First doubles dive today

[gbray]

It finally happened. Friday I picked up my double 72's and got to dive them today. Wow what a difference.Getting to the water wasn't terribly difficult but putting my fins on was a challenge. Getting out of the water was interesting also. I don't know how you who dive double 120's do it. I have a new respect for you.

Once in the water everything was different. It took some getting used to. I was a little nervous at first because I didn't know what to expect. I dive a 5mil wet suit with a 3mil hooded vest.I started with no extra weight and just my tanks with an aluminum b/p. I ended up adding 4lbs of ditchable weight. I was very unstable at first wanting to roll side to side. buoyancy was a lot more sensitive. I found my breathing affected buoyancy more than with a single al80. while trimmed out I need to look up(tilt my head to see in front of me) and the back of my head was constantly hitting the isolation valve. I am happy to report I could actually reach my valves though.

It was a fun new learning experience today. I wanted to share it with all of you and ask if the things I described are normal. Do you have any advise for me and would you like to share your first doubles experience. BTW my second dive was a lot less stressful and enjoyable. http://www.scubaboard.com/forums/images/icons/icon_biggrin.gif

 

[DA Aquamaster]

You need to approach the trim as a system where any ditchable weight, the position of the ditchable weight, the plate, the wing,, the position of the wing on the plate, the position of the tanks on the plate and the position of the tanks in the bands all play a role.

If the isolator is hitting you in the back of the head, you can move them a bit lower in the bands, provided the upper band is not already at the shoulders of the tanks, and provided that you benefit from moving the mass of the tanks aft a bit or can compensate by moving the wing farther aft as well or moving the ditchable weight farther "forward" on your body.

Trim wise, the amout of gas you carry in each side of the wing is important to keep from rolling to one side or the other, but after a few dives you will start managing that without even thinking about it.

You have twice the swing weight and are significantly more negative early in the dive. That requires a lot more gas in the wing and that larger volume of gas experiences more change in volume and lift as you change depth, so you have to make more frequent buoyancy adjustments and you will find yourself being much more precise and planful in making adjustments and you will be more cognizant of depth changes. For example if I am very slightly heavy, but will be ascending in a moment and know I'll eoither be rigth on or will need to dump gas anyway, I will compensate for the slightly heavy condition by maintaining more average lung volume by using a slightly quicker than normal exhalation and inhalation with a longer pause at the top. Similarly, I may maintain that larger than average lung volume (with an open airway) to start an ascent by extending the upward swing in the breath induced buoyancy cycle.

If you think its hard now managing doubles,wait until you add a dry suit.

Your statement "I found my breathing affected buoyancy more than with a single al80" is odd. The net effect of changes in lung volume is the same, but it may feel different as you now have more mass and a bit more lag time for any changes. I suspect the change is no greater, but that adjustments you make feel different due to the greater lag time involved, so you are probably over or under correcting when you make a change.

You will need to dive them awhile to develop a "feel" for your buoyancy and the greater lag that occurs due to the higher mass, and it will speed the process if you think about what is actually going on.

 

[halocline]

It finally happened. Friday I picked up my double 72's and got to dive them today.....I found my breathing affected buoyancy more than with a single al80.

Everything else you described is perfectly normal. I find with doubles that breathing affects buoyancy less, and I suspect you will too with a little experience. You're diving with a lot more mass and the change in your lung volume is proportionally less influential than with a single tank in terms of immediate affect. I bet you were just experiencing the newness and general unfamiliarity of doubles. Once you get used to them, to me they're more stable in the water, but it is true that you have to develop the ability to anticipate buoyancy shifts, because once the tanks are in motion up or down it takes more effort to counteract that.

Have fun!

 

[it_mike]

I did my doubles for the first time Saturday, and I agree, everything is different. Walking down to the shore with the HP100s was bad enough, but having to walk back up the hill...

The fins went on in the water, with a hand on the dock, and I was running heavy, just in case. I added the headache of new wings, and didn't notice until about half way through the dive that they had a shoulder dump. I'm accustomed to an elbow, so I was inadvertently/accidentally dumping air as I fought to control my buoyancy.

Hope you had as much fun as I did.

 

[TSandM]

In addition to what DA said about dropping the tanks in the bands, you can loosen the harness and tighten the crotch strap to keep the rig stable. If the 72s you're referring to are steel, I would imagine you were fairly head-heavy with so little other weight. Dropping the tanks will help with that, as well as with the isolator-to-the-back-of-the-head issue. For most people, having the tanks as low as they can be and still have the valves reachable is the best position to balance the gear.

Doubles have a lot of mass, and if they get off balance in any direction, they REALLY want to keep going that way. I found it very important to have the harness snug to prevent them from going one way when I wanted to go another -- having the tanks lead the dive while you scramble to stay under them isn't fun!

I have actually found that the additional inertia from the double tanks HELPS my buoyancy control, because it takes so long for them to get going anywhere, it gives me time to adjust before I'm out of there. (The flip side of that is that, once they DO get going, they're harder to stop, so if you begin to yo-yo, it's hard to damp out the oscillations.)

Anyway, except for your comment about the effect of your breath, everything else you mention is completely normal. It takes a few dives and some gear tweaking to get doubles settled -- and sometimes, a change of tanks. I struggled with my 72s for several months before strapping on a set of 85s, and taking a deep, delighted breath because I finally felt balanced.

 

[DA Aquamaster]

I did my doubles for the first time Saturday, and I agree, everything is different. Walking down to the shore with the HP100s was bad enough, but having to walk back up the hill...

It's technique more than anything else - once you get used to it, you don't even notice it.

The fins went on in the water, with a hand on the dock, and I was running heavy, just in case. I added the headache of new wings, and didn't notice until about half way through the dive that they had a shoulder dump. I'm accustomed to an elbow, so I was inadvertently/accidentally dumping air as I fought to control my buoyancy.

I am not a big fan of a shoulder dump on a doubles wing. As you discovered you can accidently dump and if it ever breaks or fails, you have a serious leak high in the wing with no ability to trap any residual gas in the wing.

You can disable the dump feature by removing the inflator form the corrogated hose. You will find a pin in the hose fitting on the inflator that connects to a pull cable. Just remove the pin and you will not longer have the ability to activate the shoulder dump accidentally or otherwise.

Long term, you can replace the shoulder dump assembly with a simple elbow from who ever made the wing - or swap it with the one on your old BC - the fittings are probably compatible in the BC and wing.

 

[vinegarbiscuit]

Ye gods, I can relate. Diving doubles was almost like learning to dive all over again. Even dressing my tanks made me feel like a novice all over again...everything from the DIN valves to the angle of the first stages' swivels to optimum house routing. As for my first walk up and down the hill in those HP steel 100s - yech. Bad enough on land, but when I thought about the challenge of gearing up on a rocking-ass boat, I felt discouraged before I even began! It was somewhat awful in the water, because I was using a borrowed harness, and the tanks were wobbling everywhere. It was much easier once I bought my own harness and got everything ratcheted down properly. I figure like most new diving challenges, it will take 25 or so dives before one identifies and irons out any kinks, and gets used to the idiosyncrasies of diving a new rig, before it feels more natural.

 

[CamG]

Greetings gbray and welcome to the doubles camp! It was like a trip down memory lane reading your thread. I to started with 72's and had like wise experiences. I quickly tried out several other sizes HP 100's, LP 95's, LP 108's, HP 119's and they all dove wonderfully. I chose 95's for the range of diving that I am doing currently and have been very pleased. You will enjoy tinkering with the tank bands, wing position, adjusting your harness, it really makes a difference. Just a little adjustment can change your trim and head up / down position. If you are diving wet be sure to carry a lift bag with you for back up buoyancy. Be sure to listen to DA Aquamasters advice about the pull dump on your wing and replace with a plain elbow. That seemingly insignificant valve caused a wing failure for me. I had just switched form my wet suit to my dry suit and carried no lift bag. I floated 95's with my dry suit and repaired the valve on the dock. I had to review the options if I had been diving wet it would have been a long walk out since I was on a night dive as well.
Overall you will fall in love and have another set of doubles sooner than you think.
I find it difficult to dive singles because of the security of redundancy. They trim out so easy and it is just a relaxing experience. Have fun and enjoy learning you will have good dives and some bad ones to. The bad ones always teach us more than the good ones. Keep us posted on your progress.
CamG Keep diving....keep training....keep learning!

 

[Jim Lapenta]

Now your real troubles begin. Mostly because you'll find that one set is not enough! I've got three total and I still drool when another set comes up for sale here, on TDS , on ebay, etc. I dove my 72's yesterday wet in one of the local quarries with one of my students. We were down for nearly an hour and used a bit over 700psi. Still have enough for two more similar dives in em. Very nice. I now have nearly 100 dives in doubles and franky they are just as easy if not more so than a single 95 that I use. For the last 50 dives or so I'e been working on barrel rolls, swimming upside down, on one side or the other, and other such nonsense. And I find that it is no more difficult. A little slower to go thru some of the manuevers but no more difficult and it's fun as hell!

 

[DA Aquamaster]

Jim is about half way there. I have two sets of X7-100s for boat dives, two sets of Faber LP 95s for cave dives and 2 sets of steel 72s with vintage manifolds for vintage dives.