It was found by a model test and then by an in-situ test of a miniature offshore oil-drilling craft that adhesive force of marine clay to the embedded sides and bottom of the mat of a craft is composed of three components: the adhesive and the suction on the bottom, and the friction on all sides. Among them suction is the major factor and dominates the other two.

The ultimate strength of adhesive force depends on the boundary conditions of the mat and on the way the craft is lifted. The distribution of adhesion and suction varies with the rigidity of the mat.

In order to facilitate the floating of the craft, it is necessary to find ways to eliminate the adhesive force; low-pressure filling and high-pressure jetting of water are the two methods suggested, and their validity is verified by model tests in the laboratory and by in-situ experiments of miniature craft.