Abstract: A method and apparatus are provided for forming an ice slot in an ice sheet by cutting discrete blocks of ice in the ice sheet, then gripping the blocks of ice with a claw-like attachment extending from a hydraulic arm and pushing the ice blocks downwardly with the hydraulic arm until the blocks reach a level with the underside of the ice sheet and then rotating the blocks under the surrounding ice sheet, whereby loads on the ice sheet are reduced and the ice blocks contribute to the load capacity of the ice sheet due to the buoyant upward pressure of the ice blocks.

Abstract: An installation 18 is protected by a circular array of drag elements 2. Each drag element is anchored to the seabed and has teeth on its upper surface which penetrate, and decelerate, moving ice structures. Ice structures which move over the drag elements and enter the protection area have insufficient momentum to damage the installation.

Abstract: The load bearing outer skin contains an inner assembly and an outer assembly. Both the inner and outer assemblies include a skin plate member which is stiffened by stiffeners welded to one side of the skin plate member. The stiffeners are located at spaced intervals from each other and are disposed substantially perpendicular to the skin plate member. The inner and outer assembly are placed substantially parallel to each other to form a composite structure having an internal cavity defined by the inner and outer plates. The stiffeners of the inner assembly and the outer assembly are disposed in the cavity at a spaced relation to each other and extend partly into the cavity. A cementitious material substantially fills the cavity thereby completing the load bearing outer skin structure. The stiffeners may be flat steel plates or may have the profile of structural shapes such as angles or T's among others.

Abstract: Environmentally harmful liquid or solid materials, especially crude oil of offshore oil fields in mudland and shallow-water regions are loaded and transferred in an environmentally safe manner in lockable basins. For performing the method according to the invention there are provided artificial islands including one or a plurality of basins lockable with barrier means, said basins being in particular equipped with counter-current systems and cleaning equipment. These artificial islands may at the same time be used for crude oil recovery, treatment, storing and processing of the offshore oil fields.

Abstract: A method is provided for constructing spray ice barriers to protect offshore structures in a frigid body of water from mobile ice, waves and currents. Water is withdrawn from the body of water and is sprayed through ambient air which is below the freezing temperature of the water so that a substantial amount of the water freezes as it passes through the air. The sprayed water is directed to build up a mass of ice having a size and shape adapted to protect the offshore structure. Spray ice barriers can also be constructed for the containment of pollutant spills.

Abstract: A floating offshore structure which is moored at a fixed position on the sea by means of mooring hawsers and anchors connected to the ends thereof respectively for conducting a submarine excavating operation from a deck of the structure. The structure includes a moorage hull part provided with a vertical through-hole formed therein for receiving an excavating drill pipe and the mooring hawsers and a movable hull part connected to the moorage hull part so as to be rotatable within a horizontal plane. The movable hull part is constituted as a hull defining the outer wall of the floating offshore structure and connected with the moorage hull part by inserting it into a moorage hull part receiving hole formed at a position closer to the bow thereof.

Abstract: An offshore exploratory drilling floatable structure ballastable to rest on a sea floor but to extend above water level when so supported and adapted to withstand arctic ice loads, comprising a substantially vertical wall capable of withstanding arctic ice loads; a structural load bearing bottom rigidly connected to a lower portion of the wall; and a floatable vertically displaceable load bearing structural deck inside the wall.

Abstract: A gravity-type offshore structure, useful as an offshore drilling platform, e.g., is provided for use in ice-covered waters such as offshore of the Alaskan and Canadian North Slope. The structure is composed of a plurality of floatable and controllably ballastable modules, each of which can be fully submerged. The modules are stackable by selective ballasting and deballasting operations in a suitable sequence to define a mobile offshore structure. The structure is assemblable adjacent a site of use and is floatable after assembly to, from and between successive sites of use. At each site of use the assembled structure is ballasted by sea water to be supported by the sea floor and to have sufficient deadweight, in combination with its support by the sea floor, to stand against ice loads urging the structure laterally of the site. Major ones of the modules preferably are constructed of reinforced concrete arranged within the modules in a honeycomb cellular fashion.

Abstract: A caisson shield for the protection of an offshore production platform and, more particularly, a caisson shield for use in an arctic environment for the protection of the offshore structure in iceberg-infested waters which is capable of absorbing the destructive forces of an impact produced by a large iceberg. The caisson shield consists of an essentially annular concrete structure encircling at least the submerged support section of the offshore production platform including vertically upstanding concentrically spaced, annular side walls, a horizontal slab base resting on the marine bottom on which the side walls are supported, and a slab top supported on the side walls, and including annularly spaced internal radial partition walls whereby the entire overall caisson shield structure provides a generally toroidal configuration incorporating a plurality of closed compartments.

Abstract: An offshore structure and a method of sinking it to the sea bed. In accordance with one aspect of this invention, the structure is sunk asymmetrically by first sinking a first end portion thereof and then sinking the other end portion. The first end portion is sunk by ballasting it while the other end portion is closed to ballast. The structure is provided with sufficient water plane area while sinking each end portion to maintain stability during the sinking process. In accordance with another aspect of this invention, at least two spaced-apart piles are provided at the end corresponding to the first end portion to absorb the force of impact with the sea bed and to maintain a skirt on the structure out of contact with the sea bed until both ends of the structure have been sunk to the sea bed.

Abstract: A subsea wellhead assembly for areas subject to iceberg scouring including an upper conductor in a well bore and a lower conductor in the well bore with the upper end of the lower conductor being within the lower end of the upper conductor and connected thereto by a weak connection and the upper end of the lower conductor being below the maximum iceberg scour depth and means for connecting said conductors, said connecting means having sufficient strength to withstand bending loads during drilling and being removable for installation of production equipment.

Abstract: A modular and floatable offshore exploration and production platform system for use in shallow arctic waters is disclosed. A concrete base member is floated to the exploration or production site, and ballated into a predredged cavity. The cavity and base are sized to provide a stable horizontal base 30 feet below the mean water/ice plane. An exploration or production platform having a massive steel base is floated to the site and ballasted into position on the base. Together, the platform, base and ballast provide a massive gravity structure that is capable of resisting large ice and wave forces that impinge on the structure. The steel platform has a sloping hourglass profile to deflect horizontal ice loads vertically, and convert the horizontal load to a vertical tensile stress, which assists in breaking the ice as it advances toward the structure.

Abstract: An offshore platform structure of the gravity type intended to be installed on a sea bed in artic or corresponding waters. The platform structure comprises a substructure intended to be completely submerged and supported by the sea bed when in installed position, a superstructure extending up from the substructure and up above the sea bed and a deck superstructure supported by the superstructure above the sea level. A fender is provided intended to protect the superstructure against drifting ice and icebergs, the substructure being provided with a preferably horizontal top support slab supporting the fender, the fender being movably arranged on said support slab and comprising a preferably compartmented cylindrical ring-shaped body with a large weight resting preferably freely on the substructure, intended to be arranged apart from the superstructure when in normal position.

Abstract: A floatable bottom-founded caisson is disclosed that is suitable for use in ice-covered waters. The annular caisson structure has a frusto-conical upwardly tapered inner wall which reduces skin friction between itself and the core fill material. By the application of heat and the use of insulation, freezing of the core fill material is prevented; this feature, together with the tapered wall, enables the caisson to be easily raised and moved to a new position. The outer, or perimetrical, wall is inclined to aid upward fracturing of the ice impinging on it. The caisson carries a deck structure for the support of offshore drilling or other equipment.

Abstract: A marine structure comprising a cellular caisson which forms a stable platform for carrying out a variety of offshore operations in the arctic and sub-arctic regions is provided. The structure may be grounded on reasonably level sea bottom with a minimum of sea bed preparation in shallow water or mounted upon a previously prepared berm. Resistance to local ice forces is provided by the hexagonal cellular arrangement of the perimeter and interior walls which make up the cellular caisson. Global foundation resistance is obtained by introducing a suitable quantity of ballast into the structure. The design allows clusters of two or more structures to be grouped together to augment the offshore installation and to permit the offshore installation to be developed in stages at the site.

Abstract: An offshore platform structure, particularly intended to be installed in waters where drifting iceberg frequently appear, the platform structure being intended to be founded in a sea bed and comprises a substructure, a superstructure rigidly affixed to the substructure and extending vertically up above the sea level supporting a deck superstructure at its upper end. The horizontal cross-sectional area of the substructure is substantially greater than that of the superstructure. The substructure rigidly supports a fender structure, the fender structure comprising an outer peripherally arranged wall and an inner cylindrical wall the inner and outer wall being rigidly interconnected by means of a plurality of vertical and/or horizontal partition walls, dividing the fender structure into a plurality of cells or compartments. The fender structure is arranged in spaced relation with respect to the superstructure.

Abstract: The invention relates to an icebreaker system for marine platforms wherein the system includes two rings of obstacles: a lower ring and an upper ring fixed around pillars of the platform to be protected. The lower ring has obstacles showing a portion sloping upwardly and rearwardly. The upper ring has obstacles staggered with those of the lower ring and showing a portion sloping downwardly and rearwardly. A ring of obstacles is mounted rotatably and/or movably in the vertical direction. The obstacles are of truncated pyramid shape and asymmetrically shaped in front elevation.

Abstract: The application discloses an ice guard for protecting a vertically extending piling positioned in a body of water from damage due to changes in water and ice levels. The ice guard is concentrically positioned around a piling and extends above the surface of the body of water. The ice guard is held in place by the surrounding ice. The ice guard includes at least one longitudinally extending sleeve which is made of a buoyant material and a means for restricting vertical movement of at least a portion of the sleeve. Various longitudinally extending ribs can radiate from the sleeve to enhance adhesion of the sleeve to the ice.

Abstract: A canopy system for deployment around the periphery of a vessel floating on a body of water is disclosed primarily for use in connection with drillships in Arctic waters.

Abstract: An off-shore ice island structure for location over a submerged drill site in waters which normally freeze in winter. The structure includes a buoyant protective caisson which freezes in position over the drill site upon onset of winter. A barge floats on water kept unfrozen within the caisson, and is connected to the caisson so it can be swivelled generally about a vertical axis to adjust the circumferential location of the drilling axis of drilling apparatus carried on the barge. The drilling apparatus is movable relative to the barge to enable further adjustment of the drilling axis location. The arrangement enables the drilling axis to be maintained in substantial vertical alignment with the drill site despite movement of the caisson caused by the surrounding shelf ice. The caisson is part of an ice island structure whose mass is built up by successive flooding and freezing steps to ground it on the sea bed.

Abstract: A mobile offshore platform has a buoyant and ballastable mat base of substantial horizontal extent. A cylindrical pylon is fixed to and extends upwardly from the center of the base. The pylon has a height greater than the maximum operating water depth of the platform. A positively buoyant deck unit has a central opening through it within which the pylon cooperates. The deck unit is movable vertically along the pylon in response to the operation of jacking mechanisms and cooperating jacking legs located adjacent the corners of the deck unit. The jacking legs are engageable at their lower ends with the base whereby operation of the jacking mechanism causes the deck unit to be moved vertically along the pylon relative to the base. In use, the deck unit is elevated to the top of the pylon after the base is submerged into contact with a sea floor and the jacking legs are thereafter disposed in a retracted position with their lower ends adjacent the deck unit.

Abstract: An ice island is constructed in a marine area having a sheet of natural ice whereby, in a basic embodiment, a lower layer of fresh water ice is made by continually adding fresh water to the ice sheet and letting it freeze until the sheet is on bottom. An impervious insulating layer is put on top of the fresh ice and an upper layer is constructed thereon from sea water or mined ice blocks.

Abstract: This disclosure is concerned with novel water-tight boxes for submergence in the sea, containing preferably fresh-water ice produced in another location and inserted into the box, with cooling means associated with the box that compensates for heat from the environment surrounding the box that would otherwise commence to melt the ice.

Abstract: In order to assist ice chunks along preferred discharge paths in a large scale ice disaggregation system employing counter-rotating twin cutters, water is pumped tangentially across the trailing edges of the counter-rotating cutters against the direction of rotation to overcome the centrifugal action which tends to cause ice jamming. Secondary hydro-jets may be employed to further urge the ice chunks away from the vessel into the open region previously cut.

Abstract: An offshore structure for use in drilling and producing wells in arctic regions having a conical shaped lower portion that extends above the surface of the water and a cylindrical upper section. The conical portion is provided with a controlled stiffness outer surface for withstanding the loads produced by ice striking the structure. The stiffness properties of the outer shell and flexible members are designed to distribute the load and avoid high local loads on the inner parts of the structure.

Abstract: A lightweight drilling structure for use in offshore arctic waters comprising a lower frustoconical section and upper section wherein the lower section is towed to location, ballasted to sink in place on the sea floor and anchored in position by flooding the stability compartments. The upper section containing the drilling rig and equipment is then floated into place over the lower section, ballasted to rest on the lower section and the two sections sealed and fastened together. The assembled structure is firmly anchored in place by dewatering chambers located in the bottom of the lower section to create a suction between the bottom of the lower section and the ocean floor.

Abstract: A man-made sand and gravel island for Alaskan oil drilling operations, the sides of the island being covered with a porous fabric anchored in place by a layer of heavy (3-ton) sand bags arranged in an imbricated manner between the high and low water levels on the island.

Abstract: An artificial island is constructed by depositing material such as sand, y or the like on the building site on the bottom and by providing inhibiting means formed by branched, relatively spaced elements positioned on the building site, to reduce the rate of effluence of the material such as sand, clay or the like along the sea bottom.

Abstract: An apparatus is disclosed for minimizing the horizontal forces on an offshore arctic structure due to ice movement. The structure includes a base portion, sloped side walls and a smooth, unobstructed top portion. The structure is substantially submerged in a body of water with the top portion at or near the water surface permitting floating ice sheets which strike the side walls to flex slightly upward and advance along and over the structure without substantially destroying the overall integrity of the ice sheet. In this manner, the horizontal forces on the structure resulting from the ice sheet are minimized due to the elimination of a crushing failure mode of the ice sheet commonly associated with conventional offshore arctic structures.

Abstract: An ice island is constructed in a marine area having a sheet of natural ice by mining ice blocks from the ice sheet, curing the blocks and placing the cured blocks directly on the ice sheet until the natural sheet touches bottom and the desired weight of the ice island is obtained. Methods are disclosed for special placement of the blocks to prevent overstressing the natural ice sheet.

Abstract: A hull heating system for an offshore production structure for use in arctic waters wherein the heat from the produced fluids is used to maintain the temperature of the outer surface of the structure above the melting temperature of the ice adjacent the structure.

Abstract: An artificial island for installing oil drilling equipment in ice covered sea areas, comprising barricades against ice which surround oil drilling equipment installed in ice covered sea-water and whose respective top portions are projected above the surface of the sea-water, means provided at the bottom portions of the barricades so as to fix them to the sea-bottom, and inclined ice breaking walls provided at the outer sides of the barricades.

Abstract: An improved offshore arctic structure is disclosed which controls the horizontal forces exerted by impinging ice masses. The structure includes lesser sloped wall sections near the sea floor and steeper sloped wall sections near the water surface. Thus, the deep pressure ridges contact the lesser sloped wall sections and the shallower ice sheets contact the steeper sloped wall section. The slope of all wall sections is chosen so as to keep all horizontal loads due to impinging ice masses below a preselected design maximum.

Abstract: A method and apparatus for forming an off-shore ice island structure in waters which normally freeze in the winter. The ice island is useful as a base for oil field operations, for oil and gas storage, for docking ships during thaw periods, and the like. The structure comprises a plurality of elongated hollow wall elements adapted to be vertically oriented and assembled in open water to form a bounded area. The elements become frozen in place during the winter and the bounded area is intermittently flooded at intervals to permit accumulation of ice sufficient to sink the ice island to the marine bottom. Additional wall elements are added to the first wall elements to form upward continuations to contain the flooding water and accumulated ice. Pumps are provided to convey water to the upper surface of the island for freezing, and to carry off brine during the freezing process. Refrigeration equipment can be utilized to keep the ice island in a frozen condition during seasonal thaws.

Abstract: Novel methods and means are provided for providing a substantially ice-free zone around a vessel out to 100 feet or more. The method includes the steps of (a) creating a finite substantially enclosed zone completely around the periphery of the vessel above the waterline, such zone including a peripheral zone approaching the waterline; then (b) continuously circulating warm air within the finite substantially enclosed zone; and finally (c) continuously injecting warm air into the peripheral zone to prevent ice formation within the peripheral zone. The apparatus includes (a) a plurality of floating modules disposed around, and each connected at one end to, the vessel; (b) a continuous, downwardly depending skirt extending completely around the outer periphery of the plurality of floating modules; and (c) a water/air heat exchanger in a selected plurality of such floating modules. The combination of the floating canopies around the vessel, and the hot air provides an ice-free zone around the vessel.

Abstract: A working platform for oil drilling operations in ice covered sea areas, which essentially comprises oil drillig equipment, an oil drilling pipe connecting the oil drilling equipment to the sea bottom, and a floating frame having a buoyancy and a strength enough to stand the pressure of an ice covering and being movable in accordance with movement of ice covering; the floating frame is disposed surrounding such a surface area of the ice covered sea as lying around the oil drilling pipe, whereby the pipe is protected by the floating frame against action of the pressure of ice covering during oil drilling operations.

Abstract: An ice barrier module for disposition around at least part of the periphery of an island in an ice bearing body of water wherein the module is a closed, hollow triangular shaped body whose hypotenuse side faces the ice and whose first and second sides opposite the hypotenuse side rest on a bottom support and abut the island, respectively, the hypotenuse side having an upper and lower section, the upper section being at a steeper angle of inclination than the lower section, the hypotenuse side having means for heating same. An island in an ice bearing body of water which has around at least part of its periphery a plurality of the aforesaid ice barrier modules.

Abstract: The invention relates to an offshore platform operable for use in Arctic locations where prolonged ice conditions may be encountered. The platform includes a lower barge hull having an exterior configuration in the general shape of a rectangular frustum and being operable to be fixed relative to a desired seabed site. The lateral side walls of the barge hull are heated for facilitating movement of contiguous sea ice upwardly relative to the barge side walls to fail the ice in bending as it advances toward the barge hull. A deck is positioned above the lower barge hull and is supported by a first and second column at an elevation whereby the lower surface of the deck will be above and out of contact with sea ice passing over the hull. The deck is positioned relative to the barge hull in a posture such that at least a portion of the deck extends beyond an imaginary vertical plane projecting upwardly from at least one longitudinal edge of the upper surface of the barge hull.

Abstract: A method and apparatus for drilling a hole in a body of ice and for destroying a body of ice. The method comprises the steps of providing a source of reactant gas of a type which will react chemically with ice to form solid compounds which are unstable and which break down rapidly to water and a dissolved gas. The reaction product which is formed is removed quickly in order to avoid a secondary and initially undesirable exothermic reaction of gas dissolution into the water so formed. The reactant gas is directed through a nozzle to generate a stream of reactant gas. The nozzle is located in close proximity to a body of ice, and the stream of reactant gas is directed against a localized area of the surface of said body of ice at a velocity and flow rate to obtain an optimum phase change reaction with the ice and to quickly remove water formed from the ice in the localized area.

Abstract: A device for protecting a pile from ice formations collecting on and subsequently extracting the pile as a result of a variation of tide level including a tapered guard member secured to the pile. The tapered guard member is firmly secured to the pile by horizontal stiffening rings and vertical fin members which also serve to prevent deformation of the guard member taper as a result of interaction with the ice formations. The guard member comprises a one piece jacket connected by a vertically extending joint or may comprise a series of tapered strips, a series of interconnected curved sections, or a series of interconnected rectangular ribs.

Abstract: An offshore well drilling and/or production operation which is carried out on top of a layer of ice which extends over unfrozen water. A ring of thermal insulation is formed on top of the ice around the area of the drilling and/or production operation so that the ice thickness under the ring is thinner than the ice adjacent the ring thereby forming an annular depression in the underside of the ice. The depression will capture and hold any hydrocarbons or other fugitive materials that may escape under the ice in the area of the drilling and/or production operation.

Abstract: An offshore structure which is able to withstand the ice forces imposed thereon by impinging ice sheets and other larger masses of ice wherein the structure has an upper conical portion coaxially positioned relative to a lower conical portion. The walls forming both the upper and lower portions are inclined at an angle to the horizontal to receive ice masses moving into contact with the structure. The angle of inclination from the horizontal of the upper portion is greater than the angle of inclination of the lower portion, and the cross-sectional diameter of the upper conical portion is no greater than that at the top of the lower conical portion.

Abstract: An ice platform suitable for multiseason use is constructed in a cold offshore region by accumulating ice on a portion of a floating natural ice sheet until the ice mass formed thereby becomes grounded on the marine bottom. A rigid wall element is driven through the ice and a preselected distance into the marine bottom so as to form a structural wall surrounding the ice mass. Subsequently an insulation jacket is installed over the top surface of the ice mass and between the ice mass and the wall. To dismantle the ice platform, the wall and at least part of the insulation jacket are removed to allow natural forces to restore the region to its natural state.

Abstract: An offshore structure which is able to withstand the ice forces imposed thereon by impinging ice sheets and other larger masses of ice wherein the structure has an upper conical portion coaxially positioned relative to a lower conical portion. The walls forming both the upper and lower portions are inclined at an angle to the horizontal to receive ice masses moving into contact with the structure. The angle of inclination from the horizontal of the upper portion is greater than the angle of inclination of the lower portion, and the cross-sectional diameter of the upper conical portion is less than that at the top of the lower conical portion so that there exists a step-like section between the upper conical portion and the lower conical portion.

Abstract: An artificial ice structure for use as, for example, a base for oilfield operations or a road, is constructed in an offshore frigid environment where the water is covered by a sheet of floating ice. A berm or dike enclosing a predetermined area is built on the ice sheet to contain flood water and a trench is cut through the ice sheet around the perimeter of the dike to separate the predetermined area from the parent ice sheet and thereby form an island. The island of predetermined area is flooded with water and the water is allowed to freeze and weight the island down until essentially the entire ice mass of the island is resting on the ground underlying the body of water. After the structure is grounded, flooding with water is continued until the island has sufficient mass, in combination with other defensive measures, to resist the forces imposed by movement of the surrounding fast ice.

Abstract: In order to prevent damage due to frost heaving of a refrigerated gas pipeline which traverses frost-susceptible soil resulting from horizontal ice lense formation beneath the pipeline, heat pipes are located in diametrically opposed pairs, one on either side of the pipeline. Frost bulbs are formed in the soil around each heat pipe adjacent to the pipeline, causing the horizontal ice lenses to be formed further below the pipeline. Heaving rate is reduced due to the lower temperature gradient in the vertical direction, a greater overburden above the horizontal ice lenses and a reduced water supply directly beneath the pipeline. Also, lateral expansion of the frost bulbs provides opposing horizontal forces to counteract the upward force of the horizontal ice lenses.

Abstract: Method and apparatus for building a thickened ice mass, such as a grounded ice island, at a cold offshore location, in which water is pumped through a fluid flow conduit and discharged from a rotating swing arm section of the conduit onto selected areas of a natural ice sheet to form circular and/or annular thickened ice bodies. The fluid flow conduit includes a first water supply line disposed in the water body between the ice sheet and the marine bottom, and, if required, a second water supply line which is installed along the top surface of the ice island after the grounding of the ice body forces abandonment of the first water supply line.

Abstract: Tabular icebergs can be used as a source of fresh water in arid regions if they are transported from the Antarctic to where there is a need for water. To help reduce the rate at which solar radiation melts the iceberg on its journey, pools of fresh water are maintained on its upper surface, thereby taking advantage of the fact that the latent heat of evaporation of water is about seven times that of fusion of ice. The pools are created by protecting a closed path on the surface of the iceberg from melting by means of flexible sheet material. The protected path then forms the walls of the pool. At its destination the iceberg's pools can be given a V-shaped bottom to help increase the rate at which the iceberg is turned into fresh water.

Abstract: A method and apparatus is disclosed for forming and maintaining an offshore ice structure in an Arctic environment. The structure is formed by a series of caissons oriented in a ring forming an enclosure capable of retaining a predetermined amount of water and thereby defining an ice island when frozen. The structure includes a passive heat extracting system which removes heat from the water within the enclosure and from the soil immediately below the enclosure and the caissons thereby advancing the freezing of the soil beneath the enclosure and water within the enclosure. In this manner, the lateral stability of the structure is improved by providing a single frozen mass of water and soil bonded in unitary construction increasing the foundational base of the structure. In addition, refrigeration means are provided to prevent surface melting of the ice within the enclosure and preserve the integrity of the ice structure during warmer months.

Abstract: A member in the form of a ring connected by radial fins to central hub includes a heater at least for its lower surfaces so that in operation it melts the ice of the iceberg (starting from the top surface thereof) and sinks therethrough with the ice re-freezing above it. The member also includes a central tube removeably attached to the central hub. The tube is fed after the sinking member to provide a vertical shaft through the iceberg. The ring serves to remove a slab of larger diameter than the tube from the lower surface of the iceberg in order to receive a propulsion unit.