This invention relates to methods for installing offshore tower structures.
Numerous sea-related activities, such as oil exploration and recovery operations, for example, are conducted from offshore platform or tower structures. Towers have been employed which rest in an upright condition upon the water bed and are of extensive height, i.e., towers higher than 400 feet have been heretofore utilized.
Problems of considerable magnitude have been experienced during the installation of mammouth offshore structures, giving rise to the proposal of various installation techniques, as demonstrated for example by the following U.S. Pat. Nos. 2,946,198, issued to Knapp on July 26, 1960; 3,633,369, issued to Lawrence on Jan. 11, 1972; 3,729,940, issued to Koehler on May 1, 1973; and French Pat. No. 1,444,839, issued May 31, 1966.
It has been proposed, for instance, to float an assembled tower in a horizontal position to an offshore worksite, upend the tower in the water and, thereafter, submerge the tower until its base rests upon the water bed.
It has also been proposed to float an assembled tower in upright fashion to the worksite and then gradually lower and immerse the tower onto the water bed.
It will be realized that massive pre-assembled towers, whether floated to a worksite in horizontal or upright positions, can be very difficult to support and maneuver, especially in rough seas. Moreover, the towers must be specially fabricated to withstand the high stress conditions occurring during transportation and immersion.
It has been suggested to install offshore structures by assembling component parts thereof at the worksite (see, for example, U.S. Pat. Nos. 2,534,480, issued to Shannon on Dec. 19, 1950 and 3,839,873, issued to Loire on Oct. 8, 1974.) Such techniques can be very time-consuming and may be hampered by unstable sea conditions, especially those involving structures which are highly susceptible to the effects of wave and wind action.
It is, therefore, an object of the present invention to eliminate or alleviate problems of the type previously discussed.
It is another object of the present invention to provide novel methods for installing offshore tower structures.
It is yet another object of the present invention to avoid subjecting offshore tower structures to high degrees of stress during installation.
It is a further object of the invention to support an immersed tower internally by means which can be subsequently removed.
It is still another object of the invention to provide novel methods and apparatus for the rapid on-site assembling of offshore tower components involving the use of removable buoyancy units which are floated within open-trussed legs of the tower and which are connectible to original leg segments and thereafter connectible to add-on leg segments of the tower to support the tower as it is gradually assembled and immersed.