Why no carbon fiber tanks?

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myself

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So I know that aluminum and steel are the standard materials for tanks, but why don't we see any carbon fiber tanks? I have seen tanks for other uses that are carbon fiber and can hold scuba level pressures, and they tend to be lighter, so why don't divers use many carbon fiber tanks?
 
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myself

myself

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horrific buoyancy characteristics....
That makes sense, they would probably be too light. I was thinking that they would be less susceptible to corroding and therefore better for underwater use.
 

emoreira

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As mentioned before, Carbon Fiber Reinforced tanks are lighter than metal tanks (Alu or Steel). However the full equation of diver buoyancy does not change, so, if the tank is lighter, the diver will need more lead, distributed in the weight belt, BCD and (if used) in the dry suit.
The experience with scuba is still limited, so long term durability is still under scrutinity.
So, one of the main advantages of CFR tanks, it's light weight, is of no use in scuba. Perhaps, people with back pain would benefit of that light weight, but the diver will need to add lead. For them side mount is the right alternative.
 

michael-fisch

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My bail-out-rebreather, a Golem Gear/ IQsub Flex rebreather has 2 1.5Ltr 300bar CFR tanks mounted on the top of it. It's perfectly neuterally boyant and balanced with half full counterlungs and 600g of lead mounted on the bottom rear of the tube. - Sweet!

Using Steel or Aluminum tanks instead of CFR would have made this RB a lot cheaper but useless.

Michael
 

broncobowsher

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Don't forget they are disposable. Limited life and they turn into landfill material. Steel tanks can last over 100 years, there is not set end of life for a steel.
 

tbone1004

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carbon fiber is also EXTREMELY fragile and you should be very careful if using them in salt water. If any salt water gets into the resin matrix through a small scratch/crack it will seep into the carbon fibers themselves. Once the tank dries the water will leave but the salt crystals remain and will abrade through the fibers as the tank expands/contracts due to temperature/pressure changes and will radically reduce their life. They are not a smart choice for in-water applications, especially salt. Perfectly fine on land, but absolutely the wrong choice for water.

Also the mention of buoyancy. Have to use steel for this because AL80's are a bit weird in terms of the squared off bottom. Current Faber FX100 weighs 34lbs and is just a hair negatively buoyant so call it neutral when empty. If you made that same bottle out of a CF composite it would weigh less than 15lbs, so call it 14 for round numbers. That bottle is the same physical size, holds the same amount of gas, but is now 20lbs positively buoyant instead of neutral. That weight has to be made up somewhere, hell even in cave diving we aren't ever THAT negative.
 
https://www.shearwater.com/products/teric/

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