JJCCR and wetsuit diving

[doctormike]

I have been diving my JJ for about 8 years. Dry suit at home with heavy fins (with tube weights and two backplates), 3 mm wetsuit in Bonaire with light travel fins. While I had buoyancy issues when I started (like most new CCR divers), I never had trim issues. So this is an interesting thread.

The one thing that stands out is the OPs use of aluminum tanks. I have never seen anyone do that.

While the nice thing about the JJ is that it's very flexible and you can rig up all sorts of alternative configurations, that doesn't seem like a common choice. Can you try standard 3L steel tanks? The only time I saw anyone dive the JJ with AL40s was once when my instructor was making the point that in a pinch you can use almost anything back there..!

 

[bubblemonkey2]

I'm fine on trim with aluminium S19's too, valves down. Even with those and a carbon backplate, still didn't need any added weight with a 5mm suit.

I think all of the instructors advise that you keep diving the JJ **without changing anything** for at least 50 hours, before you even consider changing anything about how the stock rebreather is configured.

Was probably ~20+ hours of post-certification diving before the trim and hovering tricks really clicked in, and I was already a cert'ed open circuit twinset & drysuit diver before that.

 

[rsingler]

Been watching this and finally have to comment.
Learned to dive my JJ in Florida in a 3mm and found exactly the same problem, tho' perhaps not as extreme. I didn't rotate vertical, just a bit head up.

The threads above have contained all the nuggets:
Aluminum 3l's will make things worse.
The stock backplate will be worse in a wetsuit.
Inverting the tanks, while a little helpful, will not completely fix the issue.

A lot of it is body musculature vs fat and the center of flotation.

For me, 2lb on a thin strap placed at the top of each  steel 3l made me horizontal with neutral or slightly floaty fins (Deep6 or Scubapro Seawing Nova) and the stock backplate. I was also a little heavy and carried more air in the bcd.

Carrying fuller counterlungs clearly made me rotate foot down, while optimizing my counterlung volume improved my trim.

For me, no counterweights were required with a carbon fiber backplate for horizontal trim, and my overall weighting was perfect, unless I overfilled my counterlungs. For a 3mm wetsuit.

YMMV.

And as @bubblemonkey2 noted, I didn't figure this out until I had about 30 hours on the unit. It hit home in a wreck corridor where I was waiting for those ahead of me to clear a hatch, when I played with counterlung volume and my lung volume, hovering absolutely motionless, and sensing my trim in the wreck corridor. A big breath in, and I rotated head down. A big exhalation where part of the volume now sat near my shoulders, and I slowly rotated head up. The lightbulb went on.

 

[LanceRiley]

Been watching this and finally have to comment.
Learned to dive my JJ in Florida in a 3mm and found exactly the same problem, tho' perhaps not as extreme. I didn't rotate vertical, just a bit head up.

The threads above have contained all the nuggets:
Aluminum 3l's will make things worse.
The stock backplate will be worse in a wetsuit.
Inverting the tanks, while a little helpful, will not completely fix the issue.

A lot of it is body musculature vs fat and the center of flotation.

For me, 2lb on a thin strap placed at the top of each  steel 3l made me horizontal with neutral or slightly floaty fins (Deep6 or Scubapro Seawing Nova) and the stock backplate. I was also a little heavy and carried more air in the bcd.

Carrying fuller counterlungs clearly made me rotate foot down, while optimizing my counterlung volume improved my trim.

For me, no counterweights were required with a carbon fiber backplate for horizontal trim, and my overall weighting was perfect, unless I overfilled my counterlungs. For a 3mm wetsuit.

YMMV.

And as @bubblemonkey2 noted, I didn't figure this out until I had about 30 hours on the unit. It hit home in a wreck corridor where I was waiting for those ahead of me to clear a hatch, when I played with counterlung volume and my lung volume, hovering absolutely motionless, and sensing my trim in the wreck corridor. A big breath in, and I rotated head down. A big exhalation where part of the volume now sat near my shoulders, and I slowly rotated head up. The lightbulb went on.

so the back plate matters. I was using my halcyon stainless plate. which sits low on my back to give me a good trim on doubles. i use 2 lbs of tail weight diving doubles in 3mm wetsuit.

so let me get it right... carbon plates. in 3mm wetsuit. will make me more or less be in the ball park.

but tanks is 3Liter Steel? or will i use aluminum?

 

[doctormike]

so the back plate matters. I was using my halcyon stainless plate. which sits low on my back to give me a good trim on doubles. i use 2 lbs of tail weight diving doubles in 3mm wetsuit.

so let me get it right... carbon plates. in 3mm wetsuit. will make me more or less be in the ball park.

but tanks is 3Liter Steel? or will i use aluminum?

JJ (like most CCR manufacturers, and as was mentioned upthread) recommends that you start with the stock configuration and then make minor changes slowly if you really feel that it doesn't fit your personal body metrics, etc... And I don't mean to imply that just because I never had the problem that you are having, that it isn't a problem for you. I don't like it when IT says "it works on my machine!".

That having been said, one of the things I love about JJ is the thoughtfulness and research they put into design decisions. They aren't always perfect for everyone out of the box, but I think that stock is a good starting point.

In this case, you have made a HUGE alteration in the stock configuration by using aluminum tanks. That's a major drop in buoyancy, and now you are trying to compensate for that by adjusting other parts of the rig, further away from stock. Even in a 3 mm wetsuit, I would find aluminum tanks and a carbon backplate to be very floaty. Maybe I'm less dense and negatively buoyant than you? That's possible...

You may find something that works for you, but I am just wondering if you ever tried the standard steel 3 L tanks? Maybe you mentioned that and I missed it.

 

[LanceRiley]

JJ (like most CCR manufacturers, and as was mentioned upthread) recommends that you start with the stock configuration and then make minor changes slowly if you really feel that it doesn't fit your personal body metrics, etc... And I don't mean to imply that just because I never had the problem that you are having, that it isn't a problem for you. I don't like it when IT says "it works on my machine!".

That having been said, one of the things I love about JJ is the thoughtfulness and research they put into design decisions. They aren't always perfect for everyone out of the box, but I think that stock is a good starting point.

In this case, you have made a HUGE alteration in the stock configuration by using aluminum tanks. That's a major drop in buoyancy, and now you are trying to compensate for that by adjusting other parts of the rig, further away from stock. Even in a 3 mm wetsuit, I would find aluminum tanks and a carbon backplate to be very floaty. Maybe I'm less dense and negatively buoyant than you? That's possible...

You may find something that works for you, but I am just wondering if you ever tried the standard steel 3 L tanks? Maybe you mentioned that and I missed it.

when i took the class i "rented" the inhouse equipment it had aluminum tanks. by the flat bottom. Round bottom tanks steel.

I dont really know why mine was fitted with alum tanks. but, i assume it has something to do with diving in my country is 99% salt water diving. in fact.... thinking about it .... in my approx 500+ dives i think i have dived only 1x in a lake.

Still planning to get my unit... Steel Tanks it is then... but is this ok for salt water diving?

so let's sum it up so far... let me know if im getting it wrong.


1.) stick to original config as it is in my class. Steel 3L Tanks.
2.) use lighter backplate? i do have an aluminum lying around.... carbon if it works...
3.) 3mm wetsuit for the moment.... although im planning on dry in the future., it's really not much of an option over here unless diving long hours on tech. maybe will do with ccr diving. OC Tech is like 90mins max. 3mm is still ok...


so far? is everyone ok with this?

 

[doctormike]

when i took the class i "rented" the inhouse equipment it had aluminum tanks. by the flat bottom. Round bottom tanks steel.

I dont really know why mine was fitted with alum tanks. but, i assume it has something to do with diving in my country is 99% salt water diving. in fact.... thinking about it .... in my approx 500+ dives i think i have dived only 1x in a lake.

Still planning to get my unit... Steel Tanks it is then... but is this ok for salt water diving?

so let's sum it up so far... let me know if im getting it wrong.


1.) stick to original config as it is in my class. Steel 3L Tanks.
2.) use lighter backplate? i do have an aluminum lying around.... carbon if it works...
3.) 3mm wetsuit for the moment.... although im planning on dry in the future., it's really not much of an option over here unless diving long hours on tech. maybe will do with ccr diving. OC Tech is like 90mins max. 3mm is still ok...


so far? is everyone ok with this?

You mean for buoyancy issues? 100% of my dives (since Dutch Springs closed), and I would say the vast majority of all non-cave rebreather dives, are in salt water, so I don't think that's why they would have had you use Aluminum tanks. If anything, you need more negative buoyancy in salt water, not less.

Of course, your overall buoyancy is based on your whole rig. Using a steel tank just lets you shift some of that necessary ballast from things like backplates and lead weights to the tank itself (generally a better place for it since it's the closest to your center of mass.

I have to say, I have been in the JJ world for the past 8 years, and this is the first time that I have heard of someone using aluminum tanks as their standard configuration.

As far as the lighter backplate, not sure how that would affect trim, since again it's pretty close to your center of mass. I guess if you were dropping backplate weight by using a light one, you could add that ballast on somewhere else. I have seen rEvo divers tape weight to the top handle. I like the JJ because stuff like that isn't necessary. You do have options about positioning of some backplates (they have extra holes, so you can move them up or down on the canister.

Also, the counterlungs have two sets of grommet holes. That means that you can change your trim by moving them towards your head or your feet. Did you try that?

 

[GF99/99]

@doctormike

Interesting, I see more and more people diving S19’s on the JJ in the the past years just to reduce the weight. Obviously not in cold water diving parts of the world but in warm water parts of the world I think you will find ali tanks are kind of the norm.

I suspect the reason why he was give S19’s was because he did his Mod1 in the Philippines.

For the past 5-6 years I have almost exclusively dove S19 ali tanks on my JJ unless I just can’t get them where I travel. I personally like ali tanks over steel. I am naturally very negative (even in salt water) with two 3L steel onboards and four S80 bailouts I need to have the wing fully inflated plus my suit inflated to the point where my neck seal keeps burping out gas just to stay afloat on the surface. Now if I had four 3L steels plus four S80 bailouts I can’t even image how negative I would be. For me especially with four S80 bailouts and minimum three onboard tanks (dil, O2, and inflation, and then for sub 150m I always dive a backup O2 onboard) diving Ali tanks makes a huge difference in my weighting.

I was just in Mexico for about a month cave diving with my JJ and we were doing it on a budget with some friends so all we could scavenge up from friends was enough S19’s for one JJ. One of my friends dives GUE config and is a big German guy so no issue but my other friend has the exact same body build and same negative issue I have so we rock paper scissored for the set of S19’s and I lost and was stuck diving 3L steels for a month in fresh water. WOW was I negative!!! and I hate that feeling of diving a drysuit with a lot of gas in it especially in cave. I even have a “cave cut” suit that is super trim fit.

We also saw not a lot of other JJ divers but the ones we did see if they were not in GUE config were diving S19’s as well

 

[LanceRiley]

JJ (like most CCR manufacturers, and as was mentioned upthread) recommends that you start with the stock configuration and then make minor changes slowly if you really feel that it doesn't fit your personal body metrics, etc... And I don't mean to imply that just because I never had the problem that you are having, that it isn't a problem for you. I don't like it when IT says "it works on my machine!".

That having been said, one of the things I love about JJ is the thoughtfulness and research they put into design decisions. They aren't always perfect for everyone out of the box, but I think that stock is a good starting point.

In this case, you have made a HUGE alteration in the stock configuration by using aluminum tanks. That's a major drop in buoyancy, and now you are trying to compensate for that by adjusting other parts of the rig, further away from stock. Even in a 3 mm wetsuit, I would find aluminum tanks and a carbon backplate to be very floaty. Maybe I'm less dense and negatively buoyant than you? That's possible...

You may find something that works for you, but I am just wondering if you ever tried the standard steel 3 L tanks? Maybe you mentioned that and I missed it.

when i took the class i "rented" the inhouse equipment it had aluminum tanks. by the flat bottom. Round bottom tanks steel.

I dont really know why mine was fitted with alum tanks. but, i assume it has something to do with diving in my country is 99% salt water diving. in fact.... thinking about it .... in my approx 500+ dives i think i have dived only 1x in a lake.

Still planning to get my unit... Steel Tanks it is then... but is this ok for salt water diving?

so let's sum it up so far... let me know if im getting it wrong.


1.) stick to original config as it is in my class. Steel 3L Tanks.
2.) use lighter backplate? i do have an aluminum lying around.... carbon if it works...
3.) 3mm wetsuit for the moment.... although im planning on dry in the future., it's really not much of an option over here unless diving long hours on tech. maybe will do with ccr diving. OC Tech is like 90mins max. 3mm is still ok...


so far? is everyone ok with this?

You mean for buoyancy issues? 100% of my dives (since Dutch Springs closed), and I would say the vast majority of all non-cave rebreather dives, are in salt water, so I don't think that's why they would have had you use Aluminum tanks. If anything, you need more negative buoyancy in salt water, not less.

Of course, your overall buoyancy is based on your whole rig. Using a steel tank just lets you shift some of that necessary ballast from things like backplates and lead weights to the tank itself (generally a better place for it since it's the closest to your center of mass.

I have to say, I have been in the JJ world for the past 8 years, and this is the first time that I have heard of someone using aluminum tanks as their standard configuration.

As far as the lighter backplate, not sure how that would affect trim, since again it's pretty close to your center of mass. I guess if you were dropping backplate weight by using a light one, you could add that ballast on somewhere else. I have seen rEvo divers tape weight to the top handle. I like the JJ because stuff like that isn't necessary. You do have options about positioning of some backplates (they have extra holes, so you can move them up or down on the canister.

Also, the counterlungs have two sets of grommet holes. That means that you can change your trim by moving them towards your head or your feet. Did you try that?

bouyancy i can manage... as much as someone new on a rebreather...

it's more of my trim actually. But let me work on that... 3L steel tanks. if i decide to get the unit.

reading about the manual... just found out about how the grommet holes work. but does it affect the bouyancy much? i think i used the top grommet? im a 5ft 6" guy. wears a size small wetsuit. putting the bolt on the lower grommet would let the counter lung hang more forward of my collar bone? instructor just said.. mostly our asian height.. we use the top one.. if i remember correctly.

this was the reason why it took me a long time to decide on the jjccr unit... I have been learning quickly in OC Tech. breezing thru the lessons. but somehow... the rebreather... i made it... but not as comfy.

 

[LanceRiley]

@doctormike

Interesting, I see more and more people diving S19’s on the JJ in the the past years just to reduce the weight. Obviously not in cold water diving parts of the world but in warm water parts of the world I think you will find ali tanks are kind of the norm.

I suspect the reason why he was give S19’s was because he did his Mod1 in the Philippines.

For the past 5-6 years I have almost exclusively dove S19 ali tanks on my JJ unless I just can’t get them where I travel. I personally like ali tanks over steel. I am naturally very negative (even in salt water) with two 3L steel onboards and four S80 bailouts I need to have the wing fully inflated plus my suit inflated to the point where my neck seal keeps burping out gas just to stay afloat not the surface. Now if I had four 3L steels plus four S80 bailouts I can’t even image how negative I would be. For me especially with four S80 bailouts and minimum three onboard tanks (dil, O2, and inflation) diving Ali tanks makes a huge difference in my weighting.

I was just in Mexico for about a month cave diving with my JJ and we were doing it on a budget with some friends so all we could scavenge up from friends was enough S19’s for one JJ. One of my friends dives GUE config and is a big German guy so no issue but my other friend has the exact same body build and same negative issue I have so we rock paper scissored for the set of S19’s and I lost and was stuck diving 3L steels for a month in fresh water. WOW was I negative!!! and I hate that feeling of diving a drysuit with a lot of gas in it especially in cave. I even have a “cave cut” suit that is super trim fit.

We also saw not a lot of other JJ divers but the ones we did see if they were not in GUE config were diving S19’s as well

interesting insight....

would the trim matter if i was i steel tanks vs ali tanks? the butt of a steel tank vs the butt of the ali tanks... as they are inverted in tdi ccr mod1 class... facing up... would that add weight to the upper part of the body?


i was hoping if it did... that would solve some of the trim problem. as i said earlier.. it kept pushing me leg down.. i was on recreational fins... Fourth Element Tech fins... yes they're light.. lighter than oms fins