GUE Fundamental course

[Griffo]

??? Bone, muscle, and bioprene don't ebb and flow in a constant ratio...

There's a study out there where they tested 100 men of various shapes and sizes. Basically it determined that everybody is positively buoyant with a full set of lungs, 70% or so with empty lungs.

That would indicate to me that adding a few kg's of body weight shouldn't change your weighting much at all - what changes is the amount of neoprene. If you're in a dry-suit and adding or losing body weight, it shouldn't really matter much because you're displacing more water. I know a year ago I was 12% BF and about 10 KG (22 lbs) lighter - now i'm like 22% BF. I had to add a kilo but that's because I changed to a larger wetsuit.

 

[Griffo]

Wait, really? I thought if you could swim it up after ditching your ditchable weight you were good; if you couldn't, you needed to reconfigure until enough of your weight was ditchable. So maybe a steel backplate, weighted STA, and steel tank would be OK (I still need 4 lbs. of lead on top of all that), but in switching to doubles you might need to rethink the backplate material or consider aluminum tanks. Am I mistaken?

That's my understanding too. Admittedly it's from an archived GI3 article however..

A diver must start with a balanced rig which gives him every chance to deal with emergencies. In ocean or lake diving, steel tanks should never be used without a drysuit. Double wings are an invitation to a disaster - do not use them. Elastic wings are a disaster waiting to happen. They can not be operated safely by mouth, they lose their gas if ruptured, they can not be breathed like normal wings, and they cause more drag than normal wings. For ocean, aluminum 80's are the tank of choice. If more gas is needed, take an aluminum stage, but don't risk your life being over weighted at the beginning of the dive. The buoyancy characteristics of aluminum, especially when using helium , are such that a weight belt and or canister light will provide the necessary ballast which can be dropped in an emergency, making the rig only reasonably negative when full, neutral when empty, but swimable by dropping the weight. In cave, steel must be used with a drysuit and they must be negative enough to allow the diver to stay down in a low on gas emergency. There is nothing worse than being too light to stay off the ceiling while low on gas and then struggling. For this reason, the rig must be balanced to a no gas situation prior to cave use, and weighted accordingly.

 

[lowviz]

That would indicate to me that adding a few kg's of weight shouldn't change your weighting much at all

You did read this (above) before you posted, didn't you?

A kilo here, a kilo there. Sooner or later we are talking about real weight...
Everett Dirksen - Wikiquote

A 15# body weight swing is about 7 kilos. But adipose tissue runs at about 0.9 gm/cc in density. So let's just say roughly that you need to sink an additional 100 gm/kilo of added body weight. About 700 grams. A pint is a pound so you now have to manage a bigger bubble in your suit or wing. It isn't extreme, but it is significant if you are planning to ignore the weight swing.

 

[Griffo]

You did read this (above) before you posted, didn't you?

A kilo here, a kilo there. Sooner or later we are talking about real weight...
Everett Dirksen - Wikiquote

A 15# swing is about 7 kilos...

Sorry you've lost me. I've clarified in my post that I was talking about body weight, not rig weight - was that what you were referring to?

 

[lowviz]

I believe that I did misread your post. Sorry.

What I meant to say was that a person who fluctuates 15-20 pounds of body weight will most likely want to adjust rig weight when at either end of the bodyweight swing.

The more proficient that one gets in trim and buoyancy, the more that they are aware of the feel of an ideally weighted rig. At least that has been my experience...

 

[rjack321]

Wait, really? I thought if you could swim it up after ditching your ditchable weight you were good; if you couldn't, you needed to reconfigure until enough of your weight was ditchable. So maybe a steel backplate, weighted STA, and steel tank would be OK (I still need 4 lbs. of lead on top of all that), but in switching to doubles you might need to rethink the backplate material or consider aluminum tanks. Am I mistaken?

Its really hard to make a single tank too heavy to swim up.

 

[wetb4igetinthewater]

Its really hard to make a single tank too heavy to swim up.

Oh it is easy considering how open water is typically taught here in Seattle.

 

[lowviz]

Its really hard to make a single tank too heavy to swim up.

Yes, on a properly weighted rig it is hard but maybe not impossible. (I think)

How about I splash with a steel 130, valve open, empty tank. I dirt dart to my 130' destination and decide that all is not peaches. Go to my 19 cuft pony while my 130 starts to backfill with water. 5 ATA on the outside, 1 ATA on the inside...

Not saying that this is a likely situation, just a thought experiment. Curious as to how this threat compares to not having a dual bladder wing while diving dry. MODERATOR EDIT: Keep in mind that the dual bladder discussion has been moved elsewhere. See above.

Neither situation concerns me.

 

[Griffo]

@rjack321 I’m sure there is a world in which things line up that cleanly into two nicely separable cases.

But there is.. either you have a balanced rig / enough ditch-able weight that you can swim up. If not, then dive dry.

 

[Esprise Me]

Its really hard to make a single tank too heavy to swim up.

Well, yeah, that was my point. My understanding--and the materials I have seem to confirm it--is that GUE's concept of a balanced rig is one you can swim up from depth after ditching the ditchable weight, not necessarily one you can swim up without ditching any weight. In a single-tank configuration, chances are no matter how many non-ditchable weight choices you make (steel tank and backplate vs. more buoyant aluminum, weighted STA), it probably won't add up to so much negative bouyancy that you can't swim it up in the event of a wing failure. Depending on your exposure protection, maybe you won't need any more weight; maybe you will, but as long as you make that extra weight ditchable, you'll probably be within standards. But add a second steel tank and you might have more negative bouyancy than you can swim up, without any extra lead. If so, you need to reconfigure. You can dive with more weight than you can swim up if you need it to hold a safety stop, as long as you can ditch enough of it to swim up. And I don't really understand your earlier comment about doing what works for me. I thought this was a thread about GUE standards, and that's what my post was about. Also the standard of what you can swim up by definition incorporates what works for you.