bungees and tank positioning

[Dive-aholic]

I have a clip on the end and just clip it onto the chest d-rings. The loop should be short enough and the clip small enough so it doesn't push the valve away from you. Later today I'll upload some screenshots of the configuration I used in Mexico a couple weeks ago.

 

[seedy]

I have just been studying a Steve martin video on loop bungees. His tanks are doing the same as mine. When he attaches the bungee it rotates the tank about 90degrees and the valve handle ends up facing up. I think that is the solution. It doesn't work trying to have the handles facing down, you would have to loop the bungees from the inside..... I'd love to see some photos of your al tank bungees setup Rob......

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---------- Post added February 5th, 2014 at 09:56 PM ----------

He is attaching around the post not the valve handle.....

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[Dive-aholic]

I like having my valve knobs pointing out where I can get to them with either hand. Also, pointing up makes it more difficult to feather them if needed. I have had a couple of occasions where I feathered a valve during a dive. I had plenty of gas in my other cylinder to make it out on that but I still wanted to conserve gas so I feathered and kept breathing from the compromised cylinder.

Here's a screenshot of my Mexico rig -



You can't see the bungeevery well but you can see the valve position. The tanks are too light to not have rotation if you loop around the knob or the post. But if you wrap the bungee around the neck there is no rotation.

 

[scuba127]

At what clock position are the bottom clips on this photo?

 

[seedy]

Rob, can you post a shot or describe your bungee connection to your chest D ring, if that is where it goes...? thanks mate
It looks like your cam band position is what is dictating how far back the tanks is,
and the bungee is just supporting the neck.....

 

[Dive-aholic]

The bottom clip is at 3 for the right bottle and 9 for the left.

I'll get a photo tomorrow. It's just a clip on the end of the bungee though. The tanks are as far forward as they can go without being in front of my shoulder. The cam bands are about even with the waist strap. This keeps the line on the clip as short as possible.

 

[vicp]

I also have been playing with the loop bungees trying to get the tanks to stay in place as they get lighter throughout the dive. I never did like putting the loop around the knob or extension as that rotated the tank. I finally just pulled the loops over the tank necks (with the regs and hoses facing up) and attached the cam bands to my waist belt with a carabiner or a leash to the butt plate ring on my Hollis SMS 100. This took care of the rotation, but the waist/carabiner attachment is not optimal (wing gets in the way of a sufficiently high-back waist d-ring) on the SMS 100 and with leashes, the tank tails will still start to float as they get lighter (I use Faber LP85s and LP95s).

I have just been studying a Steve martin video on loop bungees. His tanks are doing the same as mine. When he attaches the bungee it rotates the tank about 90degrees and the valve handle ends up facing up. I think that is the solution. It doesn't work trying to have the handles facing down, you would have to loop the bungees from the inside....

He is attaching around the post not the valve handle.....

I have also seen this video - and am wondering if the rotation can be used as an aid to keep the tanks in place, even with full LP 85s & 95s? If the valve knob is initially pointing down (6 clock from rear) and then looped from the outside pulling it up to 3 clock (right side - looking from rear) and the cam clip originally at 9 clock ( from rear) also rotated to 6 clock/bottom (again this is on the right side, left side would have opposite 90 degree rotation), would this in fact keep the tanks in place along side the body and allow them to be pushed out of the way for access to pockets or anything else. This sure seems what Steve Martin is doing except he attaches the loops to the extensions which rotates the knobs to an upward position (not all of my valves have extensions). He does seem to be using steel tanks. Maybe for cave-filled LPs a stronger bungee would be required. Need to try this out in a pool with video to see how this works. Otherwise, I just pull the bungee loops over the tank necks with the lower attachments either rigid carabiners to the waist belt or a leashes to the butt plate.

I have a clip on the end and just clip it onto the chest d-rings. The loop should be short enough and the clip small enough so it doesn't push the valve away from you. Later today I'll upload some screenshots of the configuration I used in Mexico a couple weeks ago.

If I understand this correctly, you use loops but clip the end of the loop to a d-ring. How is this different from single bungee (non-loop) attaching to a chest d-ring? Do you put anything through the loop?

Looping a bungee around most steel tanks works well because the heaviness of the steel tanks keeps them from rotating around as you describe. Some steel tanks will begin to rotate once they get down to a certain pressure - Faber LP85s start to rotate around 2200 psi and Faber LP95s start to rotate around 1600 psi. This usually isn't a problem because most cave divers are going to finish their dives with 1800-2000 psi in their tanks. Aluminum cylinders start get light enough to make the bottom end floaty around 2500 psi. If you loop a bungee around the valve even at 3000 psi they will rotate. At 2500 psi the bottoms will be angled up quite a bit. So rather than loop around the knob the bungee works better coming around the entire neck of the tank. This keeps the valve end where it needs to be while keeping it from rotating. Then at around 2500 psi you can relocate where the bottom clips are attached so the tanks remain trimmed out.

This is the only thing that may preclude the use of bungee rotation to keep the tanks in place when they are full and heavy (as Steve Martin seems to do). Maybe a heavier bungee?

 

[Razorista]

and am wondering if the rotation can be used as an aid to keep the tanks in place

It is the most important point (to me at least)! I am always amazed again and again how much can be accomplished with this simple trick.

The rotation lifts heavy cylinders up on the cam-band boltsnap and pulls light cylinders down onto the d-ring.
This allows you to dive nearly any type and size of steel and aluminum cylinders with the same setup - as long as you have valves that support that kind of bungee attachment (most valves can be used with experience, but some require using the less effective method of looping around the valve on one or both sides).

You do not even need a very strong bungee and rotation is minimal if the pressure between upper and lower attachment point on the cylinder is balanced correctly.

The lower attachment point has to be set far enough from valve and bungee to stretch the bungee so that the rotation has to work against that pressure.
If everything is set up perfectly the pressure will cancel out the rotation and the rotation will lift or drop the cylinder into the ideal position.
If the shift in buoyancy is as large as with 80cft aluminum stages for example a second d-ring is needed below the first one for the last third or quarter of the capacity - but most times it just feels incredibly stable.

 

[Dive-aholic]

If I understand this correctly, you use loops but clip the end of the loop to a d-ring. How is this different from single bungee (non-loop) attaching to a chest d-ring? Do you put anything through the loop?

This only works with aluminum cylinders. Heavy steel cylinders will pull the bungee down too much unless it's so tight it's almost unmanageable and the valve will sit too low.

This is the only thing that may preclude the use of bungee rotation to keep the tanks in place when they are full and heavy (as Steve Martin seems to do). Maybe a heavier bungee?

I use 3/16" bungee with no issues. Heavier bungees are just as stretchy but are more difficult to get around the knob and more easily slip off the knob.

 

[seedy]

This has become very confusing.. … I am going to use loop bungees on my steels, that works pretty well, just need to adjust slightly. With the alloy tanks I just tried Rob's method in the pool and it seems pretty good. Even with a single tank,which I will probably use a bit on shallower dives in Vanautu. So thanks for all this input......

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