Abstract: Apparatus for compensating for variations in the distance between an object or load suspended by a string of rods from a floating support or vessel and the sea floor therebelow so as to control the movement of the object or load with respect to the sea floor. There is both active and passive compensation provided by respective cylinder and piston assemblies associated with pressure accumulators. The passive compensation acts like spring. The active cylinder and piston assembly is of the double action type and disposed in parallel with the passive assembly. The active assembly compensates for residual vertical oscillations and operates as a function of two parameters : the position of the piston rod with respect to the cylinder of the active assembly and the velocity of the floating support with respect to the sea floor.