Shot Line Calculations

We often shot wrecks or potential target in order to better manage in-water and surface operations on decompression dives. I put a few calculation matrices together to aid in shot usage (and anchoring for that matter), so thought I’d share them.

• Distance to Target – given a fixed depth and shot line length, the matrix provides the distance to original drop target from the current buoy position. Use this in conjunction with a GPS to determine if the shot is on target. Given the short some time to settle in, then position boat next to buoy; if you’re any further away from the original target on the GPS than the distance in the matrix the shot is off target.
• Shot Line Angle – provides the natural angle of the shot line off the bottom for various lengths and depths. Use this to determine how long a shot line you need/want. Optimum angle is subjective, but I prefer the steepest descent angle possible. I like 60-70 degrees in current to help the shot/anchor grab, but this is all relatively to chain length, line diameter, surface float shape/size, etc…

Click here to download the file.

 Assumptions: 

• Adequate wind/current is present to allow the buoy to pull back completely.
• The shot line is linear, not bowed by shearing current, deco stations, etc…
• The shot weight/anchor is on target i.e. It did not get blown off on descent.