Semisubmersible with five-sided columns
A semi-submersible vessel comprises pontoons having a generally five-sided transverse cross section. In the case of a 4-sided semi-submersible, the columns may be arranged in a generally rectangular form with a column at each corner of the rectangular form, each column having with four sides disposed at a right angle to at least one adjacent side and a fifth side on the exterior of the generally rectangular form disposed at 45 degrees to each adjacent side.
1. A semi-submersible vessel comprising:
four pontoons arranged in a generally rectangular form;
a column at each corner of the rectangular form, each column having a top, a bottom, and a generally five-sided transverse cross section with four sides disposed at a right angle to at least one adjacent side and a fifth side on an outboard face of the generally rectangular form disposed at 45 degrees to each adjacent side; and,
at least one mooring line attached to the fifth side of each column such that the angle in planform between the mooring line and the fifth side of the column is a right angle.
2. A semi-submersible vessel as recited in claim 1 wherein a ratio of a length of a diagonal of each column's transverse cross-section that is parallel to the fifth side to a distance from a mid-point of the fifth side to a corner of the transverse cross-section directly opposite the fifth side is greater than or equal to 4/3.
3. A semi-submersible vessel as recited in claim 1 wherein the mooring line is attached to the column by a fairlead proximate the bottom of the column.
4. A semi-submersible vessel as recited in claim 1 wherein the mooring line is attached to the column by a fairlead proximate the bottom of the column and a winch proximate the top of the column.
5. A semi-submersible vessel as recited in claim 3 wherein the mooring line is routed along the fifth side of the column.
6. A semisubmersible vessel comprising:
a plurality of pontoons arranged generally in the form of a regular polygon having n sides;
a column at each corner of the polygonal form, each column having a generally five-sided transverse cross section with at least three sides of the cross section disposed at a right angle to at least one adjacent side and two adjacent sides of the column having a pontoon attached thereto disposed at an angle of 360/n degrees to a pontoon attached to an adjacent side of the column;
at least one mooring line attached to each column on a side of the column not attached to a pontoon such that the angle in planform between the mooring line and the side of the column is a right angle.