Is there a new tank close to the old steel 72 in buoyancy shifts and weight?

[Akimbo]

a little more "mainstream" would be 50-dubs....

Mainstream yes, but too negative for a zero-buoyancy suit and no BC. I use a set of double 45 Fabers valve down. I really like them, but need a thicker wetsuit or a drysuit.

 

[Akimbo]

… 2 questions
1. I used J valves from 1972 to the early 80's...don't recall any failures...though I had heard of a few divers that forgot to pull the J up prior to the dive...so there was no reserve when they wanted one.....Is this the sort of problem you refer to , or was it something else?...

Not noticing it was pulled-down accidently was a big problem, but we were diving around kelp a lot. The other problem is the reserve pressure varied a lot, especially after it wore a bit.

A really simple option is to use an unbalanced first and second stage regulator and forget the whole reserve issue if you plan to stay pretty shallow or within a range you are comfortable performing a CESA or free ascent.

The low performance regulators will slowly start to breathe harder as cylinder pressure gets low. They will reliably give you plenty of warning to surface from a no-D dive and maybe a short safety stop. That is the main reason everyone didn’t drown themselves before SPGs. Less than a third of the tanks sold in the pre-SPG days had J-valves.

… 2. How much drag would this twin tank set up have on your back? I was assuming that a long narrow hull ( like racing surf ski) is faster than a wider boat....and that with tanks, a long narrow tank is faster in the water ( or is pulled easier) than two tanks....I see each is narrower than a steel 72, but now you have the surface area of 2 tanks..... If I get the chance to demo something like this--to see how well kick and glide works with it with the Dol-Fin system or big DiveR blades, , I will jump at it

I can only give you my perception since I don’t have any actual data. The Diveator rigs seem like they have noticeably less drag and definitely better balance than a single 72. I can’t compare my double steel 45s since I have never used them without a wing, two regulators, computers, and a drysuit. I think it is fair to say that double will look cooler if that is part of the objective.

Steel 72s are 6.9" OD compared to 5¼" OD on the Aluminum 40s. The only way to really tell is to don different rigs in a current pool and hang onto a load cell. It can be as simple as one of those swim-in-place swimming pools, a luggage scale, and some rope.

Tell us more about what you want. Speed, agility, freedom? Do you really need 72+ Ft³? How about strapping on a single 19-40 Ft³ bottle with a wireless AI wrist-watch computer? Leave a second rig on the bottom to swap them out underwater if you can find your way back to a convenient spot. Use a single 19 if you are a video model and let the videographer hand you replacements. It is the old compromise. We all want the freedom and simplicity of a freediver with the diving capability of a Saturation diver.

 

[danvolker]

Tell us more about what you want. Speed, agility, freedom? Do you really need 72+ Ft³? How about strapping on a single 19-40 Ft³ bottle with a wireless AI wrist-watch computer? Leave a second rig on the bottom to swap them out underwater if you can find your way back to a convenient spot. Use a single 19 if you are a video model and let the videographer hand you replacements. It is the old compromise. We all want the freedom and simplicity of a freediver with the diving capability of a Saturation diver.

Thanks again for some great information!
What I would like, is a way to gear for our 40 to 70 foot deep reef line, that runs over an enormous expanse along the coast of Palm Beach....I would like an air or nitrox supply to last for 1 hour, as that is the maximum that the dive boats will let us stay down per dive....I want to be slicker in the water than I would be in a bp/wing, so I can better capitalize on the kick and glide techniques you can see in the Dol-fin wing video of my initial post in this thread.....it is not so much about going a lot faster....it is faster by far than a jacket wearing scuba diver, and always with a resting pulse rate

It is taking what I do now with bp/wing and DiveR freedive fins, and taking to a much higher level of efficiency.....

 

[Akimbo]

Dan

OK, several combinations can get you closer. Most competitive freedivers use a skin-out, suit to reduce drag. You can get them with Nylon or split cell inside. They come in black or silver. That may well be more important than a single vs double drag decision. There is a lot of surface area and external Nylon sets up a lot of tiny eddy currents.

Were you planning on using a wrist-watch dive computer? Adding wireless AI wouldn’t add much drag if you put it on the end of a short hose. In any case, it is pretty nice even if you just use it as a bottom-timer and depth gauge.

No data, but I would guess that a side-exhaust regulator would have a little less drag than a conventional design. A lot of boats insist that you have a signal sausage, which can probably be tucked into a set of doubles with less drag than on a single. Definitely ditch boots on the tank(s). Fun project. Please let us know what you learn.

---------- Post added March 5th, 2015 at 03:50 PM ----------

Another thought. You could get really anal and run the tank(s) valve down and make a nose-cone for the upper end(s). That would be especially important if you use the flat-bottom Aluminum bottles.

 

[rhwestfall]

Dan,

Come back up here to Buffalo. Dry suit, big doubles, stage/pony, reels, lights, etc. You will forget about all that "silliness"...

 

[danvolker]

DanOK, several combinations can get you closer. Most competitive freedivers use a skin-out, suit to reduce drag. You can get them with Nylon or split cell inside. They come in black or silver. That may well be more important than a single vs double drag decision. There is a lot of surface area and external Nylon sets up a lot of tiny eddy currents.Were you planning on using a wrist-watch dive computer? Adding wireless AI wouldn’t add much drag if you put it on the end of a short hose. In any case, it is pretty nice even if you just use it as a bottom-timer and depth gauge. No data, but I would guess that a side-exhaust regulator would have a little less drag than a conventional design. A lot of boats insist that you have a signal sausage, which can probably be tucked into a set of doubles with less drag than on a single. Definitely ditch boots on the tank(s). Fun project. Please let us know what you learn.---------- Post added March 5th, 2015 at 03:50 PM ----------Another thought. You could get really anal and run the tank(s) valve down and make a nose-cone for the upper end(s). That would be especially important if you use the flat-bottom Aluminum bottles.

Another thing I want to consider....using something like a steel 72 and put some handles on it like a big video camera, and a go pro up on the nose....and maybe a small wing for even more stability at swimming speed.....when I dive with a Gavin scooter, with canon 5d mounted to it, the scooter and the mass, acts like an u/w steady cam....If I put the tank out in front, try to cheat behind it, I may have less profile than with it on my back, less drag....Freedivers often swim with arms extended in front....there may be a way to benefit from this tank in front concept, especially as I am a videographer, and would love to find a way for the video camera not to be as aerodynamic as a large refrigerator

 

[rhwestfall]

could always try it with a pair of boat cleats for handles and a hose clamp to attach them....

 

[Akimbo]

Wow, the scooter can change the whole picture. Now you are balancing drag, battery capacity, and range. A scooter will definitely give you better panoramic videos than a mono-fin. Add enough battery and you can drive a VW buss through the water… sideways.

Is this a simple video survey or will you want to stop and look at stuff? You can pretty well kiss minimal hydrodynamics goodbye lugging a 5D in a housing around. GoPros are another story.

My gut says saddle mounting two cylinders around the body of the scooter will handle better than one in front.

 

[herman]

Dan, are you concerned about buoyancy SHIFT or buoyancy itself..ie how much extra weight you need with an AL80 compared to a S72. If it's buoyancy shift then you are only talking about roughly half a pound more, no where near enough to worry about or if you want to be closer the neutral just add another 1/4 lb of weight- I use fishing sinkers, besides you get a little more gas.
I dive no BC with AL80s all the time, matter of fact, I don't like 72s in warm fresh water because they overweight me, with AL80 I am dead on neutral with no additional weight (but usually a DH reg)

 

[dumpsterDiver]

The only doubles i ever used were double 70's. I think a big fat steel tank is easier to handle and lighter. As for the buoyancy shift, that is entirely a function of the tank volume/capacity not the composition of the tank - but i suppose you know that.

Consider the surface area of two tanks versus a fat one, the drag has to be greater with doubles.

Also, nobody local will fill those tanks will they? I have a few, they were the PERFECT tank for my wife years ago. She could dive longer on one, than I could on a 100 cu-ft aluminum tank.