difference of double and single using techniques

[duckbill]

You know, for the most part we all know body positioning very well and it is so second nature to us that sometimes we need a reminder like this for the purpose of instructing others. Thanks 'mossback'.
Nice to hear your dive reports from Cozumel. Sounds like you had mucho fun.

[nemrod]

There have been at least two new double hose divers whom I have tried with no success to emphasize just how different diving with a double hose can be and the absolute nessecity to understand the physics of positioning your body/lungs in relation to the regulator. They just did not get it until they tried to use one. Talk is talk but unitl you actually use one for real in the water you just cannot appreciate the differences.
I cannot think of two regulaotrs more different than my Teknas and my RAMs. It is a different world with them. When they are working correctly--when--and if---then nothing equals them, light, small, streamlined and the deeper you go the better they behave and perform.

Compared to my DA and Mistral, none of my RAMs are particularly position sensitive. A good RAM should breath at least adequate in any position--of course---like all double hose regs they are position sensitive and that must be accounted for in strenuous diving--just not as much so as some of the other types.

Glad that you had a good trip and your wife was not to worried.

Nemrod

[sea.explorer]

Position is important but I would also recomend running a higher IP pressure on the RAM if you are not already. I would recoment 135-140. This helps a good deal in air delivery in my experience. -Ryan

[luis]

I have been running the IP in my RAM’s from 145 to 160 psi. In my experimental RAM with the reproduction 2nd stage spring it seems like I need to crank the IP higher (near 160 psi). I would even go a bit higher, but the octopus is what starts to free flow.
I am not necessarily recommending that high of an IP. That is just part of what I have been trying.

I have been using a crotch strap for a wile and it really helps. It runs form the tank unit (back pack, BC, or harness) to my weight belt up front. That configuration allows me to release the weight belt without any tangles and it keeps the weight belt in place. My wife is also using a crotch strap to keep her BC from rising, or her weight belt from sliding when she swims down (she is not using a double hose).

[duckbill]

luis said:

I have been using a crotch strap for a wile and it really helps. It runs form the tank unit (back pack, BC, or harness) to my weight belt up front. That configuration allows me to release the weight belt without any tangles and it keeps the weight belt in place.

How do you have it rigged so the weight belt would fall free of the crotch strap if ditched? I have one of the old buckles which has a notch to trap a crotch strap clip when buckled, and releases it when the buckle is opened and the belt falls free. Actually, I just recently figured out the reason for the old crotch strap clips and the finger/notch on the buckle. Funny how it all comes together and makes sense when you have all of the pieces of the puzzle!

[luis]

I just loop the crotch strap around the front of the weight belt with a big loop. When you unbuckle the weight belt it just slides out of the big loop. I fasten the crotch strap last, and the loop is made with a small (1 inch) fast-tech buckle. I would prefer the loop made with a Velcro closure but this is what I had handy. Neither method of closing the loop is vintage, but it is convenient, and the use of a crotch strap is vintage. It is also very effective at keeping the tank in place even if you use a BC attached to the back pack.

[SeaRat]

I have used the crotch strap method for many years, as can be seen in these photos of me in Clear Lake, Oregon:

This is the traditional method of using a double hose, sans BC (actually, before BC). Notethat there is a crotch strap, and the I wear the weight belt outside the harness.

I progressed to a dry suit, and wore a different harness with a life vest. These were still less than optimal, in my opinion, so I kept experimenting. I came up with my own design for a BC, and I'll show it here:

I want to put these onto this site, as I think that the use of a double hose regulator with a back-mounted BC does cause problems. Mossback noted some of those above. But unmentioned is that even with the crotch strap, by inflating the BC the tank will rise a few inches up off the diver's back. This is a few inches more of water pressure in the normal horizontal position that a diver must overcome to breath. The design I made, which I call the Para-Sea BC, uses a front-mount BC to wrap around the chest, and push the whole diver up, rather than lift the scuba unit off the diver's back. Instead of a crotch strap, mine uses a parachute harness and hip connectors, and the scuba harness connects to each hip at the side. The only strap going around the waist is the weight belt, so there can be no confusion about what one to use in an emergency.

Unfortunately, no one would manufacture it, so it remains an expensive learning project. But the principles really help the use of a double hose regulator, in that the scuba will rest on the diver's back, with the BC pushing up from the under the diver. That is why the front-mount BCs are usually preferred by double hose divers.

You may note that I'm using a single hose regulator (Scubapro A.I.R. I) in the photo. This was for promotional reasons, in the 1980s, when I was trying to bring the front-mount BC back into vogue. Note also that even with these setups, there is significant differences in the placement of the regulator and the center of the lungs. The lower on the back, and the closer to the back, the better for double hose regulators.

The photos were taken in about 1973, 1977, and 1989, respectively. My apologies for using photos of myself, but it is a way of making the points without the potential of copyright infringements.

John

[luis]

Hi John

Since the first time I saw your Para-Sea BC it has been intriguing to me. But, obviously, it is not available to the rest of us to try it out.

I find the use of a horse collar for the purpose of buoyancy compensation far less than ideal. The air initially fills the area behind the neck and it totally offsets any horizontal balance. My Fenzy (or any other horse collar) was fine in the Caribbean, since I basically used it as a surface flotation device.

Up here in Maine, I mostly dive in the ocean and I use either of the following thermal protection:
1) A wetsuit, 7 mm farmer John with 7 mm jacket, boots, hood and gloves. This provides 14 mm insulation around my core and I require about 26 Lbs of weights to be neutral at 10 ft deep at the end of a dive. Assuming that the buoyancy of the wet suit is due to the air bubbles I figured its buoyancy versus depth to vary as follows:

Depth _____ compression fraction ____ wetsuit buoyancy (approx)
0 _________ 1 __________________27 lbs
10 ft _____ 1/ 1.3 _________________20.8 lbs
15 ft _____ 1/ 1.45 ________________18.6 lbs
20 ft _____ 1/ 1.6 ________________16.9 lbs
33 ft _____ 1/2 _________________13.5 lbs
66 ft _______1/3 _________________9 lbs
99 ft _______1/4 __________________7 lbs

2) Or a 7mm neoprene drysuit. For the drysuit I need 36 to 42 Lbs depending on how much insulation I wear under it. With the dry suit the weight belt has a quick release shoulder harness.


Either of my weight belts can be easily released, but I have to put them on before my tank. Needless to say I would never release that much lead at any depth or I would come up like Trident missile. I actually use weight pockets (from XS Scuba) on the belt so I can release 5 Lb lead blocks at a time.

The point is that since I am not in the Caribbean anymore now I require buoyancy compensation of almost 20 Lbs for a deep dive (plus about 4.5 Lbs for 60 cu ft of air consumed). That is almost 3 gallons of air in the BC! When I go for a deep dive I tend to leave some weight behind and plan on a slightly deeper safety stop.

So the best BC I have found (to use with a DH regulator) is not a back inflated but the least expensive modern vest (no weight integrated system) with shoulder and waist straps (NO cummerbund**), a sternum strap and a crotch strap.

Moving some of the weights to the tank, with a weigh integrated system or other means, would assist to keep the tank close to your back, but I have a huge problem with not being independently neutral from my rig. I want to be able to take my tank off and look at it in front of me, in any orientation (and untangle it if it gets hooked on something).

With the harness / BC that I am using (and I am still experimenting a bit with the arrangement) and by having most of the air low around my waist, the tank seems to stay close to my back. What is worst than the BC is the air bubble in the drysuit right on my back. I tend to dive the dry suit with minimal air, unless I start to get cold.


Oh… the days in the Caribbean when I could swim in all three dimensions and not worry about buoyancy chance. Thermal protection (and the need for a BC) has ruined the three dimensional world.

I still swim in all three dimensions and use my lungs for minor adjustments, but the need for a BC is unavoidable.

What ever happened to Cousteau’s non compressible thermal protection? I think he used it on Conshelf three.



** If I wear a cummerbund it will be with my tuxedo, under my drysuit, like Bond…James Bond.

[Broxton Carol]

ALLEN made me a couple custom harness with more material so I can adjust the tank down lower with the steel bands in place. Even my BROXTON and Black label navy da type breathe excellent. They breathed excellent before I changed harness, but NOW do even better.

[SeaRat]

luis said:

Hi John

Since the first time I saw your Para-Sea BC it has been intriguing to me. But, obviously, it is not available to the rest of us to try it out...
...What ever happened to Cousteau’s non compressible thermal protection? I think he used it on Conshelf three.

Luis,

Concerning the Cousteau non-compressible thermal protection, I don't think it worked well. He did use it on Conshelf Three, but let me quote from his article in National Geographic, April 1966:

...A compressor forced heliox through he yellow pipe, and a "depressor," or reversed compressor, pulled the gas through the black pipe. The oceanaut at the end of this giant respirotory system wore two heavy foam-rubber wetsuits; on his chest was our new two-way regulator for high-pressure heliox; and on his back he carried a conventional Aqua-Lung filled with heliox. Like a provitdent parachutist, he had a reserve pack.

Between wet suits the oceanaut wore an incompressible vest, the armor wiht which we hoped to overcome the ocean's main threat to deep fish men--sheer cold, exaggerated by pressure and the heat-stealing effect of helium.

Insulating Vests Resist Flattening

Near the surface, foam rubber will adequately insulate a man at 55 degrees F., but 11 atmospheres of pressure will compress its air bubbles and destroy their insulating quality. To permit oceanauts to work in deep water, we had to have incompressible foam rubber.

The patent consists of enclosing micropbubbles of gases in tiny ebonite spheres, no bigger than motes of dust, and filling a rubber blanket with millions of them. There wasn't time to make nough yardage for complete suits. We settled for vests to preserve the heat of the central organs of the body. Legs and arms can become numb and recover, but life is in danger if heart and lungs get too cold...

One photo shows two divers on the top of the "Christmas Tree" that they were working on, and shows exhalation bubbles. This photo, by the way, was also used by National Geographic as they cover photo for the issue. But they were using a completely closed-circuit system. Where did the bubbles come from? Here's an explaination in the sidebar for this photo:

Human phantoms, in a beam from the diving saucer, labor on the Christmas tree. Bubbles escape a diver as his lips shiver uncontrollably on the mouthpiece. Umbilical cords carrying heliox vanish in the darkness.

"We were buried in treacherous night," recalls the author's oceanaut son, Philippe, who as the crew's photographer brought back extraordinary still and motion pictures."

I think that the SeaLab III aquanauts were better dressed in dry suits than the Cousteau divers in two wet suits and the vests.

One other interesting observation is that this was the first time that Cousteau divers used a chest-mounted regulator. That design, which changes the water pressure difference seen on the tank-mounted double hose regulator to a positive pressure system, later became their showcase diving unit when they adopted the "...new self-contained hydrodynamic diving suit, with helmet and built-in telephone."1 After their first dives of a new expedition,

"..The only interruption was for lunch in thewardroom, which was the occasion for an impassioned discussion of the merits and defects of our equipment. There was much marshaling of interesting facts and conjecture. Albert Falco, for one, was enthusiastic about the equipment he had been testing, and he was categorical in his conclusion that the new tanks of the self-contained diving suits allowed for dives of much longer uration than the olders ones, and that the suits themselves were entirely satisfactory. On the other hand, it came out that the underwater lights, which were handled by our lighting men, were difficult to focus directly on what the camera was filming. After a bit of idscussion, I concluded that the solution was to mount the lights on the camera itself, and to mount the batteries on the cameraman's oxygen tank. We've followed that practice for almost three years now, and it works beautifully...

Of interest here was Albert Falco's discussion of the diving suit, and the new tanks. It would be interesting to know whether he was also talking about breathing characteristics from the chest-mounting of the regulator, or this was just the capasity of the diving tanks themselves. Also, I don't think these suits were the new ones with "microbubbles of gases in tiny ebonite spheres..." but if they were, that in and of itself would be interesting. Maybe Ryan could comment on this.

1. Cousteau, Jacques-Yes with Philippe Diole, Life and Death in a Coral Sea, Doubleday and Company, 1971, pg. 261

2. Cousteau, Jacques-Yes with Philippe Diole, Life and Death in a Coral Sea, Doubleday and Company, 1971, pg. 22-24

Concerning the Para-Sea BC, I only have two that were ever made. But I am thinking about what to do with the concept now.


John

[nemrod]

Speaking of BCs, that Dacor I have with the dual bladder is not the typical horsecollar. It has two bladders, an upper one inflared orally or with CO2 and a lower one that runs off the LP inflator. This keeps the lift centered at the tummy allowing horozontal swimming. These BCs were breifly popular in the caves because the horozontal swimming position reduces silt out. I think they are the best horsecollar ever made--alas, mine is beginning ot come apart after so many years and so many dives.

The BP/wing came out of the cave communty as well because it is integrated and also promotes a horozontal swimming position and best of all there is nothing on your chest. I like them and and find they work very well with a double hose--most especially when diving doubles because the tanks are positioned very close to the back. I have not found that the wing BC lifts the assembly from my back if properly set up--it should not do that. The main problem is not the wing but the design of modern BPs. They are intended for tech diving with doubles--originally. The ridge on the plate helps hold doubles securely and as I said very close to the back. Unfortuately that ridge places an alumiinum 80 just a bit further away than optimum. Maybe this winter I will fabricate a BP without the ridge for single tank diving. The old H plate I think from Healthways will be my inspiration--the dogbone shaped one.

Most people, using a horsecollar never appreciated the Dacor dual bladder horsecollar. They did not understand it, it was an idea that came along to late and was killed off by the mass switch to the stupid vests/jacket types and the cavers of course went to the BP/wing--including me. Still, it is and was the ultimate horsecollar BC.

James

[kgehring]

It is a nice travel BC and the Oceanic Islander is nicer. I have both at the shop.