Advanced Sidemount Wreck Diving: Passing Extreme Restrictions
Advanced sidemount diving techniques present a vast spectrum of new opportunities for wreck divers to safely explore previously unpenetrable sections of shipwrecks. The training for these activities is typically only available to fully qualified technical wreck (and/or full cave) sidemount divers. This reflects the high challenge involved with diving through very confined spaces, where limited/zero visibility is often encountered, there is a higher risk of entrapment and exit from the overhead might involve one, or more, time-consuming passages through restrictions; during which the individual diver may have very limited access to team support.
Approaching the Restriction
As the advanced sidemount diver approaches the restriction, they make use of their experience and training to gauge the optimal approach to passage. This may involve single or double sidemount cylinder removal; and may be head-first or feet-first. In this example, I am assessing a very small hatch opening that provides the only access into an under-deck area on a WWII Landing Craft Tank (LCT). The restriction is barely bigger than my torso.
Selection of the Appropriate Method of Passage
Beyond the restriction is an empty space, there are no hand-holds or surfaces to push off from. I elect for a feet-first entry, as this provides me with a stable surface to push-off from if I wish to abort the penetration and exit the restriction. It also maximizes the time where I retain communication and support from team members outside the restriction. If I proceeded head-first, I could find myself trapped in the restriction with no leverage with which to extract myself.
Patience and sensitivity are key qualities when passing extreme restrictions. This is not a pursuit for those with claustrophobia or a tendency to panic when immobilized underwater. I use buoyancy control to slowly sink through the hatchway, maneuvering slightly where necessary to allow my equipment to slip through the limited space available. It is very important not to use force to ‘drag’ yourself through extreme restrictions, as this can damage equipment and/or cause entrapment.
Descending until my shoulders prevent further movement through the restriction. The next step requires some agility and forward-thinking. I need to temporarily release one cylinder and squeeze my arm through the hole beside my body. My options for exit are now reduced, but I have retained one arm on the outside of the restriction so I can manipulate regulators/valves, clear mask, signal to team-mates etc. That arm also gives me leverage to push myself out of the restriction if necessary.
Then comes the tightest squeeze, pulling my head, two cylinders and my final arm through the restriction. This is the point of greatest hazard, as my options to deal with any equipment problems are very limited for the remaining duration I am passing through the restriction. Nonetheless, I have a free arm below the restriction that can access my regulators as soon as my mouth passes the gap. You need to keep a tight grip on the regulator in your mouth… and expect that your mask can get dislodged and flooded.
And my head and shoulders are through the restriction, only the tanks need to be pulled behind and re-attached to my harness on the other side. Exit is a reverse of this procedure…. and I will allow at least 5 minutes to perform the passage through this extreme restriction on exit.
As a general rule-of-thumb, I am confident to pass through any space that I can fit two cylinders through. If the tanks fit, then I will fit. This, of course, depends on your body size. My diet this year certainly helped….
Advanced sidemount training is available through ANDI training, open to divers holding Technical Wreck and/or Full Cave sidemount qualification. Please contact me for details of this course in Subic Bay, Philippines (and other locations upon request).