end of each and a delivery pipeline swivelly connected at their other ends, a suction pump operatively positioned within one of each ofthe suction mouth ends of the suction pipes,y

conduit and air conduits connected in communication at one end of each with the transversely extending pipe, said air conduits opened to the atmosphere at their other ends and said nipples extending into the suction pipes and to the interior of said motors, whereby air may enter said last-mentioned conduits, pass through the transversely extending pipe and nipples and enter the electric motors for cooling the same, means adjustably mounted on the dredge and connected to the suction pipes, said means adapted to be actuated to raise or lower the suction pipes as the work of excavation proceeds and means for swinging the suction pipes upwardly or downwardly or in a horizontal arc about their swivel connection with the delivery pipe.

5. The combination with a hydraulic dredge including dual suction pipes having a suction mouth at one end of each and a delivery pipeline swivelly connected at their other ends, a suction pump operatively positioned within one of each of the suction mouth ends of the suction pipes, electric motors, one of each of the electric motors driving one of each of the suction pumps, cutterheads connected to be actuated by said suction pumps, an electrically operated suction booster mounted in said delivery pipe line, a transversely extending pipe including nipples holding the suction mouth ends of the suction pipes in spaced retioned conduits, pass through the transversely extending pipe and nipples and enter the electric motors for cooling the same and means for swinging the -suction pipes upwardly or downwardly or in a horizontal arc about their swivel connection with the delivery pipeline.

6. The combination with a hydraulic dredge including dual suction pipes having a suction mouth at one end of each and a delivery pipeline swivelly connected at their other ends, a suction pump operatively positioned within one of each of the suction mouth ends of the suction pipes, electric motors, one of each of the electric motors driving one of each of the suction pumps, cutterheads connected to be actuated by said suction pumps, a suction booster operatively mounted in said delivery pipeline, a transversely extending pipe including nipples holding the suction mouth ends of the suction pipes in spaced relation with each other, a supporting conduit and air conduits connected in communication at one end of each with the transversely extending pipe, said air conduits opened to the atmosphere at their other ends and said nipples extending into the suction pipes and into the interior of said motors, whereby air may' enter said last-mentioned conduits, pass through the transversely extending pipe and nipples and enter the electric motors for cooling the same, means adjustably mounted on the dredge and connected to the suction pipes, said means adapted to be actuated to raise and lower the suction pipes as the work of excavation proceeds and means for swinging the suction pipes upwardly or downwardly in a vertical direction or in a horizontal arc about their swivel connection

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