Tuning a Mistral 2

[duckbill]

I hope Dr. Sam Miller doesn't mind me quoting him. It may not help with the question at hand, as the Trieste came out in the mid-1960s?:

For many years Voit made US divers rubber products in turn US Divers sold Voit hard goods. In 1970s US Divers begin making their own rubber goods under Arnie Brochinsky who gave us the red white and blue Americana line in 1976.

When they moved from LA they moved to Santa Anna in Orange county, (The famous OC on TV) US Divers on New Delhi which was changed to Warner Avenue and Voit around the corner on Harbor Blvd. They relocated about 1/2 mile apart.

A few years prior to the intro of the MR 12 and Trieste Voit became very interested in the water sports and especially Scuba, The Voit regs were designed under Charlie Jehle as the Director of Water Sports, the engineers were; maybe Fred Schuler, and certainly Bill Oliver and Ed T???
Fred Roberts also may have had a hand in its concept and initial design -It is all Roberts, with the radical approach and modual concept.
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Is it really possible to compare single hose and double hose regulators side by side? With the water column position sensitivity of the double hose once the hoses are attached, wouldn't positioning make a huge difference in the results?

Also, do "machine" tests show results that take various depths into account?

[SeaRat]

Nemrod,

It looks like in the late 1960s AMF Voit began diversifying away from USD and it's agreement with them. They still probably had to pay USD for the Aqua Lung patent, and my Trieste II does not refer to the "Cousteau-Gagnan Process" at all on its label. It could be that there was legal action over that, as there was apparently over the Sportsways Hydro-Twin and Duel Air from USD, but I don't know that for certain. It could explain the short manufacturing cycle of the Trieste II. The Trieste II actually uses the same first stage as the R-12 Titan II single hose regulator.

The MR-12 came out slightly in front of the Titan II, and was a similar design to the V123 Voit Dolphin II, with the square second stage that was made famous in the movie Thunderball[/I]. They both have the same first stages. What AMF Voit did with the MR-12 was to enlarge the exhaust port, which won them a military contract with the US Navy as the first single hose regulator that earned the "US Navy Approved" stamp, and was used by that service. Both the MR-12 and the R-12 Titan II were "U.S. Navy Approved" in their 1973 catalog. That catalog discussed a "fully balanced first stage, extra large exhaust ports, less inhale or exhale effort than other regulators..." in discussing their Titan II regulator. Then they show that the second stage is the same for both the MR-12 and the Titan II.

We in the USAF used the USD Calypso and later the Conshelf regulators, and could buy them because we did not have to adhere to the Navy standard. US Divers Company was late in improving the exhaust characteristics of the Calypso line, and let AMF Voit out-compete them for the Navy contract in the late 1960s or early 1970s. When we did get our hands on a MR-12 (it was issued to our younger PJs), they looked at it and thought it was "cheap" compared to the USD regulators that they were used to. For one thing, the MR-12 did not have as good a chrome coating as the USD regs, especially on the inside (we did not use the black ones, as we were not using them for Sneaky Peat ops). For another, the interior did not have as good a venturi as the USD Calypso did. But it was a dry breather (USD Calypso, second generation, was not). But it did tend to freeze (second stage) easier in cold water than the USD Calypso. Eventually, USD came out with their third generation Calypso, and the Conshelf, which then took all honors with the Navy and USAF, and I believe the Conshelf is still being used (metal version).

John

[nemrod]

It is as if up untl about 1965 Voit was considered premier equipment and after that they were slowly relagated to second tier and department store brands. Looking through the Voit Catalog CD which does not yet have the earliest years you can also see it. It seems to have occured at the point that all of the double hose Voits dissappeared which was 1965. The 65 Voit catalog best I can tell shows NO double hose regulators and only a paltry selection of single hose. In 1964 there was only the Navy V66 pictured. In 1966 the Trieste appeared so unless somebody can show otherwisre it appears Voit lost support of it's regulator lineup, especially double hose products, by USD Corp in 1964 because in 65 there were NO double hoses in the catalog. Therefore it is reasonable to believe that they lost the engineering support of USD and did the Trieste design on their own.

So, what am I getting around to--lol---yep--the Trieste was the "new" Mistral of it's day. I think Voit took what they could find on the shelf and stirred it around and came up with their own junk yard dog, the Trieste. Which is kinda funny because the two have a lot in common in that they both have a small diaphram and a second stage lever that looks like an enlarged standard downstream for the MR12. It appears they did this because their relationship with USD was compromised and had to come up with something in a hurry. Funny that many consider the Vintage ERA to be up through 1974. After that USD had no more double hose Aqua Masters in the catalogs and curiously they to became a department store junk company surrendering their lead to Scubapro and others. The loss of traditional large diaphram double hose regulators seems to have signaled the downward spiral of both companies into the abyss of junkdom, 64 for Voit and curiously 74 for USD. Karmic payback?

I know I am blasphemous as of late, comparing a Trieste to a new Mistral, dissing black smooth skin as non-vintage and the holy of holy, I just don't buy into wearing the tank down at your ankles any more, it should be higher, not lower for better trim and performance.

Nem

[SeaRat]

nemrod said:

...I know I am blasphemous as of late, comparing a Trieste to a new Mistral, dissing black smooth skin as non-vintage and the holy of holy, I just don't buy into wearing the tank down at your ankles any more, it should be higher, not lower for better trim and performance.

Nem

I tried the higher position when I experimented with the Dacor Nautilus last year:

It doesn't work nearly as well. The problem with the higher tank position is that the regulator is much further away from the center of the lungs, and so we must work harder for the same breath. I did find that I could compensate a bit by going head-down, which places the high-mounted regulator at the same position as the lungs, but was unsustainable during much of the dive.

But the balance is dictated mostly by tank size. Take a look at these photos:


These are the twin 90s used in the U.S. Naval School for Underwater Swimmers in 1967. Note the regulator position of the diver on the right, in relation to his lungs.


A single 72 cubic foot tank, with a USD harness, placed the regulator very high too, and contributed to the relatively hard breathing of the Dacor R-4 I was using.


Again, a long tank (80 cubic foot steel@ 2475 psi) made for a high regulator position. This was with my Trieste II before the mods made it an easy breathing regulator. Once, while diving this outfit in Southern California, I actually switched to the MR-12 second stage when the Trieste II became too much for me. That was a source of great frustration, and initiated my search for the design flaws of that regulator, as I had just had it overhauled and it did not perform worth a darn.


Here is a classic shot of Lloyd Bridges as "Mike Nelson" with his twin 38s underwater. Note the regulator position with the twin 38s. This is why I like my twin 45s and my twin 50s, as these units place the double hose regulator at the optimum for breathing risistance, nearer the center of the chest. The quad sets that Cousteau used during World Without Sun[/B] did the same thing, placing the regulator squarely between the shoulder blades. But to do that, you need at least normal-length hoses, or longer ones. The shorter (standard) hoses that came out with many of these regulators (Healthways, for instance) did not allow this type of positioning. The super-flex hoses that came out recently did allow this kind of positioning.

John

[nemrod]

The reason I don't believe in the having the tank dragging low any more is that I have tested in the pool and see no difference as long as--as long as---I have good horizontal trim. Most people tend to underwater swim with their feet about 10 degrees lower, the body angled. I don't, especially with a wing/BP (and the OP was talking about a more modern use). In fact, I find it counter productive in that wearing the tank low ruins my trim casuing my feet to drop. Pushing the tank to a more moderate position improves breathing by bringing the body into a true horizontal trim.

If you wear weights on the hip and a horsecollar BC there is a natural tendency to swim at about a 10 to 15 degree feet down angle. This may require a low tank to get best breathing but the real problem is poor trim to begin with. If your horizontal, the tank could be anywhere and it would not matter as the hydrostatic head would remain the same fore to aft.

In fact, using the Phoenix with a BP/wing, the tendency is for the body to go more head down. If I pull my feet up by bending my knees then my head drops as when doing frog kicks. If I extend my legs and scissor kick my feet drop slightly but not more than a few degrees. If frog kicking, head down, having the tank higher is actually an advantaage. IMO, the tank should be high, as long as leaning you head back does not hit the regulator.

Quote:

"It doesn't work nearly as well. The problem with the higher tank position is that the regulator is much further away from the center of the lungs,"

Again, this is exactly what I don't agree with. The distance from the lungs within reason does not matter. The difference (not distance) in hydrostatic head between the center of the lungs and the regulator diaphram is what matters. This pressure differential remains the same if the diver has horizontal position in the water--therefore--I contend the concept of wearing the tank low was to account for poor trim, one mistake beget another. This is what my testing in the pool proves to me. Leave all the Phoenix and BP/wing out of it, good horizontal trim is the goal and once achieved there is no need to degrade it by wearing the tank low (which destryoys that trim).

In the one pic you have good trim, the others the divers are head high due to work or whatever. Mike, he is not in an optimal swimming position there either because he is about to cut some hoses. I contend the tank should be set for best trim wihen horizontal, not when head high for hose cutting and underwater fighting.

Yep, the blasphemy continues, Mike was wrong, his tank is wrong and he always cut the wrong hose. If the guy cannot get the hose right, why think he would have his tank right?

Urban legend dies hard.

Nem

[SeaRat]

Well, looking at the "Mike Nelson" photo above, it looks like Lloyd is wearing a single 72, with the very old Navy harness on it. That seems much better than the backpacks that came out later, as it allows the tank to be worn lower. But this was practical only for boat diving, as sitting down with a single- or double-72 unit made for the tanks to be too high, or if worn lower, pulled on the crotch strap very uncomfortably. If you'll look at the original triple tank units used in the U.S. Navy, you can see that they allowed the regulator to be somewhat lower. This was also true of the Cousteau triple tank units Cousteau was so fond of. Here's some photos:




Note that the regulator was not alway low, but consistently could be lower than with the larger tank sets. What does this have to do with the New Mistral? Well, the New Mistral was mated to a single 80, usually with a BC, and therefore never in an optimal position for a double hose regulator.

John

[SeaRat]

Nem,

If you'll look at the lower photo here, the diver (my buddy, Bob Means), is in as horizontal position as he can be on a compass course using classical U.S. Navy equipment:

Note that he is still in a slightly head-up position, and that the tanks are not horizontal. We finished this 1500 yard swim sooner than the others due to good swimming technique, and waited on shore for over 1/2 hour for everyone to get back. But even here, with an optimum situation, the higher tank position results in a greater hydrostatic difference between the center of the lungs and the regulator.

Your use of a BP/wing make a difference, in that it inflates somewhat, and raises the regulator up away from the lungs more. For you, you are correct that it probably won't make much difference. But realize that when I created the Para-Sea BC, it was to stay away from the problems a back-mounted BC would create with the double hose regulators. You may also note that other than swimming, most underwater work is not done in a horizontal position. If I am photographing small fish or invertebrates on the bottom, I am usually not in a horizontal position, but slightly (10-20 degrees) head-up. This is because of the situation with the viewfinder of the camera.

Frog kicking, which I almost never use in open water, presents special needs, as you must keep your feet above your head to avoid kicking up bottom silt. This is not a "vintage" technique for underwater swimming, and I think on the 1500 yard open water swim, or the 3000 yard open water swim, if we had tried using a frog kick, we'd still be out there 41 years later. It is really applicable only in caves where locomotion is secondary and primary is not to stir up the much on the bottom. In short, it is a very specialized technique which should not really be used in other situations. If I tried frog kicking in some of the river currents I regularly swim in, I would not go forward at all, as the fin would be caught by the current and not function at all for forward motion. I say this as a former finswimming director for Underwater Society of America, where we were very concerned about how to gain the most efficient kick possible for time. The frog kick is not used by finswimmers.

Concerning trim, take a look of a photo of me in Clear Lake years ago:

Note that I am perfectly trimmed, but that my tank is not horizontal. I'm wearing a Scubapro A.I.R. I regulator, so the tank position is not so important here. But the length of the single 72 makes it problematic to have a lower position. This is why with double hose regulators, I really like the shorter tanks (50s or 45s) set up in doubles, as this puts the regulator in an optimum position.


Here is a U.S. Navy diver using twin 72s, on a working dive. He is not horizontal at all, even though he is trimmed correctly. Most work underwater is not accomplished in a horizontal position.

While my U.S. Navy Underwater Swimmers' School instructors would roll over in their grave if they heard this, Mike was right in his regulator position, and so far as cutting the "wrong" hose, he cut the one which would not jeopardize his stunt man's life, which was more important than reality for that TV show. (The U.S. Navy scuba instructors did not like "Mike.") But in Thunderball, James did cut the correct hose.

John

PS: Bob Means got a bit too horizontal once on this dive, did not look up, and jammed his hand into the bottom under a rock, receiving a sting from some kind of fish that was under that rock. It pays to look ahead too.

[nemrod]

What my tests show is that a higher tank position is not harmfull and in fact provides better trim without affecting breathing as long as the diver has good trim. In most of those photos above the tanks are quite high, higher than the urban legend requires, proving my point, the Navy agrees. The diver using the compass, it is hard to determine his position from that photo but it is always possible and desireable to be horizontal, fin dragging is inefficient and it does appear he is both horizontal and has a very high tank position, almost hitting him in the head.

A BP wing inflated or deflated has nothing to do with tank positon, it does not move the tank away, the tank is attached to a metal plate similar to a SnugPack which is attached to the diver via a conventional harness as has been used since forever. Full or empty, a wing has no effect on tank position and a well trimmed diver with good weighting should have virtually no air in the wing anyways.

I don't think competitive fins swimming has much to do with scuba and very few divers are fin swimmers or even know what it is.

Frog kicking has been around quite a while, before me. The frog kicking divers use is not the swimmer's frog kick.

A slight variation from horizontal as shown in the picture (which has a high tank position it appears to me) of the compass diver is insignificant to breathing effort. Further, Navy tests have shown that exhaling accounts for more than 50% of the WOB and again, tank position while horizontal or otherwise would have minimal impact on exhalation effort, higher might even be better. Therefore my previous conclusion, wearing a tank excessively low in an attempt to achieve better breathing characteristics is counter productive to that goal and results in bad trim. Two wrongs do not a right make.

Until we can instrument a regulator and a diver and measure these things we just have to go on antedotal evidence. The ONLY time I see any significant difference in breathing effort due to tank/regulator positon is when the diver is in a vertical head up position or a very fin low swimming positon. Generally a swimming diver does not spend much time vertical and head up and a diver with a severely angled feet low postion when swimming is demonstrating bad trim.

In this photo I do not have good trim. I am frog kicking to prevent my feet dropping. My feet want to drop because the weight on my hips acts to counter the bouyancy of my lungs and the horsecolar BC. The horsecollar wants to rotate me head up, the weights and heavy rubber fins want to rotate me feet down--I am not in balance and therefore I am having to draw my feet up to try and maintain some semblence of horizontal trim. In my wing/BP or sans horsecollar/BC this does not happen and my feet would be much higher and I would probably be using a flutter kick as there would be no need to fight the bad trim. Pushing the tank lower only makes the situation worse without any noticeable reduction in inhalation effort.



I think my buddy Jake took this pic through the glass at Weeki Wachee, not sure.

I would say the Navy diver with the doubles does NOT have good trim, he is feet low and it is clear to me he is fighting that.

Your Para BC picture does have good horizontal position it appears but I notice you have your feet drawn up to prevent them from dropping. This likely due to your trim being unstable (as is mine in my pic) and additionally I am saying with that good trim you could put your tank up or down (fore or aft) and it would have no effect on the WOB.

The modern wing/BP is superior to the Para BC or horsecollar or vest/jacket because it does not impart that rotaion you drew in on the slide.

BTW, a modern wing like the Oxy Mach V is biased to provide more lift near the hips and less near the chest and shoulders to prevent an imbalance unlike a horsecollar or your Para BC example.

Nem

[nemrod]

Oh, I see what your talking about, you think when I say "higher tank position" I mean further from the back--no--I mean the position of the regulator as positoned from head to toe. Some people think it is needed to drop the tank way down lowering the regulator to the middle of the chest--I am saying this is not needed and of no value for a diver with good horizontal trim. Sorry for the confusion, I think I see what your saying, we are just not on the same wavelength. Yes, I agree with you, mounting the tank a distance above the back is not a good thing and will certainly affect WOB. That is where the Phoenix gains a bit since it is about 0.5 inches longer and thus closer to the back.

Nem

[SeaRat]

Nem,

You make good points. I was talking about both, the vertical position and the distance away from the back. You can see that in this photo, with the Nautalis, it is both a few inches further away from the back because of the BC, but also higher. I was able to use it in a head-down position, with not too much problem. But when I went to get more upright, either on the bottom to look at the small fishes, or when ascending, the breathing effort was noticably worse.


In your photo, the regulator would be about one to two inches vertically lower in the water column if it was located lower on your back. With the Phoenix Royal Aquamaster, because of its performance, it may not even be noticable, but it would be there.

Concerning the Navy diver at the sub, it may not be really apparent, but he appears to be carrying a fairly heavy load, perhaps a mine. This would account for his more upright swimming position.

On the Para-Sea, if you'll look closely you will see the two vertical up arrows, one near the CG for the Para-Sea, and one at the neck, which represents a normal horsecollar BC. The Para-Sea upward component is so close to the CG of the diver, that it is very easy to overcome the moment arm. The moment arm for a horsecollar is about 4x the Pare-Sea moment arm, and therefore much more difficult to compensate for pitch-wise in the water (you know, pitch, roll and yaw are the three axis of rotation).

You are correct about the wing having a very good means of controlling pitch. But unless you are really tight in the BC harness, it will pull the scuba away a bit from the back vertically. I have not used this type of BC, and so cannot say how it would fit, and whether it would actually do this, but with shoulder straps the way I like them for modility, there would seem to be a potential to pull the scuba away with some inflation. This is why using the New Mistral with a back-mounted BC would compromise it's ability to perform well.

John

[nemrod]

Quote:

"In your photo, the regulator would be about one to two inches vertically lower in the water column if it was located lower on your back. With the Phoenix Royal Aquamaster, because of its performance, it may not even be noticable, but it would be there."

That is because as I said I do not have good horizontal trim in that picture which was the point.If I did then there would be no difference in height and I doubt even in the picture it would be more than a half inch if that.


Quote:

"But unless you are really tight in the BC harness, it will pull the scuba away a bit from the back vertically. "

This is a widely held misconception. Since the plate is fairly heavy and because there is a crotch strap it simply does not lift away. The standard jacket type and back inflate styles do lift away due to their sloppy fit but a traditional one piece harness with crotch strap combined with the built in ballast of the plate simply DOES NOT lift away. A well fitted backplate and wing are comfotable and secure,just does not slop around like you see jacket BCs with the rear of the tank for example lifting away--just cannot happen with a wing/BP. Vintage horsecollars are fun but they never really achieve good trim. However, diving sans BC depending on the tank and exposure suit etc, darn good horizontal trim can be achieved.

We will just have to wait for the day we can instrument these because I am convinced following extensive playing around with all of my regulaotrs, not just the Phoenix, in the pool that nothing good comes from wearing a tank low other than destroying trim. Good static trim would be such that motionless the diver would stay fixed in orientation and combined with good neutral bouyancy would also remain fixed in the water column, a goal to be achieved but rarely completely due to the dynamic nature of the body in motion and all the junk we tote along. Try as we might we are not fish.

Nem

[JES]

nemrod said:

.... So, what am I getting around to--lol---yep--the Trieste was the "new" Mistral of it's day. ...Nem

Wow, that hurts. Of all the regulators you could have compared it to you had to choose the new Mistral...

I prefer to think of the Trieste II like Dan Barringer describes it "One of Voit's last and finest two hose regulators, the Trieste was considerably smaller than the average regulator. The Triestes always featured an LP and HP port for accessories."

[nemrod]

I know Joe but it has been boring as of late and I thought I could stir y'all up a bit more. Only poor SeaRat is got game. I am in Columbus Ga on buisness, back in the third world.

But, when you look at it now don't the Trieste look like a new Mistral and suffer some of the same fauls for the very same reasons. OK, OK, the Trieste is better than the new Mistral. Happy

Nem

[SeaRat]

nemrod said:

What my tests show is that a higher tank position is not harmfull and in fact provides better trim without affecting breathing as long as the diver has good trim. In most of those photos above the tanks are quite high, higher than the urban legend requires, proving my point, the Navy agrees. The diver using the compass, it is hard to determine his position from that photo but it is always possible and desireable to be horizontal, fin dragging is inefficient and it does appear he is both horizontal and has a very high tank position, almost hitting him in the head...

...A BP wing inflated or deflated has nothing to do with tank positon, it does not move the tank away, the tank is attached to a metal plate similar to a SnugPack which is attached to the diver via a conventional harness as has been used since forever. Full or empty, a wing has no effect on tank position and a well trimmed diver with good weighting should have virtually no air in the wing anyways.




I think my buddy Jake took this pic through the glass at Weeki Wachee, not sure.

I would say the Navy diver with the doubles does NOT have good trim, he is feet low and it is clear to me he is fighting that.

Your Para BC picture does have good horizontal position it appears but I notice you have your feet drawn up to prevent them from dropping. This likely due to your trim being unstable (as is mine in my pic) and additionally I am saying with that good trim you could put your tank up or down (fore or aft) and it would have no effect on the WOB.

The modern wing/BP is superior to the Para BC or horsecollar or vest/jacket because it does not impart that rotaion you drew in on the slide.

BTW, a modern wing like the Oxy Mach V is biased to provide more lift near the hips and less near the chest and shoulders to prevent an imbalance unlike a horsecollar or your Para BC example.

Nem

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.

Concerning the wing, the well-trimmed diver would have air in the wing if (s)he was using a thick wet suit and greater than 30 feet deep. If the harness is such that the scuba doesn't lift away from the diver, then your argument is valid.

I have been pretty stable in my Dacor Nautilus BC too. It is actually better than the wing, as it is a constant volume system, and once the compensation is made at say 25 feet, no further adjustments in the air (releasing or adding) needs to be done. It does sound a bit weird as the air travels during a roll (it needs to go through several compartments). The Dacor Nautilus BC also allows me to use a double hose regulator and swim an my back:


I can also take off the scuba, and let it simply float in the water:


Underwater, I found that if I maintained a head-down attitude, that the double hose regulator breathed pretty well:


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.

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.

John

[nemrod]

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