Should I switch to BP/W?

[JeffG]

AFIAC, Jeff can go worship his 'balanced rig' if he wants. My question would be how did he quantitatively determine how much thrust he can deliver under what conditions for what period of time?

You are too much. Are you an Engineer?

 

[-hh]

You are too much. Are you an Engineer?

One would think that a 'Computer Dweeb' would have checked profiles before asking.


EDIT:

Sorry, that's a bit harsh. Yes, I'm an Engineer and it is profoundly frustrating at times to see divers prefer opinions and beliefs over cold, hard physical facts.



-hh

 

[JeffG]

One would think that a 'Computer Dweeb' would have checked profiles before asking.


EDIT:

Sorry, that's a bit harsh. Yes, I'm an Engineer and it is profoundly frustrating at times to see divers prefer opinions and beliefs over cold, hard physical facts.



-hh

I would of checked profiles, but a) I wanted that text in there and b) My post jumped to another page that only had my post, so your profile wasn't on that page and I was to interrupted at work to go back and check.

 

[Doc Intrepid]

You type on ScubaBoard at WORK?

 

[JeffG]

You type on ScubaBoard at WORK?

Yep...and charge them $150/hr too. I have my laptop for surfing, and a PC for programming. Less filling, tastes great.

 

[GreenDiverDown]

Leaving the rig behind scenario's occur primarily because the diver's ditchable vs non-ditchable ballast percentages were poorly planned, or not planned at all.

The basic premise of 'balanced rig' is the belief that you're going to be able to swim up from max operating depth if you have a catastrophic BC failure and no redundency, usually because you've minimized your weighting. Its also sometimes claimed to describe trim, but that's pragmatically irrelevant here.

Yes, minimizing your weighting is generally a good thing, but consider a diver in a coldwater FJ wetsuit: he's going to have around at least 10lbs worth of wetsuit compression by 100fsw, plus he will have at least 6lbs (AL80 or larger) worth of air virtually regardless of any other factors regarding the dive.

As such, if he were to have a BC failure immediately upon reaching the bottom, he's at least 16lbs negative, and if he can't generate at least 16lbs thrust for, say, two minutes, if he doesn't have lift redundency, then he's stuck on the bottom until some form of aid arrives (buddy, etc)...

...or...

...he ditches ballast. Either enough such that he's either now buoyant (not particularly desirable) or enough such that his remaining negative buoyancy can now be overcome by the amount of thrust he can deliver for the required time period.

There is no doubt that a controlled ascent is always better than an uncontrolled one, but what is being overlooked is that an uncontrolled ascent isn't the worst possibility here: what is worse than an uncontrolled ascent is NO ascent.

I'm sorry, hh, I'm not following your logic. All of the examples that you cite are of rigs that are not balanced. As such, your argument now seems to support what you originally were against.

Likewise, I see nothing here that would support the recommendation to cut off and leave behind one's gear.

At lastly, what does anything here have to do with the crotch strap?

AFIAC, Jeff can go worship his 'balanced rig' if he wants. My question would be how did he quantitatively determine how much thrust he can deliver under what conditions for what period of time? Afterall, if we've not tested ourselves to determine for sure what level of physical performance we can deliver in a time of need for how long, then all of this contingency planning has just become sabotagued by a single "Trust Me".
-hh

It's really not that hard to figure out. One doesn't even need to pick up a pencil. But you do get to get wet!

BTW... you have some very nice photos on your page. You must be a left-hand dominant engineer!

 

[JeffG]

It's really not that hard to figure out. One doesn't even need to pick up a pencil. But you do get to get wet!

Thats not what they do. They want to know where Jupiter is so that they can adjust their calculations on how the gravitation field changes the required adjustment to the BCD for neutral buoyancy.

 

[GreenDiverDown]

Thats not what they do. They want to know where Jupiter is so that they can adjust their calculations on how the gravitation field changes the required adjustment to the BCD for neutral buoyancy.

Duh! But you have to look for Jupiter when it's raining.

 

[-hh]

I'm sorry, hh, I'm not following your logic. All of the examples that you cite are of rigs that are not balanced. As such, your argument now seems to support what you originally were against.

Then what's your definition of a balanced rig?

As for me, hearkening back to my original premise of "diving naked", diving with no thermal protection is the only common dive configuration where you don't have any compressible thermal protection -or- compressible air bubble under a drysuit, which means that the Diver's total volume is unchanging, so the only source of "Diver as a System" density changes is the change of mass of the air in his tanks.

If we want to define a balanced rig as one that achieves neutral buoyancy at all times without adding air to the BC, then even this one doesn't qualify.

But if we want to define a balanced rig as one that can be close enough at all times to neutral buoyancy so that the diver can then swim up in the event of a BC failure (which is what I'd call it), this system can be configured out to be no worse than 6lbs negative at the bottom while still avoiding becoming at all positive at the end/surface. As such, the assumption here is that 6lbs is acceptable because a diver is expected to be able to successfully generate 6+lbs of thrust sustained for the appropriate duration for the depth at hand.

While that's a fairly reasonable assumption IMO, it is still an assumption and personally, I have made dives with buddies who were not capable of having this level of sustained physical exertion (before one jumps to any conclusions about poor fitness, you're off base: Leo was a double-amputee).

The slippery slope happens as soon as we add any thermal protection, becuase this must increase the air bubble in our BC system at depth because nearly all thermal protection systems are not non-compressible, which means that whatever value that swimming thrust requirement ends up being is higher.

It's really not that hard to figure out. One doesn't even need to pick up a pencil. But you do get to get wet!

True, and the basic "problem" here goes back to an old Engineer's adage: "If you don't have data, then all you have is an opinion".

When does it become too high? People are welcome to their opinions, but only so long as they don't misrepresent them as 'facts'.

As for me, if I have a loss of BC bladder @ depth, I'll most certainly try to swim it up. Simiarly, I'll also try to avoid ditching the $5000 I have invested in my UW camera. But as I was taught, "Weightbelts are cheaper than a Casket", which I've since learned that it really means that the risk of DCS is preferred to drowning. I'm sorry if I sound so morbid about this, but diving is never risk-free (despite all the pretty glossy ads), and respect for the hazards of the environment has kept many of us alive in said environment for a long time now.

Likewise, I see nothing here that would support the recommendation to cut off and leave behind one's gear.

I don't think there is one. As far as I'm concerrned, if you have to cut off your gear, it had better have been because it was entrapped in a wreck or something: a diver who fails to configure his gear with sufficient ditchable weight deserves to die in it - - assuming that his stupidity doesn't increase my insurance rates or in any other way inconvenience my diving.

At lastly, what does anything here have to do with the crotch strap?

Its normal topic creep. The OP, a Jacket BCD user, asked about BP/W's and trades, and then specifically about the crotch strap. I stated that IMO the WB should go over the crotch strap to assist in WB ditching contingencies, which lead to a disagreement over proper protocols. This has then spun into claims that the 'balanced rig' concept of configuration makes the need for contingencies that require positivfe buoyancy on the bottom to be irrelevant. This has then lead to two uncalled-for personal attacks from JeffG.

BTW... you have some very nice photos on your page. You must be a left-hand dominant engineer!

Thanks. I'm physically a righty, but I'm left-eye dominant, which is a strength for photography as well as Design, but it does make it a royal nuisance to shooting weapons.

FWIW, I'd like to see the flammage on this thread subside (I don't like hitting the "Report to Moderator" button) and get elements of this discussion tangent answered: I'm personally very interested to see if Bob can learn from NAUI as to precisely why their training did a literal 180 on this particular over-vs-under element, or if its a training void (I'm very much hoping that the answer's not that Bob has not been following standards). If it has indeed changed, I'm very interesting to hear what their logic is for justifying the change. There might be a case to be made, but the DAN reports frequency with which dead divers are found still wearing their weightbelt is a sobering statistic that doesn't go away with hand-waving.


-hh

 

[DA Aquamaster]

There are two points of view developing here.

One is a very logical approach based on observation and thoughtful consideration of what is done and why it should or should not be done that way.

The other approach is a more authoritarian and indoctrinated response based on some another person or persons who used a logical and thoughtful approach in the past to develop solutions to the problems being discussed.

There is room for both approaches and a lot of learning can occur from a respectful discussion of the differences in the opinions expressed here. Geroge Bernard Shaw once stated that all progress occurs due to unreasonable people who are not willing to accept the way things are currently done. So there is plenty of room for debate and differing opinion, especially by people who may regard each other as "unreasonable".

However, there is no room for character assassinations or disrespectful comments about other people's opinions, even if they are considered to be cute or funny by their authors. If posters in this thread are not able to stay on topic and refrain from personal attacks, it's going to have to be moderated pretty heavily.

Let's please keep it freindly in here.