Negative Entries - A Bad Idea???

[Ayisha]

i’m not trying to be pedantic - just accurate for others that might take away the wrong message from reading “weight to be neutral with empty tanks”.

It's just so that if stuff hits the fan and you actually do surface with a nearly empty tank, you can still make a controlled ascent to the surface.

Someone who weights themselves to be neutral with 500 psi in the tank is likely actually slightly underweighted. Weighting oneself to be neutral with 500 psi at 15 or 20 feet is likely to be even more underweighted.

Weighting oneself to be neutral with nearly empty tanks and an empty BC at about 3m/10 feet gives a slight buffer if one might have to ascend with a tank with less than 500 psi.

 

[Bob DBF]

Shouldn’t you be able to still be neutral with ~500 psi in your tank? I’m not sure how one holds a 3 minute safety stop when OOA with an empty tank???

Assuming an Al 80, you would just have to use your lungs to compensate for about a pound and a half of positive buoyancy. I've done it on a few occasions.

Someone who weights themselves to be neutral with 500 psi in the tank is likely actually slightly underweighted. Weighting oneself to be neutral with 500 psi at 15 or 20 feet is likely to be even more underweighted.

It depends, my definition of properly weighted is holding a 15' stop with 500# in the tank and an empty BC while breathing normally. It's not written in stone and I have no problem with anyone carrying more weight, however if you are carrying 5,10, or more pounds over this standard, one might rethink why they need that much extra weight.

Weighting to this standard has not been a problem for me, however if it is particularly rough or surgy, I will carry a few extra pounds. It's a matter of knowing what you need.

 

[Nick_Radov]

with no air in your BC or drysuit?

Yes, of course I am close to neutral with nearly empty double steel tanks and no gas in my wing or drysuit.

I don't wear a dry or wetsuit, so I usually use a double bladder BC. And a sausage for OW.

Even when diving naked there is no need for a double-bladder BC. It is an unnecessary convolution and doesn't solve any real problem. Carrying an SMB is a good idea for OW, but the little ones that most of us use don't have much lift.

But, if you're diving a drysuit, you have built in redundant buoyancy.

A drysuit is not a reliable source of redundant buoyancy. I mean you can get a little extra lift from a drysuit if you need to, but if you add much gas then the neck seal will burp it out. The point that some divers seem to still be missing is that having a balanced rig largely obviates the need for redundant buoyancy. Instead of coming up with convoluted solutions to self-inflicted problems, just eliminate the problems in the first place.
For big dives that require a lot of gas we'll usually also have scooters because it's hard to swim while hauling so much gear. So, if you have a wing failure then you can use the scooter to get up to the surface and then to the boat or beach. A scooter won't float you at the surface like a BC, but as long as you have some gas left you can just breathe off a reg until you get out of the water.

 

[happy-diver]

Yeah I dive kilos overweighted, one wing, tiny dsmb, manifolded hundreds, in a wetsuit, been lucky I suppose
and can count on one finger the amount of times I've bobbed around waiting for those stragglers of the herd

and mega plenty others dive the same with steelies

It's negative entry every dive head down first or feet

 

[lostsheep]

Buoyancy Compensators

"Many divers mistakenly believe that they must have large buoyancy
compensators to support their diving needs. Actually, divers do not need
excessive amounts of lift; large wings, because of the additional material
they require, only serve to increase drag. However, if, in fact, a diver does
need more than 65 pounds of lift for diving doubles, or more than 30
pounds for diving singles, then they do not have a balanced rig and are
an accident waiting to happen.5 The diver should be able to drop unnecessary
weight and swim up without a functioning BC. Use of large steel
cylinders indicates an aggressive dive, one that should only be done in a
dry suit, which provides not only good insulation but also additional lift.
As with all diving, the key component to proper buoyancy is diving with
a properly balanced rig.
Divers using dual BCs have experienced an array of problems; these
include increased drag, additional task loading and uncontrolled inflation.
There is never a need for “redundant buoyancy” in a properly
balanced rig. A small leak from the inflator can continually add air to an
unaware diver’s BC. As the diver becomes more positive, s/he will usually
try to empty his/her primary BC, all the while remaining unaware
of the secondary inflation. If the diver is unable to correct this problem
quickly enough, s/he may find her/himself at the surface experiencing
any number of problems. The DIR approach avoids the use of dual BCs,
and instead stresses."

 

[The Chairman]

Yes, of course I am close to neutral with nearly empty double steel tanks and no gas in my wing or drysuit.

We obviously use different steel over here.

It is an unnecessary convolution and doesn't solve any real problem.

You dive you and I'll dive me. When I'm a couple of thousand feet back in a cave with big ass steels (Lp 130s), a double bladder only makes sense to me. I have no wetsuit or drysuit and I'm not going to try using a lift bag or SMB back there. Convolution? It just sits there waiting for Murphy to show. Have you ever seen a double bladder wing?

And you think you have -no- air in that dry suit? Try flooding it and see just how "balanced" you are.

 

[The Chairman]

Divers using dual BCs have experienced an array of problems; these
include increased drag, additional task loading and uncontrolled inflation.

A double bladder BC does have an extra corrugated hose. You don't need an lp hose from your tank, unless you lack the skill needed to orally inflate your BC. It adds zip to my task loading while providing much needed redundancy. It's why I carry at least three lights, two reels and a few finger spools.

As for needing a drysuit when doing an "aggressive dive": when you're built like a manatee, you get to dive like one. I'm good for 4 to 5 hours in the North Florida Springs.

Consider me your DIR Strokesperson. I'm even in the GUE promotional video from way back when. I hear they still show that at the beginning of fundies.

 

[Nick_Radov]

We obviously use different steel over here.

I doubt it.

You dive you and I'll dive me. When I'm a couple of thousand feet back in a cave with big ass steels (Lp 130s), a double bladder only makes sense to me. I have no wetsuit or drysuit and I'm not going to try using a lift bag or SMB back there. Convolution? It just sits there waiting for Murphy to show. Have you ever seen a double bladder wing?

This thread is about ocean diving and my comments only apply to that context. Double LP130s are not suitable for ocean diving, even with a drysuit. They are simply too negative when filled with standard mixes, and too bulky. If more bottom gas is needed for an ocean dive, then bring a stage (or do multiple shorter dives or look into rebreathers).
I am not qualified to comment on cave diving.

And you think you have -no- air in that dry suit? Try flooding it and see just how "balanced" you are.

No excess gas in that drysuit. If I put the dump valve at the highest point and push the button, then no more gas comes out. That's what we use for weighting and buoyancy checks.
I have experienced major drysuit leaks. This does not prevent having a balanced rig. Seawater inside the drysuit is neutrally buoyant relative to seawater outside the drysuit. A leak does not significantly impact buoyancy. If you don't believe me, it's easy enough to test for yourself: just intentionally flood your drysuit by pulling on a seal (in a safe confined water environment) and then do a buoyancy check. Even with a leak, the drysuit will still hold gas pretty well unless the neck seal completely detaches or something. But because I am not relying on the drysuit for buoyancy anyway, this is more of a hypothermia risk than a buoyancy issue.

 

[lostsheep]

I doubt it.

This thread is about ocean diving and my comments only apply to that context. Double LP130s are not suitable for ocean diving, even with a drysuit. They are simply too negative when filled with standard mixes, and too bulky. If more bottom gas is needed for an ocean dive, then bring a stage (or do multiple shorter dives or look into rebreathers).
I am not qualified to comment on cave diving.

No excess gas in that drysuit. If I put the dump valve at the highest point and push the button, then no more gas comes out. That's what we use for weighting and buoyancy checks.
I have experienced major drysuit leaks. This does not prevent having a balanced rig. Seawater inside the drysuit is neutrally buoyant relative to seawater outside the drysuit. A leak does not significantly impact buoyancy. If you don't believe me, it's easy enough to test for yourself: just intentionally flood your drysuit by pulling on a seal (in a safe confined water environment) and then do a buoyancy check. Even with a leak, the drysuit will still hold gas pretty well unless the neck seal completely detaches or something. But because I am not relying on the drysuit for buoyancy anyway, this is more of a hypothermia risk than a buoyancy issue.

You and I both know of at least one guy local to us that dives double PST 120s in the ocean and he is not a big guy; the PSTs and the LP130s aren't radically different in buoyancy swings. I absolutely agree about 8" diameter tanks.

To the second part in bold, I'd really like some data on that one but I am not volunteering. I always reserve the right to be wrong but I am skeptical of your claim.

 

[The Chairman]

This thread is about ocean diving

The OP didn't specify. No need to move the goalpost to garner a "win".

Double LP130s are not suitable for ocean diving,

Not if you don't have the gear or skill to dive them. I do just fine. If you can't run with the big dogs, stay on the boat!

No excess gas in that drysuit. If I put the dump valve at the highest point and push the button, then no more gas comes out. That's what we use for weighting and buoyancy checks.

Wow. You really have no idea how heavy you'll be if you suffered a complete suit flood? You only plan for panacea diving all the time? Murphy's a hard assed sumbitch, and odds are you'll meet him someday. It can be painful, if not deadly if you're not prepared.

I have experienced major drysuit leaks.

Define major? Seawater might be neutral, but you won't be if you have a complete blowout. Been there, done that, shivered for a couple days. Glad I had a BC that could float me.

The problem with a "balanced rig" is that many define it in a way to make themselves appear to be a superdiver. If you can't swim it up with a full flooded drysuit and no air in your BC, then calling it balanced is nigh on to delusional. And murphy is sneaky, and patient. He springs his hijinks when you least expect it.