Negative Entries - A Bad Idea???

[PfcAJ]

Total suit flood and a wing failure is pretty unrealistic.

If you wing can float your rig without you in it, then it will certainly float you if your neck seal disintegrates.

 

[Nick_Radov]

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.

Not sure which exact tanks you're referring to. Pressed Steel and Faber (maybe other manufacturers as well) did manufacture some LP120s (2640 psi rated pressure, typically overfilled to 3000 psi) but they were seldom used outside of cave diving. LP120s are kind of ridiculous for ocean diving. You can only assemble a properly balanced doubles rig with them if you limit yourself to really high helium mixes in order to keep the back gas weight down.

The more common 120s we see are HP120s, either the older ones rated for 3500 psi or the newer E-7 series rated for 3442 psi. Those are smaller and have different buoyancy characteristics. But even so, you have to be careful about the gas weight.

 

[lostsheep]

I’m talking about the PST 3500psi HP120s used by one of your BAUE buddies.

 

[tursiops]

These dives I would class as sports diving not recreational.

CMAS says sport diving and recreational diving are the same thing.

2.1.62 “Sport diving” shall mean diving to a depth no greater than 40 meters, using only compressed air or Nitrox (with no more than 40% oxygen) as a breathing gas, never requiring a mandatory decompression stop and having direct vertical access to the surface from which an emergency swimming ascent is possible during an emergency. A synonym for sport diving is “recreational diving”.​

 

[Nick_Radov]

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

Actually, the OP did specify negative entries from a boat into a current. That is ocean diving. As for winning, I wasn't aware that I was even playing.

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!

Skill or lack thereof is not the issue here. You might want to ask Jane Orenstein, Andre Smith, Mike Elkins, and John Claypool about this issue. Wait you can't. Despite all having quite a bit of skill and experience they drowned while diving unbalanced rigs in the ocean. Lost buoyancy control, sank to the bottom, and couldn't get back up. Some of them were using double-bladder wings, which apparently didn't help.

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.

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.

I know how heavy I'll be. My BC can float me. I can also ditch weight, like we learned in OW class. I don't rely on my drysuit for lift.

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.

You do not understand the definition of a balanced rig. Ditchable weight forms one essential component of the overall system. In ocean diving, if you suffer a complete loss of all lift then you should be able to ditch enough weight to get close to neutral with full back tanks. The beginning of the dive when your back tanks are full is when the risk of a wing failure is highest; later in the dive after you use up some gas it becomes less of a concern. After you ditch some weight, swimming up is no problem. Or ride your scooter up like I mentioned above.

Some highly experienced ocean divers go with no ditchable weight out of a misguided desire to be "slick". I don't think this is an optimal practice, although they can probably get away with it even in an emergency by using other techniques.

But how exactly am I going to end up with a completely flooded drysuit and a failed wing simultaneously? Like seriously what is the scenario? A shark attack or something? At some point you have to either play the game or stay home.

Anyway, I'm far from being a super diver: mediocre at best. Because I am not particularly skilled, I try to proactively prevent problems before they occur rather than subjecting myself to unnecessary risks or relying on convoluted solutions. If someone has a specific on-topic question, then I'll try to help but otherwise I'll bow out of the thread for now and you folks can dive as you please. Good luck.

I’m talking about the PST 3500psi HP120s used by one of your BAUE buddies.

As mentioned above, those are smaller and have different buoyancy characteristics than the old LP120s. It is certainly possible to have a balanced ocean diving rig with steel 120s of either flavor plus a drysuit, especially for larger divers. You just have to be careful about what gas mix you fill: with air or nitrox and a full fill you have 18 lbs of gas strapped to your back which isn't ideal but put in 30%+ helium and it becomes more reasonable.

 

[lostsheep]

As mentioned above, those are smaller and have different buoyancy characteristics than the old LP120s. It is certainly possible to have a balanced ocean diving rig with steel 120s of either flavor plus a drysuit, especially for larger divers. You just have to be careful about what gas mix you fill: with air or nitrox and a full fill you have 18 lbs of gas strapped to your back which isn't ideal but put in 30%+ helium and it becomes more reasonable.

lp120S...larger divers...

SMDH

SCUBA Cylinder Specifications – Huron Scuba, Snorkel & Adventure Travel Inc. PADI 5 star IDC in Ann Arbor, MI

huronscuba.com

 

[rjack321]

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).

This might come as a surprise but double 130s are one of the most popular sets of doubles in the GUE-BC and GUE-Seattle communities. Hp100s are probably close to tied with the 130s. Hp119s least popular and a clear 3rd. Even with 32% its max 18lbs of gas and between fins and the drysuit not a big deal to swim up with a failed wing.
Most doubles users in WA and BC are either recreational or Tech1 and not technically qualified to use bottom stages.

As a general rule, with the advent of scooters the sites where negative entries are actually performed around here is close to zero. Negative entries are not required or even helpful at even our most current sensitive sites (eg the SS Governor or Tacoma Narrows bridge center sections come to mind)

 

[The Chairman]

they drowned while diving unbalanced rigs in the ocean.

If only they had a double bladder!!!

I can also ditch weight,

How do you need weight with twin steels?

But how exactly am I going to end up with a completely flooded drysuit and a failed wing simultaneously?

Give my regards to Murphy when you meet.

I am not particularly skilled,

Now I understand why you don't dive 130s.

Again. You dive you and I'll dive me. You may not understand how I dive and I'm OK with that.

Actually, the OP did specify negative entries from a boat into a current.

Actually, he never mentioned "boat" in his OP. Stop inventing crap. There are lots of currents in springs and there's at least one spring we overweight by 5/10 pounds to make descent easier.

 

[NW Dive Dawg]

CMAS says sport diving and recreational diving are the same thing.

2.1.62 “Sport diving” shall mean diving to a depth no greater than 40 meters, using only compressed air or Nitrox (with no more than 40% oxygen) as a breathing gas, never requiring a mandatory decompression stop and having direct vertical access to the surface from which an emergency swimming ascent is possible during an emergency. A synonym for sport diving is “recreational diving”.​

I guess I must be missing something here in this statement.

I'm thinking that a dive to 40 meters on 40% would be a bad idea.

I personally have always used a MOD of 111ft on 32%..... and even with that I add in some additional safety and pretty much as a personal rule do not exceed 100ft on 32%.

 

[tursiops]

I guess I must be missing something here in this statement.

I'm thinking that any dive to 40 meters on 40% would be a bad idea.

They are simply defining sport diving as less than 40m, less than 40% O2, no deco, and no overhead. Break any of those constraints, it is not sport diving any more.
Or maybe you were trying to make a joke?