Abstract: The disclosure provides a wave sheltering vessel used to reduce the significant wave height of waves. The wave sheltering vessel includes a hull, a plurality of anchors, and a propeller system. A length of the hull is greater than or equal to 60 meters. A ratio of the length to a design draft of the hull is less than or equal to 6.5. A ratio of the length to a breadth of the hull is less than or equal to 3.5. A ratio of the breadth to the design draft of the hull is less than or equal to 2.3. The anchors are installed at the hull along a longitudinal direction of the hull. The propeller system is disposed at the hull.

Abstract: A bipod for use in ice prone offshore environments comprising a deck connected across a pair of members, each member having a neck, and angled portion disposed at the sea surface, and a base secured to the seafloor. The base is secured using a gravity-based system or pilings. An interior zone is defined between the pair of members which is maintained largely free of ice and provides ready access to the sea surface for resupply or emergency egress.

Abstract: The present invention relates to a monohull offshore drilling vessel comprising a hull with a bow and a stern and a moonpool extending through the hull, the hull having an upper deck. A firing line hoist system comprising a mast is mounted on the hull. A drill floor is provided at a firing line side of the mast, which covers a portion of the moonpool while the firing line extends through an opening in said drill floor. Furthermore marine equipment and drilling equipment for performing auxiliary operations for the drilling or drilling related operations is provided, which equipment is mainly provided in the hull of the vessel below the upper deck. According to the invention, the drill floor is flush with the upper deck.

Abstract: Provided is a damper structure for an enclosed derrick, which can constantly compensate and maintain a pressure of an inner space of an enclosed derrick structure. The damper structure for the enclosed derrick includes: one or more communication ducts installed in a side of the enclosed derrick; and one or more open/close dampers coupled to the communication ducts to open or close the communication ducts, whereby air is selectively supplied to or exhausted from the enclosed derrick.

Abstract: The present invention disclosed in this application relates to a semi-submersible platform with a landing bay. The landing bay has a movable platform that allows the docked vessel to be raised/lowered from/to a body of water. The landing bay also has a stabilizing mechanism for holding a docked vessel stable when the platform is in motion.

Abstract: A vessel and method for breaking ice drifting in a predominant direction relative to an offshore installation such as a drilling vessel. The vessel is used to deploy an anchor in a position at a distance from the offshore installation and in a direction which, seen from the offshore installation, is substantially in parallel with the direction of movement of the ice. By means of the machinery of the vessel, the direction of the anchor line is adjusted and so is the orientation of the vessel relative to the anchor line to the effect that the propellers can be used to crush and dispose of the ice without using motive energy to hold the vessel against the pressure of the ice.

Abstract: The invention relates to a vessel or a floating structure operating in ice-covered waters comprising a hull or the like (1, 1?) including at least one bow-like end or a similar hull portion (2, 2?), which is exposed to the loading effect of the ice, while the ice or the vessel is moving. Said bow-like end or a similar hull portion (2, 2?), in the underwater part of the hull, is equipped with means for leading one or several strong, mainly upwards-directed flows of water towards the ice or the ice field encountered by the bow-like end or a similar hull portion (2, 2?). The invention also relates to a method of using the vessel or the floating structure.

Abstract: The invention relates to a watercraft having improved characteristics for travel in ice, particularly an icebreaker, supply vessel, cargo vessel or corresponding, which watercraft has a hull, which has at the stem portion a propulsion and steering arrangement, which is mainly responsible for movement and steering of the watercraft and which includes at least one skeg-like projection, in which is located at least one propeller device. In accordance with the invention, said skeg-like projections comprise two units located on different sides of the centre line of the hull. Said propeller device is located at the stem end of the skeg-like projection. In addition, the skeg-like projection has between the propeller device and the hull of the watercraft, in the longitudinal direction on the skeg-like projection, one or more thruster devices to provide a water flow mainly transverse in relation to the hull.

Abstract: A drilling vessel may function both as an ice breaker and, if needed, as a drilling platform for drilling a relief well. The vessel may be provided with a mast that may be stowed when drilling operations are not being conducted.

Abstract: A method to utilize an ice-breaker (10) in a novel way such that tanks of the anti-roll system and/or tanks (21, 22, 23 and 24) of the heeling system are used for recovering and/or processing oil (16) to be recovered from water. The oil is separated from water in a tank of the anti-roll system and/or a tank (21) of the heeling system of the ice-breaker, which tank contains warm water (15) and steam heat pipes (19). The tanks of the anti-roll system and/or tanks of the heeling system of the ice-breaker have separate oil recovery piping which is used when the heeling tanks of the ice-breaker are used for responding to an oil spill.

Abstract: A boat hull form includes a dual circular curved outer surface area that is circular concave relative to the plane of symmetry of the hull when viewed horizontally parallel with the plane of symmetry of the hull, and circular convex relative to the plane of symmetry when viewed vertically parallel with the plane of symmetry of the hull, with the hull outer surface area extending in a vertical sense from a lower area extending in a direction that tangentially intersects the plane of symmetry or optionally a plane extending parallel with the plane of symmetry on the same side of the plane of symmetry as the dual circular curved outer surface area and upwardly in a direction tangentially intersecting the waterline plane of the hull or a plane extending parallel to the waterline plane.

Abstract: A watercraft has a hull with a first end and a second end and is equipped at its second end with a propulsion arrangement that includes at least three propulsion devices each provided with a propeller. A majority of the propulsion devices are rudder propeller devices, and the propeller of at least one of the propulsion devices is at a first distance from the second end of the hull and the propeller of at least another one of the propulsion devices is at a second distance, greater than the first distance, from the second end of the hull. In ice conditions the watercraft is operated with the second end ahead, so that at least one propeller at the first distance from the second end of the hull breaks ice and at least one propeller at the second distance from the second end of the hull moves disintegrated ice or ice chunks away from the ice build-up.

Abstract: A system and method for clearing an approaching floating ice mass comprising locating a hydrocarbon development platform in a marine environment, and determining a direction from which the ice mass is approaching the hydrocarbon development platform. The method also includes providing an intervention vessel having a water-agitating mechanism associated therewith for propagating artificially generated waves towards a leading edge of the approaching ice mass to fracture the ice mass along the leading edge, thereby causing small ice pieces to separate from the ice mass.

Abstract: A vehicle for use in arctic environments, the vehicle comprising a hull for accommodating people, and a pair of rotatable propulsion screws connected to the hull for propelling the vehicle on water, ice, snow and land. Each propulsion screw comprises a shaft having at least one blade helically disposed therearound.

Abstract: To keep the water around an off-shore installation (1) free from a harmful impact of ice, a vessel (5) is used to deploy an anchor (6) in a position at a distance from the off-shore installation (1) and in a direction which, seen from the off-shore installation (1), is substantially in parallel with the direction of movement (P) of the ice. By means of the machinery of the vessel, which preferably comprises azimuth propellers, the direction of the anchor line is adjusted and so is the orientation of the vessel relative to the anchor line to the effect that the propellers can be used to crush and dispose of the ice without using energy to hold the vessel up against the pressure of the ice.

Abstract: To keep the water around an off-shore installation (1) free from a harmful impact of ice, a vessel (5) is used to deploy an anchor (6) in a position at a distance from the off-shore installation (1) and in a direction which, seen from the off-shore installation (1), is substantially in parallel with the direction of movement (P) of the ice. By means of the machinery of the vessel, which preferably comprises azimuth propellers, the direction of the anchor line is adjusted and so is the orientation of the vessel relative to the anchor line to the effect that then propellers can be used to crush and dispose of the ice without using energy to hold the vessel up against the pressure of the ice.

Abstract: A floating support for off-shore oil production in an arctic or antarctic zone, the support being fitted under its hull with a disconnectable turret from which there extend anchor lines connected to the sea bottom and bottom-to-surface connection pipes. The hull including lateral sides extending in its longitudinal direction. The longitudinal lateral sides of the support carry respective pluralities of devices for localized destruction of pack ice, each device having a destruction tool having at least one pointed portion suitable for breaking pack ice by repeated actuation in vertical pivoting and/or translation of the tool relative to the side, the point, on moving downwards, thus bearing in localized manner against the surface of the pack ice with a force that is preferably at least 10,000 kN. The tool being actuated in pivoting and/or translation with the help of a pivoting and/or translation guide structure applied against the side of the support.

Abstract: A drilling vessel may function both as an ice breaker and, if needed, as a drilling platform for drilling a relief well. The vessel may be provided with a mast that may be stowed when drilling operations are not being conducted.

Abstract: The invention relates to a barge arrangement comprising a barge unit with a first end (11) and a second end (12) and a tug unit provided with a propulsion unit, which barge unit is adapted to receive the tug unit at one end. In order to achieve an efficient vessel combination for loading, transport and unloading of cargo the barge unit (102) is adapted to receive a first tug unit (2) at its second end (12) in order to be pushed by the first tug unit (2) with the first end (11) of the barge unit (1) in a forward direction (F) of motion. Further, the barge unit (101) is adapted to receive a second tug unit (3) at its second end (12) in order to be pulled by the second tug unit (3) with the second end (12) of the barge unit (1) in the forward direction (F) of motion.

Abstract: The invention relates to a vessel or a floating structure operating in ice-covered waters comprising a hull or the like (1, 1?) including at least one bow-like end or a similar hull portion (2, 2?), which is exposed to the loading effect of the ice, while the ice or the vessel is moving. Said bow-like end or a similar hull portion (2, 2?), in the underwater part of the hull, is equipped with means for leading one or several strong, mainly upwards-directed flows of water towards the ice or the ice field encountered by the bow-like end or a similar hull portion (2, 2?). The invention also relates to a method of using the vessel or the floating structure.

Abstract: The invention relates to an ice-breaking system for floating bodies in or near ice, having a protruding stem and at least two trim tanks (10, 16) for generating a stamping motion of the floating body, wherein the at least two trim tanks are connected fluidically by means of at least one trim channel (12, 13) to high-power delivery devices (18, 19) for the trim medium, and the trim system is designed as a closed loop.

Abstract: A system mechanically alters the geometry of the surface of the water by breaking the water surface with a mechanical device. The mechanical device may comprise a plurality of propellers, a plurality of aquafoils in the shape of plows, a wire whip, or other mechanical device to reduce the coefficient of reflectivity of the air-water interface.

Abstract: A vessel and method for breaking ice drifting in a predominant direction relative to an offshore installation such as a drilling vessel. The vessel is used to deploy an anchor in a position at a distance from the offshore installation and in a direction which, seen from the offshore installation, is substantially in parallel with the direction of movement of the ice. By means of the machinery of the vessel, the direction of the anchor line is adjusted and so is the orientation of the vessel relative to the anchor line to the effect that the propellers can be used to crush and dispose of the ice without using motive energy to hold the vessel against the pressure of the ice.

Abstract: A system and method for clearing an approaching floating ice mass comprising locating a hydrocarbon development platform in a marine environment, and determining a direction from which the ice mass is approaching the hydrocarbon development platform. The method also includes providing an intervention vessel having a water-agitating mechanism associated therewith for propagating artificially generated waves towards a leading edge of the approaching ice mass to fracture the ice mass along the leading edge, thereby causing small ice pieces to separate from the ice mass.

Abstract: An offshore floating production, storage, and off-loading vessel has a hull of generally cylindrical or polygonal configuration surrounding a central double tapered conical moon pool and contains water ballast and oil and/or liquefied gas storage compartments. The exterior side walls of the polygonal hull have flat surfaces and sharp corners to cut ice sheets, resist and break ice, and move ice pressure ridges away from the structure. An adjustable water ballast system induces heave, roll, pitch and surge motions of the vessel to dynamically position and maneuver the vessel to accomplish ice cutting, breaking and moving operations. The moon pool shape and other devices on the vessel provide added virtual mass for increasing the natural period of the roll and heave modes, reducing dynamic amplification and resonance due to waves and vessel motion, and facilitate maneuvering the vessel. A disconnectable turret buoy at the bottom of the moon pool connects risers and mooring lines.

Abstract: The invention applies to shipbuilding dealing with the construction of Arctic heavy-tonnage carriers. The Arctic heavy-tonnage carrier comprises an underwater cargo hull and above-water body in the form of the main deck with a superstructure. The underwater hull is connected to the main deck with an ice-resistant pylon along which the ship load waterline passes and which is located in the fore body of the underwater hull directly behind the forepeak symmetrically related to the center plane of the ship hull. The upper deck of the underwater ship hull has in the area of the pylon a strengthened construction. The pylon structure is a bearing one for the main deck. The underwater hull can be made in the cross-sectional view to the shape of a round-angled rectangle the height of which is 10-12 m and a height-breadth ratio does not exceed 1:6. The underwater hull of said ship has along each side the aft arranged retractable mooring bollard.

Abstract: A jackup rig having a built-in capability of driving and extracting piles without need for dedicated pile drivers or extractors. The jackup rig provides an ice breaking functional capability, supplied by a jacking system, for operating in icy waters.

Abstract: A three-hulled oil combatting vessel (500) has a separating structure (100), which pushes ice blocks (J1), which move between the middle hull (SH1) and side hulls (SH2, SH3) from the prow to the stern, underneath the water surface (WL1). The separating structure (100) may be a grate in the longitudinal direction of the vessel (500). The density of the oil (B4) or oil refining product to be collected is smaller than that of the water, so the oil (B3), which has been separated from the ice blocks (J1) that were pushed down, tends to rise through the separating structure (100) to the water surface. The separating structure (100) separates the oil (B3) from the ice blocks (J1) for easier collection into a container. The separated (B4) oil can thus be collected from the relatively ice-free water surface (WL1) with an oil collecting device (200), which may have a brush skimmer.

Abstract: Ice is broken with a motor-driven watercraft with three hulls, i.e. a trimaran (4), having a middle hull (3), a propulsion device (9), a right (1) and a left (2) side hull and a deck (5). The three hulls are attached. Ice is broken with the middle hull (3) of the trimaran. The propulsion device (9) is arranged in the middle hull (3) and a keel (7) in the longitudinal direction of the middle hull is arranged in the bow (3a) of the bottom of the middle hull for breaking ice.

Abstract: The invention relates to a barge arrangement comprising a barge unit with a first end (11) and a second end (12) and a tug unit provided with a propulsion unit, which barge unit is adapted to receive the tug unit at one end. In order to achieve an efficient vessel combination for loading, transport and unloading of cargo the barge unit (102) is adapted to receive a first tug unit (2) at its second end (12) in order to be pushed by the first tug unit (2) with the first end (11) of the barge unit (1) in a forward direction (F) of motion. Further, the barge unit (101) is adapted to receive a second tug unit (3) at its second end (12) in order to be pulled by the second tug unit (3) with the second end (12) of the barge unit (1) in the forward direction (F) of motion.

Abstract: An icebreaking additional propulsion system includes at least one retractable thruster capable of vertically moving into and out of a hull of a ship. The retractable thruster includes a pair of guide rods vertically installed within the hull, a column vertically movable along the guide rods, a drive unit mounted to an upper end of the column for vertically moving and swiveling the column, and a propeller attached to a lower end of the column for generating propelling power.

Abstract: A multi-hulled vessel for upward ice-breaking is disclosed. The vessel has side hulls that are at least partially submerged while the vessel is underway. The side hulls each have a ridge on their upper surface. To break through ice at sea, the side hulls are positioned under the ice and the trim is adjusted for an upward trim angle. As the vessel moves forward, the ice is lifted and force concentrates along the ridge on the side hulls. The ice breaks along this force concentration, aided by the weight of the ice itself.

Abstract: The invention is a multi-purpose icebreaker having main propulsion devices in the front part of the vessel and steering device in the aft part of the vessel. This kind of icebreaking vessel has excellent steering characteristics and it can efficiently and constantly push the ice field. The main propulsion devices at the bow are azimuth propulsion devices or conventional shaft propulsion devices. The steering devices are tunnel thrusters or smaller azimuth thrusters.

Abstract: System for loading and unloading of hydrocarbons in waters with varying conditions, comprising an icebreaking vessel (10) moored to a sea bed (12) by a turret buoy (11) and where a tanker (16) by at least one hawser (17) is moored with its bow to the aft end of the icebreaker either at a distance from the icebreaker (10) in situations without influence from ice, or in physical contact with the icebreaker in situation when ice is present. The system further comprises at least one hose (24) and valve system for transferring hydrocarbons from the icebreaker (10) to the tanker (16).

Abstract: System for loading and unloading of hydrocarbons in waters with varying conditions, comprising an icebreaking vessel (10) moored to a sea bed (12) by means of a turret buoy (11) and where a tanker (16) by means of at least one hawser (17) is moored with its bow to the aft end of the icebreaker either at a distance from the icebreaker (10) in situations without influence from ice, or in physical contact with the icebreaker in situation when ice is present. The system further comprises at least one hose (24) and valve system for transferring hydrocarbons from the icebreaker (10) to the tanker (16).

Abstract: To ensure the possibility of offshore shipping of a liquid medium, primarily oil, from an onshore tank farm into sea-going tankers in the winter time in the ice conditions by ensuring both mooring to an offshore terminal and single-point mooring of a tanker at any time, without depending on the dominating wind and sea condition, in a direction most convenient for it with the possibility of its roundabout turning, with the subsequent servicing of it by transporting a liquid medium into such a tanker the following transformations have been made: a known ice breaker (1) is provided with: a diving station (5) installed on its deck (3), the diving station being provided with a diving trunk (6) made in the hull (2) of the ice-breaker (1), a device for the protection of a flexible hose (8) of an underwater pipeline against ice action, the device being made, according to the first embodiment, in the form of a cylinder (7) provided with guides (13) for moving in a guiding trunk (10) made in the stern side of the hu

Abstract: A body of water is aerated by propelling in the body of water a water pumping arrangement including a sheath having a turning propeller that (a) sucks water from the body into the sheath interior via openings in the sheath, (b) forces the sucked water upwardly and (c) forces the upwardly forced water through another opening in the sheath below the surface of the body of the water. Water forced through the another opening (i) has speed greater than the speed of the water sucked into the sheath and (ii) causes air bubbles to be induced in the water above the another opening.

Abstract: Wake vortices are made less detectable or reduced in their effect on nearby vehicles by re-orientation of vorticity about an axis in the direction of vehicle motion to transverse vorticity interacting with the longitudinal vorticity. The re-orientation may be by a flapping foil, and arrangements of a plurality of foils moving toward or from each other may be used. Alternatively, fluid may be injected longitudinally between opposite surfaces each having a port so that selective suction through the ports alternately attaches the fluid to the surfaces to deflect the fluid from the longitudinal direction and generate transverse vortices. Oppositely rotating vortices may be formed by separators extendable from each surface to engage the deflected fluid, and extension of the separators may be varied to control vortex trajectory. The transverse vortices may be intermittent, selected for speed, or made asymmetric for maneuvering.

Abstract: A complex of facilities for iceberg insulation for further production of fresh water includes a technological ship with a set of equipment for towing and maneuvering the doubled roll made of a special cloth having a considerable length. The cloth is manufactured of two layers of waterproof material. The layers are attached to one another along the lines forming a net out of cells of air cushions joined by air ducts connected into a single unit through which pipes for saline water removal are also laid. The method of iceberg insulation includes submerging of the doubled roll of the cloth mentioned above under the iceberg, embracing its underwater part, pumping in the air into the air cushions rows in the cloth according to the given program, cloth unrolling and complete enveloping the underwater part of the iceberg, and then enveloping all the iceberg, tightening the belts of the gigantic capacity formed and giving an elongated shape to it.

Abstract: The present invention provides a remotely controlled, water-borne vessel to retrieve floating game on a given body of water, which water-borne vessel is sized, shaped and marked to resemble a waterfowl so as to encourage or attract game birds or waterfowl to the operating site of the water-borne vessel. The water-borne vessel, thus configured is further outfitted with either a grappling structure or ice-breaking member for retrieving or removing downed, floating waterfowl or other surface matter from a body of water. A user may thus propel the outfitted water-borne vessel into adjacency with downed, floating waterfowl, grapple the downed, floating waterfowl and steerably propel the grappled waterfowl to a recipient for retrieving the downed waterfowl. Alternatively, the user may steerably propel the water-borne vessel through skim ice for removing the skim ice or other surface matter from the water surface for alluring waterfowl to the resultant ice-free water surface.

Abstract: For reducing drag, the velocity of a tacking sailing vessel is increased by isolating the supporting member of the ballast bulb from the sea stream by a jacketing hollow rotatable fin.

Abstract: A service vessel that is designed for navigating both in the open sea and in ice conditions is provided with a demountable propeller nozzle. For an ice-free navigation period the propeller nozzle is mounted around the propulsion propeller of the vessel, whereas for a navigation period in ice conditions the propeller nozzle is removed. The power absorption of the propulsion propeller is maintained constant during nozzle and nozzle-free operation.

Abstract: A relatively wide vessel is assisted through an ice field by an icebreaker having a relatively narrow hull. The icebreaker includes two steerable propulsion mechanisms at the opposite ends respectively of the hull, and the propulsion mechanisms are used to propel the icebreaker through the ice field in a direction at a substantial angle to its keel line, thereby opening in one pass of the icebreaker a passage having a width substantially greater than the waterline width of the icebreaker.

Abstract: A self-powered icebreaker attachment for connection to a parent vessel. In the preferred embodiment, the icebreaker attachment includes a spoon-shaped bow, an ice knife positioned aft of the bow, and a propulsion system including fully rotatable Z-drives. Preferably, the icebreaker attachment is itself a flotable vessel whose propulsion system can be coordinated with the propulsion system of the parent vessel to minimize ice-breaking-related forces on the parent vessel. The propulsion systems of the two vessels can be controlled by either the crew of the parent vessel or of the icebreaker attachment vessel.

Abstract: The present invention pertains to sloped-faced, ice control elements that are each spaced apart across a riverbed adjacent to a floodplain region. The elements arrest a breakup ice run. The size and spacing of the ice-resisting elements can vary with river size and average ice piece size diameter. The ice-resisting elements, for example, can comprise three or four quarried granite blocks buried in the riverbed in a relatively narrow river of 100 feet or less. This arrangement allows gaps between each ice-resisting element for easy canoe and fish passage. These gaps prevent the ice pieces of the ice jam from passing through during breakup ice runs. The ice-resisting elements may be formed from various materials such as quarried rock, poured concrete, rock-filled cribs, etc. After the ice-resisting elements have retained and stabilized the ice jam, water levels recede and warming water temperatures melt the ice in place behind the ice-resisting elements.

Abstract: For icebraking ships whose forward quarter is designed like a pontoon with an underside rising obliquely forward, and having icebreaking configurations on its sides, the hull can be equipped on both sides over the entire length of the ship with balcony-like flanks that improve the maneuverability of the icebreaking ship. The undersides of the balcony-like flanks can drop off obliquely downward and preferably lie at the level of the water line so that, during the turning of the ship, the oblique undersides can break off the edges of the ice. Further, the underside of the bow in the vicinity of the icebreaking configurations can be designed wider that the water line of the afterbody, to thus provide a clearance between the edges of the ice and the hull.

Abstract: An icebreaking ship is equipped, on the forward quarter of the hull, on both side flanks in the vicinity of the water line, with first and second icebreaking structures, with the second icebreaking structure located at some distance behind the first. Between the two icebreaking structures is a recessed area, which has a curve profile which approximately matches the radius of curvature of the inside turning circle of the ship at the crown or zenithal line of the turning circle. The second icebreaking structure is designed so that it does not exceed the width of the hull and the recessed hull wall area between the icebreaking structures is designed as a waistline-like indentation in the hull.

Abstract: An icebreaking ship has a hull including a forward part and an aft part and a screw arrangement in the aft part of the ship. The screw arrangement is designed for propulsion of the ship in the forward direction and is turnable substantially in a horizontal plane, whereby the screw arrangement serves for steering the ship. The screw arrangement and the form of the hull of the ship are dimensioned and designed for allowing the ship to move in the aft direction in heavy ice conditions.

Abstract: An icebreaker ship has a V-shaped bow and an S-shaped stem line with a wedge extending from the bottom of the stem line below the design waterline of the ship towards the sides until maximum width is reached. The wedge is incorporated into the hull by means of a knuckle between the top of the wedge and the hull envelope of the ship. Upon breaking of the ice by the bow, the cusps of ice move downwardly into the water along the sides of the bow until the wedge is contacted. The cusps of ice are tripped and moved away from the ship's sides and under the unbroken ice, thus protecting the propellers and leaving a clearer channel behind the icebreaker.

Abstract: A ship's hull designed for traffic in icy waters has a general form defining a bottom that is substantially horizontal in longitudinal section and has a central longitudinal keel line, and, at both sides of the bottom, sides that extend upward from the bottom. The bottom of the hull is formed with a depression at each side of the keel line. Each depression has a rear edge oriented obliquely relative to the keel line and extending to the rear of the hull from an inner location close to the keel line to an outer location farther from the keel line and at which the depression is open towards one side of the hull. The rear edge of each depression forms a substantially vertical guide surface for ice chunks under the hull's bottom.