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Hi Mike,
I'm one of the Halcyon divers that you saw. Let me try to answer some =
of your queries.
We were preparing for a 30m dive when you met us and as such we did not =
carry deco bottles with us for that dive. For our planned bottom time =
and backgas (30/20) there was no need for it although our deco bottles =
were on the boat - for use on subsequent days.
It is standard procedure to use the twin bottles carried either side of =
the unit. The bottles are connected by an isolated manifold and we use =
our standard open-circuit regulator set-up. The only addition is 2 =
extra hoses - one which drives the RB and the other feeds the regulator =
on the mouthpiece block.
All dive planning is done as though we were on open circuit - including =
decompression. The Halcyon is not a fixed ppO2 unit so the perceived =
"big advantage" of such units do not apply here. We do an open-circuit =
decompression on all dives. If you find that you're getting a big deco =
advantage moving from open circuit to fixed ppO2 closed circuit then =
you're probably doing the wrong deco and/or using the wrong gases.
There are a number of advantages to this - your bailout deco is the same =
as your planned deco. You can easily mix halcyon divers with OC divers =
and everyone is still running the same plan. The gas that you carry for =
the dive is also your bailout gas - our stage bottles are 7L (45cuf) so =
they hold all the deco gas we need should we go open circuit for deco.
I guess one of the most important things to remember about the Halcyon =
is that it is a gas management tool. It allows us to achieve good gas =
efficiency on our dives. We typically go high on helium on many dives =
for a number of reasons and as you know, helium is expensive in this =
country. The gas savings that we make by using a halcyon make it easier =
to do this.
In deciding on stages, back mounted gas etc, you need to consider the =
worst possible scenarios, look at how to get out of them and plan =
accordingly. Typically, the worst scenario is both RB's fail resulting =
in both divers going to OC, then 1 diver experiencing a complete OC =
failure. This results in 1 diver passing the long hose and both divers =
exiting on 1 diver's backgas. In the ocean, this means a safe ascent to =
the depth where the divers can switch to deco gas, or if shallow enough =
not to require deco gas, then to the surface. In cave, this would mean =
sharing until you reach a stage drop (although typically, WKPP do not =
use the backgas but use stages - backgas is for emergencies).
With this in mind, we always use the twinset mounted with the unit. We =
could carry our gas in a stage bottle, but for the type of diving we do, =
we don't feel that's suitable. To answer some of your questions =
directly - we would use deco gas for deeper dives (our deco gas is 100% =
oxygen and 50% as well if diving deeper) and indeed did use it on =
subsequent dives. Our deco is OC deco.
Hope this helps.
Best,
John.
On a resent diver trip down south (Waymouth) we met some DIR divers. =
Some dived the Halcyon Rebreather (open water).
=20
It was rigged with two 7 litres (45 Cft.) on the sides of the unit. =
We asked if they did not use stages for DECO, and the answer was : NO
=20
They dived to about 30 meter (100 ft) so I can se why they might opt =
to leave stages, but when we asked if they used stages on the deeper =
dives the answer was still : NO.
=20
My question is therefor. Is this standard DIR(WKPP) procedures. If =
so why? Since this unit is NOT constant PPO2 you must have a longer =
hangtime compared to OC (and what about OC bailout?).
=20
Secondly why are the bottom mix carried on the back (on the sides of =
the unit) when a single stage would do the same, and easily can be =
carried along the deco stages?
=20
It doesn't make sense to me, so please enlighten me.=20
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<HEAD>
<META content=3Dtext/html;charset=3Diso-8859-1 =
http-equiv=3DContent-Type><!DOCTYPE HTML PUBLIC "-//W3C//DTD W3 =
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<BODY bgColor=3D#ffffff>
<DIV><FONT color=3D#000000 size=3D2>Hi Mike,</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT><FONT size=3D2>I'm one
of the =
Halcyon=20
divers that you saw. Let me try to answer some of your=20
queries.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>We were preparing for a 30m dive when you met us and =
as such=20
we did not carry deco bottles with us for that dive. For our =
planned=20
bottom time and backgas (30/20) there was no need for it although our =
deco=20
bottles were on the boat - for use on subsequent days.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>It is standard procedure to use the twin bottles =
carried=20
either side of the unit. The bottles are connected by an isolated =
manifold=20
and we use our standard open-circuit regulator set-up. The only =
addition=20
is 2 extra hoses - one which drives the RB and the other feeds the =
regulator on=20
the mouthpiece block.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>All dive planning is done as though we were on open =
circuit -=20
including decompression. The Halcyon is not a fixed ppO2 unit so =
the=20
perceived "big advantage" of such units do not apply =
here. We do=20
an open-circuit decompression on all dives. If you find that =
you're=20
getting a big deco advantage moving from open circuit to fixed ppO2 =
closed=20
circuit then you're probably doing the wrong deco and/or using the wrong =
gases.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>There are a number of advantages to this - your =
bailout deco=20
is the same as your planned deco. You can easily mix halcyon =
divers with=20
OC divers and everyone is still running the same plan. The gas =
that you=20
carry for the dive is also your bailout gas - our stage bottles are 7L =
(45cuf)=20
so they hold all the deco gas we need should we go open circuit for=20
deco.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>I guess one of the most important things to remember =
about the=20
Halcyon is that it is a gas management tool. It allows us to =
achieve good=20
gas efficiency on our dives. We typically go high on helium on =
many dives=20
for a number of reasons and as you know, helium is expensive in this=20
country. The gas savings that we make by using a halcyon make it =
easier to=20
do this.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>In deciding on stages, back mounted gas etc, you =
need to=20
consider the worst possible scenarios, look at how to get out of them =
and plan=20
accordingly. Typically, the worst scenario is both RB's fail =
resulting in=20
both divers going to OC, then 1 diver experiencing a complete OC =
failure. =20
This results in 1 diver passing the long hose and both divers exiting on =
1=20
diver's backgas. In the ocean, this means a safe ascent to the =
depth where=20
the divers can switch to deco gas, or if shallow enough not to require =
deco gas,=20
then to the surface. In cave, this would mean sharing until you =
reach a=20
stage drop (although typically, WKPP do not use the backgas but use =
stages -=20
backgas is for emergencies).</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>With this in mind, we always use the twinset mounted =
with the=20
unit. We could carry our gas in a stage bottle, but for the type =
of diving=20
we do, we don't feel that's suitable. To answer some of your =
questions=20
directly - we would use deco gas for deeper dives (our deco gas is 100% =
oxygen=20
and 50% as well if diving deeper) and indeed did use it on subsequent=20
dives. Our deco is OC deco.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>Hope this helps.</FONT></DIV>
<DIV><FONT size=3D2>Best,</FONT> </DIV>
<DIV><FONT size=3D2>John.</FONT> </DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 solid 2px; MARGIN-LEFT: 5px; PADDING-LEFT: =
5px">
<DIV><FONT color=3D#000000 size=3D2>On a resent diver trip down =
south (Waymouth)=20
we met some DIR divers. Some dived the Halcyon Rebreather (open=20
water).</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>It was rigged with two 7 litres =
(45 Cft.) on=20
the sides of the unit. We asked if they did not use stages for DECO, =
and the=20
answer was : NO</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>They dived to about 30 meter =
(100 ft) so I=20
can se why they might opt to leave stages, but when we asked if they =
used=20
stages on the deeper dives the answer was still : NO.</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>My question is therefor. Is this =
standard=20
DIR(WKPP) procedures. If so why? Since this unit is NOT constant =
PPO2 you=20
must have a longer hangtime compared to OC (and what about OC=20
bailout?).</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>Secondly why are the bottom mix =
carried on=20
the back (on the sides of the unit) when a single stage would do the =
same,=20
and easily can be carried along the deco stages?</FONT></DIV>
<DIV><FONT color=3D#000000 size=3D2></FONT> </DIV>
<DIV><FONT color=3D#000000 size=3D2>It doesn't make sense to me, so =
please=20
enlighten me.</FONT> </DIV></BLOCKQUOTE></BODY></HTML>
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