In Truk on the popular shallower wrecks 18 to 33m depth range, a stem-to-stern full ship length traverse lead by an experienced wreck guide through cavern type cargo holds and superstructure overhead passageways can be considered as one long progressive penetration. There are usually exit/egress openings visible along the route, so running a primary reeline is optional.
The only time we would run a primary reel mainline as mandatory procedure is going into a multi-level black hole labyrinth of an engine room or capsized hull, especially 45m or deeper where there is only one entryway/exit way. To lose the penetration line with low-viz in this environment can be just as bad or worse than a zero-viz lostline scenario in a large open space area: you would be constantly running & banging into machinery with potential safety spool entanglement points (boiler pipes & tubes, catwalks, railings, stairs, ladder rungs, engine fixtures, levers, valve control wheels, tool spanners etc), while searching for the mainline. The way an individual teammate dealt with this contingency was to momentarily hold in place in Lost Buddy Protocol for at least 30sec, before initiating a safety spool lostline search as a last resort, given all the hazards listed above. . .
A dilemma especially for the team oriented GUE Cave and UTD Wreck-trained Divers as to overhead protocol: you will either be with a dive guide who will lead your team on traverses through the shipwrecks' cargo holds, superstructures & engine rooms etc. --all without running line-- or choose to run a reel-line & egress out on reel-line without using a leading dive guide.
The advantage of running a reel-line is of course safety & standard operating overhead procedure as trained; the disadvantage is that you won't have as much bottom time to fully explore the wreck than if you did a through-and-through traverse. In other words, the dilemma will be whether to do "
Trust-Me" dives with a Dive Guide or not. . .
The Trust-Me Dive goes both ways in Truk --the Guide is vetting you on the initial easy checkout dives, making sure of your general trim & kicking technique as well as your aptitude & temperament for wreck diving. He's gotta be sure that you won't panic when the rust & silt starts "percolating" all around you. . .
There will be times where you will be in a tight engine or crew space in a near silt-out; or momentarily lose sight of the Guide around a corner corridor or up through a vertical gangway;
or going thru 'Black Hole' caverns -burned out blackened ship spaces that totally suck-out the illumination from your canister light (and where the worst of all zero-viz conditions can occur -"Black Ash Silt-outs"). You have to trust that the Guide knows where you are at all times as well as all wreck egress pathways, and the Guide has to know that you won't make a potential emergency contingency worse by freaking out. . .
A compromise best solution is to have a "Pathfinder Team" --that is a team with a primary reel laying a mainline with a Dive Guide in front leading a traverse through the wreck; and then having other teams come in later following that line to video/take pictures/sight-see etc --and then finally later a "Clean-Up Team" traversing back in the opposite direction and winding-up the reel-line. . .
The best "road map" to begin learning for these types of advanced wreck techniques is to go to a location where an instructor lives in residence and has daily experience & practice, as well as international expedition diving on the kind of wrecks you're interested in which require these specialized protocols. For example, if you're interested in WWII Indo-Pacific wrecks sunk-in-action, the best training locale "laboratory" is Subic Bay Philippines (
Tech Asia or
Scuba Tech Philippines).
