Abstract: The novel method substantially reduces the pressure pulse generated by an implosion of a cavity within a body of water by aborting the implosion. The abortion of the implosion is produced by generating within the cavity an explosion at the instant that this cavity attains its maximum volume.The method can also be used to generate within a body of water an impulsive acoustic signal by generating a first explosion within the body of water to produce therein a powerful pressure pulse and a cavity of very low pressure, and then generating a second explosion within the cavity so as to establish hydrostatic pressure inside the cavity while the volume of the cavity remains within a few percent of its maximum volume.

Abstract: Apparatus for positioning a first part with respect to a second part is characterized by a cylindrical guide respectively attachable to each part, a helical surface being disposed on each guide, each helical surface including a right hand half and a left hand half. A piston-cylinder is disposed on the second part, the piston being extendable to engage the guide on the first part to axially align the guides. After alignment, the piston is retractable to bring the helical surfaces into contact to generate a torque and align the parts. In another embodiment, the guide for the second part is formed on the piston while the guide on the first part has an axial alignment member projecting therefrom to engage the guide on the second part to align the guides. Once aligned, the helical surfaces contact each other with the piston extended. The contact between the helical surfaces causes the rotational alignment of the second part with respect to the first part.