In an article in Scuba Diving mag, they mentioned as a problem with deep dives a concept I have heard before, but have yet to understand the physics of. Namely Self-propagating negative bouyancy at depth.
Lessons for Life
1 Deep diving requires proper training, planning, topside support and gear. Divers need a larger gas supply, high-performance regulators and high-capacity BCs.
2 Extra Weight is dangerous on a deep dive. The compression of wetsuits and BCs compounds negative buoyancy. At about 200 feet, negative buoyancy is self-propagating.
3 Rapid Descents aggravate nitrogen narcosis. The maximum safe descent rate is 70 feet per minute. Pauses allow the body to compensate for the increasing pressure.
Can anyone explain what is meant by the last sentence of item #2?
roturner
September 12th, 2003, 02:11 PM
indiana*joe once bubbled...
In an article in Scuba Diving mag, they mentioned as a problem with deep dives a concept I have heard before, but have yet to understand the physics of. Namely Self-propagating negative bouyancy at depth.
Lessons for Life
1 Deep diving requires proper training, planning, topside support and gear. Divers need a larger gas supply, high-performance regulators and high-capacity BCs.
2 Extra Weight is dangerous on a deep dive. The compression of wetsuits and BCs compounds negative buoyancy. At about 200 feet, negative buoyancy is self-propagating.
3 Rapid Descents aggravate nitrogen narcosis. The maximum safe descent rate is 70 feet per minute. Pauses allow the body to compensate for the increasing pressure.
Can anyone explain what is meant by the last sentence of item #2?
It probably means that a typical inflator can't put air in a BCD fast enough to overcome the increasing compression of a sufficiently quick descent at that depth. I dno't know how fast you would need to be descending for that to happen but I would venture that it's very fast. I wouldn't lose any sleep over it.
R..
CD_in_Chitown
September 12th, 2003, 02:25 PM
Consider this, a buddy of mine descending with us to 110fsw in blue water decided to race us down and doesn't start adding air until 100fsw or so. When he got to the bottom it looked like a bomb had gone off (mushroom cloud) because you can't wait that late to add air. That's rate of descent problems, I'm not clear what the 200fsw mark means in this context but the rate at which you cannot overcome negative buoyancy would have to be shallower than that I'd think.
Now on a hard-bottom dive in safe rec. depths that's not such an issue (you will stop at the bottom). I had another buddy descend on a wall in Honduras (swears he was adding air by 75fsw) who couldn't stop his descent until 153fsw, with no bottom in site. I wouldn't lose any sleep over it, but I'm aware that it does have pertinance to me.
Chris
pdoege
September 12th, 2003, 02:50 PM
As you go deeper your wetsuit and BC compress and lose bouyancy, so you become more negative and go deeper, wash rinse repeat.
200 feet is sort of deep to be dive bombing anyway.
I did talk to a guy once who used a dual bladder wing and a drysuit. He claimed to be able to dive bomb down to 220' and then hit the brakes by inflating all three items at once.
Silly thing to do, but there you have it.
Peter
indiana*joe
September 12th, 2003, 03:48 PM
Assuming pressure in the bc to be equal to ambient pressure, at 200fsw does it take any more volume (bc) to get to neutral than at 100fsw. Beyond 60fsw I would assume that even a 7mm is not going to change significantly in bouyancy and a drysuit should maintain shape (because of added air) in either situation. Or even assume skin (brrrrrrrrrr!) Everything else being equal - only a change in bc volume - does it take more volume to counter the weight of the object at depth or not? Do you have to displace the entire column above the object or just the volume of the object itself. (Must have been asleep in physics that day.....)
divermasterB
September 12th, 2003, 04:07 PM
indiana*joe once bubbled...
Beyond 60fsw I would assume that even a 7mm is not going to change significantly in bouyancy and
A 7mm farmer john can add about 15 lbs of buoyancy over a naked diver (takes 15 lbs to sink just the suit) at the surface. Roughly you could say it takes 7 lbs to sink at 33, 5 lbs at 66, and 3.5 at 100 ft.
So, a diver diving to 100 ft, in a 7mm and not adding air to the bc will need to compensate for an 11 lb shift in buoyancy over that 100 ft.
All of these numbers are of course approximate.
a drysuit should maintain shape (because of added air) in either situation.
That is assuming adding air, plus, the affects I am talking about are even more pronounced in a drysuit, if the diver does not add air.
Or even assume skin (brrrrrrrrrr!) Everything else being equal - only a change in bc volume - does it take more volume to counter the weight of the object at depth or not? Do you have to displace the entire column above the object or just the volume of the object itself. (Must have been asleep in physics that day.....)
The weight of an object in water is it's weight on land minus it's buoyancy (determined by calculating Volume (ft3) * 64 lbs/ft3).
To make that neutral you will need a volume of air to displace a weight of water equal to the neutral weight of the object. So we know sea water is 64 lbs/ft3 you can calculate it...
roturner
September 12th, 2003, 04:25 PM
indiana*joe once bubbled...
Assuming pressure in the bc to be equal to ambient pressure, at 200fsw does it take any more volume (bc) to get to neutral than at 100fsw. Beyond 60fsw I would assume that even a 7mm is not going to change significantly in bouyancy and a drysuit should maintain shape (because of added air) in either situation. Or even assume skin (brrrrrrrrrr!) Everything else being equal - only a change in bc volume - does it take more volume to counter the weight of the object at depth or not? Do you have to displace the entire column above the object or just the volume of the object itself. (Must have been asleep in physics that day.....)
Well, in a way yes. If you have a kg of negative buoyancy (equal to one litre of water more or less) at the surface then you have to add 1 litre of air to your BCD to counter it. At 200 ft that's about what..... 7 ata or so .... so even though you have to add 1 litre of air to your bcd, it's compressed so you're acutally needing to pump 7 litres of air out of your tank and into your bcd.
Is this what you're after?
R..
Don Burke
September 12th, 2003, 10:36 PM
indiana*joe once bubbled... In an article in Scuba Diving mag, they mentioned as a problem with deep dives a concept I have heard before, but have yet to understand the physics of. Namely Self-propagating negative bouyancy at depth.
Lessons for Life
1 Deep diving requires proper training, planning, topside support and gear. Divers need a larger gas supply, high-performance regulators and high-capacity BCs.
2 Extra Weight is dangerous on a deep dive. The compression of wetsuits and BCs compounds negative buoyancy. At about 200 feet, negative buoyancy is self-propagating.
3 Rapid Descents aggravate nitrogen narcosis. The maximum safe descent rate is 70 feet per minute. Pauses allow the body to compensate for the increasing pressure.
Can anyone explain what is meant by the last sentence of item #2?
I think the writer is trying to say that the deeper you go, the more things compress. Every object put in the ocean does this to some extent. If you don't keep adding gas to the BC on the way down, you'll accelerate until you slam into the bottom, go below where the IP of your regulator can overcome sea pressure, ox tox, or get so narked you forget how to operate your inflator.
I don't know what is so magical about 200 feet. About half of the buoyancy loss is in the top 33 feet.
At 200 feet, you are dealing with about 88psig of sea pressure or 7atm, which will take quite a bit of the buoyancy out of anything made of neoprene. The volume of gas (as expressed in SCF)required to make substantial changes in what lift the BC is providing increases with sea pressure, so it would be best to be adjusting your BC all the way down.
I disagree with the high capacity BC statement.
Your BC needs to overcome the gas in your tanks, neoprene compression and the full in-water weight of any stage/deco bottles you are carrying.
If you are wearing double 131s, that's about 16 pounds. Stage bottles will only add about two pounds each. I'll call it 20 pounds so far.
If you are wearing a wetsuit that is 20 pounds positive at the surface, it will be a little more than 10 pounds positive at 33 feet and a little more than 5 pounds positive at 100 feet (foamed neoprene doesn't compress quite as much as a free bubble). That means it only has five pounds to lose below 100 feet, so "larger BC for deep" doesn't wash. If it needs to be big, it needs to be big shallow too.
Since you weight for a shallow depth, say 10 feet, the wetsuit will be about 16 pounds positive, so the change is actually from 16 pounds at 10 feet to about 3 pounds at 200 feet for a swing of 13 pounds.
20 plus 13 comes to 33. Allowing for safety factor, a 55 pound wing will do it for this dive even if your stages are quite a bit heavier than the 2 pounds I used.
Incidentally, if you held a gun to my head and told me to make this dive, I'd tell you to go ahead and shoot.
Scuba_Vixen
September 13th, 2003, 05:09 AM
That in a dual bladder BC, you can inflate both bladders for more bouyancy! That's Absolutely False. Either bladder can inflate to fill the entire space within the wing. There are 2 of them for redundancy only, incase one fails, or the reg to that inflator has to be valved off. If you inflate them both, you'll likely rip the wing apart. OK next issue..
You're power inflator inflates your wing at the same rate (in effective volume per time) no matter what depth..... That's what the regulator is for..it supplies air at the ambient pressure, plus the IP (usually 135# to 150#) This means if you're 10# negative at 30' or 10# negative at 300', your bc will correct in the same time at either depth. If you're at 200' and need 7 times the air, you get it because the reg is giving you 7 times the surface pressure, plus the ip. OK, next issue...
The whole story is an excercise in sensationalism, speculation, and scare tactic. Any modern regulator in reasonable condition will work at 200'. He couldn't have equalised if he was descending as fast as the story tells, and would have stopped the descent because of the pain early on. Here they are, going down like cannon balls, pain like you could only imagine, and they keep on going, ... gimme a break.....You can make a controled descent to 200' and spend 4 minutes of NDL and work back up a wall maintaining a no stop dive, and still swim around the reef on top the wall for a while, all on 1 Al 80. That self propagating negative bouyancy thing while it may sound impressive and profound, is poetic license for the story, but otherwise pure crap. If there were anything to it, I couldn't be posting this. If wetsuits are suicide for deep diving, then hummingbirds and bumblebees can't fly, and I'm posting from beyond.
I'm not suggesting they weren't doing something stupid, or that it was ok to do, it's just that No One is that effing stupid. I mean Darwin Award candidates here......Which is what makes me think the story is either fiction to scare you out of doing dumb *shinola*, or an actual accident that's been turned into a full blown "urban legend".
Sorry for getting into such a rant, I just believe divers need clear facts and true information, and they can think for themselves. If you can't dazzle me with brilliance, don't try to befuddle me with B___ l S___t ......
Darlene
japan-diver
September 13th, 2003, 06:01 AM
Have to agree with no wetsuits for deep dives come on!!! Had my wetsuit on plenty dives beyond 180fsw with no problems. But then again the water temp yesterday was 87F!!
Dryglove
September 13th, 2003, 11:58 AM
At what depth would a wetsuit compress to its max and no longer be affected by the pressure as it is compressed to its max. Lets just use a 7mm as an example.
The reason i am asking if a wetsuit is fully compressed at lets say 90ft what difference would it make if you used at 150ft if it is already fully compressed at 90ft. It shouldnt affect your buoyancy a whole lot more.
I dive a trilam drysuit so i dont have to deal with all the wetsuit isues with losing buoyancy. :D
Scuba_Vixen
September 13th, 2003, 12:36 PM
once I get past about 60', and it's not much of an issue after 40 or 50...and that's a fairly new 7mil SP S-Tek. I have a custom Body Glove in 5mil, and that's not noticeably different much past 30 to 40. Even on reef dives, both are just Non-Issues ... I add between 8 and 10 pounds for the 5 or 7 based on what I use for a 3mil. Both have been in that 300' range many times....the water temps here are in the 80's to upper 80's all year long (it's not that much colder, even very deep, I've welcomed the cooler depths often, it was so warm above). As long as you're comfortably warm at depths where the suit is compressed,... Wetsuit compresion as an issue on deep dives is a load of dung that some folks shovel to push dry suits, there's no other logical rationale. Exposure protection is there to keep you warm, if what you have does that, that's all that you need. You wear a BC to take care of the bouyancy issues.
Darlene
Dryglove
September 13th, 2003, 12:48 PM
Scuba_Vixen once bubbled...
once I get past about 60', and it's not much of an issue after 40 or 50...and that's a fairly new 7mil SP S-Tek
That answered my question. If your wetsuit is fully compressed at 60ft its gonna have the same buoyancy characteristics at 150ft.
People make it sound like the deeper you go the more buoyancy your gonna lose due to your wetsuit compressing. But if your wetsuit is fully compressed at 60ft theres not much to lose. The main thing as you have stated is that you are warm and have a bc with enough lift to offset the wetsuit compression and being properly weighted.
Don Burke
September 13th, 2003, 02:40 PM
lal7176 once bubbled... That answered my question. If your wetsuit is fully compressed at 60ft its gonna have the same buoyancy characteristics at 150ft.The answer you got was "not much of an issue" not "fully compressed".
I have a heck of a time figuring out what is compression of my wetsuit and what is compression of the bubble in my BC when it comes to buoyancy.
I also have a heck of a time figuring out what is compression of my wetsuit and what is thermocline when it comes to thermal performance.
Below about 40-50, put me in the "not much of an issue" category. Then again, my current wetsuit is getting pretty old.
lal7176 once bubbled... People make it sound like the deeper you go the more buoyancy your gonna lose due to your wetsuit compressing.That was one of the themes of the article. The author greatly overstated the problem and then expanded on that.
I endorse the statement, "The whole story is an excercise in sensationalism, speculation, and scare tactic."
lal7176 once bubbled... But if your wetsuit is fully compressed at 60ft theres not much to lose.If the wetsuit was fully compressed, there would be nothing to lose.
In practical terms, the difference between a wetsuit at about 50 feet and the same wetsuit at 200 feet gets lost in lung volume and changes in water density due to temperature. It doesn't fully compress.
lal7176 once bubbled... The main thing as you have stated is that you are warm and have a bc with enough lift to offset the wetsuit compression and being properly weighted. The same pressure that takes the buoyancy also reduces the R-value. It has to be pretty warm to be doing deep wetsuit dives of any length. The people who dove the Andrea Doria wet were nuts IMO.
One of the things that was brought up was the concept of doing a screaming descent to get more bottom time. The difference between 60fpm and 120fpm doesn't come to very much bottom time. It's false economy.
The big BC was to be used as a dive brake or lift bag. I think those are also bad ideas. There are better ways to accomplish both things.
Scuba_Vixen
September 14th, 2003, 02:54 AM
I can relate some of the things that irritate me so much when I see those piles of horse feathers, that seem so easy for the average diver to believe. I live on an island in the caribbean, we have a dive location that is touted as the closest to shore true wall of anywhere in the world. It's a couple hundred yards out from a nice beach with a diveshop and beachbar and grill. (several of them in a row, actually) The top of the wall is a deep spur and groove formation, big coral heads with sand chutes between like canyons.They slopedown from about 50' to 80' depth. At the 80 to 90' point, you're looking down the steep slope of the wall. It looks like it goes endlessly down into the blue. Your natural assumtion is that it's a steep sand and plant life slope all the way to God knows where. The depth between here and the next island north (about 40 miles away) is 13,000' plus. It's truely some wonderfull diving. The water temp runs about 85F and vis is 80 to 100' average, sometimes close to 200'. It doesn't take any great level of advanced training to dive the wall, if you pay attention to your gages and set realistic depth limits based on skill and experience, you'll be fine. There are Very few mishaps, and most tend to be minor. While you might expect divers to get bent a lot because of the depths available, it doesn't happen.
Unfortunately.... It seems every few years, we loose a diver (or 2) to stupidity...alcohol and/or testosterone are usually involved somewhere.
And they never had to try to get a DO to take them out there, or charter a small boat from college kids, and they never hatched the hokey idea to try to go down like a crate of cannon balls..... Now tell the truth, how many of you that read the story said to yourselves, "what morons, I'd never do anything that stupid!" ....
My point Exactly, you all did. That's what made the story not apply to you, and feeling safe from the same mistakes they made, you read on out of amusement, actually loosing the real warnings of risk of diving too deep. (relative to skills, training, equipment, and conditions)
Divers get into trouble for two reasons:
#1 is they Overestimate their ability, and
#2 is they Underestimate the requirements of the dive
Either way, what you don't know can kill ya.
Now getting back to the real life eqivalents to the guys in the story.... As you go out over the wall, when vis is quite good, you look down and it looks like an open elevator shaft way down below. It looks about 10 yards diameter, and "not that much deeper to get there or take a closer look" It's like a syren of the deep calling suseptable divers. Actually, at 220' on air, it looks like you're almost there, maybe 50' more to go. Our guys aren't about to die yet, so they ascend and after a few beers and burgers on the surface interval, decide to dive the hole. Neither has had nitrox training where they would have learned about O2 toxicity at depth ... all that PO2 stuff and CNS hits and such. Both are young and strong and are used to the buzz off a 6 pack, woooaaaa, who can't handle a 6 pack and still drive....I bet every one of you know one of these guys, some see him in the mirror in the morning. But off they go, down the beach into the water for their last dive, not that they have that thought yet though. But, hey, when you're not gonna get narc'd, or if ya do, you can handle it easy, then what's to go wrong!
Well, you can see where these guys are gonna end up, either narc'd into semiconsciousness and airing up a bc and doing the polaris missle ascent, or drowning after the cns hit and never being recovered.
The really bothersome thing about the guys we loose here, is that they are about like most of the rest of the newer, less skilled/experienced, but eager beaver guys we see diving all around us. Trying to scare people into changing their behavior seldom works, (at least in a slasting manner) in example, I give you the gory movies from drivers ed or defensive driving class.
What saddens me most, I think, is that there are still a lot of guys flirting with diving the hole, I get them every so often as I gear up or I'm rinsing off after at the shop there, tell me how deep they went, or what it's like inside, or to see it close up. I smile, shrug, and suggest more training and proper gear. If I tell them what's really there, they'll know I know they lied/exaggerated grossly...and then they'll really try to go there and see if I'm putting them on.
Anyway, thanks for letting me ramble on, Just don't call me Sea Jay, his rambles are wayyy better than mine. But if I make someone rethink a foolish dive, I've accomplished something positive. I doubt anyone rethought anything from that tabloid scare tale. Maybe next ramble I'll tell ya what's really down there, it's wayyy more awesome.
Darlene
divermasterB
September 15th, 2003, 08:47 AM
lal7176 once bubbled...
At what depth would a wetsuit compress to its max and no longer be affected by the pressure as it is compressed to its max. Lets just use a 7mm as an example.
The reason i am asking if a wetsuit is fully compressed at lets say 90ft what difference would it make if you used at 150ft if it is already fully compressed at 90ft. It shouldnt affect your buoyancy a whole lot more.
I dive a trilam drysuit so i dont have to deal with all the wetsuit isues with losing buoyancy. :D
At what pressure is Nitrogen "Fully compressed"? The gas in the suit is responsible for the compression.
ew1usnr
September 15th, 2003, 09:07 AM
DeepTechScuba once bubbled...
Wetsuits are definitely NOT technical gear. Diving deep with a wetsuit on is russian roulette, if not suicide.
You just ain't "tech" without a dry suit.
roakey
September 15th, 2003, 10:41 AM
ew1usnr once bubbled...
You just ain't "tech" without a dry suit.
Yhea, I was wondering about that quote too. Little did I realize that being a couple thousand feet back in a cave wasn't technical because I was wearing a wetsuit..
Roak
Scuba_Vixen
September 15th, 2003, 04:36 PM
"At what pressure is Nitrogen "Fully compressed"? The gas in the suit is responsible for the compression."
Really comes thru when you figure the suit is compressed to a point where there's maybe a pound or so more bouyancy that could be squeezed out of it at near infinite depth by the time you get to about 60 feet or so. For all Reasonable intents and purposes, That's Fully Compressed. If you are properly weighted, and have a properly sized wing...and you can stay neutral at 60', then you can be neutral at 160', or 260'. Argueing over that small a bouyancy change is no more intelligent than saying a nitrox blend has to be accurate to less than one tenth of one percent.
DeepTechScuba once bubbled...
Wetsuits are definitely NOT technical gear. Diving deep with a wetsuit on is russian roulette, if not suicide.
How about giving us some supporting facts and a connected series of statements to validate that conclusion........ Or did you just swallow the whole shovel load.......
I wouldn't suggest wetsuits for most deep or technical diving, but they do have there niche.
Darlene
Marvintpa
September 16th, 2003, 08:19 AM
Earlier in this thread someone put forth the ideas that:
1) inflating both bladders in a wing at the same time would not increase buoyancy and was therefore erroneous to the discussion
2) ear pain caused by a rapid descent would cause the dive to be aborted, and this entire issue was just journalistic sensationalism
To respond:
1) A diver wearing doubles who has correctly configured them to operate from separate posts will manage to fully inflate FASTER than someone inflating only one bladder (the final amount of buoyancy will be the same, but the speed to attain it will be different) and the issue in question was arresting descent in a hurry, which this would address.
2) Free divers in the "unlimited" class ride a weighted sled to 500' at speeds greater than it's possible to descend with scuba gear, which would seem to suggest that clearing ears is not an issue (sure, some freedivers purposefully flood their siunuses to avoid some of these issues, but not all)
Scuba_Vixen
September 17th, 2003, 02:38 AM
is indeed possible, and would be faster ...by what, 3 or 4 seconds to max inflation!.. A whopping 10 feet max at a 120' /min plus descent rate. .. And at a risk of damaging the bc and failure..only room for 1 fully inflated bladdder in there, how do you know when both are half inflated and it's time to stop. The notion of inflating both simultaneously for any legitamate reason is just Nuts. No agency that condones redundant bladders also condones simultaneous inflation, nor do the manufacturers.
"2) Free divers in the "unlimited" class ride a weighted sled to 500' at speeds greater than it's possible to descend with scuba gear, which would seem to suggest that clearing ears is not an issue (sure, some freedivers purposefully flood their siunuses to avoid some of these issues, but not all) "
Gimme a break, that's apples to oranges if ever there was such a comparison, the Darwin candidates in the story weren't even as wise or experienced as the average AOW diver. I bet there's not a diver here that doesn't have to clear going down, and experience increasing pain as they descend if they fail to do so.
The story just isn't good journalism, it's a tabloid scare feature, and has no place in a dive publication.
Darlene
japan-diver
September 17th, 2003, 02:57 AM
Since one body was never recovered we don't know exactly what happened and the writer tried to propose a possible scenario. I have certitifed many students who could equalize quite easily and could drop very quickly. Also freedive quite a bit - though not to 400 ft - and can drop at over 120ft/min and have chased a few divers over edges and down at faster rates while divemastering.
A new diver such as these decending rapidly and being narced may not even notice pain in the ears, so ear pain stopping the dive isn't a valid theory.
We had a similar accident here a few years ago that resulted in a couple dead and couple bent while new divers tried to find the bottom of one of the dead walls around here. Divers plummenting a couple aborted but two continued down and bodies were found at over 150ft and 200ft.
The story I think was presented to make a point and that I think it did, I don't find the facts that out of porportion to what may have actually happened.
BrendanC
September 18th, 2003, 03:33 PM
Dual bladders, dual inflators, dual posts. . .it always seemed way too complicated to me. I've used a wet suit and doubles and single wing and been fine. Of course, the doubles have to be aluminum 80's; there's no way you'd get me in a set of big steel doubles with a wetsuit on.
I've seen some pretty interesting failures with BC's. One of my favorites was the first stage failure that led to a BC autofilling. With a single bladder and single inflator, the solution was simple: dump gas out of the lower dump while shutting down the reg that failed. Add another bladder, inflator, and butt dump, and you've got a heck of problem on your hands.
I like the idea of having my buoyancy in one, easy to adjust location. If my wing fails, I have my weight distributed so I can drop some lead and swim on up.
B.
indiana*joe
September 18th, 2003, 04:00 PM
I have been amused at reading all of the sentiment expressed. I was looking for the facts. I have not read anyone stating that an object is any less bouyant at depth (barring compressed air spaces) so, the only factors is compression. So, divermasterB appeared to be focused on what was actually happening. The suit compresses, giving a bouyancy swing of 15+ lbs. The other "facts" are that the air in the BC compresses at the diver descends so, in theory, a "weak" inflator assembly "could" find itself in a situation where the air being delivered to the BC (at ambient pressure as one post made it plain) is actually being compressed as fast or faster than the next volume of air can fill the space caused by the compression. That sounds too confusing.
A. 1 ml of air is placed in the BC at ambient pressure creating 1ml of volume.
B. Diver descends 10-20 ft
C. Air delivered in A. is compressed to space X
D. Repeat cycle....
Does air delivered to the BC at 100fsw at ambient pressure compress to 1/2 its vollume at 133fsw? Does the little chart we learned about atmospheres reset as we are starting over each time with air at ambient pressure? If that is the case the above situation becomes more real. Otherwise, the air would not show any noticable decrease in volume over the 33' from 100 to 133.
So, the only 2 factors possible seem to be compression of the air in the BC and compression of any protective gear (BC or Dry - Drysuits are tough to inflate orally!)
Finally, to all who says that they would never attempt such a dive or say it would never happen to them, are only touting fate. There are such things as accidents, problems created by the situation, equipment failures, buddy problems, ad infinitum.....
I don't believe that anyone who finds themselves in a bad situation planned it. I hope to look at the reasons why things happen differently underwater than they do up here on land so if I happen to find myself there, I might have a better chance to react in a sensible and informed way.
Dive safe kids!
joe_at_subtidal
September 19th, 2003, 01:07 PM
The science is:
If we have a volume of 40 cuft at the surface, we'll have 10 cuft at 99' (4 ATAs) and 8 cuft at 132' (5 ata's), so the compression from is less than half.
JJT
Scuba_Vixen
September 19th, 2003, 10:25 PM
thrown in for good measure, Everyone basically concured that the concept of "self perpetuating negative bouyancy" is a total crock.
The "weak inflator" thing holds no logic, Any inflator fills the bc as fast at any depth as fast as it does at the surface. If it doesn't seem fast enough, you can do it orally, doing it orally at 200' is no harder than orally at the surface. The rate of inflation is NOT depth dependant.
"I like the idea of having my buoyancy in one, easy to adjust location. If my wing fails, I have my weight distributed so I can drop some lead and swim on up."
OK, so you drop some weight and start swimming up...Just about the point you get to your deco stops, your suit starts uncompressing and you're facing that polaris missle ascent. I'll have to pass on that skill.
If you have a blow-by on an inflator (bad 1st stage/stuck inflator/whatever), just disconnect the hose to it, With a redundant bladder, reach back for the redundant inflator (it's on the other reg, (dump the filled bladder) and do a safe, normal, in-control ascent on the redundant bladder. It may be a bit inconvenient, but it beats the snot out of a trip to the chamber.
Safe diving,
Darlene
Dryglove
September 20th, 2003, 12:46 AM
DeepTechScuba once bubbled...
Zeagle makes one, called The Big Bertha. Its lift capacity is 85 lbs. It is interchangable and fits onto any Zeagle B/C system.
Why do you need a bladder with 85lbs of lift. I suppose you dive this with a single tank too.
ew1usnr
September 20th, 2003, 06:38 AM
****Anti-flame preliminary disclaimer: I am not an expert and am not challenging anyone's expertise. The situation I am discussing applies to open water, non-technical diving. The concept discussed may not be in accordance with the philosophies of some or all dive instruction organizations."*****
Scuba_Vixen once bubbled...
If you have a blow-by on an inflator (bad 1st stage/stuck inflator/whatever), just disconnect the hose to it.
My inflator hose connects and disconnects very easy when there is no pressure in it. When it is pressurized its harder to get off. If the inflator is stuck in the fill position, and I'm going up while trying to yank the dump valve while also trying to get the disconnect off at the same time, its not fun, and its not especially simple.
Scuba_Vixen once bubbled...
Any inflator fills the bc as fast at any depth as fast as it does at the surface. If it doesn't seem fast enough, you can do it orally, doing it orally at 200' is no harder than orally at the surface.
Exactly. When I was certified we used manual inflators. Shortly after that I tried my first auto-inflator and thought that it was terrific. I've used them (for the most part) ever since. Now, at least where I live, you can't go on a dive boat without one. But, auto-inflators aren't perfect. I've seen mine and other people's screw up on a number of instances. They require maintenance, and even so, they can still malfunction. I am beginning to wonder if the risk that auto-inflators represent (through run-away inflation ) outweighs their convenience. If the inflator plug is capped, the inflator can be used manually, the inflator hose can be done away with, and the risk of inflator malfuntion is eliminated. If I want to go on a boat dive I can always put the inflator plug back in. My question is: Should the auto-inflator be regarded as an optional convenience item, or as a necessary safety item whose benefits far exceed its added liabilities?
Scuba_Vixen
September 20th, 2003, 12:17 PM
and as such, seldom are accorded the maintainance they deserve. To compound the problem, they are routinely dragged thru the sand, muck amd bounced off rocks and coral heads.
If you maintain your inflator as well as your regulator, you can expect an equally long and trouble free life. You wouldn't believe what the inside of a lot of Air2's look like when they come in for service.....and that's your backup regulator.
