The following guidelines are what I have used:
1. Never penetrate a wreck on your first dive on it. Recon the
outside thoroughly first.
2. Look on the outside of a wreck the same as you would a reef,
begin your dive at the deepest end, then circular multi-level
diving to the highest point. This will maximise your divetime
safely.
3. Where possible, use a shotline. This should be tied off to the
wreck by a disposable waster line. Otherwise the shot will drift
off of it while divers are doing their stops.
4. Greatest hazard on the outside of wrecks, esp. in bad vis.,
is a net. These can float like a shroud above you, waiting for
your ascent. Better to spend time gathering the net(s) around
a mast, or whatever it's caught on, and tieing it down. Makes
the wreck more diver-friendly for all.
5. If the wreck's hull is made of wood, then it may be too
unstable for safe penetration. If made of steel, probably no
shortage of sharp edges inside.
6. Wreck penetration has one major difference over cave penet-
ration. The cave is natural, the wreck man-made - with those
sharp edges, loose cables, snags Etc. Be sure you and your
gear are streamlined. Christmas Tree rigs invite hang-ups!
7. When penetrating a wreck, do the opposite of the outside dive
profile. Begin your penetration at the highest point, e.g.
wheelhouse first, then the forward shelter deck. By doing it
this way you are continuing to get a "feel" for the wreck, and
can gauge its silting level.
Also, if you do get snagged, lose track of time, or whatever,
you have given yourself more time - and air - to extricate
yourself.
8. The first thing you look for before entering the wreck is an
alternative exit! Stick your head in, maybe half your body,
leave your light OFF, let your eyes adjust to the gloom.
Can you see another exit? Big enough to get through without
leaving half your BC behind?
Yes - then turn on your light and see what obstacles are along
the way. Then safely negotiate the shortest route to that exit,
look around and see what silt you have stirred up.
If very little, then it may be safe to proceed with caution,
using the same protocol as you would on a night dive:
9. Charge your instruments by shining your lamp on them.
Have a back-up light with you.
Don't shine the lamp in your buddy's eyes!
Mark a single exit with a suitable light source - inside!
10. Your buddy, with whom you already have agreed will remain
at the original entrance until you have reached the alternative
exit, can - if there is adequate room for two in safety - be
signalled to join you. Each diver should then tour his half of
the area, with his own emergency exit to hand, if need be.
11. No alternative exit in sight? Then reel off from a point outside
the entrance, and take a route along one side only - not
across the room. With your lamp on, you should be able to
safely travel a distance that will allow you to check out the
internal environment. Pause, look around, silt behind? If you
don't like what you see, reel back to your buddy waiting at the
entrance, and leave.
12. Never go te "whole hog" on the first single-exit wreck entry.
Use progressive penetration, a bit extra each dive. Too many
divers reel out to the farthest back wall, then try to inspect
the wreck while exiting!
13. Change your finning technique to suit the environment. I
normally use the bent-leg, where both legs are bent and you
use short fin strokes to move forward, or single-finning,
with the non-kicking fin under the kicking fin, so that the
downward thrust is absorbed by the static fin - not the silt
on the floor below.
14. If you have a yoke valve, be very aware that one bump off
an overhead girder/crossbeam can bend/dislodge the yoke,
leading to a potentially dangerous loss of air!
Which is why a redundant air supply is recommended for all
overhead environments. One with an independent reg.!
15. When pasing through a door, it is easier to have your cylinder
be at a top corner when entering, in other words, a quarter
turn will allow you the most room for getting through without
getting stuck - or damaging equipment.
16. Having completed your tour, preferably with two-thirds of
your main cylinder's air supply left, you should now be back at
your chosen exit - with your buddy, I might add - and ready
enjoy a nice, easy multi-level safe ascent. A job well done!
The above is no more than an introduction to wreck diving and
penetration for divers seeking a solid base method for safe wreck diving. It is no more than that, for the learning curve goes on.
Safe diving,
Seadeuce
