Mailing List Archive Mailing List Archive
> I'm wondering if anyone could give me some info. I live in NYC and have
> been diving in the NE for a number of years, mostly wreck diving. I'm
> looking to progress into more technical diving and would like some info on
> doing decompression dives, types of tables and algorithms applicable,
> recommended dive computers, equipment set-ups, etc. If anyone has some
> experience to share, it would be greatly appreciated.
Disclaimer: I am not a diving instructor; you need to take a technical
diving course to be safe.
In order to make safe decompression dives, you must much more carefully
plan the air, decompression, and redundancy requirements than for a
no-stop dive. I feel that it is very important that you have a good
"feel" for gas and decompression requirments before you make a computer
assisted decompression dive. I would have a thorough understanding of how
to work out the gas required to complete a given dive and all its
decompression stops, derived from tables or (shameless plug) desktop
decompression programs like MiG Plan. You should be able to answer a
question like:
How many PSI would I need to complete an ascent from depth and
decompression lasting 30mins? 60mins? Sharing air?
You should MEMORIZE the answer to that question, so that you can look at
the ascent time on your computer and compare it with your PSI to make a
good decision about when to begin an ascent. It's best that you develop
some simple rules for yourself, and try to dive the same way every time.
As a pilot, it was drilled into me that if you follow the procedures
properly time and time again, you will be very safe; once you start
deviating, things can easily go wrong.
In my case, I know that I can easily complete an ascent from 240FT and one
hour of deco with 1500PSI in my double 100 cylinders. Therefore, I ALWAYS
begin my ascent, regardless of depth (never deeper than 220FT on air,
right?) before I reach either 1500PSI, or one hour of deco. In practice,
I don't like to decompress that long, so instead I come up at 1500PSI or
30MINS of deco. This works very well becuase I have a little safety
margin in the deco department in case I have to spend time working the
anchor loose, etc.
(Warning: another shameless plug) It's a good idea to use a program like
MiG Plan, which has a tissue loading graph, to get a feel for how quickly
deco time increases. For example, on a 80FT reptative dive, deco time
starts building MUCH faster than on a 200FT first dive becuase your slower
tissues are the ones going into deco first. This "feel" is important
because otherwise you can look at your dive computer and see one minute of
deco, and then be awefully surprised when just five minutes later you have
30 mins of deco!
As far as dive computers, my first choice would be an Aladin Pro or US
Divers Monitor II. My second choice (nearly as good) would be the Suunto
Solution. Do NOT get an air integrated computer; I have seen too many
people run out of air because of them, not to mention the failures...
I like to have fully redundant equipment for a decompression dive. That
means two tanks on a dual outlet manifold, two first stages with shutoff
valves in case of freeflow, two computers, two masks, and a backup BC or
liftbag/reel. If diving in currents, I like a "John Line" to tie
yourself to the anchor line, and prefer to always carry a liftbag/reel to
shoot up to the surface if I get blown away from the anchor line.
I find that double 100's can get me into and out of more decompression
than I'm interested in doing, so I don't carry pony bottles or stage
bottles. IMHO I think they are only a good idea when they are used for
mixed gas. I prefer to use surface supplied O2 for padding deco stops,
rather than the risk or carrying it on the dive, except again in the case
of mixed gas dives where it is required to safely complete the deco.
I hope this is helpful.
Jody Svendsen
MiG Technologies
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]