Doubles "discussion"

[technidiver]

I was using my LP72 steel doubles today for the second time. Doubles are still new to me and they have some niches and a bit of a learning curve. No wing or BCD either, the real way to dive. Or as my friends call it, "hooligan diving".

I run an aluminum apex backplate to save weight, and a dive right hogarithian harness. Both courtesy of NESS. I use 7.25 inch bands with a steel bolt kit I pieced from the hardware store. Nice and tight on the 72s. Sherwood dual outlet manifold, no J valve. That's for another project

So I went into the pool today, and I finally got a rough estimate of my weight. Last time I was overweighted and sunk like a stone in the pool. I had a Farmer John 7mm with gloves and booties and some apeks RK3's which aren't buoyant. I needed 12 pounds of weight to be slightly buoyant at 1000 PSI (tanks were half empty).

Question: will I need a few more pounds to compensate or if I start with 2400 PSI will I have the weight necessary to be slightly negative?
(I'm also aware of wetsuit compression at depth, so that's a factor in OW but not in a pool)

I was also slightly negative towards my head so my tanks shifted forwards and acted as a hydro-plane on a submarine and sent me into a vertical dive everytime. I don't use a V weight yet and used the weight on my belt. I also don't have a crotcg strap yet. Is there any way to prevent the tanks from shifting forward and sending me into a vertical dive like a U-Boat?

The pool water was 64 degrees Fahrenheit so I only putted around for about 300 psi and got out. Just had to do a few spins and test my regs and gather enough information to ask questions.

Let me know what you think.

TD

[Deleted]

My take and someone or many will probably correct me. You want to be slightly positive on the surface with full tanks. Swimming down so feet, the weight of the water above you will push you down. Example: diving at Possum Kingdom lake back in the 60's there was a ledge that divers normally left their weight belt on before continuing on down. Collecting it on their way back up so they didn't Polaris as they got closer to the surface. I cheated and used a May West vest to help my boyuancy at depth, but it was a real pain emptying coming back up.

I know this is not feasible for most diving in open water, so you need to adjust your surface weight so you don't get too heavy at depth......others may have a better way or trash my comments totally....In fact I bet SeaRat has a ton of advise for this since he did a lot of twin tank diving without anything other than his skivvies in the Navy
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[technidiver]

I've heard rumours, more like stories, of divers doing that with their weight belt. Now I can understand why. Diving without a wing or BCD really is a skill, but I don't care to waste air during the dive puffing up some nylon vest. More bottom time more fun.

The first time I had my steels on in the pool I sunk like a rock in my tee shirt and shorts. Lucky I didn't burst an eardrum dropping to 20 feet!

I'm thinking about getting some trim pockets and positioning them on the rig and playing around with different weighting too. Dive Gear Express sells the DGX brand for $10 a pouch.

TD

[snark3]

TD- I'll throw my 2 lbs in here.Keep in mind my numbers are estimates. If I remember correctly a steel 72 is -3.5 negative when full and +.5 when empty. You've got them doubled up so you're looking at -7 lbs full and +1 empty. Let's assume you're not going to drain your tanks completely. The estimate I would use is a 7 lb variation from dive beginning to dive end. Depending on your dive plan and personal comfort, do you want to start your dive heavy and be close to neutral at dive end or neutral at dive start and floating at dive end. What I did when I dove double 72's with no BC was put my suit on and attain neutral buoyancy with the suit only, then take a 4lb weight off. I'd go in a little negative and be a little positive at the end. Most of my diving was (is) beach diving so its not like I'm rolling off a boat and sinking like a rock. The other thing I did was attach my dive flag to a car inner tube, I could hang on to it if I was a little heavy on the surface. As I got light at the end of my dive I might toss some rocks in my "goodie bag". This is all personal preference and what you feel comfortable with.
As far as the tanks moving toward your head and putting you in a constant "dive" a crotch strap will keep the tanks lower on your back, which is more desirable if you're using a double hose. You might also consider some ankle weights to help with your trim.

[SeaRat]

It has been quite a while since I dove twin 72s. Here is a photo of a dive in about 1975 in Newport by our Pararescue Team from the 304th Aerospace Rescue and Recovery Squadron:

304th ARRSq historical002 by John Ratliff, on Flickr
Note that we were wearing a military harness, and that harness always had a crotch strap. In salt water, these tanks were a bit heavy when full, and light but not floating when empty. They were designed for diving, and their density was designed with divers in mind.

The first aluminum tanks I owned were the long 2475 psig 72 cubic foot tanks, the "floaters," which required about 8 pounds of lead to sink in fresh water. Here they are in Cloar Lake, Oregon in about 1984.

John using twin AL 72s in Clear Lake by John Ratliff, on Flickr
Note the PVC tube in the back, with the 8 pounds of lead cylinders inside it. Again, I was using a military harness.

Here is Terry Wetzel and Stephen Samo diving twin 72s with the military harness in Okinawa in 1968.

PJ Okinawa Dive003 by John Ratliff, on Flickr
Note the lack of any weight belt at all. Both Terry and Stephen were diving the USAF method of the time, and had on LPUs (underarm life preservers) that were issued as standardi dive gear in that 1968 era. There was no buoyancy compensation at that time.

I don't currently dive with twin 72s. They are simply too heavy, and my dive site requires about 200 yards of walking down to the Clackamas River and back up to my Honda Pilot SUV. So I've converted to twin steel 50s, which I dive with a weight belt, or my twin steel 45s, or my twin AL 45s(?). Here are photos of those:

IMG_2647 by John Ratliff, on Flickr
This set requires about six pounds to be neutral in the water. They were produced by U.S. Divers Company as a lighter, shorter alternative to twin 72s. Their working pressure is 2100 psig.

IMG_2888 by John Ratliff, on Flickr
These steel twin 45s are neutral in the water when empty, and don't cause too much negative buoyancy even in fresh water as their working pressure is 1800 psig.

My newest twin addition are these twin AL tanks (and I'm trying to remember their capasity--45 cubic feet???;
I'll have to re-look at this). These guys are slightly buoyant in fresh water at the end of a dive, but held down by their manifold.

IMG_2601 by John Ratliff, on Flickr
Note the burst HP line from my SeaVew vintage pressure gauge, on its last outing (dive didn't occur, as this happened upon pressurization of the line when I was donning the scuba)--ever. I also just realized a possible reason for the burst hose--I put this vintage Sea-Vew gauge on a 3000 psig system, when it was only designed for 2475 max psig. Even though the gauge goes to 3000 psig, don't do this!

I recently came back from snorkeling in Maui, and found myself slightly too buoyant for good free diving (had to work to get to 25 feet), and so next time will probably wear about six pounds of weights when diving sans wet suit in the tropics.

I dive with about 16-20 pounds in fresh water on my weight belt currently, although I've lost a few pounds this last winter, and may have to re-look at that when I get in the water again later this week. I try to be neutral at the surface on a full breath (float vertical at eye level on a full breath) with a full set of doubles (or a single, for that matter). That way, I can exhale and dive easily, and am not too buoyant when the tanks are low. I routinely use my Para-Sea BCD (which I patented in the 1980s and remains the most expensive BCD ever bought--nobody bought my design), and so do add some air at about 25 feet with my wetsuit.

IMG_2704 by John Ratliff, on Flickr
Me, diving my Para-Sea BCD with a single 72, using my Healthways Hybrid Scuba regulator (Gold Label innards). Note that to compensate for buoyancy loss with this regulator setup, the BCD is orally inflated.


John

[technidiver]

Thanks Skip and John for the input!!

I do agree the 72s are fairly heavy. There's pretty much only fresh water in Canada so I might be able to shed some pounds off the belt compared to diving in salt.

I think I'll need a crotch strap if I plan to dive the dubs successfully. And I might also add a grab bag to add some rocks if necessary, that's a good idea Skip.

I'm thinking I'd rather be slightly heavy at the beginning of the dive and neutral towards the end, so I'm gonna play around with my weight for that. Ankle weights are also an option too. But the prices for a little pair of ankle weights is ridiculous. $45 at my local shop.

When diving the dubs with the double house I never noticed the hoses being too buoyant or uncomfortable, so at least I've got that part right.

Speaking of the Sea Vue gauge, I recently picked up one in a box of scuba stuff. Thanks for the tip John. I'll only use them on 2500 and below.

The reason why I'm getting all my ducks in a row in late May is because I plan to go to Tobermory this summer. Best fresh water diving in North America. Cold too. With the doubles I use a Conshelf 14/Supreme as my backup reg with a 1085 USD second and the original Calypso second stage with the unique diaphragm. IMHO it breathes as well as a Titan second stage.

TD

[Deleted]

Speaking of carrying a grab bag for rocks........twice I have had to use something such as that. Back in 88 I was with my youngest son on our first trip to Cozy-mel......he was a skinny 12 year old and sank like a rock, but when he hit the salt water the first time at Cha-ka-nob park he couldn't stay down with the 6 lbs he was wearing.....our BC's were new, Zeagles and they had liners that came out in each pocket of the bc.......there was a large rock on the bottom (at the entry point) that I had him hold on to, while I filled those two liners with sand. (probably some marine life as well)......worked quite well.........the second time was in 2006. I was solo diving in Cozy-mel with my RAM w'hooka port adapter I designed, and using again those pesky alum. 80's I am not accustomed to, could not stay down.....so I filled my bc pockets with two rocks.....worked well. The next day I rented another tank and when the young fellow asked me how much weight I needed...I simply told him 9 lbs and two rocks worked ok the day before
.......he gave me 12 lbs. Was enough.