Diving shot

A diving shot line, shot line, or diving shot, a type of downline or descending line (US Navy), is an item of diving equipment consisting of a ballast weight (the shot), a line and a buoy. The weight is dropped on the dive site. The line connects the weight and the buoy and is used by divers to as a visual and tactile reference to move between the surface and the dive site more safely and more easily, and as a controlled position for in-water staged decompression stops. It may also be used to physically control rate of descent and ascent, particularly by surface-supplied divers.

A "lazy shot" is a shot which is suspended above the bottom. It may be tethered to the main shot line at a convenient depth. It is used for decompression and frees the main shot line for other divers. The lazy shot's line does not need to be longer than the decompression depth and is often only deep enough for the longer stops. It only needs a weight heavy enough to provide diver buoyancy control and sufficient buoyancy to avoid being dragged down under reasonably foreseeable circumstances.

The shot has several purposes. The basic purpose to facilitate control of descent and ascent rate by the diver, and to control the location of the diver during descent and ascent. The line is useful for divers in conditions of low visibility or strong tides where underwater navigation between the surface and the dive site is difficult or on deep dives where a navigation error would dramatically reduce useful underwater time. Divers can use the line to help buoyancy control, to ease long decompression stops and to prevent drift when ascending in a current.

The buoy marks the dive site for the people on the surface, who are generally on the dive boat, who provide safety cover for the divers. This helps them focus on the place where the divers are likely to return to the surface and helps them return to the dive site more quickly after the boat has moved away from the site.

Several configurations are in general use, depending on the conditions.

The basic shotline has a line fixed to the weight and the float, and does not compensate for depth changes. This is adequate in many circumstances, and has the advantage of simplicity. If there is any current or wind, the buoy will drift until tension in the line prevents further movement. Large waves will cause the buoy and the top end of the line to bob up and down, jerking on the line.

A bottom tensioned shotline controls the tension of the line in one of two ways:

Top tensioning is achieved by running the line through a loop on the buoy and hanging a small weight on the end. This weight will hang down and double its weight will pull on the float due to the mechanical advantage of the system. This is not usually a major problem, as it is relatively easy to get a buoy of adequate volume.