the removable bottom founded structure is an offshore platform for petroleum drilling and producing operations which is deployed in waters with severe weather and iceberg conditions . the structure is normally held down by gravity , but during the deballasting procedure a hold - down system is employed to keep the platform on the subbase until site evacuation . the system that is used to hold the platform down onto the subbase is located where the platform meets the subbase . it operates on the principle of hydrostatics . on the underside of the columns , there are multiple chambers which may be evacuated by pumping and which are vented to the outside atmosphere . flexible seals that define these chambers are positively engaged by water to create a fluid - tight seal so that no seawater will enter the evacuated chambers . the reduction of the buoyancy forces will hold the platform onto the subbase until such time as the platform is totally deballasted . once that has occurred , the hydrostatic hold - down system is disengaged and the platform will quickly rise to the surface .