Buoynancy issues with new setup, overweight, resulting in failed dive.

[Frantisek Jelinek]

Hello all,
I would like to ask for hint in troubleshooting my new diving setup. I experienced really bad dive, with lot of failures, which I am aware of, I share this because I want to improve, so please do not reprobate me.
I am average diver with OWD certification and about 75 dives in total, recreational free diver, at the moment I am in AOWD course. I used to dive with wetsuit in tropical see mostly, with 3mm short or body wet suit, ursuit 16l wing, 12l air bottle, with very good buoyancy control, no troubles at all, fairly good SAC, and I was enjoying diving almost all the time with empty BCD, using only my lung capacity to slightly change depth. So far so good. Now I want to adapt to local conditions, which means low visibility, cold water, mostly flooded mines - simply dark and cold water. This requires change in my equipment, so I have now 2x10l 235bar twin independent setup (steel bottles with frame weighting in 20kg empty, rather heavy), ATX100 and DS4 1.stages with DIR long hose setup, Anhinga wing 21l, Mares Isodry drysuit neoprene, not using real undersuit, but only cotton trousers and shirt. Before going outdoor to real dive, I checked the configuration and weighting in pool (7m), and found this: my instructor told me to start with 12kg additional weight put in side pockets, I hit the bottom like a rock, removing some weight, tried again.. and I ended with 0kg, still feeling a little bit overweighted, but ok, I was able to keep the level, and fair trim like that. It is needed to confess that I was not feeling completely fine with the setup, it is huge difference against my previous experiences with wetsuit and singletank, when I was able to quickly compensate just with my lungs, now this way is limited, and I really need to operate BCD often to be neutral. Well, I though I am more or less prepared to try outdoor.
With the new setup we went to have sharp dive in mine, visibility was around 4-5m at most, 14°C water temperature, almost no chance for visual reference to anything due to bad visibility, aiming to dive to max. 17m practicing navigation to swim around the mine, instructor and two buddy teams. I got additional 4kg of weight from my instructor, put in side pocket. From initial descent everything was "not right", I descent faster then I liked to, and had to play around with BCD to level in neutral, but still I had troubles to keep steady and hover nicely, orienting only with depth gauge of computer, with no visible reference to wall, bottom, etc. To worsen the situation, I hit the leading line which I was not aware of, as I couldn't see it below me, tried to untangle from it and somehow it slips my both fins off, making swimming almost impossible. I was able to catch them, descent to the bottom at about 7m, and negative buoyant I tried to get them back on, which I managed with huge effort only, fighting with drysuit and low visibility. Then ascent and I removed 4kg of weight, descent again and continued with dive, which I was able for about 5min, then I had again troubles to keep the level, and moreover I experienced cramps in my calves, possibly the result of pushing hard to get fins on previously. This I have signaled to the other divers and end the dive.
There was a lot of factors involved, new setup, bad visibility, low temperature, trouble with fins, etc., I failed as a buddy having a lot of problems with myself, my buddy has also troubles (another interesting and potentially dangerous point - inflator hose was disconnected during the dive, luckily there was enough lift to ascend - I have checked for correct function within pre-dive buddy check, but forgot to check if inflator is secured to fitting, now I will never forget to check it as well), buddy team failed completely - so nothing I can be proud of, and generally we were close to really dangerous situation, I felt really bad about the dive - it was my worst experience ever. I also found that this is up to myself, our instructor with us basically didn't know what happened, and I definitely don't want to put myself or my buddy in danger - so I found that I am definitely not prepared to dive on with this setup in those conditions, I go back to train in safe pool conditions, building my buoyancy control and confidence.
Still I have a couple of questions:
1] Is it possible that my twin bottles are simply to heavy to my body weight ? I weight in about 70kg, have 0% body fat, twins have about 25kg filled. Always my instructors try to attach some additional weight to me, but I really feel overweight even with no lead at all. I just thought my chances are to either increase my lift with additional underlayer in drysuit, or to change for lighter twin cylinders. I hope you understand my point - all I want is to achieve good buoyancy with minimal BCD inflating and deflating, which I believe can be done only when my weight and lift are closely equal (of course I am aware of lift change during dive) ?
2] Position of twins on the back. I encountered slight shifting of backplate and thus cylinders during the dive, especially when turning, or rolling. I adjusted and shortened shoulder straps and also strap between the legs, but still have a feeling that rig not 100% in place. Is there anything I could do about it ?
3] Fins. I have seeman natures wing type fins, they are like "split" in the middle of fin blade, with rubber straps. It is possibly due to my overweight, but I felt like I miss the power from kicking, and also when turning I felt like fins are too soft not giving me proper resistance against the water. Maybe I should switch to proper DIR fins with solid blade and spring fitting ?

Ok, that's it, I would be grateful for helping me, I believe I can overcome the troubles I'm having right now and can hopefully dive with twins and drysuit safely and nicely one day... Thank you for answers, and sorry for my possibly stupid questions.

 

[Doby45]

Sounds like you need actual training in Drysuit and Intro to Tech. There is no simple internet fix all for the issues you are facing.

 

[Frantisek Jelinek]

I agree with that 100%. I will take Drysuit complete training as soon as possible.

 

[HantsDiver]

and I ended with 0kg, still feeling a little bit overweighted, but ok,

On a twinset you are going to have a much bigger swing in buoyancy as you use the gas up. However, if you do a weight check and are overweight at 20bar then you should change the backplate for aluminum.

 

[HantsDiver]

Still I have a couple of questions:
1] Is it possible that my twin bottles are simply to heavy to my body weight ? I weight in about 70kg, have 0% body fat, twins have about 25kg filled. Always my instructors try to attach some additional weight to me, but I really feel overweight even with no lead at all. I just thought my chances are to either increase my lift with additional underlayer in drysuit, or to change for lighter twin cylinders. I hope you understand my point - all I want is to achieve good buoyancy with minimal BCD inflating and deflating, which I believe can be done only when my weight and lift are closely equal (of course I am aware of lift change during dive) ?
2] Position of twins on the back. I encountered slight shifting of backplate and thus cylinders during the dive, especially when turning, or rolling. I adjusted and shortened shoulder straps and also strap between the legs, but still have a feeling that rig not 100% in place. Is there anything I could do about it ?
3] Fins. I have seeman natures wing type fins, they are like "split" in the middle of fin blade, with rubber straps. It is possibly due to my overweight, but I felt like I miss the power from kicking, and also when turning I felt like fins are too soft not giving me proper resistance against the water. Maybe I should switch to proper DIR fins with solid blade and spring fitting ?

1. Yes. Your twins can be to heavy. I've already said one way to resolve this. With my "big" twinset of twin 18l's I am very overweight even with an aluminium backplate. Being overweight isn't a huge drama though - you can learn to work around it. A different undersuit will also make a reasonably big difference.

2. You don't want to shorten the shoulder straps. The shift and movement is normal. Use it to your advantage and give them a wiggle when you want to straighten out. A twinset should not be tight.

3. With a twinset and a drysuit I use Hollis F1's. They are very stiff and very heavy and do the job nicely. I also have jetfins which again are stiff. You need a stiffer fin with that sort of set up. My advice would be to get some F1's - as it will make a big difference. They have a very nice foot pocket and are great in the water.

 

[Marie13]

And cotton under drysuit is a big no-no! Gets damp with sweat and you get cold. You need something like polyester fleece on top of a sweat wicking layer. A lot of the guys here swear by merino wool.

If you already have any layers for outdoor sport, try those under your drysuit.

And yes, drysuit is totally different than diving wet. It will take some time to get everything dialed in.

 

[rongoodman]

Your twinset is going to try to put you head down. Along with being stiffer, a heavier fin like the F1 should help with that.

 

[stuartv]

I have now 2x10l 235bar twin independent setup (steel bottles with frame weighting in 20kg empty, rather heavy), ATX100 and DS4 1.stages with DIR long hose setup, Anhinga wing 21l, Mares Isodry drysuit neoprene, not using real undersuit, but only cotton trousers and shirt. Before going outdoor to real dive, I checked the configuration and weighting in pool (7m), and found this: my instructor told me to start with 12kg additional weight put in side pockets, I hit the bottom like a rock, removing some weight, tried again.. and I ended with 0kg, still feeling a little bit overweighted, but ok, I was able to keep the level, and fair trim like that.

@HantsDiver already alluded to this. With a twinset, if you are weighted properly, you WILL feel overweighted compared to what you are used to in a shorty and a single tank. You are carrying twice as much gas, so you need to be twice as negative at the start of your dive.

To explain: At the end of your dive, with almost empty tanks and an empty BCD, you want to be able to be neutral, right? You never want to be positively buoyant with empty tanks and an empty BCD. That would cause an uncontrolled ascent.

If you are neutral with empty tanks and an empty BCD, then that means that at the start of the dive, with all the gas you're carrying, you would be negative by an amount equal to the weight of the gas you're carrying.

With a 10l twinset, I think you would be carrying somewhere around 5kg of gas. I'm in the U.S., so metric tanks are not my strongest suit. That means you would need to start your dive 5 kg negative. If you have been diving in a 3mm shorty and a single tank, and you have been properly weighted, then being 5kg negative will feel very negative.

Being 5kg negative also means that when you descend, you will have to put 5l of gas in your BCD to get neutral. That is more gas in your BCD than you are used to and having that much gas in there will make your buoyancy harder to control than what you are used to.

Those are just the facts of life when diving a twinset. It is a little harder. You can't "fake" it by weighting yourself to start the same amount negative as what you're used to with a single tank. That will just result in your being too light at the end.

Like others have said, I also use the Hollis F1 fins for diving in a drysuit and doubles. They are about 1kg negatively buoyant (for a pair of size XL, in fresh water). Being that negative and on your feet definitely helps quite a bit to counteract the twinset being extra heavy close to your head.

 

[AJ]

Sounds to me you're going through a steep learning curve. Every twinset diver has faced this curve. Twin diving is different from single tank, you have to get used to it by practice.

What do concerns me is weight. Did you and you're instructors do a proper weight check? It's the only way to know for sure if you're correctly weighted.

 

[DanielRJones]

They are not to heavy for your body just very different to what you are used to.
You need to be 4-5kg over weight at start of dive when using twin 12's so for most of your dive until your safety stop you will have to have a fair bit of air in your bcd or drysuit (I only add enough air to stop the squeeze). This 4-5kg will feel like alot when you are used to not having to add any air or only a little bit.

Drain your tanks down to 40bar remove all air from your drysuit and then perform a weight check.