Carbon Fibre Tanks And Weighing

[G9]

I am thinking about buying some Carbon Fibre (CF) tanks. Partly because they are much lighter than Steel or Ally's and I sometimes want to drag tanks through dry cave to get to sumps. Lighter is obviously easier to carry.
However this isn't really a big advantage if I will have to carry a lot of extra lead for weighing me. Also, I am not keen to put a lot more weight onto me in principle. I currently dive steel mostly.

I have been trying to find out what changes one has to make to ones personal weighing when diving CF tanks, and I am becoming confused. A spec table I have found has CF tanks with the same buoyancy characteristics as Ally's, but a few comments on forums say that CF tanks are a lot less buoyant than Ally's.

Does anyone have experience of diving these, and how much extra weight do you have to (or not) put on your harness?

 

[KevinNM]

I have no idea what the regulatory regime you are under has approved in the way of tanks.

US DOT rules make this not very feasible unless you just need 50% more gas at the same weight as an AL80.

The Luxfer specs say an S106W (hoop wrapped tank) is a 300 bar 11L tank, weighing 15.3kg with a salt water buoyancy of +1.4kg empty and -2.2 full.

An S080 (AL80) is a 207 bar 11 liter tank weighing 14.3kg with a salt water buoyancy of +0.8kg empty and -1.3 kg full.

 

[Littlerayray]

Honestly the cf tanks have their application and that is for firefighting why would you want to carry more weight on you hips and remove it from you back tbh imho cf tanks have no business in scuba
There's a reason you don't see them being bought/sold often

 

[Patoux01]

Honestly the cf tanks have their application and that is for firefighting why would you want to carry more weight on you hips and remove it from you back tbh imho cf tanks have no business in scuba

More gas for same volume... Without being incredibly heavy.

They're "quite common" here around in cave diving. Many users do wrap them in a lead foil, still keeps them lighter than 300b steel tanks and protects them from the impacts while sump diving.

However, there's many different types of carbon tanks... So you can have many different buoyancy specs.

 

[Littlerayray]

I stand corrected
Me personally I would rather the weight off my hips after wearing a tool belt for over 16 years my hips don't luke the extra weight

 

[decompression]

CF tanks have their application, certainly in sidemount where the tanks weight isn't part of the divers weight equation. 130 steels can be very neg compared to a CF tank, which I've only seen in large capacities 130, 149 Cuft. If the neg weight is on the diver then it's much easier to compensate with a BCD or drysuit.
I've yet to have much hands on with them as they are still pretty rare around here.

 

[WarrenZ]

To fragile and too short of a lifespan for me to use them.

 

[KevinNM]

Outside the authority of the US DOT there are different designs that are more useful for divers. But I have no idea what is approved for use where.

 

[dreamdive]

We have gotten rid of our steel and alu rebreather tanks and dive nothing but CF. These tanks are aluminum lined unlike the fireman's or paint ball CF tanks.

We just signed up with CF tanks that are steel lined for our bail-outs. They weigh no more than ALU 40 but pack >80 cft. We are in the process of getting rid of all 40's and 80's bail out tank and switch to 3 CF steel lined tanks. Makes life so much easier and certainly is a lot (!) less weight.

I would imagine that these tanks would lend themselves for side-mounting, too.

CF does not = CF! There are alu and steel lined which are different than pure CF tanks!

 

[kelemvor]

Interesting, does anyone have any links to information about tanks that are actually being used for diving?