Diving doubles

[John C. Ratliff]

To give you an idea of what Luis is speaking about, I put together this force diagrams:

It was meant to show the difference between a horse collar BC (Fenzy is an example) and one I developed and patented, which never made it into the commercial arena. But it shows the situation underwater with a regular horse collar BC.

For a time in the 1980s I had a wet suit with a sandwich of two sheets of 1/8 inch neoprene built into its back with a BC inflator hose that Bill Herter of Deep Sea Bill's, Newport, Oregon built. He started out with an inverted "U" of neoprene, and progressed to a full back sheet of neoprene on the custom wet suits he built. This was perhaps the most streamlined BC ever designed.

One of my favorites, which I still dive, is Dacor's Nautilus BC, which is a hard-shell with a regulator. Once it has been trimmed at depth, its buoyancy does not change with depth.

It's a bit awkward in that it is pretty massive, but works very well.

Luis, the earliest BC that I have heard of was in the 1960s when cave divers were apparently using two chlorox bottles, on a line strung under their arms. Anyone else heard of this type of BC?

Concerning doubles, the twin 72s really do not change buoyancy greatly. They are slightly negative when full to neutral when empty in sea water; I don't know how much, but never really had to deal with it much when I wore them (see the attached photo). I don't think we wore weights with them or worried about it much.


SeaRat

 

[DaleC]

I use a NOS Seatec horsecollar and really like it as a BC (just used it again this weekend actually). It is the only type of BC that will float an unconscious diver face up on the surface and I can also surface swim face forward with it (by trapping the bubble under my arms and floating on it like a kickboard). Unlike Luis's Fenzy, there is not much room behind the neck to trap air. It has a port for a small CO2 cartridge (the toggle to it is under the power inflator in the pic) that is currently sealed with a LP port plug.
The key is to make sure the straps are adjusted correctly so it won't float up around your head (been there, done that).
One of my better flea market purchases ($20)

Here's an old Nemrod

and an old UDT deep diver vest. I believe the shallow diver had only one CO2 cartridge. One day I plan to freak my buddies out by wearing this on a dive (while actually diving sans BC). It doesn't hold air but the CO2 cartridges are charged.

 

[elan]

Thanks a lot guys for all the great information you are giving, I feel like I'm rediscovering the world of SCUBA again, it feels like back to the OW class, so great!

Can't wait to get the wet suit and double up my LP66, my wife though told me that she will kill me if I double them up as she loves that light tank as a single tank and for her that LP66 is the same as LP85 for me I would have to buy her an LP72 in return, so I was told

Dale what suit do you wear on the west coast ? I was thinking about getting the freedivers 2 piece suit. My buddy who I dove DHses in Toronto recommended me one. I think he has a 5 mil suit.

 

[AfterDark]

I use a NOS Seatec horsecollar and really like it as a BC (just used it again this weekend actually). It is the only type of BC that will float an unconscious diver face up on the surface and I can also surface swim face forward with it (by trapping the bubble under my arms and floating on it like a kickboard). Unlike Luis's Fenzy, there is not much room behind the neck to trap air. It has a port for a small CO2 cartridge (the toggle to it is under the power inflator in the pic) that is currently sealed with a LP port plug.
The key is to make sure the straps are adjusted correctly so it won't float up around your head (been there, done that).
One of my better flea market purchases ($20)

Here's an old Nemrod

and an old UDT deep diver vest. I believe the shallow diver had only one CO2 cartridge. One day I plan to freak my buddies out by wearing this on a dive (while actually diving sans BC). It doesn't hold air but the CO2 cartridges are charged.

That UDT vest is great! I had the shallow water version back in the late 60’s / 70’s. I used the oral inflator underwater for buoyancy control, worked well back then.
Wish I still had it.

 

[AfterDark]

That UDT vest is great! I had the shallow water version back in the late 60’s / 70’s. I used the oral inflator underwater for buoyancy control, worked well back then.
Wish I still had it

 

[DaleC]

Hi Elan,
I usually dive dry but have a Pinnacle polar 7/5mm one piece WS with merino wool lining for the summer. I've also used a Bare arctic 7mm two piece before. Big bouyancy swings with both. This summer I hope to have a hydroglove so my turning towards the dark side will be complete.

 

[John C. Ratliff]

Thanks a lot guys for all the great information you are giving, I feel like I'm rediscovering the world of SCUBA again, it feels like back to the OW class, so great!

Can't wait to get the wet suit and double up my LP66, my wife though told me that she will kill me if I double them up as she loves that light tank as a single tank and for her that LP66 is the same as LP85 for me I would have to buy her an LP72 in return, so I was told

Dale what suit do you wear on the west coast ? I was thinking about getting the freedivers 2 piece suit. My buddy who I dove DHses in Toronto recommended me one. I think he has a 5 mil suit.

Elan,

I forgot that you were doubling up the LP66s. I took my steel LP50s (1800 psi) into the pool yesterday, with the military harness and found a bit of a problem. This was my first dive with them, and they are actually buoyant when full, so much so that I would have liked a crotch strap with them and about 4 pounds of weight, in fresh water. So double them up, then take them into the pool to get a good feel for their buoyancy characteristics, if possible. If not, go prepared for the potential for a surprise (take a few more weights, and do a weight check). These off-size tanks may not have the same buoyancy characteristics as the standard 72 tank.

One other thought; I put single tank J-valves on mine, with a cross-over manifold for the doubles. I too think I'll dive them as singles sometimes, and in this configuration I can take them apart easily in less than five minutes. That means I can decide at the dive site (if I have some tools) whether to dive them as doubles or singles. Some people have criticized the cross-over manifold as "unsafe" or a "suicide manifold." I have been using mine for over thirty years with no problems whatsoever. But, I always use a double-band system when I put the doubles together. I'll get you a photo to see soon.

SeaRat

 

[Paladin]

Elan,

I forgot that you were doubling up the LP66s. I took my steel LP50s (1800 psi) into the pool yesterday, with the military harness and found a bit of a problem. This was my first dive with them, and they are actually buoyant when full, so much so that I would have liked a crotch strap with them and about 4 pounds of weight, in fresh water. So double them up, then take them into the pool to get a good feel for their buoyancy characteristics, if possible. If not, go prepared for the potential for a surprise (take a few more weights, and do a weight check). These off-size tanks may not have the same buoyancy characteristics as the standard 72 tank.

One other thought; I put single tank J-valves on mine, with a cross-over manifold for the doubles. I too think I'll dive them as singles sometimes, and in this configuration I can take them apart easily in less than five minutes. That means I can decide at the dive site (if I have some tools) whether to dive them as doubles or singles. Some people have criticized the cross-over manifold as "unsafe" or a "suicide manifold." I have been using mine for over thirty years with no problems whatsoever. But, I always use a double-band system when I put the doubles together. I'll get you a photo to see soon.

SeaRat

I have one of those "suicide" manifolds, too. They are great for when you don't need a permanent set of doubles. Like you, I've had no problems when using mine.

 

[DA Aquamaster]

Luis, the earliest BC that I have heard of was in the 1960s when cave divers were apparently using two chlorox bottles, on a line strung under their arms. Anyone else heard of this type of BC?

I have an old cave diving manual (I'll have to look but it is I think 1973 vintage) that outlines the clorox bottle approach and has a few other methods as well - but they are all clearly referenced as ancient cave diving "history" and the horsecollar BC is the clear standard of the day. (The irony here is that the Scubapro Buoyancy Control Pack came along shortly after (1975 or 1976) and ushered in the whole wing era.) (The further irony here is that the then new jacket BC's were also very popular as a place to start with for modifications to create the early DIY sidemount systems of the era.)

I do know that horsecollars with thin collars around the back of the neck were more highly prized by cave divers of the day due to the reduced trim issues otherwise caused by too much air migrating there.

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The same manual also addresses cheater bars and pig tails as means to connect two ingle tanks and discusses the relative merits of single outlet manifolds, independent doubles, cheater bars/pig tails, Benjamin conversions, and the not yet created but envisioned "ideal" manifold - a modern isolator manifold.

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Speaking of blasts from the past, I saw some 1" button gauges at Beneath the Sea that, unlike most button gauges that just have a small hole in their base, were milled to accept an HP spool, so you could conceivably put them on the end of a high pressure hose like a mini Seaview gauge.

 

[Akimbo]

…
One other thought; I put single tank J-valves on mine, with a cross-over manifold for the doubles. I too think I'll dive them as singles sometimes, and in this configuration I can take them apart easily in less than five minutes. That means I can decide at the dive site (if I have some tools) whether to dive them as doubles or singles. Some people have criticized the cross-over manifold as "unsafe" or a "suicide manifold." I have been using mine for over thirty years with no problems whatsoever. But, I always use a double-band system when I put the doubles together…

I have one of those "suicide" manifolds, too. They are great for when you don't need a permanent set of doubles. Like you, I've had no problems when using mine.

I am with you guys. After having to manually lap my third used doubles manifold (50-60s era) to stop leaks I figured O-ring seals with separate cylinder valves were a better idea anyway. I used doubles manifolds on the Voit single band backs for years and never had a problem, but they were on short 38s and 50s.

I am still not too crazy about the modern isolation manifolds. Rule #1 in HP piping design is to have a bend or loop in the tubing to absorb vibration, allow expansion, and ease assembly. Years ago I saw some manifolds with 360° pigtails between the cylinders. I really like the inverted AGA doubles manifold, photo attached.