Method and apparatus for protecting offshore structures against forces from moving ice sheets

In combination with a marine structure fixed in a body of water and having an upright support extending through the water surface, apparatus for reducing forces exerted on the support by a moving ice sheet at the water surface, the apparatus comprising:

• a vertically movably shield surrounding the support, the shield having a sloping working surface extending, in a lowered position thereof, from above the water surface downwardly away from the marine support, at least in a direction opposite to which the ice is moving toward the support, to a lower position disposed below the water surface;
• means for normally positioning the shield in a position thereof facing upstream, in terms of ice movement, so the working surface lower portion projects below the moving ice sheet;
• a floodable chamber in the shield and means for removing water from the chamber to increase the buoyancy of the shield for raising the shield to an elevated position in which the lower portion of the shield working surface is disposed below the water surface, the shield during raising thereof being adapted to engage and to lift and to break ice disposed above the working surface, the lower portion of the shield surface being configured to support broken ice pieces adhering to the shield surface;
• means for rotating the shield about the support, while the shield is in the elevated position, to move the working surface of the shield downstream, in terms of direction of ice movement, from the marine structure support so that broken ice pieces can be carried on the shield surface to the downstream position;
• and
• means for flooding the chamber to lower the shield from its elevated position to discharge the broken ice into the water at said downstream position.

A marine structure located in a fixed position in a body of water having a moving ice sheet at the surface of the water, the marine structure comprising:

• a platform located above the surface of the water;
• an upright support member extending through the water surface and supporting the platform above the water;
• a vertically movable shield adapted to be positioned adjacent the marine support and having a sloping working surface extending, in a lowered position thereof, from above the water surface downwardly away from the support, at least in a direction opposite to which ice is movable toward the support, to a lowered position disposed below the water surface;
• means for raising the shield to an elevated position in which the lower portion of the shield working surface is disposed below the water surface, the shield during raising thereof being adapted to engage and to lift and to break ice disposed above the working surface, the working surface being configured to support pieces of ice broken during raising of the shield;
• means connected to the shield and operable for moving the shield in the elevated position thereof to a position of the working surface downstream, in terms of the direction of ice movement, from the marine structure;
• and
• means for lowering the shield to a lowered position in which the working surface is submerged in the water to facilitate discharging the broken ice pieces from the shield surface in the downstream position.