Posted to the DIR_UK list

Assymbled from a number of posts

>I've been thinking over the last few days about a problem I often
encounter
>on wrecks, particularly ones I know well.
>
>Many wrecks have swim through sections which are frequently well away
from
>any exits.  Typically, you go in, swim for a while, it gets dark, and
you
>swim a bit further and you see an exit.  You either then exit at that
>point, or swim through another dark bit to another exit.
>
>This begs the question of how you lay guidelines for this.
>
>One answer is to lay a line and cut it and tie off when you exit, but
the
>lack of lines seen on many of the wrecks I'm thinking about leads me to
>think that not many poeple actually do this.

The correct answer is if you enter any hole from which you cannot see
an exit that is big enough for the team to exit from, you should lay a
line

In cave diving there are 3 original (from Sheck Exley) and a few add on
(from the agencies) reasons for death (as they are relevant for wreck
penetration let me reflect them here)

1. Running out of gas - so always use at least a rule of thirds for
entry, exit, surface - also do not ever enter a wreck with less than
150 bar in your cylinders

2. Getting lost - no continuous guide line to open water.

3. Diving outside ones capabilities / training

4. Wrong Gas choice, too deep etc etc

The reason you don't see so many lines inside wrecks is that most
people don't do it properly

At a very least If you think the hole is a swim thru but is just out of
sight, one diver should enter the wreck with a line to the other diver
who stays outside, using basic line signals if the hole becomes a swim
thru the penetrating diver signals the outer diver who can swim the
line in.  However this should NEVER be used for any distance ( a rule
of thumb is greater than the daylight zone - ie if the penetrating
diver is going out of the area where the daylight glow can be seen),
this should be considered an exploration and a line should be ran from
outside and the team enters as one and exits as one

Consider the rest of your equipment as well, as expected low drag, no
danglies and a long hose - If your doing penetrations of this type you
need a primary light and TWO back up lights, you also need a safety
spool, such that if you do come off the line in bad vis you can do a
controlled search using your safety spool.  If you are running a main
line for exploration and will be T'ing into this line for side
exploration you need line arrows to indicate the out direction

>Another answer is to go back the way you came, but given the silt
inside
>wrecks, I'm not sure I'd always want to do this.

With correct fin & buoyancy technique in the team, you should be able
to swim back with only a small change in viz - the one thing we cannot
protect from is the crap that is dislodged by the exhaust bubbles
hitting the ceiling - this can often be worse than the silt.