Twin 38s and Twin 50s

[OystrPir8]

Would love to hear anybody and everybody's input when it comes to the use of TWIN 38s and TWIN 50s - particularly buoyancy characteristics, floating at the surface, the difference between th beginning of the dive with full tanks and the end of the dive with emty ones...

I have a pair of 38s that I have hesitated to get tested because I was told they were terrible but have heard some positive things here as well. I also have a guy who wants to sell me some 50s - should I? I usually dive with a 72, currently.

[Broxton Carol]

Heres some thoughts from experience. First of all you dont need them. Any of them. They are a bear to pack, lug around, and keep in service. The manifolds on the older ones have to be very carefully assembled or they will leak. I have had a set of 50' aluminum, and set of steel 38 cu footers too. Back in the 60's I had a set of blue dacor doubles which I liked a lot, they were made of steel. The 50s were nice to look at, but never really used them after I got them, so on ebay they went. Next I got a mint set of usd 38's from 1961. These were super lookin too, BUT, the cost of the hydros, and the stupid visuals will eat you up, and every time you loosen that manifold, it might not seal again in the joints. The 38' footers get VERY BOUYANT so remember that. Stick to your 72 and youll be diving with the best. If you feel you need 2 tanks after all this hash, just get another 72. Have a great one, Chucko

[Deleted]

Chuck and I don't normally disagree on stuff but here I guess we do........I have two sets of 38's.....one set I've had for close to 12 years, the other I won on ebay last year......I also have a set of 45's and a set of twin alum. 50's.......I prefer them to my 72's for one reason. They don't hit me in the butt and I can sit down in a boat with them......

Using them with a standard backpack takes some getting use to due to their tendency to roll off your back if the harnesses are not snug.......I created my own bacpac system with wings that solved that problem with my first set.......the second set has the original harness straps.....aka....vintage........

Chuck is right on the manifold issues and the cost of hydro's......not to mention cost of filling.......but I have my own compressor, carry a wrench or two on dive trips for tightening stuff......and have enough 38's and up to not have to have a local trip refill.......

They look cool..........I always wanted a set thanks to Mike Nelson on Sea Hunt........weight is not a problem, it an't that far from the truck to the lake.......and with the 45's, I need less weight on my belt.........I don't experience a bouancy problem but I tend to sink regardless if I have anything on or not..........

My two cents.................

[OystrPir8]

Would you recommend switching the 38s with 72s? I would imagine that you would need identical 72s. Thats a LOT of air (But a lot of weight too.)

I just like the look of doubles. Very Thunderball.

Maybe I will pass on buying the 50s. The guy who was selling them was a bit of a moron anyway. Kept trying to sell me broken old cracked junk that I dont think had been rinsed off and hadnt been touched since the 70s as if it were new ($$$) and would get kind of iratable when I said I didn't think I was interested. He kept showing me his instructor card to prove he knew what he was talking about and kept repeating "This stuff was top of the line when it came out...."

But if 50s were REALLY GREAT tanks I might have been willing to deal with him again.

[Broxton Carol]

I really did think the "mike nelson" look was super tough, but I never could get used to lugging them around. Your going to think im a real dope for this addition, but back in 1969 I borrowed a guys steel 72 DOUBLES, and hauled them all the way to the keys in my 62 corvair. I never was real strong, and I couldnt get the dam things lifted out of the trunk, which if you recall was in the front!!!!!!! I had my steel 72 SINGLE along too and remember diving off the shore then, and it was super clear!!!!!!!! Nobody around, you could sleep on the picnic benches under the starry sky. Its all changed now, so commercial. What regulator was I using? Well it was my 1962 usd Hydro Lung single hoser, with sea dive guage on it. Real heavy duty stuff.

[OystrPir8]

Wouldnt they tend to flip you on your back? Gosh - I would think that at the surface with a wetsuit and/or a horse collar you would end up like an otter. (very humerous to watch from the beach)

[SeaRat]

oystrpir8 said:

Wouldnt they tend to flip you on your back? Gosh - I would think that at the surface with a wetsuit and/or a horse collar you would end up like an otter. (very humerous to watch from the beach)

No, actually you don't. The doubles have some qualities to consider, especially the smaller units such as the twin 50s and twin 38s. They are:

--They feel better on your back, as they ride (using a military harness) on the back's muscles and not the spine.
--Doubles allow the double hose regulator to be positioned lower on your back, which gives the regulator better breathing performance.
--When lower on your back, they allow easy snorkeling, or you can roll to your stomach to swim (if you or someone turns off your air supply).
--As mentioned above, you can easily sit down on a boat or shore without the bottom of the tanks banging around, or you being suspended by the harness.
--In the water, you are more balanced with small doubles than with longer tanks.

The disadvantages:

--They are more expensive to maintain (but that has been overstated above).
--They probably weigh more.
--There is more water resistance when swimming.
--Even the twin 50s and twin 38s are heavier than a single 72.

So you have to make a choice, but both the twin 38s and twin 50 are excellent systems for use with vintage diving. Here's a photo of me with my twin 45s:


John

[Seahuntjerry]

Hi,
The metal to metal fitting on US divers can be sometimes impossible to seal.
There is a removable metal cup on the reserve side that usually doesn't seal.
Ron Miller said they used to heat them till red to rehardend them.


In my own experience I WILL never take them apart at the manifold.
On the 3/4 O ring sealed valves spin the tanks of while on the ground.

Someone else may have a better suggestion thats just my experience.

Jerry

[SeaRat]

I have been taking them (USD manifolds) apart for years, and gotten them to re-seal. Yes, it is metal-to-metal, but it is also soft metal to soft metal. Things I do not do is to try to clean them; where they seal, they will be clean. If I don't have a seal, I find it by water immersion, then tighten that side a bit more. Mine have sealed after that. If there is any scratch, that can be a problem, and that is in the way they are treated after being taken apart (when they are vulnerable to the scratch). I believe (memory) that you can get a bit better surface if there has been a problem by putting the tanks together while laying down, tightening the monifold nuts until there is good contact, then turning the center piece forward and back, but I have not needed to do that. We used to take these manifolds apart and put them together in the USAF and US Navy School for Underwater Swimmers without problems. I would never heat them, as that may do something to the metal's temper, or may even distort the ball. By the way, I don't remember a removable metal cup; all the cups I'm familiar with were integral to the manifold.

I have gone away from the USD manifold to the Sherwood metal-to-metal sealing manifold (with two posts), and still have no problem with them.

John

[duckbill]

OystrPir8,
Double 72s are SUPER heavy (out of water)....obviously more than twice as heavy as a single 72!
You didn't say whether the 50s you're considering are aluminum or steel. Mine are steel (see my avatar as of now).
Here are the specs and measurements I have taken on my own sets (1- twin 38s, 1 twin 50s):

Twin 38s, 1954 USD, 1800 psi
dry weight: 44.5 lbs. full
6 lbs. buoyant at 300 psi (13 cu.ft.) reserve in sea water
1 lb. buoyant when full in sea water

Twin 50s, 1971 Healthways, 1800+10%=1980 psi (twin 45s at 1800 psi)
dry weight: 56 lbs. full (1980 psi)
4.5 lbs. buoyant at 260 psi (13 cu. ft.) reserve in sea water
2.5 lbs. heavy when full (1980 psi) in sea water

Compare to average steel 72 on plastic backpack:
dry weight; 39.5 lbs. when full (2475 psi)
neutral at 450 psi (13 cu. ft.) reserve in sea water
4.5 lbs heavy when full (2475 psi) in sea water

Hope this helps, but not all twin 38s or twin 45/50s will have the same characteristics as mine- even though they may be at the same working pressure.

[OystrPir8]

I am thinking of startig another thread just to deal with those who have or do dive twin 72s (Is that what Mike Nelson dove? - Sadly I have not yet ever seen an actual episode of Sea Hunt) Do you know the specs for those? Dry/Wet, empty/full? This is GREAT information!
What are 44s like? I think Ryan Spences C shell uses 65s?
Tell me about tripples.

[fishb0y]

I dive double 72s... but having dove twins of various sizes with stage bottles attached... I think the 72s are light. I dive the 72s without any weight, however a wetsuit (3mm) is needed to give me the required bouyancy.

[duckbill]

oystrpir8 said:

I am thinking of startig another thread just to deal with those who have or do dive twin 72s (Is that what Mike Nelson dove? - Sadly I have not yet ever seen an actual episode of Sea Hunt) Do you know the specs for those? Dry/Wet, empty/full? This is GREAT information!

The specs for twin 72s would be double those for single 72s (see my post above), plus the weight of the manifold.

And, no.......I believe Mike dove little twin aviator oxygen bottles. I have a pair of those (1942 U.S.Navy, 1800 psi, with bushed necks and USD manifold), and they seem to be 38 cu.ft. each. The specs on them are probably very similar to the ones I gave for my diveable twin 38s.