WYDT once bubbled....
.....
2. Weighting for 15' kills close to HALF of a wetsuit's buoyancy. MOST of the compression happens in the first atmosphere, and half of that is, well, roughly 15'. Weighting for neutral at 15' with a heavy wetsuit is a VERY BAD IDEA, because if you accidentally exceed that ceiling on the ascent you will find yourself a half-dozen or more pounds POSITIVE - an in an unstoppable ascent. For this reason I consider the chestnut about weighting at 15' with 500psi of air to be dangerously incorrect. A low-on-gas situation is the last time in the world you want to be unable to maintain depth without heavy exertion (e.g. finning downward!)
Huh?? If you are at 15ft with NO gas in your wing and no gas in your tanks (I didn't say 500psi, I said EMPTY!) how long are you going to stay there??? You gonna do a deco stop with no gas?? I'd like to see that! Remember if you dropped your weightbelt (or other ditchable weight the sheet has hit the fan and you want to be up... If you have deco and are sharing on a buddy's tank you can easily do your last stop at 20ft.... that's where I do my last stops anyway and you aren't going to go blowing to the surface once you pass 15ft anyway....
Uh, excuse me, but the last 500psi is only about 1lb of buoyancy. Second, 500psi will last you a LONG time at 15'. I can probably stay there close to 25 minutes with that in an AL80 if I need to. That is, if I can just hang out, neutral and horizontal, without having to WORK! If I have to FIGHT to stay down then that 25 minutes will be more like FIVE minutes, and the latter might get me bent in a low-gas situation.
If I ditch I'm ditching on the SURFACE. Ditching at depth is, literally, a "last-ditch" choice (that or certain death.)
3. My 3 mil wetsuit is roughly a DOZEN pounds positive. Add a 5 mil shorty over that for springs or cold water and I add another 15lbs or so of required weight. Nothing I can do changes this - its the neoprene, not me!]
So your saying you need 27 POUNDS to sink a 3mm wetsuit and a 5mm shorty??? Interesting that I can sink a 7/5 with ~11lbs. How do you explain that??
Different wetsuits? I don't know, to be honest. What I do know is what it takes to sink my 3 mil (and booties) all on their own. I live on salt water and have tested this behind my house in two feet of water (with me NOT in the suit!), so I KNOW it is not trapped air or somesuch. I also know that I attempted to put a 5 mil over it and then dive in (cold!) fresh water and had to add about 10lbs more to get under! That got real cute as after the first 15' boy was I negative, and ascending that last 15' as slowly as I like got tricky as well, since the suit regained its buoyancy as I ascended. Took a bit of adjustment.
Now frankly, I think that 5 mil oversuit was too much; I will probably be buying a 5/3 (5 hood, 3 body) hooded vest to wear UNDER the 3 mil; that will likely require quite a bit less weight to sink overall, but its still quite a bit.
3.5 Ditching a canister or other device DOES NOT SOLVE THE PROBLEM of being unable to stop an ascent! The chestnut about carrying things you can throw away falls short for this reason.
The ONLY way your going to be out of control on ascent is if you are severly overweighted to begin with.... which you are since you're not a large person.... right??
No, I'm not a large person. 6', 185. I need just a couple of lbs to sink in a bathing suit. But the weight shift from a wetsuit looks to me to be unavoidable and something that has nothing to do with the type of material my tank(s) are made of.
4. My RIG is inherently about 9lbs negative (SS BP + STA).
5. If I dive an AL80, it is 4lbs positive empty. I must therefore have about 16lbs of TOTAL negative buoyancy to be able to meet condition (1) above. I add a couple more when spearfishing, because my gun is positive by about that much with the shaft out (and it is possible for me to foul it and have to cut it loose; I am willing to lose the shaft, but not the gun!) Ergo, my "usual" weightbelt has 9lbs of lead on it with an AL80.
6. PST says their HP100 is -1.4 empty. If I was to replace the AL80 with the PST100, I could therefore subtract about 6lbs from my belt. I would still have a belt on
7. If I DOUBLED HP100s, I'd be able to substract another 2lbs or so. I'd STILL need a pound or two, diving wet, with that 3 mil suit.
8. If I double AL80s, I need to ADD 4lbs more to my belt, because the second tank is ALSO positive when empty! That's no good either!
Your thinking too hard about this.... put the calculator down and go hit the pool... take weight off your belt and see...
The pool is fresh water (got one of those too.) Its easier to go out back and get in the bay (which is salt water) - and I've done so.
9. The swing in buoyancy from the AIR does not depend on the material the tank is made of.
So again, what's the argument against HP100s and FOR LP104s, when the latter are 15 lbs heavier OUT OF WATER, assuming you are NOT going to overfill them?
Here it is... your rediculous arguments aside...
More gratuitous insults. There's nothing rediculous about pointing out that what a tank is made of has nothing to do with the buoyancy shift that neoprene goes through as you decend.
1. You CAN overfill PST 104's, You CAN NOT overfill HP100's (if this part irritates you ignore)
If you say so. DOT says you can't, and there are rumors that this is going to become something that is cracked down on, especially here in cave country in Florida.
(Yes, I have heard the arguments about PST and Faber selling the "same" tanks in Europe with different ratings. Its not true, by the way - the "empty weights" differ in the two markets. Gee, how's that if the tanks are IDENTICAL?! Two things, identical, and one magically grows mass in europe?! That's a hell of a trick!)
2. You may not always be able to get a HP fill giving you no more than a set of heavy 80's in the case of HP100's. With 104's you still have 104cu ft. even with only 2640psi!!
I can get an HP fill anywhere around here, and I have no intention of lugging the tanks on vacations. Second, those HP100s are the same mass as an AL80 when you account for the buoyancy shift; ergo, even if you can only get them filled to 3000 psi they're no worse in actual mass than an AL80. Next argument please; this one holds water as well as a sieve.
3. 104's are MUCH better for diving Helium mixes because of their lower pressure. Ask ANYONE who dives trimix!
ONLY IF YOU DON'T OVERFILL THEM! If you push them to 3500 psi then Helium has exactly the same compressibility issues in a LP tank overfilled to 3500 as it does in an HP tank AT 3500!
4. LP 104's have perfect buoyancy for diving dry (Most technical divers dive dry, this may shock you but they do and the original question asked about what tanks to get for technical diving)
I'd like diving dry in 30, 40 or 50 and probably even 60 degree water too. But the water I dive in is typically 70 or 80-something degrees, where a drysuit is a pointless waste of money. This is likely to be true even if I am diving extended range, at least around here (Florida panhandle)
Again, the issue of DIR saying "don't dive steel wet" APPEARS to revolve around a false premise - that the wetsuit compression is somehow altered by the tank material.
Second, you have not demonstrated a significant difference between LP tanks and HP tanks in buoyancy. I'd argue that a 2lb difference between a twinset is not a difference worth mention.
5. LP 104's will last longer due to less stress on the tanks (you said assume no overfills haha) ok, I admit I have no evidence to back this one up but it sounds good...
6. Regs/hoses/guages/o-rings will last longer due to less pressure (once again if your not overfilling you have to take this into consideration, if you are overfilling then mute point)
Again, if you're overfilling the LPs neither of these matter (and neither does the helium argument.) The former is horsefeathers out of the box, as PST figures their tanks for 10,000 cycles. How many years would it take for you to put one of their tanks through that many cycles?
The latter argument may have SOME merit, on the other hand its limited to the HP seat in your regulator first stage, the DIN O-ring and your SPG hose; nothing else sees tank pressure. Further, the difference between 3000 and 3500 psi is nowhere near that between 2600 and 3500; the former is what is in nearly all AL80s, so the changeover from there does not appear to be all that material.
7. You mentioned PST above.... There's a reason their LP tanks are called PRO and the HP tanks are called SPORT. They know the deal!
So if I call something "PRO" that makes me all-knowing and all-seeing? Gee, that's pretty good! Reaching a bit to find reasons, are 'ya?
The ONLY argument for HP100's is that they are lighter on land right.... who gives a rats @ss! Work out, get stronger buy a dolly whatever you have to do but get the RIGHT tanks!
No, that's not the only argument.
There are two far more significant arguments, which I made before and which you've ignored:
1. INERTIA applies to ALL masses, underwater or above water. In fact, this is one of the things that I find so interesting about the entire DIR-style argument.
JJ and GI make a BIG DEAL about inertia and overweighting, in fact. Not just due to the risk of not being able to swim up the rig, but ALSO due to the impact it has on your
breathing rate. Well, guess what - they're right about that! Every kilogram of MASS you carry into the water is a kilogram that you must accelerate every time you move through the water. Whether it WEIGHS anything is irrelavent to this - mass is NOT dependant on apparent weight and buoyancy.
30lbs is a LOT of mass. It is, for the average, fully-kitted technical diver, about 12% of his all-up mass. It is therefore reasonable to expect that it will contribute significantly (probably at least 5% and perhaps as much as 10%) to his gas CONSUMPTION.
Removing that mass for the kit, ASSUMING YOU DO NOT NEED THE GAS IT CAN CONTAIN WHEN OVERPRESSURIZED, is a net-net win, UNLESS there is some kind of other overriding consideration.
This FACT - that mass is mass, and you can't escape it by making it buoyant, is why I question the entire claim and preference in the first place!
2. The smaller cross-section of the HP100s means LESS DRAG IN THE WATER. That's the OTHER part of the "DIR" argument about not overweighting (more weight means more gas in the bladder which means more cross-section and thus more drag!) Yet that
same argument points towards HP100s instead of LP104s, because the tanks are of smaller cross-section!
See 7 reasons above. (I probably left some others out, will add if I think of them tonight)
If you're overfilling, I think I've left you with zero reasons. If you're not, then I've left you with one (helium compressibility), but that may be offset entirely (and certainly is partially) by the mass and cross-section problem and its effect on your breathing rate.
The "DIR" way wasn't made up by a bunch of idiots it was a coming together of the best practices and intigrating them into a whole. JJ and GI3 didn't sit down one day and say "Hey, let's do it this way". It was standardized to assure the SURVIVAL of their team while diving to 300+ feet with penetration distances of MILES into a cave!
So what?
I agree with an awful lot of it, by the way. I dive long-hose. Why? Because I see the VALUE of handing off my best-performing regulator in a low-gas situation, and I see the VALUE in two people being able to sit at a safety (or deco) stop while not in a death-grip bear-hug as is virtually NECESSARY with a standard-length Octo hose. I ALSO see the other argument for it, in that in an overhead environment it may be NECESSARY for you to swim out single-file (kinda hard to do on a 39" hose, isn't it?)
I see the value in a bungied backup, because I know EXACTLY where it is ALL THE TIME and can reach it with no hands. That's a nice thing to know!
I see the value in a BP+Wing, because I like how I am trimmed in the water with it. It "just works" and is the most stable "BC" I've ever worn.
I see the value in much of the other DIRisms
because they make sense.
But this one looks to me to be pure religion and hyperbole.
You may be able to dive HP100's wet if you properly balance your rig (maybe)... I think you're severly overweighted to begin with though. Once again all I'm hearing from you is "anti-dir" with flawed logic.
Wanna argue with the lead and my wetsuits? Go right ahead. Its a losing argument, but you're free to make it if you'd like.
The original argument is which tanks to buy for technical diving... I think I explained pretty well why PST104's are better than HP100's for TECHNICAL diving.
Not so far. All I've taken from this so far is that if you DO NOT overfill the LP 104s that they will accept Trimix in a better fashion and with less hassle. I'll give you that, since I happen to understand more than a bit about the behavior of gasses under extreme pressures, including Helium, and understand that there might be some issues with Helium's compressibility at 3500 PSI. Whether its material is another matter, and one that I'll have to sit down with the calculator to figure out.
But if you overfill the LP104s then the argument disappears, since the same pressure is in both tanks. And whether you overfill them or not you can't get away from the mass and cross-section (drag) issues.
Like I said... there's a REASON they do what they do.... NO ONE has been able to do anything even remotely close to what they do....
That someone has done certain things in a certain way doesn't make them all-knowing and all-seeing.
Part of critical thinking is examining the claims and positions and expecting to find justification that is borne out by the facts. In most of the areas of the DIR "religion" I find that upon close examination, and have adopted a great deal of it in my personal diving.
But this tank issue is one place where I can't locate the logic, and certainly not at the level of emphasis that JJ and GI put on it.
The idea that the material that a tank is made of somehow influences the amount of negative buoyancy necessary to compensate for a wetsuit is remarkable. So long as I am neutral at the surface with no gas and with some amount of ditchable weight, no matter how small, I argue that the material my tank(s) are made of is immaterial.
The counter-argument sounds like screeching on the chalkboard to me, and simply does not make sense.
but I guess you know much better than they do don't you.... get out in the real world of technical diving and you will see... and not just what "they say".... you'll see why they do what they do...
I'm not going to waste any more time trying to explain it if you can't get the message from this post. I'm going diving!!
Funny that, I was doing exactly that today and will be doin that tomorrow.
Still haven't gotten my answers on the tanks though. I guess I won't either - will just have to find someone who has a couple of HP steelies and a couple of LP steelies to try and see if I can discern a difference, since objective, rational, fact-based distinctions seem to be absent in the opinions I'm receiving - both at the local shops and here.
