Diving Configuration

[rstofer]

I have a DA AquaMaster and the Phoenix conversion is on order. I am also considering a 2d AquaMaster with no conversion and only modern diaphragms and such. Almost strictly stock!

I also purchased a brand-new-in-the-box US Divers backplate with harness - pretty cool.

But now I could use some information on actually diving the DH system.

First, let's assume I am going to forgo the horsecollar BC and depend on a surface float of some kind.

Second, let's assume we're talking Lover's Pt at Monterey Ca: maybe 50 deg F and perhaps 30' deep using an AquaLung SolaFX one-piece 7/8 mm wetsuit. Clearly I will lose buoyancy at depth.

Third, let's select a tank of modest capacity. Certainly 100 cf or less. I don't necessarily care that the tank work with the backplate. I am certainly willing to buy the new vintage harness as long as the tank bands will fit the selected tank. There aren't a lot of 6.9" diameter tanks available new and buying an old steel 72 via eBay isn't something I am inclined to do. "Used tank - last hydro in 1968" is not going to be my first choice. An aluminum 50 is 6.9" but that might be on the low end for capacity. Suggestions for a tank?

Fourth, I have and am willing to use a J-valve. For the purposes of this project, an SPG is optional. I just want to walk in, swim around in the shallows and walk out.

I am looking for two things, really: suggestions for a tank (and the related issue of harness vs backplate) and recommendations on how to set up my buoyancy. Obviously, I would like to be positive at the end of the dive. In this regard, a small tank might be better. It will get empty about the time I get bored. Short attentiion span...

I know that if I am just neutral at the start of the dive I will be negative at depth. I don't know how negative but I'm guessing that for the limited depths I am considering that it might not be a problem. But I don't know that!

Can I actually expect to be able to dive a configuration like this with a modern wetsuit? I realize it will compress a lot more than the vintage wetsuit on Sea Hunt. I am also not diving in Florida!

Thanks for any advice you can give and thanks to all for the previous info re: my Phoenix conversion. It is appreciated!

Richard

 

[SwimJim]

Well for tanks, use a 72. Nope, ebay is not the answer, your LDS is. Most of them have a couple old 72's around they are willing to sell. At least they are around here. No BC, even a horse collar means weighting for depth. You want to be neutral or a tad heavy at target depth. This means you'll be positive at the surface. This will take a little experimentation. It will vary with the thickness of your suit and the size of your body. For small adjustments at depth you'll be using your lungs. I dove the Monterey area 30 years ago in a quarter inch suit wearing about 12 pounds, but I had a good old horse collar. Properly weighted you'll have to kick down the first few feet, but after that it will be a breeze. Saftey stops? You don't need no stinking saftey stops, this is vintage. Besides, at thirty feet you be out of air long before your out of time. Test your rig in a pool first and tweak it. You'll be fine.
Read some of the older dive instruction books and learn how to clear a double hose and other related issues. You need to know that before the big day. Have a good time and be safe!

Jim

 

[rstofer]

I had planned to spend the vast majority of next summer messing around in our pool. I have the old "The New Science of Skin & Scuba Diving" and I am working through it. Particularly things like doff and don, hose clearing and that left rolling mask clearing - very cool.

I am not planning on trying to get my LDS to sell one of their tanks. I think the old steel 72 is out of the question even if it is the right diameter. Maybe if I could find a couple in current hydro on Craig's List or something.

It's never been clear to me what the weight and buoyancy characteristics of the steel 72 might be. I have a couple variations in a spreadsheet I found:

PST MP 72 3500 psi, 6.9" diameter, 30 lbs empty, -6# empty, -11.4# full
Faber 72, 3300 psi, 6.75" diameter, 28.7 lbs empty, -3.7# empty, -8.45# full

I realize that neither of these are LP 72s. I just haven't found data for them.

I have been thinking about a Worthington X7-80:
3442 psi, 7.25" diameter, 27.7 lbs empty, -3# empty, -9# full
I am assuming that the new yoke can handle the pressure.

I am also considering a Luxfer Al 63:
3000 psi, 26.6 lbs empty, +2.6# empty, -2.1# full.
I realize the aluminum tanks require more lead - maybe 6# worth.

For ballast, I think I'll use my DUI Weight & Trim Classic Harness. I don't have hips to support a weight belt.

Maybe I should do like the book says and take a string of weights to the bottom and, one by one, remove weight until I am neutral at my target depth - say 25' (midway between 20' and 30' - my areas of interest).

You are right about the safety stop. I can't possibly get anywhere near an NDL and for this iteration, that's the way I plan to dive. Use a smaller tank until I am out of air and the dive is over. No pushing the limits, no attempts for greater depths, just nice simple dives. I'll play with the J-valve until I think it is reliable and see how it goes.

Richard

 

[micklock]

here is a faber hp71, it might work for you
https://www.diverightinscuba.com/catalog/product_info.php?cPath=141_145&products_id=2284

 

[Luis H]

Here are the specifications for a steel 72.

72 cu ft Standard
Service pressure: 2250 psi
Working pressure: 2475 psi (2250 psi +10%)
Actual air capacity: 71.2 ft3 (at a working pressure of 2475 psi)
Outer diameter: 6.9 in
Length without valve: 25.1 in
Empty weight: 26 lbs (w/o valve)
Buoyancy Empty: 0 lbs (w/valve)
Buoyancy Full: -5.4 lbs (w/valve)


The Phoenix RAM can be used at any of the modern tank pressures. It uses the modern yoke (and all internal parts) rated to 3500 psi. Per my calculations the yoke can easily operate at higher pressures.

The internal parts are also rated to higher pressures. I haven't seen the actual max rated pressures in the Aqua Lung web site.


An original DA Aqua Master will not like the 3500 psi (or 3442 psi) tank pressures. With a full tank it will breathe poorly since it has an unbalanced first stage. Also the high pressure will put extra wear on the HP seat and the yoke will tend to flex a bit.

The vintage yoke will not actually break, but it will flex enough to highly increase the chance of an O-ring extrusion (and O-ring blow out).

The maximum recommended pressure for a DA Aqua Master is 3000 psi, but 2500 psi is better. The Navy used the DA Aqua Master for years with 3000 psi tanks, but they also had an unlimited supply of replacement HP seats as they wore out.

 

[captain]

My advise would to not completely rule out the old 72. I have 10 of them I bought over the years, only one was bought new and of the rest some were in and some were out of date when I bought them.
The whole idea of the 72 is it was designed for diving before BC's came into use so it is the better choice when going back to that type of diving. Just about all of the tanks used in the before BC era were designed to have the least effect on buoyancy.

 

[simonbeans]

I don't understand why you are dismissing a 71.2 cu ft steel tank. I have at least a dozen, none of which were bought new by me. All have passed hydro and vizuals as required. The dive store where I work uses 72s in all aspects of training. Galvanized for pool use and vinyl for open water dives. I am also in full agreement with Luis about using a HP tank with the DA. I would consider a Royal AM or a Phoenix as both regs use currently available HP seats. Finding original DA seats is a bit problematic. As for bouyancy characteristics. Everybody seems to be so concerned about weighing these days. In the 1960s we took a guess as to how much weight to use and dove. If we were too heavy, swim. If too light, grab a rock or two and next dive add a couple of pounds. I think everybody seems to think that being perfectly neutral at all depths is imperative. Sure it is nice, but in the 1960s, no big deal. Recently I saw my buddy while diving with a vintage double hose without a BC, horse collar or even a "snorkel vest", pick up a small plastic pail and with the aid of exhaust bubbles, add some bouyancy for the dive. Don't spend so much time worrying about bouyancy numbers, just go dive. As for 72s, check back in a couple of months as I will be have two nice vinyl over galvanized 72s for sale. Got them on Craig's List, will be hydroed and vizzed.

 

[pescador775]

Concerning the buoyancy of the steel 72, below is a message written a few months ago. It addresses the buoyancy of a particular European cylinder and mentions the vintage, steel 72:

The math looks OK with one small error. It affects things a little. The tare weight of 14 kg and supposed buoyancy of -.61 would indicate the bare tank is neutral buoyant although I believe now that it is a little bit positive.

I went out and weighed a 72 on the old bathroom scale and the result was 27.5 lbs, heavier than I thought (if the scale is accurate). Using ratios, that would put your tank buoyancy (bare tank) at -2.5 or about 1 kilo which is still heavier than your calc, so I started wondering if the 72 is neutral after all. Using ratios is still an estimate only but the result should be pretty close if "conventional wisdom" of weight and buoyancy of the 72 is right. Using that as fact may have been a mistake. The 72 internal volume is actually about 1% larger than 12 liter but that should not make a difference. It may be that I also heard wrong about the buoyancy of the "72" and that it is actually positively buoyant. It doesn't take a large discrepancy to change the result so as to be significant for diver's buoyancy. The 72 weighs 12.5 kilos = 1.6 liters steel. 12.1 + 1.6 = 13.7 L salt water = 14.1 kilo = 31 lbs. IOW, the 27.5 lb tank displaces 31 lbs suggesting the bare tank has a buoyancy of +3.5 lbs. A 72 with valve would have a buoyancy of about +2.5 pounds. I don't know for sure but the math seems to confirm.

Pesky

 

[DA Aquamaster]

A plastic milk jug on a short piece of line tied to the valve was a common poor man's "BC" for years. But if you are really concerned about being neutral at depth I would not rule out a horse collar. They add very little drag and are still quite vintage.

I also agree a steel 72 is a good choice for a tank. With due respect to Luis's specs, and in confirmation of Pescadors, they were made by at least a few companies and they varied a bit. At one point I hade a dozen or so and most of those floated when empty and a couple others sank. Last week I assembled a set of double steel 72's with light weight bands and a NOS 1958 vintage USD manifold with about halh the metal of a modern manifold. To my mild surprise the set floated in the tank with about 500-700 psi in them while I was checking the manifold connections for leaks. I roughly estimated that each tank had to be at least 2.0 lbs positive for that to occur. At least it floated evenly suggesting the tanks each have similar buoyancy - not a surprise as they were pretty well matched by height, age and manufacturer. It was not a major surprise as the same tanks required an 8 lb v-weight to have comparable buoyancy traits to double X7-100's with the same modern manifolds and similar slightly heavier bands.

At the other extreme I have had other steel 72's that were distinctly negative when empty even in fresh water so be advised that buoyancy could vary a pound or two either side of neutral for any given vintage steel 72, but on average they are probably going to be a couple pounds positive when empty.

Be aware that the newer shorter high pressure 72's are also more negative. A PST MP 72 (3300 psi service pressure) is 6 lbs negative when empty and 11 lbs negative when full, and the Faber 3000 psi 72 is about 3.5 lbs negative when empty and 8.5 lbs negative when full.

In terms of larger tank selection X7-100's are about 1.5 lbs negative when empty, but the swing weight is also greater due to the larger volume. For that reason I would be very careful considering any tank larger than 80 cu ft with out a BC of some sort.

Another popular option in the day were double steel 45's or steel 50's - they tend to run somewhere between 0 and -1.5 lbs regative when empty each, so approx 3 to 6 pounds negative with bands and manifold when empty. I had both as my first sets of doubles and wish I still had them as they trimmed and dove really nice. (I broke them up for my 12 year old when he started diving and sold them to another parent for his kids a few years later.)

In any case, regardless of whether you use a horsecollar and whatever tank you use, it works pretty well to weight yourself so that with all your stuff on and with a near empty tank(s), you float at about eye ball level when vertical in the water and with full lungs. You should then just barely sink when you fully exhale.

That will leave you neutral at about 15-20' with average lung volume in the average wet suit and will not leave you excessively negative at depth with a full tank. But be advised you will be about 5 lbs negative with a full tank at the same 15-20 feet and will be even more negative due to wet suit compression at depth.

Configuration wise with a PRAM you can set yourself up with a normal inflator, octo and even a dry suit inflator if you go that route. I have had good luck with getting the nozzle to seal and have the HP port pointed at about the 4 o'clock position, leaving 3 LP ports pointing in about the right directions and still not being interfered with by the hookah port.

With a DAAM, you can add an SPG using a banjo fitting (assuming you have a long yoke) and you can add an LP accessory with an adapter on the hookah port. Normally either an octo or an inflator for a horse collar BC. In the latter case, the USD horse collar with the vintage inflator works great as it works well with the right side angled hookah port. These do show up on E-bay on aregular basis - just be sure the bladdr is in good shape as the polyurethane bladders have a habit of getting hard and cracking. There are a few new bladders available on vintage diving sites now and then.

The single bladder Scubapro horse collar is also a good choice as it is virtually indestructable and easy to repair - but it has the hose on the left side in a conventional manner so horse routing for an inflator gets interesting with a DAAM. BUt oral inflation is a workable option.

If you get an LP adapter for the hookah port and opt for an octo, a 90 degree elbow may be handy to route the hose down under your arm. You could also potentially add a splitter on the hookah port adapter and run an octo and inflator, but I suspect in addition to the ugly/rube goldberg factor, the hose routing would get messy.

I have both original cam packs and backplates. With a DAAM, the cam packs work great and most are fairly short and designed to ride fairly low on your back, placing the can of the reg in between your shoulder blades where it should be. With a PRAM it can be a bit more problematic as the nozzle adds enough extra lenght that it can interfere with the tank sliding low enough in some cam packs and can make getting the reg low enough a bit of an issue. In my case, I prefer to use a back plate with my PRAM.

My "vintage" diving/PRAM backplate has slightly longer shoulder straps to help it ride lower on my back and with a single tank I use a single tank adapter with the strap through the center set of slots to help the tank ride low enough. With doubles 72's on the same plate, I use vintage single outlet manifolds with the outlet underneath tthe crossbar and with the upper band mounted just below the shoulders of the tanks. That combination again leaves the can right between the shoulder blades.

J-valves work fine but I guarentee that at some pioint in your J-valve diving career it will get hard to breathe, you will reach back to pull the valve and discover it caught on something and already got pulled during the dive - meaning it is hard to breathe because you are OOA.

Many older J and K valves have a 3/8" port in them to connect to an SPG hose. That is another alternative to a banjo fitting. Old Seaview gauges show up now and then on e-bay in excellent condition and they make a nice vintage diving SPG and they are interesting as the SPG hose screws straight into the back of the gauge, not the side.

 

[pescador775]

At the other extreme I have had other steel 72's that were distinctly negative when empty even in fresh water so buoyancy could vary a pound or two either side of neutral.

I would like to point out that buoyancy numbers are given for salt water and that a tank which is positive in salt water may actually sink in fresh water. I am certain that you know this so the above quote is possibly an eggnog moment.

In their sales literature, US Divers stated unequivocally that their 70 cf steel tanks were "positively" buoyant and with good reason. This was a major design criterion for any tank sold in the USA in an age before buoyancy compensators. Furthermore, my calcs strongly suggest that the 71.2 was/is also positively buoyant.

Why get exercised? Well, for one reason, being positively buoyant on the bottom is absolutely miserable. Also, as one might surmise from my previous msg; some months ago, I wasted time and was embarrassed through reliance on crap data from a "vintage" source. Won't happen again.