Dual using cylinders as sidemount and stage cylinders

[dimito]

Hi all,

I'm currently diving backmount with doubles. I got cave certified this year and I want to get sidemount certified so that I can dive the caves that require it.

My idea is to only dive sidemount when it's needed or to train. This would mean that I have these two tanks that I could potentially use as stage cylinders. I could put this cylinders to good use by also using them as deco bottles or for multi-stage dives when needed. This issue with this is that these cylinders will not have the correct stage rigging, the handle and the top bolt snap are missing, making them difficult, if not impossible, to use as is as stage cylinders.

What are the options to convert the tanks from sidemount to stage and the other way around? Currently I'm thinking of:

• Completely disassembling and reassembling the hose clamps and the rest of the rigging. This is probably the nicest to dive with in both configurations, but it might cause wear on the hose clamps.
• Using removable/travel rigging with a cam band. Easy and fast to convert with added benefit of being able to use the rigging on vacation as well, the disadvantage is that the cam band adds extra bulk and a failure point when going trough restrictions.
• Making a removable handle that slips over the tank valve and then attaches to the bottom boltsnap in some way. This seems simpler, but less ideal when using the cylinders as stage tanks.

Is there another way of doing this that I'm missing? What's your opinion on these options? Does anyone have experience with doing something similar?

Regards,
Dimitri

 

[Caveeagle]

Several ways to rig tanks for sidemount diving, but there seems to be one basic way most people rig stage tanks.

One consideration is what type of tanks are you backmounting and planning for sidemount? Most cave divers in Florida use steel tanks for both BM and SM. Steel tanks don’t typically make very good stage tanks. Either AL80 or AL72 are far better for stage-dropping as they don’t Impact your total buoyancy as much.

More on sidemount rigging. This was a frustration of mine, that very little material exists that does a good job illustrating options for rigging SM tanks. Even a couple popular books on sidemounting somehow manage to pack in a ton of fairly useless information, but not one close up picture or illustration on how to make top or bottom attachments. (Wtf)

Here is the best description I have found that shows your options for rigging your sidemount bungees: *Thanks to the folks at Dive Rite for producing this for free!
Sidemount Bungee Styles | Dive Rite

Here is another link that shows how many people rig their stage bottles,
F K D

The type of SM rigging you choose will have a lot to do with how ans where you dive. There are pros and cons to each method.

FWIW, I use the “Ring Bungees” for both my SM and most stage tanks. I know many sidemount evangelists will call this an inferior system, but here is my logic. I dive BM doubles with stages, Sidemount steel tanks (when it makes sense), and dive a BM CCR with a steel backplate and use dual LP steel tanks SM for Bailout. I am able to have the exact same bungee and tank rigging on all of these rigs and tanks. The same LP50 or LP85 tanks get used for sidemount diving open circuit, and are used for CCR bailout with no changes. The Ring bungees give a very secure upper attachment for boat diving too. I keep a pretty large fleet of tanks, and it really helps to have them all rigged the same way.

*I do have my first trip to Mexico planned, so I have to think through how I will deal with Aluminum sidemount tanks.. so that will be new. Lol

 

[dimito]

One consideration is what type of tanks are you backmounting and planning for sidemount? Most cave divers in Florida use steel tanks for both BM and SM. Steel tanks don’t typically make very good stage tanks. Either AL80 or AL72 are far better for stage-dropping as they don’t Impact your total buoyancy as much.

I live in europe so everything here is metric. I have a smaller twin set that is 2x7L @ 300 bar (I have no idea what that compares to). I have a big twinset that is 2x12L @ 232 bar (I think this compares to a twin HP 85 cuft). I want to split up the big twin set and use it for side mount. I'm getting a good deal on a friends second hand sidemount set (2 x 80cuft + rigging, xdeep side mount harnes and regulators). The smaller one I want to keep because it's great for the more recreational dives I'm doing. I would be nice to suplement the small twin set with an extra 80 and/or deco cylinder when I need more gas.

I live in Belgium and will mostly be diving locally (Belgium, Germany, France). This means drysuit and thick undersuit. Because of this I will propably be diving the steels most of the time. So switching the alu tanks from stage to sidemount is probably not that big of an issue now that I think of it.

How is it to take one tank of and hold it in front of you when you're diving sidemount with steel tanks? They say aluminium is better for this because it impacts your buoyancy less. My teacher is more pro aluminium than pro steel.

*I do have my first trip to Mexico planned, so I have to think through how I will deal with Aluminum sidemount tanks.. so that will be new. Lol

Good luck and have fun! Let me know how it was.

 

[Degenerate]

I live in europe so everything here is metric. I have a smaller twin set that is 2x7L @ 300 bar (I have no idea what that compares to). I have a big twinset that is 2x12L @ 232 bar (I think this compares to a twin HP 85 cuft).

2x12L tanks filled to their 232 bar service pressure is 5568L, or 196.63cuft.
Roughly rounded up to twin HP100 I suppose.

 

[dimito]

2x12L tanks filled to their 232 bar service pressure is 5568L, or 196.63cuft.
Roughly rounded up to twin HP100 I suppose.

Thank you for explaining that. But how do you know then what the physical size of the tanks are? You calculate it using the cuft and the pressure?

 

[Bowers]

Thank you for explaining that. But how do you know then what the physical size of the tanks are? You calculate it using the cuft and the pressure?

the US makes this harder than metric but 14.7psi is a bar.
So for a 3000psi 80cf bottle (really not 80 but for our purposes ill leave it be), you divide 3000 by 14.7 which equals 204bar.
Now take 80 divided by 204 and you get liquid volume of tank as 0.39cf.
There are 28liters per cf. so multiply 0.39 and 28 to get 10.9.
So al80 is close to an 11L

 

[Bowers]

Also “shotgunning” steel tanks does tip your balance forward worse than aluminums but with lp85s ive found that as long as im in motion the weight change doesn’t throw me off that much, its if i try to stop and hover that it gets hard.

 

[tursiops]

Several ways to rig tanks for sidemount diving, but there seems to be one basic way most people rig stage tanks.

One consideration is what type of tanks are you backmounting and planning for sidemount? Most cave divers in Florida use steel tanks for both BM and SM. Steel tanks don’t typically make very good stage tanks. Either AL80 or AL72 are far better for stage-dropping as they don’t Impact your total buoyancy as much.

More on sidemount rigging. This was a frustration of mine, that very little material exists that does a good job illustrating options for rigging SM tanks. Even a couple popular books on sidemounting somehow manage to pack in a ton of fairly useless information, but not one close up picture or illustration on how to make top or bottom attachments. (Wtf)

Here is the best description I have found that shows your options for rigging your sidemount bungees: *Thanks to the folks at Dive Rite for producing this for free!
Sidemount Bungee Styles | Dive Rite

Here is another link that shows how many people rig their stage bottles,
F K D

The type of SM rigging you choose will have a lot to do with how ans where you dive. There are pros and cons to each method.

FWIW, I use the “Ring Bungees” for both my SM and most stage tanks. I know many sidemount evangelists will call this an inferior system, but here is my logic. I dive BM doubles with stages, Sidemount steel tanks (when it makes sense), and dive a BM CCR with a steel backplate and use dual LP steel tanks SM for Bailout. I am able to have the exact same bungee and tank rigging on all of these rigs and tanks. The same LP50 or LP85 tanks get used for sidemount diving open circuit, and are used for CCR bailout with no changes. The Ring bungees give a very secure upper attachment for boat diving too. I keep a pretty large fleet of tanks, and it really helps to have them all rigged the same way.

*I do have my first trip to Mexico planned, so I have to think through how I will deal with Aluminum sidemount tanks.. so that will be new. Lol

In the linked DiveRite discussion of styles of bungees, one advantage they give of the Ring bungee is:

It is easy to convert a stage bottle into a primary sidemount tank by adding a choker to the top bolt snap.​

 

[RainPilot]

How is it to take one tank of and hold it in front of you when you're diving sidemount with steel tanks?

My 7L 300 bar tanks are great for drysuit sidemount when I don't need a lot of gas for the dives (in theory its 90% of an AL80 but you never really get that amount) but I can't gun the tanks with any kind of ease, they turn me into a lawn dart quite handily. If I push them ahead in a constriction its fine but not in open water.

My 12L steel 232 bar are a bit easier but steels don't lend themselves to the fancy sidemount tank tricks like an aluminium tank does.

 

[rjack321]

How is it to take one tank of and hold it in front of you when you're diving sidemount with steel tanks?

1) you basically wont ever need to do this for years
2) you can if it is a really small space and the only way through is to superman a tank... and even though you get really head heavy - its already small! You are stuck moving through the hole that you have to work with anyway, being head heavy doesnt matter.
3) if you are trying to show off in open water you will lawn dart into the bottom - but its open water - you deserve that for trying