Different Shape SCUBA Tanks

[O2BBubbleFree]

Buoyancy is due to the weight of the gas the container holds and has nothing to do with the weight of material the container is made of.

Just to pick nits, the buoyancy SWING is due to the gas. Just saying Buoyance would also refer to positive or negetive, which does have something to do with the material.

I know you know this, and that's what you meant, I just thought I'd post it for those in the bleachers.

 

[Jimmer]

My mistake you guys are correct. I misunderstood what I first read, the issue with those is because they are like a buoy, it takes rediculous amounts of weight to sink them, taking away the benefits of a lighter cylinder.

 

[pupdiver]

Does anyone know of any other shape SCUBA tank that has been tried (successfully or not) other than the standard cylinder? I know the cylinder is typical because of its ease of manufacture and inherent strength, but I was curious if there had ever been another type. I saw the Cousteau special on PBS a while back where they wore slim back pack style units. I know some were rebreather units, and the rest are just housings with regular tanks inside, but that kind of thing would be ideal for streamlining if you could make a tank with that shape.

A wider thinner tank, like a large briefcase size with rounded edges and ends, would be closer to the body and nearer the natural center of gravity. It would also cut down on cross section and potential entanglements. I know all sorts of materials advances have been made just in the last 10 years with Honeycombs, Kevlar laminates and various new alloys. So has this been applied to radically new tank shapes or designs???

Assuming it had the same gas storage as regular tanks I would think the cavers and wreck divers would want this for the obvious benefits.

Cylindrical and spherical shapes are very practical shapes, not only for volume efficiency, but because the stress in the tank walls is simplified (only tension and compression). Cylinders have very little bending or shearing stress and spheres have none. Other shapes will have stress concentrations near corners. Plus, scuba tanks have to be designed to withstand net internal pressure and net external pressure.

Composite materials offer some strength advantages but also bring some technical issues when used as pressure vessels (delamination, fiber cracking, fiber-matrix separation, etc). Inspection of laminated structures is much more expensive and difficult than metallic structures. You can expect that a composite tank would be much more expensive to buy, much more expensive to maintain and inspect, and would have a shorter lifespan than a metallic tank.

The main reason we use composite materials for pressure vessels in the spacecraft industry (where I work) is that the structure can be made lighter weight and weight is a premium on a spacecraft. In scuba, saving weight in the tank doesn't offer an advantage so it isn't a desirable design route.

I think the humble steel and aluminum tanks are going to be the norm for quite awhile.

 

[jonnythan]

If you take away the large amount of dense metal from the tank, you have to put it back on yourself somewhere if you want to dive.

If your tank goes from 35 lbs to 15 lbs, that's an extra 20 lbs of lead you have to wear on your weight belt.

 

[rndboulder]

Cousteau et al. developed and used a very compact set of 4: 5000psi titanium alloy tanks in a streamlined housing back in the early 1980's. The set holds 140 cf & only weighs 30 lbs empty but you need a lot of weight on the belt as described earlier. They also built a prototype with fiber wrapped tanks (photo 2):

http://www.flashbackscuba.com/museum/rediscovery/rediscovery-Pages/Image12.html

http://www.flashbackscuba.com/museum/rediscovery/rediscovery-Pages/Image13.html

-Ryan

 

[Gilldiver]

Most of the units used by Cousteu including the streamlined packs were conventioanl open circuit units containing three small cylinders and often fairly high pressures and they used Mistral double hose regulators. N

He used tripple 30's that had a three part US Divers manifold in the yellow fiberglass back pack. The manifold was a total PITA to assemble and get all the connections not to leak as they were brass on brass compression fittings. Much like the Sherwood manifolds on many old twin 72's sets. You had to get a "Big" wrench to tighten the caps down.

The yellow backpack was developed to be better looking for his films.

The MK 15 rebreather uses a sphear for O2 and dilutant. It is one of the problems with getting a MK15 or MK15.5, the sphears are almost imposable to replace.

 

[rndboulder]

He used tripple 30's that had a three part US Divers manifold in the yellow fiberglass back pack. The manifold was a total PITA to assemble and get all the connections not to leak as they were brass on brass compression fittings.

Not to hijack the thread but the unit you describe is the UDS-1. They were developed to capitalize on the Cousteau look but were not used by the teams. You are absolutely right about the UDS-1 being a PITA. You can see all the major tank sets used by Cousteau & company at Flashback Scuba. -Ryan

 

[ams511]

The scooter is cool, what is the story with the projections?

 

[shadragon]

If you take away the large amount of dense metal from the tank, you have to put it back on yourself somewhere if you want to dive.

If your tank goes from 35 lbs to 15 lbs, that's an extra 20 lbs of lead you have to wear on your weight belt.

My point was if you made the tank thinner in profile, or in a different shape that conforms to the body better, the center of gravity would be moved closer to the normal COG and the weight would be easier to carry. It is like backpacking. The closer you can bring the load, the easier it is to maintain balance. I did not suggest you reduce the weight because of your point exactly.

I know cylinders are de rigeur, but I know there are enough free thinkers out there who may have tried something different. The Cousteau packs shown earlier in the thread are an example. My original question was one of curiosity rather than an attempt to change the industry. You never know. Someone may invent a better mousetrap...

 

[rndboulder]

Interesting topic. It is too bad that experimentation is so expensive. The Cousteau units for example are great but you could buy a lifetime supply of tanks for you and all your friends for the cost of one of those units. I definitely enjoy the balance of diving with multiple small tanks. My favorite setup is a set of triple 30's. They are low profile and stable. The trade off is 3 hydros.

As for the question about the scooters:

www.flashbackscuba.com/museum/rediscovery/rediscovery-Pages/Image15.html

The pods on the the sides were designed to hold the small 35cf titanium cylinders so they could breathe off the scooters for shorter duration exploratory dives. The original concept of breathing off the scooter dates back to the equipment developed for filming the Undersea World Series. The 40yr anniversary of the launching of that expedition is next month. -Ryan