Question Turn a single bladder rig into Dual Bladder

[jstotz]

The Hollis Katana II is sold in a single bladder and dual bladder variant.

I found a single bladder at a good price, but I suspect I will, in the future, want to do some warm, technical diving, not in a redundant lift drysuit.

Is there anything to stop me from modifying this single bladder katana II into a dual bladder version, assuming Hollis will sell the second bladder separately?

 

[grantctobin]

There are holes missing. 1) unnecessary (if you’re in a wetsuit, you’re in AL80s and or the dive isnt very long) 2) Rig is balanced, swim up.

 

[Centrals]

deleted.

 

[jstotz]

There are holes missing. 1) unnecessary (if you’re in a wetsuit, you’re in AL80s and or the dive isnt very long) 2) Rig is balanced, swim up.

I appreciate my one and only response on this .... baht:

Let's assume you're diving two aluminum 80's and first you try weighting yourself to be neutrally buoyant when both tanks are full. You start breathing your air and you will immediately become positively buoyant.

So obviously, we instead weight ourselves to be neutrally buoyant, when possible, when tanks are empty (at the end of a dive). THEN we add 2 x ~6.5 lbs = 13lbs of compressed air to our tanks.

Therefore, at the beginning of a dive with aluminum doubles, you are *at a minimum* 12-13 lbs "over-weighted", assuming you're weighting yourself properly to avoid an uncontrolled ascent at some point of your dive.

In the case of a bladder failure, while 12lbs negative, I don't know that "swimming up" is a great solution.

I admit I'm not very experienced; perhaps redundant lift in warm water with alu80's is unnecessary for other reasons that I don't understand.

 

[eightytwenty]

I appreciate my one and only response on this .... baht:

Let's assume you're diving two aluminum 80's and first you try weighting yourself to be neutrally buoyant when both tanks are full. You start breathing your air and you will immediately become positively buoyant.

So obviously, we instead weight ourselves to be neutrally buoyant, when possible, when tanks are empty (at the end of a dive). THEN we add 2 x ~6.5 lbs = 13lbs of compressed air to our tanks.

Therefore, at the beginning of a dive with aluminum doubles, you are *at a minimum* 12-13 lbs "over-weighted", assuming you're weighting yourself properly to avoid an uncontrolled ascent at some point of your dive.

In the case of a bladder failure, while 12lbs negative, I don't know that "swimming up" is a great solution.

I admit I'm not very experienced; perhaps redundant lift in warm water with alu80's is unnecessary for other reasons that I don't understand.

Why not make some of that 12-13lbs ditchable? Your ditchable weight shouldn't be more than the weight of gas in your cylinders, but being able to ditch some lead if you're worried about not being able to swim up your rig seems like the reasonable answer, instead of wading into the world of convolutions and goober gear.

Who knows though, I don't do sidemount, I just know there is always a better solution than a dual bladder wing.

 

[jstotz]

Why not make some of that 12-13lbs ditchable? Your ditchable weight shouldn't be more than the weight of gas in your cylinders, but being able to ditch some lead if you're worried about not being able to swim up your rig seems like the reasonable answer, instead of wading into the world of convolutions and goober gear.

Who knows though, I don't do sidemount, I just know there is always a better solution than a dual bladder wing.

I'm not sure ditchable weight is ever used in technical diving. As evidence for this claim, you'll notice that technical diving is done with Backplate+wings or sidemount rigs, while ditchable weight pockets are generally only found on jacket-style recreational BCD's.

Why this is I can only theorize:
I believe the idea of ditching weights in an emergency is considered a shallow-water (0-60ft) option that is likely to lead to an uncontrolled ascent. In the 0-60 ft regime, as long as you don't close your glottis, you are likely to survive such an event. But an uncontrolled ascent from deeper would be increasingly likely to lead to life-threatening levels of DCS.

Your idea was to therefore limit the ditchable weight to safe levels to avoid uncontrolled ascent. I would argue that (especially in an emergency) it would be difficult or impossible to judge the effect of releasing weight until after you've released it, and once you've become positively buoyant in this manner it would be impractical to regain control of buoyancy.

 

[jstotz]

Why not make some of that 12-13lbs ditchable? Your ditchable weight shouldn't be more than the weight of gas in your cylinders, but being able to ditch some lead if you're worried about not being able to swim up your rig seems like the reasonable answer, instead of wading into the world of convolutions and goober gear.

Who knows though, I don't do sidemount, I just know there is always a better solution than a dual bladder wing.

To your credit I believe drysuits are most often the preferred source of redundant buoyancy as technical diving generally entails deeper, colder water that warants drysuits anyway.

I was also trained with a lift bag in AN+DP for redundant buoyancy, though it seemed to me less practical to whip out, inflate, and control in an emergency.

 

[OTF]

Carry a closed-bottom DSMB, train to use it as a backup lift option. Practice ascents straddling it like a pool noodle. Among many other uses.

 

[jstotz]

Carry a closed-bottom DSMB, train to use it as a backup lift option. Practice ascents straddling it like a pool noodle. Among many other uses.

That was my idea. My instructor still made me buy and carry a 50lb lift bag.

Out of curiosity do you know what the buoyancy of a fully inflated 6-7ft DSMB would be? My guess is plenty

 

[eightytwenty]

I'm not sure ditchable weight is ever used in technical diving. As evidence for this claim, you'll notice that technical diving is done with Backplate+wings or sidemount rigs, while ditchable weight pockets are generally only found on jacket-style recreational BCD's.

Why this is I can only theorize:
I believe the idea of ditching weights in an emergency is considered a shallow-water (0-60ft) option that is likely to lead to an uncontrolled ascent. In the 0-60 ft regime, as long as you don't close your glottis, you are likely to survive such an event. But an uncontrolled ascent from deeper would be increasingly likely to lead to life-threatening levels of DCS.

Your idea was to therefore limit the ditchable weight to safe levels to avoid uncontrolled ascent. I would argue that (especially in an emergency) it would be difficult or impossible to judge the effect of releasing weight until after you've released it, and once you've become positively buoyant in this manner it would be impractical to regain control of buoyancy.

Your worry is being able swim up a full rig. if you carry the weight of your gas (or less) ditchable, then you mitigate that problem.

To your credit I believe drysuits are most often the preferred source of redundant buoyancy as technical diving generally entails deeper, colder water that warants drysuits anyway.

I was also trained with a lift bag in AN+DP for redundant buoyancy, though it seemed to me less practical to whip out, inflate, and control in an emergency.

You don't need redundant buoyancy if you balance your rig. That 12-14lb range is also usually what is generally considered the upper range of weight the average person can swim up.

I'd say more, but you seem pretty sold on buying the dual bladder wing.