Twin Tanks - Help Please

[rob.mwpropane]

Interesting, kind of scary I would think.

I'm just starting to dive with a ds and I won't even take my camera (nothing fancy) because I feel like I need to learn the ds before I add anything. I could not imagine adding doubles and ds at once. How would you know what issue is caused by which gear?

 

[CaptainChris]

I sympathise with you and agree too much going on at the same time.

I recently got a new drysuit and had a lot of trouble getting under with a single 15L steel tank. Added loads of weight but still had problems. After serious thought later I suspect I did not manage to get all the air out of the DS.

I have done a DS course but a while ago. I also dived on twin steel 12L's in a different DS two months before and had no problem getting under with 8kg weight belt. The problem on that dive was I got VERY wet - suspected neck seal was bad fit. Thats what decided be to buy a brand new DS ( the other was used and will hopefully be sold - Waterproof Draco)). I just could not be bothered to mess about getting a new neck seal glued in.

I'm diving tomorrow in my new suit, first with full twin kit ( steel 12's, steel backplate harness etc) and do a full weight check. Plan is twins will be around 50 bar pressure only and weight check and practice in about 7 metres of depth and practice holding deco stops around 3 - 5m to get weighting bob on. Once that is cracked out of water, change kit to my single rig and perform similar weight check with a 50 bar steel 15L tank, since I dive twin 12L & deco tank, and sometimes single 15L steel (no deco). My buddy will help me with weighting adjustments as we will take extra's in with us.
Once weighting is cracked just practice descents, ascents, stops and also figure out how much squeeze I can let the DS have on me, since I am usually a wetsuit diver. My new DS is a Waterproof DX1 Hybrid and the inner lining virtually eliminates squeeze, so its just a matter of getting familiar with the suit.

Personally I think it is too much to handle the unfamiliarity of a drysuit plus twins on a backplate and wing since it is very different to a BCD.
I would suggest crack the DS first, then learn twins with a wing, only then put the two together.

I did the TDI Advanced Nitrox and Deco Courses in September and used twin steel 12L, 7l Al deco tank and a 60 pound lift wing. I was quite new to twins then and had some very interesting experiences on the first few dives getting the hang of the big wing, ass up in the air suddenly, lost buoyancy etc etc. I was frustrated since I am an Instructor and set high standards of myself and forgot what it was like to be a student. Fortunately my instructor was VERY patient and told me it takes time to get used to the wing. I did some additional dives apart from the course dives to crack that monster wing and got there in the end - so much so that I got myself a 50 lb wing ( thought behind being I might eventually do a Trimix course so got plenty of lift) and have had no issues when in a wetsuit with twin rig, no weights needed.

I found with twins patience was the key and not beating myself up every time the wing got in control of me, rather than the other way around - I shall apply the same principle tomorrow with the DS. Fortunately my buddy is a very experienced diver and an Instructor and we often do fun dives together and he is just helping me out crack the DS weighting.

Hope a few of the above may be useful and I am sure you will get there in the end and I wish you all the best of luck.

 

[AustinV]

I learned doubles and drysuit at the same time - but not together. I spent some time in pool learning doubles in wetsuit, then started learning drysuit at quarry, ordered my own drysuit while continuing to work on doubles skills, drysuit came in and got used to it in single tank, etc.

 

[Paul M]

Hi @MarjG ,

You wrote that you have +300 warm water dives. How many cold water dives have you and how cold is cold? For us cold is below 45F and often 35F. In some places they consider 65F-70F cold.
I ask because I am thinking you could try multiple dives with the twin set in a 5mm or 7mm quit comfortably.
Get into a drysuit a bit later after some practice.

 

[MarjG]

Thank you for all of your feedback and encouragement, I was thinking of trading my gear in for knitting needles after that crazy weekend, I thought maybe I was getting too old for this. A bit more background. I signed up for Tec 40/45 as I was planning on going to Truk in the next few months. It is cold here by my admittedly wimpy standards especially for long deep dives (water temp in the low 50's) so I said I would take the DS class with Tec given timing of everything. They did not disagree. The classwork for Tec 40/45 went great, no problem there. My computer from diving in Belize showed a very low SAC rate so the instructor deemed that I could handle all the changes at once. Even after day 1 he felt it was worth going after day 2 in the same manner. Obviously that did not work so we are going to the heated pool now to take out some of the new variables and let me learn fewer things at once. If I have to do the Tec without a DS, I may have to run to warmer climates.

 

[Angelo Farina]

I think you changed too many things at once.
But I doubt the problem was the twin tank. As others already suggested, you had problems mostly from the dry suit, and possibly the (large) wing.
I started diving with twins, at the time no one was using a single here in Italy.
No BCD, no dry suit, a thin wet suit with smooth rubber external surface (for minimal friction in water) and the steel twins were with their own harness (no backplate) and a good couch strap.
With them it was easy to stay perfectly horizontal, and to swim fast with minimal drag.
When, some years later, I used a single tank for the first time, I had some problem, as that cylinder was bulky and heavy on the bottom, making it difficult to stay horizontal and to swim with little drag. And this despite the smaller quantity of air available (3000 liters instead of 4000).
So I think that twins are more streamlined and give you a better trim than a single.
All the problems you have got are caused by other factors, do not blame the twins...

 

[AfterDark]

I wouldn't know where to start to help you OP. You must have a lot of self confidence to attempt a dive with that much new/unknown/untried gear. After 51 years and <2000 dives I wouldn't have done that dive instructor or not.

Someone posted to try the twins in a wet suit. I'm waiting for the proclamations of your impending death if you do that.

That is how I learned twins however, in a wet suit. The dry suit came sometime later and the combo after that. This was all learned thru reading, trial and error and mentors, tech classes and dry suit classes were still a thing of the future. I still dive my doubles in a wet suit and I'm still alive.

One of the most over looked and probably the least liked piece of gear that IMO is helpful for twins or any B/Pwing rig is a crouch strap. It helps to stabilize the rig and keeps it from riding up when inflated, thus keeping the balance and buoyancy characteristics of the rig stable. I usually tighten mine 1st then tighten the shoulder straps. When I get to 20FSW I re-tighten the straps in the same order plus my weight belt. When I get to max depth I repeat the tightening again.

 

[BlueTrin]

Hey I am new myself so I thought maybe my experience may be useful to you since it is still fresh.

In my experience, you are better off trying to stay in flat trim all the time with a drysuit or a twins. If you use a wing with your twins the air in your wing will wrap around the twins so it will actually work against you if you roll.

Like others said, IMHO that’s the drysuit which is the hard part rather than the twins: I think the only hard part with twins is to be able to reach the valves if you use a manifold.

Do not stress too much about it, it comes quite fast if you keep practising.

Also don’t forget that if you use the same weight for two dives with twins, you should be fairly negative at the beginning of the first dive: that’s because to be able to hold a stop with nearly empty cylinders you’ll have to hold two tanks worth of air. This means that you will have to inflate your BCD to be neutral at the beginning of the dive. This may add instability if you are not neutrally buoyant as you move up and down.

Agree with @AfterDark : it helps a lot to adjust the crotch strap to not be baggy, and to keep the harness belt tightened around the waist.

 

[Lorenzoid]

I can relate to your plight. As others have said, "too many changes at once." When I decided to learn how to dive a technical gear configuration, some people recommended learning the drysuit first and then learning the doubles, but at least one mentor of mine suggested tackling drysuit and doubles at the same time. I followed my mentor's advice, took a class from a knowledgeable tech diving instructor, and indeed had pretty much the same difficulties as you.

It has taken YEARS since then to get good enough in this gear configuration to satisfy the requirements of the agency I have been training with, GUE, to even allow me in the door as a student in their tech-level classes. I mean like 3+ years of a couple of days a month spent in the shallow water, just practicing holding my depth and trim while doing things like sharing air, shooting an SMB, etc., in the doubles-and-drysuit configuration, interspersed with some normal just-for-fun diving in the configuration. Whether GUE's threshold of competency for admission to tech training is unnecessarily high and/or PADI's is something different may be a topic of debate elsewhere, but my point here is only that it can take a long time to get really skilled with this configuration. You want to get skilled enough that when you are taught the mechanics of tech diving, you don't even have to think about how to keep still and horizontal at a selected depth--achieving that kind of stable platform should be on autopilot.

If I understood your most recent reply, you are going to do some more poolwork with the instructor, and that sounds like a great plan. It may even take multiple sessions with an instructor before you are able to maintain your stable platform while task-loaded with tech skills. You may want to spend time on your own practicing. Tech training can be a long road. I know the wrecks of Truk are slowly rusting away--I would like to visit them myself when I have the training needed to give them the kind of thorough look they deserve--but don't rush the training.

 

[rongoodman]

I signed up for Tec 40/45 as I was planning on going to Truk in the next few months. It is cold here by my admittedly wimpy standards especially for long deep dives (water temp in the low 50's) .

Truk water temps are in the 80-85 range, so you'll probably be diving wet with twin aluminum tanks and maybe a single deco bottle. Why not try that combo in a pool if the local water is too cold for it. I think you'll find things much easier.