Abstract: To enable the release and consequent recovery of a support float which supports a load, e.g. a pipe, as it is lowered to the sea bed, a marker buoy is lowered with the float to be released when the load reaches the sea bed, the marker buoy having an inflated flexible envelope which is trapped in a housing fast with the float and having an opening through which the float can escape only when it has been compressed to a predetermined extent under the effects of a predetermined hydrostatic pressure. The marker buoy is connected to the float by a cable and the float is released from the load either by operations on that cable, or on a release cable connected to the float, on appearance of the marker buoy at the water surface.