CA1278798C - Submersible hydraulic cutter suction dredging system - Google Patents

Abstract

ABSTRACT
A submersible hydraulic cutter suction dredging system which includes a self-propelled submersible dredger, a floating vessel for controlling the dredger and a ladder universally mounted to a ladder end of the dredger and extending outwardly therefrom. A excavating head is affixed to a distal end of the ladder for excavating material while hydraulic actuation is used for pivoting the ladder universally forwardly of the platform. A pump is coupled to the dredger for removing material excavated by the cutter head and a buoyancy tank is mounted of the ladder for providing lift thereto in order to offset the weight of the ladder in response to being filled with air. The buoyancy tank on the ladder enables the use of heavier construction material in the ladder assembly as well as a larger excavating head. A drive mechanism is used to propel the dredger over a seabed and apparatus is provided to control the orientation, lifting and sinking of the dredging.

Description

1;~7~ 8 _ACKGRO~ND OF THE INVENTION_ _ The present invention relates to a submersible platform dredge.
Various types oE dredges have been developed over the years to meet varied classes of materials and varied excavation requirements. The various dredges generally fall into two basic categories, namely, bucket dredges and hydraulic dredges. Bucket dredges include grab, dipper and ladder dredges while hydraulic dredges include plain-suction, draghead and cutterhead dredges.
Bucket dredges all have one limitation--the discharge must be alongside the place of excavation or put in barges or scows which can carry it away. The grab dredge is essentially a grab bucket operated from a derrick mounted on a flat topped barge. Although a grab dredge works well in silts and stiff muds, it is unsuitable for hard materials such as hard clays.
The dipper dredge is a power shovel operating from a barge.
It is effective in hard materials but has a limited dredging depth of about a maximum of 65 feet.
Ladder dredges use a continuous chain of buckets which are supported on an inclinable ladder and move up and down on two pivots called tumblers. As the buckets go around the lower tumbler, they scoop up the material, carry it up the ladder and dump it into a chute or trough as they pass over the upper tumbler. One disadvantage to the this dredge is that it has to be moored with 5 or more lines and anchors.
These moorings are a constant hindrance to traffic and moving and resetting them is time consuming. In addition to its poor mobility, the ladder dredge also is unstable when towed due to its high center of gravity. Maximum digging depth for the ladder dredge is around 40 feet, but 75 feet is not uncommon.

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Hydraulic dredge.s employ a centrifugal pump ~ischarging either into the hold of the dredge itself, into barges alongside, or ashore. They also all have a suction line through which the pump is supplied with material. The means of loosening and picking up the material is where they differ.
A plain-suction dredge is similar to a ship in hull construc-tion, but has its suction pipe in a well in the bow.
They often have water jets at the lower end of the suction to break up the material. They are ineffective in hard o materials.

Draghead dredges are formed by using a special suction head called a draghead attached to the end of the suction line. The draghead dredge requires the head to be in contact with the bottom and the dredge in motion while dredging.
Material is pumped to hoppers on the dredge which when full require the dredging to stop so that the material can be transported to a disposal area. In addition to the disadvantage of requiring the cessation of dredging while the material is transported to a dumping area, such dredges are extremely expensive.

Cutterhead dredges, also referred to as cutter suction dredges, employ a rotating cutter mounted at the head of a suction pipe, both of which are mounted on a ladder. The ladder is pivotally mounted to the pivotal vertical dredge hull pontoons and is raised and lowered and moved from side to side by a series of winches and cables. This type of dredge is mounted on a barge which is not self propelled and is held in place and pivoted about a spud mounted at its aft end.

Cutter head dredges are effective for all type of materials, but are limited to efficient dredging in only protected waters of less than lO0 feet deep, although depths of 130 feet have been attained. With depths greater than lO0 feet, dredging accuracy is greatly reduced.

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AlL ot the above dredging systems are vulnerable to bad weather, surface congestion, varying ocean bed soil conditions, depth Limitations and c>ther ~actors depending on the type of dredge.
The recent increase in interest in offshore drilling for oil and gas has created a need tor a dredge which can withstand a certain degree of bad weather, operate to depths exceeding 300 feet, excavate at a hitherto greater rate than previously known dredging systems presently in use at these depths, function in ice packs of up to 2 feet or more in thickness and be capable of underwater side cast discharge of dredged material or surface discharge of such material to hopper scows or throuyh a tloat line mono-buoy.

SUMMARY OE` THE INVENTION
According to the invention there is provided a submersible hydraulic cutter suction dredging system, which includes a self-propelled submersible dredger, a floating vessel for controlling the dredger and a ladder universally mounted to a ladder end of the dredger and extending outwardly therefrom. An excavating head is affixed to a distal end of the ladder for excavating material while hydraulic means are provided for pivoting the ladder universally forwardly of the platform. Pump means are coupled to the dredger for removing material excavated by the excavating head. A buoyancy tank is mounted on the ladder for providing lift thereto in order to offset the weight of the ladder in response to being filled with air. Means are provided for propelling said dredger over a seabed.
Provision of a buoyancy tank on the ladder enables the use of ~3 1~78''~'3f~

heavier construction materials in the ladder assembly as well as a laryer excavating head and excavating head drive system.
~bviously, the heavier construction material increases the overall strenyth oL the ladder and the bouyancy tanks provide stability and trim to the dredge platform. A larger excavating head enables faster digging and, a greater excavation rate and hence a lower cost per unit volume of material excavated.
The platform interior is divided into one or more water tight flotation compartments. Means for directing water into and out of selected ones of the compartments and means for supplying compressed air into the compartments to minimize the pressure di~ferential across the walls of the compartments may also be provided. Within each compartment are hard buoyancy tanks used to provide trim and stability during ascent and descent modes. Thus, by minimizing the pressure differential across the walls of the compartments, the walls may be made of siynificantly thinner gauge material which also results in a lower expense, a lower overall weight of the dredger and a much greater maneuverability of the latter.
The ladder may be mounted to a ladder gimbal including a gimbal ring having opposed flat pivoting surfaces to which the ladder is ~ournalled for horizontal pivoting movement, a pair of flat gimbal mounting surfaces through which the gimbal is ~ournalled to brackets affixed to the platform for vertical pivoting and a hollow interior to permit passage therethrough of a suction hose coupled to the excavating head.
Hydraulically driven cables may be mounted on either side of the ladder end of the platform and affixed to the ladder along a line of action intersecting the ladder axis proximate a ~3 ~'~787~

dital end thereo~. ~y utiLiziny cables which join the ladder along a line of action intersectiny a longitudinal axis of the Ladder proximate a distal end thereof, it is possible to apply a much greater torque on the ladder for a given tension on the cables. By so positioning the cab]es it is also possible to obtain a greater swing of the ladder and a greater swing and sloughing force thereby enabling the dredger to be operated in harder materials with a taster rate of excavation.
Preferably an air line with nozzles is affixed to the bottom o~ the platform for selectably blowing air downwardly below the platform to assist in releasing the platform from underwater mud. Because of the large underwater pressure ordinarily encountered in the depths in which the dredger operates, any air present between the mud and the platform bottom is driven out and a vacuum forms therebetween. By injecting air between the interface, the vacuum present is broken, makiny it much easier to release the platform from the sea bed.
Advantageously, a plurality of water jet emitting devices or thrusters, one proximate each corner of the platform and each independently operable enables selective orientation of the platform while ascending or descending only. Thus, it is possible to compensate for ocean currents which can often be significant, when positioning the dredger at a desired location while it is being submerged.
Means may be provided for propelling the platform including a pair of augers mounted to the underside of the platform on opposite sides thereof and motor means coupled to the augers for independently rotatably driving the platform.
Ballast means may include a plurality of air tight ~ , - 5 ~

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compartments within the pLatform, and an air line and nozzles runniny into each compartment ~or blowing air into, and thereby controLliny the amount of water in, each compartment.
By providiny for selectably blowing air into each compartment it is possible to provide ballast to the platform in order to maintain it in a level orientation and to assist in releasing the platform or any portion thereot from an ocean or seabed A sonic receiver may be mounted on the platform and a pair o~ sonic emitting transponders for positioning may be mounted on either side of an area to be dredged. The transponders and receiver provide position and orientation information with respect to the submersible dredger. A like system is utilized to position the surface vessel.
A plurality of forward and aft levelling and digging spuds may be mounted on thé platform and are vertically extendable and retractable. Each spud may have a levelling pad for engaging the ocean floor and inhibiting further penetration thereof by the spuds.
One or more hydraulic piston cylinder may have one end horizontally and vertically pivotally mounted to the platform below the ladder and the other end pivotally mounted to the ladder for vertically raising and lowering the ladder relative to the platform.
Means may be provided for loading the dredger into a floating vessel for transport thereof. A pump mounted on the platform and a suction line running along the ladder connected to the pump at one end and proximate to the excavating head at the other end exhausts material from the excavating head.

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BRIEE~ DESCRIPT:tUN OF THE DRAWINGS
In drawinys of a preferred embodimeqts of the invention:
F'IGUR~ 1 is an elevation view of the dredging system showing the submersible dredger and its support barge;
F'IGURE ~ is a perspective view of the submersible dredyer;
FIGURE 3 is a plan view of the submersible dredger;
E~IGURE 4 is an elevation view of a portion of the submersible dredger plat~orm with a partial cut away of the plat~orm showiny the driving augers;
FIGURE 5 is an elevation view of an alternative auger drive;
FIGURE 6 is an elevation view of a top portion of the mast of the submersible dredger;
FIGURE 7 is a side elevation view in section of the ladder gimbal ring and bounce damper cylinder;

~'? - 5b 1'~78~798 FIGURE 8 is a front elevation view in section of the ladder gimbal;
FIGURE 9 is a side elevation view of the loading area of the barge showing the submersible barge in both the initial loading and loaded positions; and FIGURE 10 is a plan view of the barge with a helicopter landing pad cut away to show the loaded submersible dredger below.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS
10AS illustrated in figure 1, the dredging assembly consists of a submersible dredger 10 operating on a floor 14 of a body of water 21 and a barge 16 anchored proximate the dredger 10 by anchor lines 18 suspended from a plurality of anchor cable spuds 20 affixed to the barge 16. Corresponding 15anchor winches 142 located on a deck of the barge 16 raise and lower the anchor lines 18. A dredged material discharge line extending between the barge 16 and dredger 10 is made up of a plurality of sections of rubber hose 22 interconnected by quick disconnect pipe ball and bell joints 23. A pair of sonic transponders 24 and 26 are positioned on either side of an area 12 to be excavated and transmit sound to an 360 sonic receiver 31 positioned on the submersible dredger.
The submersible dredger 10 as shown in figures 2 and 3 has a platform 19 which is formed on the sides by a plurality of dredging platform hull plates 15. The interior of the platform is divided by water tight bulkheads 29 into a plurality of flotation compartments. Passing through these compartments are air pipes 28 having valve outlets in each of the compartments. Also running through the bottom of the compartments is an air piping 33 having nozzles which pass through the bottom of the hull and communicate with the 1~78'~'9f~

underside thereof. In the side external hull plates 15 of the water tight compartments are respective water ports 57 controlled by a door (not shown) Eor letting water Elow in and out thereof in response to externally supplied contol signals.
Exhaust air vent valves 97, normalLy closed, are located at the highest point of each compartment to assist in compartment flooding.
On either side of the platform 19 there is rotatably mounted a travelling auger 76 shown in more detail in Figures 10 4 and 5 and located below auger tubes 85 and 98. The augers are each coupled to hydraulic travel auger drive motors 88 through drive gears 86. On the forward and aft hull plates are mounted respective pairs of spuds 74 and 72, respectively, with spud levelling pads 71 affixed thereto. The spuds 72 and 74 are extendable and retractable in response to external control signals.
On the deck 13 of the platform 19 there is mounted a pump 66 slightly recessed below the platform surface to lower the center of gravity of the platform 19. The pump 66 is driven by a variable speed electric motor 45 and has coupled thereto a dredge pump suction pipe 62. A stone box cleanout 73 adjacent pump 66 on the suction pipe 62 provides access to clean accumulated debris Erom the pump 66. To the discharge of the pump 66 is connected a platform discharge pipe 17 which in turn couples to the discharge rubber hose 22.
To the forward end of the platform, there is mounted a ladder 40 which extends forwardly to the platform 19. To either side of the ladder 40 there is affixed starboard and port buoyancy pontoons 44 and 46, respectively. The buoyancy pontoons admit therein and discharge therefrom water in response to an external control signal. The end of the ladder 40 is inclined downwardly 15 degrees to enable excavation ~'~78'79f~

without 90i L b~tween the excavating head 42 and the platform 19 blockiny downward pivotiny of the l.ad~er 40. This angle may be up to 3U degrees. To the torward end of the ladder is mounted an excavating head 42 ~or breaking down into small particles material to be dredged. The excavating head 42 is driven by a variable speed drive motor 39. Suction pipe 62 extends along the la~der 40 to proximate the excavating head 42.
As seen in Figure 7 and 8 the ladder is coupled to an octayonal yimbal ring 118 by means of ladder gimbal pins 120 which permit horizontal movement of the ladder 40. The gimbal ring is ~ournalled to platform mounting brackets 119 by means o~ trunnion ring pins 116 which provide for pivotal movement of the ladder 40 in a vertical plane. Rubber suction hose 63 permits movement of ladder 40 through gimbal 118 without breakiny pipe 62. A ladder mast 32 is coupled by means of base pins 117 to bracket 119.
~ etween a ladder bracket 114 at the bottom of the ladder 40 and a cylinder mounting bearing 110 at the forward end of the platform there is connected a hydraulic piston-cylinder 75. The cylinder 75 functions to absorb shock due to sudden vertical movement of ladder 40. It also functions to provide extra vertical force to force the excavating head 42 into hard material and to hold the ladder in position in the event of a failure of the ladder hoist cable 27. The mounting bearing 110 is pivotably connected to the platform 19 by a cylinder bearing pin 112 to permit horizontal pivoting of cylinder mounting bearing 110. Cylinder mounting bearing 110 includes a thrust bearing surrounding pin 112. Bearing pin 111 coupling the piston cylinder 75 to mounting bearing 110 1~7~'7~3~
permits verlical movement o~ the cylinder 75.

The top of the :Ladder mast 32 is pivotally coupled by means ol a top mast trunnion pin 138, a swivel mast section 67 which is Journalled to a top mast swivel frame support 25 by pin 137. The swivel frame support is affixed to mast 32 by a ladder mast pin 55. The mast section 67 has journalled thereto top mast swivel sheaves 51. A ladder hoist cable 27 is wound around swivel sheeves 51 and water block sheeves 53 Journalled to a water block 38. Cable 27 is wound around a hydraulically operated ladder hoist winch 64 located behind the mast 32. Upon tightening ladder hoist cable 27 the water block 38 and attached ladder hog wires 47 and 49 (see F~igure 3) are pulled towards swivel sheeves 51 thereby raising the excavatiny head 42 and ladder 40. At the top the swivel frame support 25 is affixed the 360~ sonic receiver 31. To the bottom end of swivel trame support 25 on either side thereof are affixed starboard and port ladder mast strong backs 36 and 34, respectively, which are coupled to the platform 19.

Side to side movement of the ladder 40 and cutter or excavating head 42 are controlled by swing cables 52 and 56 coupled to sheeve wheels 60 and 77 and dead ended at pad-eyes 54 and 58 on swing arms 65 and 69, respectively, on the starboard and port sides of the ladder 40 proximate the distal end thereof. The swing cables 52 and 56 are wound around swing arm cable sheeves 59 and 61, respectively, journalled to the distal end of swing arms 65 and 69, respectively. Where lighter materials are involved, sheeve wheels 60 and 77 may be eliminated and the lines dead ended on ladder 40 near sheeve wheels 60 and 77. Swiny arms 65 and 69 are pivotally coupled g 1~8~9~3 by pins 3~7 to the starboard and port sides ot the pLatform 19 near the ~orwar~ end thereot. Swing arms 65 and 6Y are raised and lowered by cyLinders 35 and are stabilized by swing arm strong backs 41 and 43, respectively. Horizontal movement of ladder ~0 and excavating head 42 are controLled by hydraulic winches 48 a~ 50 which alternately apply tension to swing cables 52 and 56, respectively. The winches 48 and 50 are bidirectional variable speed units with tension pull off. The angle measured in the horizontal plane between the ladder 40 and the platform 19 is indicated by a plurality of proximity switches 153 spaced apart radially by angular increments of approximately 5 degrees. A de-slugger valve 156 is located in suction pipe 62 on the ladder 40 to prevent consolidation of the solids passing through the dredge pump suction pipe 62 and subsequent blockage thereo~. A pin connection (not shown) is provided to lock movement of ladder 40 and retain it in a fixed position before raising swing arms 65 and 69.
On each side of platform 19 are a plurality of dry docking rollers 70 which roll on rails 130 as seen in Figure 9 on each side of a docking ramp on barge 16. The submersible dredge is loaded onto barge 16 by a dry docking cable 132 attached to a bracket on the aft of the platform 19 and wound on dry docking hauling winch 134.
Details of the auger drive system as shown in Figure 4 include the travelling auger 76 rotatably supported by thrust carrier bearing 82, 83 and 84. Auger 76 extends below the drive shaft 80 and hull 30 of platform 19. The forward and aft ends of the travelling auger 76 is tapered to a narrower diameter and the platform hull plates 30 on either side upwardly incline to enable the submersible dredge to negotiate :~

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sudden increases in anyle ot torward or aft movement without diyging into the ~sea bed.
An alternative travelling auyer drive mechanism as seen in Fiyure 5 includes a central auyer blade 90 affixed to an auyer shaft 81 rotatably supported by bearing 92, 94 and 96.
The central auger blade 90 and shaft 81 are coupled to an upwardly inclined torward auger blade 102 and shaft 89 by a universal auger shaft ~oint 104. The auger tube 85 is upwardly inclined at the aft and forward ends of the platform 19 to accomodate the upwardly inclined auger blade 102 and shaft 89. The latter shatt is rotatable supported by bearings 98 and 100.
The barge 16 as shown in F~igure 10 includes a helicopter ladiny pad 140, below which is loaded the submersible dredger 10.
The barge 16 has an under deck discharge piping 143 to which is attachable the discharge rubber hose 22. The piping 143 couples to a discharge float line deck pipe 144 through discharge diversion gate valves 141. Piping 143 also couples to a spider discharge rubber trunnion system 145 to a spider discharge pipe 148 extendable by support davits 149 for loading a barge docked alongside barge 16. Instrumentation, control, power and air lines are wound around drum 147. At the aft of barge 16 are located diesel electric generators 146 for generating electrical power for use by the submersible dredge 10 and barge 16.
Housings for electric drive motors 45, 39 and others are adjustably pressurized with air to a level equal to outside water pressure and the electric motors cooled by an air water heat exchanger.

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In operation, the barg~ 16 is anchored in position and dredge 10 is lowered by unwinding dry dockiny hauliny winch 134. As the dredge 10 moves away from barge 16 dry dock bay, winch 147 is unwound and discharge rubber hose 22 is connected to pipe 17 and additional sections of hose 22 added as required, swing arms 65 and 6~ are lowered and locked in position and a ladder swiny lock disengaged. Pontoons 44 and 46 and compartments in the platform 19 are gradually loaded with water permitting the dredge 10 to sink. Pressure sensitive depth indicators 152 located on each corner of platform deck 13 and pressure sensitive depth indicator 151 near cutter drive motor 39 on ladder 40 signal depth read-outs to control level descent and ascent of dredger 10. Sonic transponders 24 and 26 are dropped at convenient locations within 1000 ~eet on either side of the area 12 to be excavated. once on the sea bed the dredge 10 is propelled in a desired direction by rotating augers 76.
On each corner of the deck 13 of platform 19 there is mounted a jet or thruster pump 155 which directs a stream of water outwardly of the platform 19 substantially along a notion at extension of a diagonal line joining the corners thereof. By selectively operating the jet pumps 155 the platform can be rotated in any desired direction to maintain a preselected heading during descent and ascent.

The position of the dredge 10 is determined by the signals received by the sonic receiver 31 from transponders 24 and 26. Orientation of the dredge 10 is determined by signals received from a magnetic compass 154 located on dredger 10.
Once in position the hydraulic dredge pump 66, the dredye excavating head 42 are started and the dredge ladder 40 is -. ~

~:7~7~8 lowered by unwindiny ladder cable winch 64 until cutter head 42 engages the sea bed. As excavating head 42 loosens and cuts up the sea bed, material is then sucked up through suction pipe 62, drawn into pump 66 and discharged therefrom up discharye rubber hose 22. When dredging, it may be necessary to lower spuds 72 and 74 in order to stabilize or to level the plattorm 19 laterally. The ladder 40 is moved from side to side by swing winches 48 and 50. In the event the in situ material is hard, piston cylinder 75 is retracted to assist in forciny excavatiny head 42 into the material.
~therwise cylinder 75 is used in a shock absorbing mode.
Sudden increases in slope encountered by the dredge l9 would ordinariLy result in the forward end of the platform jamming into the sea bed. Provision of tapered forward ends of the travelling augers and hull 30 assists in engaging increased slopes without digging into the slope and becoming stuck. A
taper on the auger aft ends is also provided for reverse movement. The alternative auger drive system as shown in ~igure 5 provides another mechanism for engaging increased slopes. The upwardly inclined front auger sections provide lift up any increased slope and thereby prevent the platform ~rom becoming stuck.
In the event the submersible dredge becomes stuck in soft material it may happen that a partial vacuum may develop between the earth and the bottom of the platform 19. Thus provision is made for blowing pressurized air in pipe 33 out of nozzles passing through the bottom surface of the platform 19 to counteract any such vacuum.
The auger drive system allows the dredger 10 to work to unlimited depths and to negotiate short radius turn dredging.

~ - 13 -l~7s~sa Once dredyiny is complete and the pipe 22 is tlushed out, the excavating head 42 and pump 66 are stopped and the ladder levelled and centered to the platform 40. The dredye compartments and pontoons are tilled with air thereby raising the dredger 10 gradually to the water surface. Dry dockiny cables 132 are attached to the aft end and the dredger 10 pulled toward the loading ramp by hauling winch 134 until dry docking rollers 70 engage rails 130 thereby causing the dredger 10 to roll into its loaded position as seen in Figure 9 and 10. Prior to docking however, the ladder swing locking device is engayed and swiny arms 65 and 69 are raised to a vertical position by extending piston cylinders 35 below the swiny arms 65 and 69. As the dredger is docked, rubber hose 22 is removed in 40 foot sections and stored on the deck of barge 16 so the control and air lines can be rolled onto drum winch 147.
The inclined end of the ladder 40 may be hinged and pivotally driven by hydraulic piston cylinders on each side of the ladder 40.

Other modifications, variations and departures lying within the spirit of the invention and scope as defined by the appended claims will be obvious to those skilled in the art.

Claims (12)

1. A submersible hydraulic cutter suction dredging system, comprising:
(a) a self-propelled submersible dredger having a dredger platform;
(b) a floating vessel for controlling said dredger;
(c) a ladder universally mounted to a ladder end of said dredger and extending outwardly therefrom;
(d) an excavating head affixed to a distal end of said ladder for excavating material;
(e) hydraulic means for pivoting said ladder universally forwardly of said platform;
(f) pump means coupled to said dredger for removing material excavated by said excavating head;
(g) a buoyancy tank mounted on said ladder for providing lift thereto in order to offset the weight of the ladder in response to being filled with air;
(h) means for propelling said dredger over a seabed; and (i) means for controlling the orientation, the lifting and sinking of said dredger.

2. A dredging system as in claim 1, wherein the platform interior contains a plurality of water tight flotation compartments, means for directing water into and out of selected ones of said compartments and means for supplying compressed air into said compartments to minimize the pressure differential across the walls of said compartments.

3. A dredging system as in claim 2, wherein said ladder is mounted to a ladder gimbal including a gimbal ring having opposed flat pivoting surfaces to which said ladder is journalled for horizontal pivoting movement, a pair of flat gimbal mounting surfaces through which said gimbal is journalled to brackets affixed to said platform for vertical pivoting of said ladder, a hollow interior to permit passage therethrough of a suction hose one end of which is proximate said cutter and hydraulically driven cables mounted on either side of the ladder end of said platform and affixed to said ladder along a line of action intersecting the ladder axis proximate a distal end thereof.

4. A dredging system as in claim 3, further including a plurality of water stream emitting devices, one proximate each corner of said platform and each independently operable to selectively orientate said platform to a preselected orientation while ascending and descending.

5. A dredging system as in claim 3, wherein said means for propelling said platform includes a pair of augers mounted to the underside of said platform on opposite sides thereof and motor means coupled to said augers for independently rotatably driving same.

6. A dredging system as in claim 5, further including a sonic receiver mounted on said platform and a pair of sound emitting transponders for positioning one on either side of an area to be dredged, said transponders for transmitting position signals to said receiver, thereby facilitating determination of the position of said submersible dredger.

7. A dredging system as in claim 6, further including a plurality of forward and aft levelling and digging spuds mounted on said platform and vertically extendable and retractable and each having a spud levelling pad for engaging the ocean floor and inhibiting further penetration thereof by the spuds.

8. A dredging system as in claim 7, including a hydraulic piston cylinder, one end horizontally and vertically pivotally mounted to said platform below said ladder and the other end pivotally mounted to said ladder for vertically raising and lowering said ladder relative to said platform.

9. A dredging system as in claim 8, including means for loading said dredger into a floating vessel for transport thereof a pump mounted on said platform and a suction line running along said ladder proximate said excavating head at one end and connected to the pump on said platform at the other end for exhausting material from said excavating head.

10. A dredging system as in claim 9, wherein said pump means include a discharge line coupled at one end to said pump and positionable to discharge excavated material either underwater or above water from another end thereof.

11. A dredging system as in claim 6, including means coupled to said dredger to determine the orientation of said ladder relative to said platform and the orientation of the platform relative to the ocean surface with depth sensing means coupled to said platform to provide control signals for determining the attitude of said dredger.

12. A dredging system as in claim 3, including an air line and nozzles affixed thereto coupled to a bottom of said platform for selectably blowing air downwardly below said platform to assist in releasing the latter from underwater mud.