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Curt,
First of all, I very much enjoyed the latest issue. I've found only one
techincal glitch so far: the article on decompression safety implies in
the first paragraph that dissolved gas and "silent bubbles" are the same
thing. Of course, they are not (dissolved gas molecules are, by definition
dissolved in solution; silent bubbles are, also by definition, bubbles,
which are in a gaseous state).
Now, as to your questions about drift decompression diving. Although I'm
not a wreck diver so much, deep drift diving is something I do with great
frequency. It would take me more time than I have right now to describe
all the different methods I/we use for drift decompression dives. For
now, I'll just take a stab at answering some of your questions from my
perspective.
> What procedures, equipment, precautions do you use when planning a dive with
> strong currents?
About a dozen different things, depending on the circumstances (wall or
deep ledge, buddy teams or solo, current likely to change or not likely to
change, sharky area or not sharky area, rebreather or open circuit, big
boat or little boat, windy or not windy [and relative direction of wind],
rough sea surface or calm, boat driver or no boat driver, etc, etc, etc).
Basic, general methods:
1) Anchored boat:
Boat is anchored throughout dive with stage bottles hanging beneath. Dive
is conducted within reach of anchor. Anchor is sent to surface at end of
dive with a lift-bag, and decompression is done adrift.
2) Drifting boat:
Lead diver or all divers have line attached to boat. Boat has all deco
gases hanging beneath. Divers drift along bottom tethered to boat. (this
system doesn't work well on big walls or in strong wind).
3) "Live" boat:
a) Drift Line:
Lead diver, or all divers, carry a line connected to a surface float (one
of those "Bay Watch" lifegaurd floats with a dive flag mounted on top),
with a 2-lb weight or small anchor hook at the diver's end. Dive is done
drifting, with boat following float(s) (Very rarely do we use more than
one float - almost always just the lead diver). At the end of the dive,
weight is sent to the surface with a lift bag (this is more complicated
than it sounds - it involves a reel). Boat comes to lift bag or float
(determined prior to dive) and drops decompression gases on a separate
drop line with a larger float. If no or light wind and relatively calm
surface, boat ties off to decompression line.
b) Free Drift: (my preferred method)
Divers do dive without any lines to surface, boat driver keeps boat in
appropriate area (based on current direction & strength and bottom
topography). On the ascent, diver sends bright orange "condom" (we use a
more vulger word) to the surface with a reel, usually from about 130 feet.
Boat drops decompression line at "condom" with appropriate decompression
gases, etc.
c) High-tech free-drift (Invented by two guys who used to do the craziest
diving I've ever seen. Both are dead, one by motorcycle accident, the
other by helicopter crash): (Requires at least two divers, totally
self-contained)
Divers make dive with no lines to surface. Boat drifts wherever (with
driver aboard). At the completion of all decompression, divers wave a
bright orange flag at the end of a long stick (pole-spear). Boat comes to
get them. If boat driver does not see flag, divers get their UHF radios
out of their machined aluminum housings, which they carried with them on
the dive (both divers must have one for redundancy). Divers call boat on
radio, boat has directional finder and tracks down divers.
That's a VERY general outline of some of the options we occassionally use.
Regardless of method, ALL divers carry an "upline" and their ouwn float or
lift bag. My new toy is a self-inflating SMB made in England. I *love* it.
> Do you plan your dive so that all divers will be exiting the wreck at the
> same time?
In my experience, drift decompression is MUCH better done solo. In fact,
this is the MAIN reason I prefer solo diving. If buddies or a team, it is
almost ALWAYS imperitive that the decompression station to boat ratio is
1:1. In other words, with one boat, all divers need to begin
decompressing together, or if the upline is attached to the bottom, it
cannot be broken free of the bottom until the last diver ascends.
> Do you take down the float line with you and clip it to the wreck?
Quite often when I do float-line dives, I'll tie it off to a rock and work
in the general area, then untie it on the way back up.
> Do you just drift descend to the wreck and then pop your lift bags at the end
> and drift deco?
That's my preferred method. See variations above.
> What emergency procedures do you plan for if you or a team member gets
> separated and blown from the wreck?
You've hit the nail on the head on why this is better done with solo
dives. Otherwise, you need to plan contingencies so that each diver has
all the equipment needed to decompress solo. The tricky part is figuring
out which decompression station the boat should follow. If you're
careful, there will be at least one decompression rig (complete with
gases) on the boat for EACH diver in the water, in case for some reason
they all end up decompressing solo.
> If using mixed gas, what do you do with your stage tanks?
I carry everything I need to get back to the surface on my back (In my
case, I can't even use side-mounts because the hinder my ability to
collect fishes). Otherwise, see above.
> If using a down line, do you use knots or rings in
the line?
I'm not totally sure what you mean by "down line", but our decompression
lines are 5/16" woven nylon with one rope loop, one brass clip, and one
brass ring every 10 feet.
> What procedure do you use for deploying your lift bag?
Clip to my reel and send it up; usually from about 130 feet (I usually
carry one 130-foot reel and one 250-foot reel, with two floats - condom
and self-inflating emergency float). Sending the anchor or weight from
the drift line to the surface is trickier. We have a largish brass or SS
rin around the line at the diver's end. We clip the lift bag to the
weight or anchor, and clip the reel to the ring. The ring acts as a pully
for the drift/anchor line to pass through, and the reel gives us some
slack to play with until the bag reaches the surface:
Lift Bag Boat _______
_____O__________________\______|_________
\ /
\ /
\ /
\ /
\ /
\ /
\ /
\ /
\ /
\0 -- Ring
|
|
|
| - Reel line
|
|
|
o)
O Diver
/|
> Do you use a wreck reel?
I'm not sure if it's a "wreck" reel or a cave reel -- what's the difference?
> Well the questions could go on and on
Yup, and so could the answers. This is a very complicated topic, perhaps
the most complicated of all open-water diving techniques. I look forward
to your article.
> P.S. If anyone has a few good slides or photos of techdivers on a drift line
> and would like to see them in DeepTech issue #3 with credits, please let me
> know.
I have some cheesy computer-generated graphics, but not many photos.
Aloha,
Rich
Richard Pyle
deepreef@bi*.bi*.ha*.or*
*******************************************************************
"WHATEVER happens to you when you willingly go underwater is
COMPLETELY and ENTIRELY your own responsibility! If you cannot
accept this responsibility, stay out of the water!"
*******************************************************************
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