Technical Diving Articles
For many divers the greatest thrill is exploring ship wrecks. But, as you
progressed through your open water training, you were no doubt constantly
reminded about the dangers of entering wreckage or any overhead environment. The
dangers are real and valid whether you are a relative new comer to diving or a
seasoned dive professional with many thousands of dives. Overhead environments
take various guises, but more divers obtain cavern and cave training nowadays
over wreck. Although similar,
caverns and caves are hardly as challenging or as interesting as swimming
through the twisted and sharp confines of the sunken museum.
differences between cave and wreck are many.
Caves have generally one exit and this makes them seem dangerous. Wrecks,
however, appear to have many, and this leads to diver complacency and failure to
obtain training. The cave typically has an out flowing current to help your
exit, whereas the wreck offers no assistance or consistency and actively seeks
to entrap you with its rusted metal claws.
you enter any wreck you should obtain Advanced Wreck diver training which will
help you start appreciating the added hazards that go hand in hand with your
trips into the magnetic overhead environment. Proper training will provide in-
water skill building focussing on the emergency drills needed to safely exit
should trouble occur. On completion
of training, you will be able to cast off your “open water safety wheels”
and enter the most hazardous of the underwater domains…the rusty shipwreck.
Penetration by definition means going into an area where direct access to the
surface is not available. Even a brief “look see” means you have penetrated
the wreck and should have laid a line to show your exit route. Wreck penetration
should always involve line laying, and good line technique is an art in itself.
Wreck penetration techniques are beyond the limits taught in a standard wreck
Standard wreck courses, often called a specialty course, offer an insight into wreck history, focus more on basic mapping and offer very little in line laying or actual overhead environment experience. These speciality courses are aimed at the relatively neophyte diver who seeks more interesting dive destinations without the hazards and dangers of entering the overhead environment. Typically, a linear distance to the surface limit is imposed of say 40m, which means that a wreck laying in 35m allows a maximum penetration of 5m. An Advanced wreck course generally has a maximum depth limit of 50m while breathing air, but it would be advisable to use trimix inside wrecks deeper than 30m.
are no restrictions on penetration other than adhering to the following safety
entering areas that two divers cannot enter side by side
1/3 rd's gas management protocols adhered to
equipment to be removed within the overhead environment
Guidelines to be used, in all overhead environments.
entering a wreck the guideline will be attached in two places called the primary
and secondary tie offs and you should always lay a new line if you suspect an
old one. Unlike the tourist caves of Florida or Mexico the wreck diver will not
have the luxury of simply following a permanent guideline.
propulsion technique will ensure you have relatively clear water to exit in.
Many experienced wreckers simply use a pull and glide technique as this tends to
preserve the visibility. There are some awkward skills to master, what with
laying the guideline sensibly and holding your dive light all while navigating
the wreck and avoiding silt outs.
is a potential killer while wreck diving and no matter what your fin style, Silt
will rear its ugly head at every chance. Silt is defined as particles occurring
in the water, and due to their suspension, affecting visibility during the
course of the dive. Silt can be either manmade or natural, i.e. rust particles
or clay particles. There are various types of silt you may encounter in a wreck,
Sand grains: the least serious, generally falling out of suspension very quickly.
A bit more serious, because it is easy to disturb and may take a long
time to settle .
More serious, easy to disturb, takes hours to settle, sticks to anything
While not exactly common, proves a serious problem due to magnitude of
deposit and fineness of particulate. Some popular sites in the Philippines
suffer very badly, with ash deposits almost a metre deep in places
Due to the many types of substances used in ship construction, the
following are included: Rust particles, carpet fibres, hardboard, and wooden
panels, expanded foam panels. Oil /fuel residues, becoming re-suspended, Coal
lay in all manner of positions on the seabed; it would be very difficult to say
where most silting would occur. With floors becoming ceilings and sidewalls
becoming floors, its best just to watch where you are going, and use the most
suitable propulsion techniques. In areas of suspected silt build up, it would be
prudent to maintain a closer position to guideline, often maintaining a “loose
ok” sign where visibility is compromised. A good approach to entering a silty
overhead environment is to touch nothing and watch where you are going!
exploration is better accomplished with a dive buddy, but not a dive party!
The buddy behind can illuminate possible line placements and help with
any wreck entanglement problems. The bigger the group that enters the wreck the
poorer the visibility and this will have a dramatic effect on group safety.
size of the corridors inside allows, divers may wish to use a frog kick or
modified flutter kick. These types of kicks direct the power of the fin kick
backwards and not up or down which will help maintain visibility. With the fin
power directed behind, you should obviously have perfect buoyancy control or you
will find yourself constantly falling to the floor!
sorties into a wreck should be limited to the no decompression limits, until
your experience and subsequent training allow for more adventurous penetrations.
Any decompression cylinders should be clipped off just inside the primary tie
off point, as they would drastically increase entanglement risk. The
use of Rebreathers inside the narrow confines of a wreck is also to be avoided as they are huge line
tangles waiting to happen.
safely proceed through a multi deck shipwreck requires a series of dives each
designed to fulfil a single objective. The early dives should focus on map
building and reconnaissance. As a greater knowledge is built and guidelines
extended, the dead end areas of the wreck can be eliminated and the desired
destination more quickly reached, whether it’s the engine room or the
should be stream lined with no danglies. Spare masks or back up knives or tools
should be kept in pockets, (but back up lights are never put in pockets). A
rusty wreck tentacle will actively attract the ill prepared wreck diver, and
often, sadly leads to an indefinite bottom time!
a cave, wrecks have no out flowing current to impede your entry progress.
Therefore there will be nothing to assist the exit either. This had led many cave trained
wreck divers miscalculating the exit time and gas reserves. Any good training
course will have an extensive kit shaping session. The equipment will have all
first stages routed “hoses down”, to avoid damage. Manifold use must be
mastered in a hovering horizontal position. If greater depth necessitates helium
use and therefore suit gas in an argon bottle, much thought needs to address the
bottle placement. On the mixed gas train of thought, divers should routinely
lower their equivalent narcotic values when planning a wreck penetration, to
increase alertness in a stressful situation.
the wreck, divers should be visualizing the exit they came from and any closer
exits as they emerge (If decompression tanks have been left by an entrance then
this is the only exit). Finding safe and interesting wrecks to explore is
difficult and time consuming. The skills learnt on a wreck training course, are
easy to remember but very difficult to do smoothly without constant practice.
During Advanced Wreck training you will get familiar with line laying into the wreck and being a
competent buddy. Once line laying skills are perfected, you get to hone your
emergency skills. Exiting while air sharing, via a long regulator hose seems
quite straight forward, until, you add a buddy with questionable buoyancy and
some depth changes. In any situation like this you will try to stay as calm as
possible and always swim at a pace that does not elevate either divers
breathing. To add some additional spice to the training, your instructor will
have you navigating the wreck will your eyes closed to simulate poor visibility
and may combine this with air sharing also!
signals can play a big part inside a wreck. You may have the brightest, most
expensive dive light there is, and two back ups, but if the visibility is nil
then they won’t help you… A touch contact system has been devised that
allows a team of two or more to exit safely and quickly. Devised by Don Rimbach
(well known Cave Diver), as a means for several divers to exit an overhead
environment. This method uses squeeze signals. Lead diver waits on guideline for
diver behind to make contact (above knee preferably). Second diver PUSHES ONCE
to GO. To stop exit Second diver SQUEEZES ONCE (lead
diver waits). To back up second diver PULLS BACK on lead divers leg
In a low visibility situation, dive team members find guideline immediately. Lead diver waits for next diver to make contact either just above knee or maybe divers bicep area. When team is assembled last diver “Pushes” next and so on and group exits maintaining “Loose OK” on the line until visibility improves. In the event of an entanglement diver “squeezes” the next to signal stop. Should a diver need to back up, he simply “Pulls back” with his hand. Group should wait until problem is fixed and “Push” squeeze is felt to continue. All team members should maintain contact at all times when visibility is compromised. This skill should be practiced often.
pull on the guideline
imagine you and your buddy, in zero visibility, are following a line and you
encounter a “dead end” and need to turn around. Discuss with your buddy a
suitable touch signal you could use to achieve this
Advanced wreck course is a mostly practical experience, but for completeness a
thorough course will have a training manual to cover the basics and give a
reference source for the material. Although very little of use has been written
in the way of wreck diving techniques, my own guide to Advanced Wreck Diving provides
a fresh and innovative way of mastering the academic phase of wreck diving.
are various new light and hand signals to learn, these signals are very similar
to any used in the total darkness environment.
below are the special hand signals particular to the overhead environment.
Standard open water hand signals are not included. If in doubt standard hand
signals should be reviewed with your Instructor
above hand signals show some new signals peculiar to the overhead environment.
These signals are very similar to those used in Cavern and Cave diving. The
signals for “OK”, “HOLD”, “EXIT” are control signals. They are to be
mirrored back to originator to make sure that they are understood.
in any overhead environment, any diver can call the dive at anytime for any
reason. Never succumb to peer pressure and enter the wreck if you don’t feel
“up to it”. All divers have differing performance levels that vary from day
enrol on an Advanced Wreck Course, the pre requisites are a recreational wreck
or cavern speciality ticket along with 50 dives. A very useful pre qualification
would be nitrox and or decompression diver, as these will enhance the experience
greatly. The course should typically include 6 dives inside proper ship wrecks
not sterile McWrecks. As with any advanced diver training, your instructors
experience is invaluable (check they have some) .Before shelling hard earned cash
over, always check out the training sites on a fun dive, ensuring that the
overhead environment is actual and not virtual! You owe it to yourself to ensure
that the training you receive has value and will prepare you for dives
unsupervised. Guided wreck penetration is very rare. Inside a wreck is the last
place for an ill prepared badge collector!
REMEMBER...NARCOSIS TURNS FERROUS TO BRASS! LEAVE IT DOWN THERE...