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Post by ductapeman on Nov 26, 2006 15:55:56 GMT -8
Hi, I'm getting back into diving in general and the old US Divers twin-hose rigs in particular after a (very) long absence, and I've been wondering about what sizes of tanks are suitable for a twin-tank setup? I've seen, or guessed at, 38s, 63s and 72s-- very interested in hearing the pros and cons of these, or other, setups. And as a side note, something has been really bugging me for a long time: what size are those tanks that the Cousteau crew used in the triple-tank lashup??? Thanks in advance for any help-- Lee
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Post by ductapeman on Nov 26, 2006 18:27:54 GMT -8
Thanks again, Mossback-- it's the multitude of opinions that I'm after. Back when I was diving-- back when air compressors were powered by coal-- a lot of guys were diving twin rigs, and I always thought they looked severely cool, but I never had the coin to be able to think about one. Now I've got a little bit of disposable income, but my back isn't what it used to be, so this kind of information is a great help.
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Post by duckbill on Nov 26, 2006 20:45:10 GMT -8
Low pressure twins usually end up being buoyant at the end of the dive. Not all sets do so I have been told, but both my twin 38s (1800 psi) and 50s (1980 psi) wind up being 6 and 4.5 pounds buoyant respectively at 13 cu ft left in the set. I've heard that aluminum 50s are even more buoyant, but I'm not familiar with them. Twin 72s end up pretty near neutral, but thay are larger and carry a working pressure of 2475 psi. So, doubles themselves are heavier than singles, AND you may also need to carry more weight for the smaller ones. Doubles also increase drag substantially.
BUT: Doubles do look cool, are shorter, and allow double hose regulators to be mounted as low on the back as possible if the manifold can have the yoke pointing down.
I'm sure there are other pros and cons I can't think of right now. I'm in a bit of a hurry. I'll check back later on.
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Post by SeaRat on Dec 2, 2006 20:19:19 GMT -8
My Aluminum 50s are not real buoyant. I like them, and don't do much about the weight difference between them and the twin 45 steel tanks (1800 psi).
Between the two, I like my steel 45s just a bit more than the twin 50s.
I have thought about putting together a set of Al 40 cubic foot tanks, as they would be about the same as my USAF steel 40s that I had in the 1980s. So that is one option that I like for doubles.
The other option is for triple tanks. Ductapeman, you asked about Cousteau's tanks, the triple sets. I don't know their capacity, but in his book, The Silent World[/B], Cousteau said that some (at least) of his tanks operated at 150 atmospheres. If that's true, then these original Cousteau tanks were filled to about 2200 psi (14.7psi/atm x 150atm = 2205 psi).
John
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Post by nemrod on Dec 2, 2006 23:21:07 GMT -8
"I've heard that aluminum 50s are even more buoyant, but I'm not familiar with them."
No, that is not a true statement. The Luxfer aluminum 50 is 1.4 lbs (each) positive when completely empty.By the time you put a heavy double post manifold on them like the Sherwood they are approx neutral when empty. When full they are 2.3 lbs (each) negative plus the additional weight of a dual manifold. Essentially double aluminum 50s are quiet nice underwater. I would prefer they be slightly lighter and go slightly positive to the end maybe by a couple of pounds total but they are what they are and it is pretty good. On land they weigh about 45 lbs compared to 32 lbs for an aluminum 80 and the additional weight is noticeable.
The triple 30s I am considering for my Nemrod triple manifold will be about 38 lbs on land, will be three lbs negative total (all three combined) full and just under four lbs (again all three) positive when totally empty but then the valve will be factored in but it is not as heavy as the Sherwood plus bands so about two pounds positive I figure. Not bad.
James
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Post by duckbill on Dec 3, 2006 15:23:44 GMT -8
Thanks, James. The buoyancy figures I see from three sources for the Luxfer aluminum 50s confirm the 1.3 to 1.4 lbs buoyancy when empty, but the only source which specifies whether their figure includes the valve or not says that it does. Still, though, the cylinders should never be completely empty anyway, and the given figures look good. Thanks for clarifying that for me. I should have studied it better before I said that, but, as I said, I was just repeating what I've heard before.
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Post by SeaRat on Dec 3, 2006 16:18:08 GMT -8
I just used my twin 50s in the pool (write-up later on the 1961 Calypso regulator). I would also point out that those figures in Nemrod's post above are for salt water, as in fresh water the twin 50s are just a bit heavier, and the tanks themselves do not become positively buoyant when empty. This is an important tidbit for those of us who do dive fresh water a lot. Concerning the triples, I have figured out a way of setting up triple tanks without a triple manifold. Get the tanks you want (the triple 30s that Nemrod discusses above sound great), use a modern twin-post manifold, then mount the tanks using double tank bands (two sets, or four bands to get both sides). Set the cylingers up so that the middle cylinder is the main post for the double hose regulator. Mount the third (reserve) cylinder upside down on the right side. You may wish to use a single K-valve with a manifold guard here. Put a balanced first stage on the third tank, and tie it into the LP port of the double hose regulator (Aquamaster, Trieste II, etc.) with a LP line (you can use the seat of a AMF Voit MR-12 regulator to make this connection, as it can be reversed, and both sides are threaded for an LP female connection). I was originally thinking of using the OMS 45 cubic foot cylinders for this, as they already have the manifold and bands available. They also make a manifold guard for the single K-valve. But, again the finances are not yet here for that. This setup would weigh about 65 pounds too, which is quite a bit more than the triple 30s. But they would also have 135 cubic feet of gas available. Here's the OMS website: www.omsdive.com/cyl_spec.htmlThis style of scuba is almost exactly what Emile Gagnan and Jacques Cousteau described in their patent, except that they connected the tanks using a HP line rather than a LP line off a first stage (which had yet to be invented). Interestingly, their patent actually foresaw that this is a possibility (the use of two regulators), in that instead of a single two-stage regulator, Gagnan and Cousteau saw the possibility of placing two single stage regulators in line. The difference here is that the double hose regulator (in my case, a Trieste II) would be a two-stage balanced regulator handling the two cylinders (center and left), while the other regulator would be a balanced single stage (probably an MR-12), which would connect into the second stage of the Trieste II for the reserve tank. Anyway, I thought you would like to hear about these thoughts. I'm not sure I'll ever put this together, but it is a distinct possibility using only vintage gear, and no triple manifold. The neat thing about this is that you would have two posts for redundant regulators (the left, which so far we have not touched), and the right with the first stage on it (which would be logical to also have a second stage on it, if for nothing else than ease of removing the first stage). I wonder what the dive boats would say about such a rig, complete with a BC? John
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Post by nemrod on Dec 3, 2006 16:39:09 GMT -8
The figures I gave for the bouyancy is with a K valve but a Sherwood double post valve is heavier than two K valves by quite a bit.
Nemrod
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Post by Terry on Dec 3, 2006 19:09:02 GMT -8
I've got a pair of twin 50's (Luxfer) and I've never had any problems with them regarding buoyancy. With my Voit Navy and backpack it makes for a pretty good looking rig. As for weight though; Mossback does bring up an interesting issue; because these tanks do somehow seem to gain weight with our age. I have given some thought myself to getting a pair of 38's as he mentioned. They seem as though they would be much easier on the back and more comfortable, and still LOOK COOL! ;D As a matter of fact the only other thing that is worse when we talk about "Vintage Diving" is when I remember all too well that I was diving this "Vintage Stuff" when it was brand new "State of The Art" equipment ;D Heah SeaRat; Does that mean that You and I are Vintage? On that note; enjoy and Happy Holidays To All! Terry Stevens
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Post by SeaRat on Dec 3, 2006 23:34:34 GMT -8
Terry,
I think so; I bought my first Mistral as a new regulator in 1970 when I was in Florida, and my Trieste II as a new regulator too in 1973 when I was back home in Oregon (a lot happened beween those two dates for me).
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Post by nemrod on Dec 4, 2006 0:34:02 GMT -8
Terry, in you avatar pic, what is that rig you got there?
James
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Post by Terry on Dec 4, 2006 15:46:55 GMT -8
James; In my avatar pic I'm wearing twin 63's (Luxfer); an Oceanic Chute II BC, and a Nemrod Snark III Silver Reg.. By the way; if you check the Buy, Trade , Sell section on Thes VSS message you'll see this reg is up for sale or trade. Also in this pic I have and SPG connected to the HP port, and my BC inflator hose connected to the LP port of this reg. Terry
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YankDownUnder
Pro Diver
Broxton 'green label' Aqua Lung and 1954 USD Rene triple 44s.
Posts: 162
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Post by YankDownUnder on Dec 6, 2006 0:24:44 GMT -8
What's wrong with a single steel 72? They are the most successful tank of all time. What other tank was made in such quatities, so long ago and is still in use. You only have the cost of buying one tank, servicing one valve, paying one test, and one VIP. If you didn't get cold enough on the first tank you can surface and get another one. I loved the look of Mike Nelson's twins, but as they are behind me, I can't see them anyway. The single 72 has about the same air as the twin 38s, and there are no manifold connections to leak, and less drag in the water.
I admit, as a collector, I have a triple 44 USD set, 2 Australian Porpoise twin 50s and a Siebe Gorman twin 40. However, while they all work and are in test, it is more trouble than it is worth to dive them. I have two steel 72s and if I want pain, I can double them with a vintage doubling manifold and a set of twin bands. 72s seem to be very cheap to buy too, and always seem to pass the hydro. So much for my two cents worth.
In any case, I hope you have fun. That's what it's all about.
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Post by nemrod on Dec 6, 2006 1:47:19 GMT -8
The Sherwood valve allows redundancy for deep vintage dives for one thing. Doubles and triples look cool and sit closer to the back and don't roll like a single in a harness (well--not really a problem) and because doubles and triples look way vintage even if the tanks themselves are not. I cut an end cap from hardwood as an experiment and bonded it to the square bottom of an aluminum 30----hmmm--it looked really old fashioned. I could possibly do this in aluminum and use a Pro Seal to bond it.
This from a guy with a triple in his avatar--lol--just kidding you.
James
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Post by duckbill on Dec 6, 2006 21:49:09 GMT -8
The regulator on twins with the yoke turned down sits around 1 to 2 1/2 inches lower than on a single. That's a good thing. AND, they don't hit you in the rear or make it difficult to sit (unless they're 72s, 80s, etc of course).
But, as mentioned, they are twice as expensive to keep serviced, and some shops will double charge for air. Make sure to explain to them that they hold less air than an aluminum 80 and have a single yoke to which to connect, AND are lower pressure. They aren't independent double 80s, so why the double charge? Stick to your guns, and they may hem and haw, but they will have to admit that you are right. I've had to do it that way many times. Common sense, LDS!
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