Abstract: The method involves erecting a very large-diameter column from a plurality of buoyant columnar members at a selected site in a body of sea water. Each columnar member is floated erect to the site. The first or lowermost columnar member is pulled down and fully submerged to a predetermined depth over the site. The second columnar member is then positioned directly over the lowermost member. The lowermost member is allowed to move up and lift the second member out of the water. The two columnar members are securely interconnected to each other in a watertight fashion. The partial column is then pulled down to a fully submerged condition and the third columnar member is positioned directly over the second member. The partial column is allowed to move up and lift the third member out of the water. A secure watertight connection is made between the third columnar member and the second columnar member.