Wings suitable for both double-7s and double-12s

[cool_hardware52]

When you day "demand" more, you mean that I get the ballast from the gas itself, not from needing to add more lead, right ? For practical purposes I consider the 130's and 100's essentially the same buoyancy empty

Yup. You need to be negative by the weight of the gas at the start of the dive, if you carry more gas you need to be more negative. In the case of tanks of similar empty buoyancy the gas it'self will cause you be more negative as the capacity increases.

Sorry if I failed to make that clear. It is this requirement for increased negative buoyancy with higher capacity tanks that dictates greater wing capacity.

Tobin

 

[Rainer]

Exactly. You need to weight for the swing in gas lost. Large cylinders mean more weight is needed.

Edit: This often cracks me up as I've seen divers go from say an LP85 to a HP130 and post they were able to drop lots of weight. Not only did the two cylinders have nearly the same inherent negative buoyancy, but the diver should have ADDED weight for the larger cylinder, even though it's obviously more negative when full.

 

[JeffG]

Exactly. You need to weight for the swing in gas lost. Large cylinders mean more weight is needed.

Edit: This often cracks me up as I've seen divers go from say an LP85 to a HP130 and post they were able to drop lots of weight. Not only did the two cylinders have nearly the same inherent negative buoyancy, but the diver should have ADDED weight for the larger cylinder, even though it's obviously more negative when full.

Huh? If the tanks end at the same buoyancy level (in this case the 130 is ~1lb negative, so lets say the 85 end at the same.), there would be no change to the weighting of the diver.

It just that the diver using the larger tank would start out the dive more negative. (due to carrying more gas)

 

[dsteding]

Huh? If the tanks end at the same buoyancy level (in this case the 130 is ~1lb negative, so lets say the 85 end at the same.), there would be no change to the weighting of the diver.

It just that the diver using the larger tank would start out the dive more negative. (due to carrying more gas)

Well, and to think about it a bit more, if you use the "neutral at 500 psi" rule, assuming the 85 and the 130 have same inherent buoyancy, then you need a bit less weight with the 130. Reason being, 500 psi in a 130 is more gas in terms of cubic feet than 500 psi in an 85 (about 5 cubic feet, or a whopping .4 pounds).

 

[dsteding]

Yup. You need to be negative by the weight of the gas at the start of the dive,

if you carry more gas you need to be more negative. In the case of tanks of similar empty buoyancy the gas it'self will cause you be more negative as the capacity increases.

Sorry if I failed to make that clear. It is this requirement for increased negative buoyancy with higher capacity tanks that dictates greater wing capacity.

Tobin

Yeah, what Tobin said-we are saying the same thing.

 

[JeffG]

Well, and to think about it a bit more, if you use the "neutral at 500 psi" rule, assuming the 85 and the 130 have same inherent buoyancy, then you need a bit less weight with the 130. Reason being, 500 psi in a 130 is more gas in terms of cubic feet than 500 psi in an 85 (about 5 cubic feet, or a whopping .4 pounds).

Well that is just swell for the engineer type, propeller wearing crowd

 

[dsteding]

Well that is just swell for the engineer type, propeller wearing crowd

Engineer? I'm a lawyer.

okay, with a science Ph.D.

 

[Friggincold]

I use a Halcyon Explorer 40 for double pst E8-130/AL BP. Halcyon makes an Evolve 30 for use with the twin 7 liter tanks. So If your trying to match which is best for both sets of tanks I would think the Halcyon Explorer or Evolve 40 would work.

 

[JeffG]

Engineer? I'm a lawyer.

okay, with a science Ph.D.

Even worse.

 

[limeyx]

Huh? If the tanks end at the same buoyancy level (in this case the 130 is ~1lb negative, so lets say the 85 end at the same.), there would be no change to the weighting of the diver.

It just that the diver using the larger tank would start out the dive more negative. (due to carrying more gas)

Perzactly! I thought I was going crazy there for a second.
The 130's are what -1 ? -1.5 empty, and the 100's are -2 ish so I dont change weighting.
No need to add more weight for the extra 4 or 6 pounds of gas -- it's just the empty buoyancy of the tanks.