Side-mounting 2 different sizes (ex: 80cu & 40cu).

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SlugMug

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I recently started looking into a redundant air-source, and may suggested side-mounting. Then the idea of side-mounting both my main (80cu) and redundant (19cu or 40cu) came up. This seems like it would be great for the type of diving I do (boat with small ladder). My only question is, does anyone have advice for running this configuration? For the most part, I'd want to leave my small air-supply untouched.

For example:
  • Should I mount the 80cu on the left, so I can easily plug in the inflator hose? I'm relatively ambidextrous, and don't mind the main being on the left.
  • Does this configuration feel noticeably unbalanced in terms of drag or bouyancy?
  • I have 4x weight pockets, what's the best place to attach them on a backplate setup & would I likely want more weight on one side?
  • Is there anything important, I'm probably missing about running in this configuration?
 

rjack321

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I recently started looking into a redundant air-source, and may suggested side-mounting. Then the idea of side-mounting both my main (80cu) and redundant (19cu or 40cu) came up. This seems like it would be great for the type of diving I do (boat with small ladder). My only question is, does anyone have advice for running this configuration? For the most part, I'd want to leave my small air-supply untouched.

For example:
  • Should I mount the 80cu on the left, so I can easily plug in the inflator hose? I'm relatively ambidextrous, and don't mind the main being on the left. Its fine
  • Does this configuration feel noticeably unbalanced in terms of drag or bouyancy? Not with only an AL80 see "monkey diving" which seems to not be a big topic of debate lately but whatever
  • I have 4x weight pockets, what's the best place to attach them on a backplate setup & would I likely want more weight on one side? maybe 2 or 3 lbs shifted to the right side but its not critical
  • Is there anything important, I'm probably missing about running in this configuration? people will laugh at you if this is a serious effort at sidemount & redundancy
 

SlugMug

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Please post pics of this o_O

Joking aside, why not just sidemount LP50s?
If the general idea is ridiculous, let me know. That's part of why I'm asking. Most of the suggestions I've gotten so far suggest running the redundant-air supply as a side-mount, and that there's not much difference between 19cu and 40cu when you're in the water. I could always put the 80cu rear-mount, if running it side-mount is asking for trouble.

2x LP50s? That would mean buying 4x tanks, for 2 dives. That would also be 4 fills for 2 dives. I want the redundant air supply to mostly just be there for emergencies.
 

SlugMug

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Thank you for the info. If people laughing at me is the worst problem I'd face with asymmetrical side-mount (or monkey-diving) I'm cool with that. I'm less worried about if it makes anyone else uncomfortable, and more interested in my own comfort and convivence. I suppose if the side-mount single-80 is annoying, I could always back-mount the 80, and side-mount the 40.
 

JonG1

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Not quite the same thing, but I side mount a steel 12 on one side and an ali 80 on the other on rebreather dives, the steel usually has around 50% helium in it so it has very different buoyancy characteristics to the heavy 65% nitrox ali 80.

I don't notice this in water and have no reason to think you would with a 40 and an 80.

Both are rigged the same, albeit that the bottom boltsnap location in terms of how far around the cylinder it is away from the meridian of the modular stub is different to account for the cylinder diameter and buoyancy differences.
 

lermontov

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I recently started looking into a redundant air-source, and may suggested side-mounting. Then the idea of side-mounting both my main (80cu) and redundant (19cu or 40cu) came up. This seems like it would be great for the type of diving I do (boat with small ladder). My only question is, does anyone have advice for running this configuration? For the most part, I'd want to leave my small air-supply untouched.

For example:
  • Should I mount the 80cu on the left, so I can easily plug in the inflator hose? I'm relatively ambidextrous, and don't mind the main being on the left.
  • Does this configuration feel noticeably unbalanced in terms of drag or bouyancy?
  • I have 4x weight pockets, what's the best place to attach them on a backplate setup & would I likely want more weight on one side?
  • Is there anything important, I'm probably missing about running in this configuration?
yes, it could work but what are you actually gaining ? can't you climb the ladder with a backmount?
 

Searcaigh

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If the general idea is ridiculous, let me know

First of all it's not ridiculous.

I've come across several people sidemounting with one tank, so sidemounting a second smaller tank for redundancy should not be an issue.

I would recommend though that you perhaps get the right kit for sidemounting and do a sidemount course to better understand how this all works.
 

SlugMug

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Not quite the same thing, but I side mount a steel 12 on one side and an ali 80 on the other on rebreather dives, the steel usually has around 50% helium in it so it has very different buoyancy characteristics to the heavy 65% nitrox ali 80.

I don't notice this in water and have no reason to think you would with a 40 and an 80.

Both are rigged the same, albeit that the bottom boltsnap location in terms of how far around the cylinder it is away from the meridian of the modular stub is different to account for the cylinder diameter and buoyancy differences.
Perfect, this is exactly the kind of info I'm looking for. It looks like I might be over-thinking it, and need to just give it a try once I get my pony-bottle.

yes, it could work but what are you actually gaining ? can't you climber the ladder with a backmount?
I climb the ladder with a back-mount all the time. However, I'm experimenting and optimizing all the time.

The two advantages I might get is (1) lower risk twisting my back climbing the ladder while there are waves and (2) potentially faster gear setup with clip-and-go. Now, I might discover first-hand, that it's less convenient. However, that's fine, because I'll be getting some side-mount experience, and when ready, I could always clip 2x 80s for longer/deeper dives.
 

rjack321

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Perfect, this is exactly the kind of info I'm looking for. It looks like I might be over-thinking it, and need to just give it a try once I get my pony-bottle.


I climb the ladder with a back-mount all the time. However, I'm experimenting and optimizing all the time.

The two advantages I might get is (1) lower risk twisting my back climbing the ladder while there are waves and (2) potentially faster gear setup with clip-and-go. Now, I might discover first-hand, that it's less convenient. However, that's fine, because I'll be getting some side-mount experience, and when ready, I could always clip 2x 80s for longer/deeper dives.

The swinging cylinders and unstable mass shifting are actually harder on your back than a stable backmount cylinder aligned with your center of gravity. With <50 dives I would just concentrate on your core buoyancy and trim skills in a single tank and leave all your optimizing aside for another 50+ dives. You dont have the experience to evaluate what is or isnt really working or optimal
 
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