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Post by duckbill on Mar 5, 2008 22:42:52 GMT -8
(Linda, we need one of those popcorn-eating smilies )
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Post by SeaRat on Mar 5, 2008 22:54:22 GMT -8
Quote: "I think I mentioned that your discussion of the Para-Sea concept was a bit lacking, in that there are two moment arms in that photo, with the shorter one being the Para-Sea. Also, I was very stable in that position I was in and could have maintained it as long as I wished. " There are several things, it is easy to draw arrows on a picture but how do we know those vectors represent real forces and then the other problem is that there are still multiple moments. Ideally there would be two opposing, gravity and center of bouyancy. Quote: "But when you say that position low on the back makes no difference, you need to qualify that by saying that this is only if you stay completely horizontal in the water, and the scuba unit itself is completely horizontal. If not, then the physics of the vertical water column takes over, and there is a difference. As I stated earlier, I rarely am completely horizontal in the water throughout a dive." I did and one does not have to be exactly horizontal, they need only be approximately so because the minor difference of a few tenths of an inch by my tesing is of no consequence with a well tuned high performance double hose. Horizontal trim is a goal, why set your gear for a non optimal condition? I have dove a Nautilus many years ago and comparing that to a modern wing is of no value, apples and oranges, one works and the other does not which is why they quit making them after a limited run (kinda like the new Mistral). I certainly use a double hose with my wing/BP and I do surface swim on my back with it as always. Quote: "As I stated earlier, I rarely am completely horizontal in the water throughout a dive." I try to be horizontal as much as possible, much more efficient swimming, of course during the course of any dive there will be departures from any position given as ideal. I try to remain in and trim for and rig for the ideal condition for the best efficiency overall--horizontal. The ParaBC reminds me of the Dacor double bladder SeaChute, pretty good because it put the center of bouyancy under the belly button but because it was UNDER the diver and because the heavy tanks were over the diver it would impart a rolling moment that is not present in a wing. Quote: "Again, just because this is a New Mistral thread, I think this is part of the problem that regulator had, in that the position of the regulator in relationship to the diver's chest is critical, and that was not discussed as much as it should have been in the literature for the regulator." Well, that is what started the tank position discussion, I don't agree that the tank position is critical and neither did AL apparently. Most modern divers and in particular tech sorts are trained to try and achieve horizontal trim. That being the preferred positon in the water then the tank/regulator positon becomes much less critical--and that is the thought that AL must have had as well. I don't think AL is ignorant of these things, I think they understand them fully and decided it was not especially important to them. Just because the new Mistral was not the stunning success it could have been had they spent a little more time designing it does not mean they don't understand the principles involved. They just did not want to invest in doing it right and used as much off the shelf as they could get away with,well, they did not really get away with it did they. We need to hook a magnehlic up to a mouthpiece of a diver and take some measurements, the type that measure both positive and negative so we could have inhalation and exhaust would be interesting. Nem Nem, First, how do I know about the force vectors on the Para-Sea? Well, I designed it, for one. Second, I tested it and have dived it for over 20 years. So I know it pertty well. About the multiple moment arms, they are always there in most BCs, and are position-dependent. I want you to imagine taking your wing, and wrapping it around your chest. This is what the Para-Sea does--it is a wrap-around, chest-mounted BC. Because of this, it is exceptionally stable. When vertical, the main buoyancy is in the neck and chest. When horizontal, some of that goes into the wing section around the chest. Dipping your head places more in the wings, so that the moment moves closer to the weight belt, and the CG of the diver. This was intentional. Your criticism of the Para-Sea with buoyancy under the diver and "heavy tanks over the diver," remember that the tanks I was using, and still use today, are not "heavy" in the water. A single or twin steel 72, a single or twin AL 80, twin steel 1800 psi 45 cubic foot tanks, and twin AL 50s are not heavy underwater. They are close to neutral, and the AL 80s are somewhat buoyant. So that criticism doesn't hold under the circumstances that I used to test the Para-Sea. Third, I rejected the tank-mounted wing (then known as the At-Pak (for attitude control pack) which in the mid-1970s was the "wing" design being used by the then-"tech" divers, on several counts. --They lacked streamlining, and placed more bulk on the scuba. --In life-saving situations, they would not keep an unconscious diver face-up on the surface. Both these criticisms still hold. A diver with a "wing" is less streamlined than a naked diver, or a diver with only a weight belt on a wet suit. So far as the Nautilus, it did not succeed for a number of reasons; weight, bulk, and time to understand the concept were three. It takes a minimum of 3-5 dives to simply get used to it. But it still has the same problem (which Dacor, like you I suppose, dismissed) in that it cannot keep an unconscious diver face up. Dacor stated in their instruction manual, Tech divers don't have this advantage, which is why I don't really like wings. I experimented with a similar concept, a sandwiched back wet suit where the entire back of the wet suit was inflatable. This was actually superior to the "wing" concept, in that it was independent of the scuba, and it was completely streamlined. After these experiments, I did not stop there, but published my results in two articles in the Proceedings, NAUI Sixth International Conferennce on Underwater Education[/B], IQ-6, October 4-5-6, 1974. My two articles, "The Life Vest" and "Comments on Buoyancy Control and Emergency Procedures," included the following drawings from the latter article: Concerning your comments about Aqua Lung's understanding of these concepts for the New Mistral, I don't think they listened to their own engineers; I think the marketing people made decisions on this, which is what is commonly happening in companies now in the USA. Quality has declined in the USA, and this is one reason. Paying attention to these details would have helped gain acceptance to the New Mistral, even in its present engineering condition. Now, one observation. You are not diving vintage when you use "modern" heavy steel tanks, a wing, and a Phoenix Royal Aquamaster. The Phoenix is brand new, and not vintage at all except that it's a double hose reg. The At-Pak (the "wing" of the 1970s) was not used even with a double hose regulator, as it required LP ports. These heavy, HP tanks are a relatively recent equipment item, and have caused a lot of divers grief when learning scuba, as it is almost impossible for them to be neutral in the water without a BC, or air in the BC, without a wet suit. So they become "BC-dependent" for their diving. This method of training has made for divers who don't realize that they are way too overweighted when they get into the water; they simply compensate with their BC, not realizing that this causes other problems for them in the water from streamlining to bulk and the need for underwater scooters to get around. I know of divers who thought a 200 yard surface swim with a slight current was an emergency situation, and signaled for a pickup, because they simply could not move forward. In the 1970s, we called it "push-button diving," as these divers know how to go up and down, but not how to swim forward with efficiency. Concerning the work of diving, and the use of a magnetic, Glen H. Egstrom, Ph.D., University of California, had one which he used to measure the work of diving using different types of fins under different work loads. He published his work too, so it should be available (I have one of the publications, Human Performance and SCUBA Diving[/B], Proceedings of the Symposium on Underwater ZPhysiology, Scripps Institution of Oceanography, La Jolla, California, April 10-11, 1970, where Dr. Egstrom explains his work on pages 5-17. That apparatus would quantify the amount of work needed to breath in different positions, but I'm not sure it still exists. A drawing of it does though, and I may put it up here if I get more time. Well, so much for my rant on these topics, but realize that I've been working on these problems for a very long time. John PS--Duckbill, enjoy the popcorn
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Post by SeaRat on Mar 7, 2008 9:01:01 GMT -8
Nem,
I want to make clear that I don't think anything bad about the Phoenix Royal Aquamaster, or diving a wing or heavy steel tanks. It was just an observation that they are not "vintage," as they did not exist in the 1960s and 1970s. I have no problem with improving performance of the regs, and I hear that the Phoenix Royal Aquamaster does this nicely. My redesigns of the Trieste II are another example of taking an older style regulatory and improving it. The Phoenix would be the same, and a lot of thought went into that design.
Concerning the wing, again it is my preference not to use one. It was not "vintage" diving in my experience, and I was making decisions about my Para-Sea when NAUI and other agencies took seriously what happened to an unconscious diver on the surface. This seems to have fallen as a priority in the industry, but that's just an outsider's observation as I have not seen the recent diver rescue materials (last 15 or so years). So I may be a bit "jaded" in that observation too.
Anyway, I wanted to clarify my thoughts here.
John
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Post by nemrod on Mar 7, 2008 9:48:50 GMT -8
What started this discourse is that I no longer accept the "low tank" and feet dragging low diving positon of urban legend as beneficial to good breathng and efficiency with a double hose regulator. The connection with wings/bp and the Phoeinix is that it was through my testing in the pool with the Phoenix in various configurations from wing/BP to in a simple Sea Hunt harness without a BC and a variety of horsecollar BCs that I discovered that the "low tank" was myth and incorrect for a well trimmed horizontal diver. Therefore the concept is the same, horizontal trim is my goal, vintage diving or not for best efficiency and double hose regulator performance.
As to the important aspect of a BC floating an unconcious diver face and head up--bah humbug. A wing or an optimally designed BC is not a lifejacket, it is a bouyancy compensator, it's function is defined by the name. It should not have or serve a life jacket function at all and therefore compromising the design to rotate the head up is a bad thing--not a good thing. I would not want a BC that was designed to function as a life jacket. Nothing on any BC I have ever purchased had a tag that says USCG approved. It is not a life support or an approved floatation device and should not pretend to have any such function. Besides, properly set up, a wing will allow you to rest vertically on the surface when inflated, another urban myth that dies hard. As to the unconcious diver, very few BCs except for the old Mae Wests and horsecollar type would likely keep an unconcious diver head up with clear airway. Adding a front mounted emergency vest would severely complicate the entire rig and would not gaurantee a head up positon anyway unless the rear chamber was automatically deflated when the chest chamber was inflated. No, I would rather keep the BC function pure and leave the life jacket concept aside as irrelevant to the purpose and fucntion---neutral bouyancy.
Another misuderstanding, the Voit SnugPack came out in about 1960 or so, it uses a harness just as does my modern plate or Freedom Plate (which is a steel SnugPack) therefore it is closer to vintage than the modern cumberbund ubiquitous poodle jackets many of which have no harness. A sleek wing has virtually no drag penatly but yes a "naked" diver in a simple harness might have the least drag.
Whether vintage or not, the physics are the same, a diver with good trim will be more efficient in vintage gear or modern gear. There is no point in shoving the tank down to the ankles in a falsely misconcieved notion it is needed to get good breathing because with good horizontal trim there is no breathing disadvantage to placing the tank at a good positon to allow the diver to trim out. Urban legend dies hard, we repeat what we have been told until it becomes the truth.
In the drawings with four divers, note they are horizontal and if you put a straight line through the regulator and through the center of the lungs shifting the tanks fore and aft would have no impact on hydrostatic head. Again, that drawing has unverified force vectors that do not correspond to the actual diver as equipped as he is with those units he would not likely be in that posion but would more likely find himself head high and feet dangling behind lower--bad trim, vintage or modern. I note that your drawing accepts that horizontal --exactly horizontal is optimal. Your drawings are not all entirely correct, the force vectors on the wing (lower LH) are not exactly correct per my observations and use of a wings for some 30 years. The weight of the plate and tank and trim weights offset the up arrow, a diver outfitted thusly might not have any weight belt or only enough weight on the belt that if ditched he would become marginally positive so the result is more like what you have in the lower right diver.
It is not so much your drawings are wrong as there is no way you can sum them since there is no quantatative values assigned them, putting four pounds lead at this place or six pounds of lift at another does not translate to those numbers in practice, the individual human body screws that all up. I can put arrows all over but the concept of neutral bouyancy and neutral trim, irrespective of art work, the summation of vector forces would be zero for a given diver, how he gets to that equilibrium may not be the same as for another.
I am searching ebay for a magnehelic, they are not expensive, perhaps later this year I can have time to rig a test, the YMCA thinks I am a nut anyways. BTW, there are about to be complete performance tests on several Aqua Masters, should be very interesting and useful.
Nem
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Post by SeaRat on Mar 7, 2008 12:36:19 GMT -8
Nem, There is one fatal flaw in your argument against a lower tank position. It is the "feet dragging low diving positon." Why does a low tank position automatically in your mind mean that the diver is not in proper trim, and horizontal? Is in because you are diving very heavy tanks? A twin 50 set is not heavy in the water, and even when worn low, are not out-of-position from the standpoint of neutral trim. There is one other thing that I must remind you of, and that is that the force vectors of the tank were much different in 1972-74 than they are today. In the accompanying article, "The Life Vest," I pictured my brother Ken wearing an aluminum 2475 psi single 72 cubic foot tank, which at that time was the "norm." That tank was very buoyant in the water. We were trying to look at buoyant ascents at the time, and I had figured out a technique (the "raised elbow technique") that allowed a diver to ascend face-up in a buoyant ascent. But the tank of that time, the 72 cubic foot 2475 tank, was about 6 pounds buoyant empty. So when you discuss my 1974 diagrams, keep that in mind. By the way, unless you can quantify the work involved, your use of the magnahelic underwater won't tell us much. Here's the apparatus that Dr. Glenn Egstrom used to quantify his experiments on underwater work: I know that you are completely uninterested in how a diver is supported on the surface, but that was part of the basis for my patent on the Para-Sea concept. Here is a representation of the reason the Para-Sea is better than a horsecollar BC. This was put together in the late 1980s. If you want to see more, and my reasoning behind the concept, see Patent #4,623,316, as it explains the reasoning behind the Para-Sea concept. Concerning the vectors, no they are not quantified, but they are also real. The head weighs about 20 poinds, and out of water, it will exert a force down. The weight belt on a diver with a thick wet suit weighs between 16 and 25 pounds, and it also will exert a significant force downward (or we would not use them to overcome buoyancy--kinda basic I think). The Para-Sea BC, fully inflated, has a buoyancy of between 40 and 50 pounds; I did quantify that in the 1980s, but cannot put my finger on the exact figures right now. John
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Post by duckbill on Mar 7, 2008 14:20:49 GMT -8
John, are you refering to the early aluminum 72s? According to Diverlink, they were very buoyant, as you said. But if you are refering to steel 72s, then I understand they are about 3.5 lbs. buoyant empty, and I don't think that includes the valve which would make it less buoyant.
By the way, no matter where you place the tank, the valve will always be above the waist line (unless the tank is upside down). I guess a heavy valve helps "trim".
Heck, I just dive this stuff for the fun of it ;-)
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Post by SeaRat on Mar 7, 2008 15:36:01 GMT -8
Duckbill,
Thanks for the clarification--it was a aluminum 2475 psi 72 cubic foot tank, and it was very buoyant. I've corrected the text above.
John
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Post by Nemo on Mar 7, 2008 16:06:03 GMT -8
I think the depth of the diver’s lungs relative to the air source is a factor effecting breathability to some degree, even with a second stage regulator. But with an AM-type rig, breathability is also (and most significantly) affected by the depth relationship between the regulator diaphragm and the mouthpiece. With a double hoser, regulator-deep conditions produce a forceful free-flow at the mouthpiece whether the lungs are involved or not. And for the most part, when breathing, it is this “supercharging effect” that makes it easier to inhale. And vice-versa, of course. That’s how it seems to me, anyway. VBR, Pat
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Post by Nemo on Mar 7, 2008 16:33:43 GMT -8
Oh, and uh...pass the popcorn, please. ;D
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Post by SeaRat on Mar 7, 2008 17:41:32 GMT -8
Hi Nemo, It's easy to think that it is the difference between the mouthpiece and the regulator that makes the breathing hard or easy for a double hose, but that's not quite correct. It is correct for a free flow, as the system is then "open" to the water. But once you put it into your mouth, it becomes a closed system, and the breathing effort is initiated in the lungs, so it is the difference between the demand regulator valve (second stage) and the center of the lungs that determines the overall breathing resistance. Bill Barada, in his book Lot's go Diving![/I], published by U.S. Divers Company in 1962 had a diagram which really shows this difference, and it is this that Nemrod and I have been discussing: With the New Mistral sitting high up on a single tank, with a back-mounted BC, the difference in the water column between the regulator and the center of the lungs can be pretty far (8 to 10 inches), and this will affect the perceived breathing resistance, no matter the performance of the regulator. I just reviewed a National Geographic Magazine book, World Beneath the Sea[/I], and looked at each photo which included a scuba or hookah diver. There were 77 divers depicted, and of those, 24 were in a horizontal or near-horizontal position; 53 were in other positions, mainly towards the vertical. So Nemrod, I am not alone when I say that I don't spend most of my time underwater in a horizontal position. I do when swimming, but when I'm doing work, it's a lot of times kneeling on the bottom. This is where the lower position for the regulator valve comes in handy from a breathing ease perspective. John
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Post by Nemo on Mar 7, 2008 19:47:56 GMT -8
Hi John, Just got out of the water after doing it with a DA / 72. The "supercharge boost" happens whether the mouthpiece is in my mouth or not. I think basically we're saying something similar here: a lower regulator position can make for easier breathing, especially in an upright body position. This is especially true with a Leagues rig, where the diver is almost always standing upright. Adjusting the harness so the regulator rides only a couple inches up or down makes a huge amount of difference. VBR, Pat Hi Nemo, It's easy to think that it is the difference between the mouthpiece and the regulator that makes the breathing hard or easy for a double hose, but that's not quite correct. It is correct for a free flow, as the system is then "open" to the water. But once you put it into your mouth, it becomes a closed system, and the breathing effort is initiated in the lungs, so it is the difference between the demand regulator valve (second stage) and the center of the lungs that determines the overall breathing resistance. Bill Barada, in his book Lot's go Diving![/I], published by U.S. Divers Company in 1962 had a diagram which really shows this difference, and it is this that Nemrod and I have been discussing: With the New Mistral sitting high up on a single tank, with a back-mounted BC, the difference in the water column between the regulator and the center of the lungs can be pretty far (8 to 10 inches), and this will affect the perceived breathing resistance, no matter the performance of the regulator. I just reviewed a National Geographic Magazine book, World Beneath the Sea[/I], and looked at each photo which included a scuba or hookah diver. There were 77 divers depicted, and of those, 24 were in a horizontal or near-horizontal position; 53 were in other positions, mainly towards the vertical. So Nemrod, I am not alone when I say that I don't spend most of my time underwater in a horizontal position. I do when swimming, but when I'm doing work, it's a lot of times kneeling on the bottom. This is where the lower position for the regulator valve comes in handy from a breathing ease perspective. John[/quote]
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Post by SeaRat on Mar 9, 2008 12:41:41 GMT -8
Nemo,
I agree, we've been talking a bit of sematics here. For me, because I'm not horizontal all the time, the lower tank position is better. I confirmed this in a series of pool sessions about two years ago using my twin 45s. I have one regulator, my DX Overpressure, which has extremely long hoses (the venturi is not affected, as it works on a "hose-within-a-hose" theory that is not used today). I wore the scuba at various degrees of lowering on my back, and the lower positions produced the best results for me. Part of this has to be with my back, as I have a pretty good curve in my shoulders. Even when I'm horizontal, my scuba usually is not (see photos above). Moving the regulator down several inches makes at lease a one-inch water pressure difference in a horizontal position for me, and up to five inches when I'm more vertical.
I should qualify my statement about Nemrod not diving vintage with a wing and back plate, as I experimented with the Mar-Vel Pak which houses 20 pounds of weight on the tank in the early 1970s. I found that it worked pretty well, but because it was flat, it tended to give me a back ache after an hour in the water. Nemrod has said that heavy tanks need to have a wing and backplate, and perhaps this is to take that pressure off the back (which tries to make a curved spine straight) by floating the heavy tanks enough to relieve that pressure.
John
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Post by Nemo on Mar 10, 2008 1:34:53 GMT -8
Yup. I agree. I think regulator location does make a difference; and I, too, like my regulator a little lower if anything. I know I posted a pic here of me with a DA and the regulator was kinda high, but we didn't plan anything that day. Just grabbed the gear, jumped into the lagoon, and Lynn shot the pic. Actually, as fat as I was at the time, and with that particular "Rube Goldberg" harness, I couldn't have gotten it lower if I'd tried. But I usually wear it lower than that. VBR, Pat Nemo, I agree, we've been talking a bit of sematics here. For me, because I'm not horizontal all the time, the lower tank position is better. I confirmed this in a series of pool sessions about two years ago using my twin 45s. I have one regulator, my DX Overpressure, which has extremely long hoses (the venturi is not affected, as it works on a "hose-within-a-hose" theory that is not used today). I wore the scuba at various degrees of lowering on my back, and the lower positions produced the best results for me. Part of this has to be with my back, as I have a pretty good curve in my shoulders. Even when I'm horizontal, my scuba usually is not (see photos above). Moving the regulator down several inches makes at lease a one-inch water pressure difference in a horizontal position for me, and up to five inches when I'm more vertical. I should qualify my statement about Nemrod not diving vintage with a wing and back plate, as I experimented with the Mar-Vel Pak which houses 20 pounds of weight on the tank in the early 1970s. I found that it worked pretty well, but because it was flat, it tended to give me a back ache after an hour in the water. Nemrod has said that heavy tanks need to have a wing and backplate, and perhaps this is to take that pressure off the back (which tries to make a curved spine straight) by floating the heavy tanks enough to relieve that pressure. John
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Post by nemrod on Mar 12, 2008 20:39:52 GMT -8
Urban legend dies hard. I will stay with everything I said.
I don't think a life jacket is a desireable concept for scuba divers since it is a huge compromise and introduces clutter and complexity to the pure function of providing bouyancy compensation mostly for suit compression.
I dive vintage vintage more often than not, in either case, wing and BP or pure vintage, good horizontal trim is preferred by myself.
The Para BC is a good concept for rescue jumper or public works diver but I have spent years trying to elimiate clutter in front of me which is what finally drew me back to vintage and the wing/bp for my other non vintage diving. No clutter or pretentions to any other purpose.
The wing/BP does not positon the tank any further from the back than many other vintage backpacks and is closer than a SnugPack. A SeaHunt style harness is fun but they have some limits for more general diving which is why by the mid 60s most divers had switched to various "backpack" type rigs but that is about the only vintage rig that is significantly closerto the back than a BP/wing using a Freedom Plate etc.
The diagrams showing the divers and regulators, note they are horizontal and a line drawn through the center of the regularor and center of the lungs would represent an equal hydrostatic head no matter the fore or aft location ofthe tank. Moving the tank be it a 72 as I mostly use or a heavy LP steel or an aluminum 80 for good horizontal trim and efficiency will therefore have no effect on breathing effort.
I don't need caloric consumption data to measure exhaust and inhalation effort with a magnehelic type device to demonstrate the relation of the tank position to breathing effort for a diver in various states of trim. I am not interested in WOB for this purpose, I am only interested in the cracking point and sustaining draw.
Nem
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Post by SeaRat on Mar 13, 2008 18:57:40 GMT -8
Nem, I understand where you are coming from, but realize that divers rarely are in a completely horizontal plane. My drawings above were meant for a different audiance, discussing different ideas of buoyancy control in the 1970s. I showed this with the figures about diver's orientations in James Dugan's book, World Beneath the Sea[/B] by The National Geographic Society. Only about 30% of the divers were in a completely horizontal position. Most of the rest were toward the vertical, head up position, although a few (Cousteau divers) were head-down). Here's more what the reality of diving looks like, with the diver somewhat head-up, working with a camera or equipment, or simply looking around: Note that by simply sliding the regulator down lower on the diver's back, you can cut the distance roughly in half (my poor drawing has the line a bit high; I realize that, so it's more like 6-10 inches of water displacement difference). You may also note that the bottom of the tanks remains in the same place, as only the length of the tanks has changed, from using a single 72 to using twin 45s or 50s. This allows a lower tank position without much effect on the diver's balance. Finally, the twin valve (old style) allows a lower position for the double hose regulator as the center position is much lower than it would be for a single 72, as the valve placement is different. So far as the "Urban Legend" aspect of lowering the regulator position, it isn't. This is physics, pure and simple. Yes, in a completely horizontal, "layout" position, there is no advantage. Nem, if you can hold that position throughout your dive, then there is no reason to be concerned about where the regulator is in relationship to your head/back. But if you go head up, such as you did here, then there is an advantage: There is one other reason I like the lower position, and that is that I'm a shore diver, and make different types of water entries, from jumping in from the rocks to wading in. When I jump in, I don't want my scuba high enough that there is a possibility of hitting my head upon entry if something "funny" happens (a slip of the fin upon entry, for instance). I have made parascuba jumps from helicopters and planes (many, many years ago), and we used our smaller jump tanks specifically to keep the tanks lower and away from our heads. Concerning the measurement of cracking point and sustaining draw, that would be interesting to see. Please do share them with us when you get the figures. Who knows, maybe I'll have to change my mind on things. Old coots do change, you know. John PS: Most "Urban Legends" take place in an "urban" environment, which this decidedly is not. Maybe we could call it a "Nautical myth," but it still is actually simple physics.
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