How do you mount?

[SuPrBuGmAn]

Changing tank configurations and hoses around all the time is a PITA... and I can't afford to keep two seperate sets(tanks/regs). Therefore I chose the configuration that suited all my diving, rather than only a portion of it :P

[RN]

Strictly back mount (PST 120s) for most every cave I have done. The only times I have sidemounted were for Jug Hole (Diamonds Sands restriction) and Suwannee Blue (9' depth and low ceiling). And when I did those two it was just with PST 45s, so it was almost like wearing nothing as far as mass and weight goes.
I have noticed a heck of a lot more divers going the sidemount route, though. I wonder if these divers ever read Bill Gavin's quite logical and comprehensive article in 'The Art of Safe Cave Diving' (Ch. 5 Equipment Configuration). Of course, if the nature of the cave passage dictates sidemount config, or if one is not physically able to carry doubles on their back, or extremely long hike to cave (expedition style) then sidemounting would be the way to go. But if neither of those situations apply, then I can't see the logic in it.

How about having the valves and 1st stages where you can see them and they are more protected? Being able to reach your valve knobs to shut one down without having to contort your body. Moving the weight mass from high on the body closer to the center of gravity on your body so you are more stable in the water. Planing out your gear so you are more streamlined in the water (Waiting for Kelly to post it's not as streamlined but I think those divers weren't trimmed out properly ). Being familiar with your gear configuration and having the muscle memory in place so when the $h!t hits the fan, your hands know where to go without you having to think about it because you're diving a configuration you rarely ever dive or you forget what configuration you're in. I can go on and on, but this should be enough.

[KarsticGator]

Strictly back mount (PST 120s) for most every cave I have done.

Hey Quasimodo, you'll need a Segway to get to the dive site in a few years if you keep lugging those PST 120's around.

[Sludge]

Hey Quasimodo, you'll need a Segway to get to the dive site in a few years if you keep lugging those PST 120's around.

Judging from his other posts (his diving timeline), I'd guess he uses HP-120s (which weigh the same as LP-95s) and not LP-120s (which weigh as much as a small pickup truck).

[KarsticGator]

Judging from his other posts (his diving timeline), I'd guess he uses HP-120s (which weigh the same as LP-95s) and not LP-120s (which weigh as much as a small pickup truck).

No, he dives the LP's. I've had to listen to him whine about his tanks one too many times. And I think his spine has compressed a few inches, since we first dove together.

[Unregistered User]

No, the 120s are Pressed Steels rated at 2640. They only weigh about 115 pounds and I have made the hike up and down Olsen, Friedman's, etc. with no problems. I only weigh 160 so hiking technique is critically important. INSANE amount of air when they are cranked up to 3600 psi, though! I don't see how it would be physically possible for sidemount tanks to be more streamlined than a set of doubles, unless you mount the tanks so that they are exactly parallel to each other (like doubles). Admittedly, the addition of a second SPG will add more surface area as well, but that would conceivably be cancelled out by not having a 7' hose. Any change in forward surface area by having the tanks at any slight angle will necessarily change the resistance negatively. Unless one is capable of breaking the laws of physics.

I liked SSKasser's comment about the vehicle choice and how doubles can conceivably destroy a car. I used to have a Camry and had to replace the trunk floor with 3/4" plywood for just that very reason! I agree there doesn't have to be logical reason, and I regret typing that in my post. Familiarity and competence with whichever configuration (whatever it may be) is the correct choice for each diver.

RN said:
"How about having the valves and 1st stages where you can see them and they are more protected? Being able to reach your valve knobs to shut one down without having to contort your body."

Reaching behind my neck is hardly an impossible contortion. I would theorize that the amount of protection afforded to the valves would be identical to back mounting. The only difference is that instead of the possibility of hitting the ceiling, one would be more likely to hit the floor instead. The regs will still be positioned toward the center of the body either way. A key difference might be that since your head is right there next to the valves, a natural result will be that since most divers (and people in general) take care to protect their head more than any other body part, the ancillary benefit is that the diver will (sub)consciously avoid hazards likely to affect that area and the nearby valves.

RN said:
"Moving the weight mass from high on the body closer to the center of gravity on your body so you are more stable in the water. Planing out your gear so you are more streamlined in the water (Waiting for Kelly to post it's not as streamlined but I think those divers weren't trimmed out properly ). "

That movement of mass also spreads the tanks further apart, giving even greater stability, but increases the lateral profile. Sidemounting gives you greater freedom to navigate awkward passages but to consider it a Panacea would be to neglect the fact that manifolds are pretty robust and no one ever died from their failure. That's why I brought up Bill Gavin's chapter in the book. Out-of-air situations with each configuration that he describes are particularly interesting.

RN said:
"Being familiar with your gear configuration and having the muscle memory in place so when the $h!t hits the fan, your hands know where to go without you having to think about it because you're diving a configuration you rarely ever dive or you forget what configuration you're in. I can go on and on, but this should be enough."

That is true and can be applied equally to any configuration.

Superbugman's reasoning has great merit as well. Constantly changing hoses puts unneeded stress on o-rings and port plugs. Cave diving is an extremely costly endeavor and purchasing another 2 regs for a configuration that is infrequently used can be a luxury not every diver enjoys. Nothing wrong with that, IMO.

[RN]

I don't see how it would be physically possible for sidemount tanks to be more streamlined than a set of doubles, unless you mount the tanks so that they are exactly parallel to each other (like doubles).

My cylinders are pretty close to parallel with each other and my body. The way I mount them also causes a significant portion of the cylinders to be located under my shoulders so the surface area is significantly reduced.

Admittedly, the addition of a second SPG will add more surface area as well, but that would conceivably be cancelled out by not having a 7' hose.

Are you serious?? How does a second SPG add surface area? How do you think the SPGs are mounted? Mine are right in front of my shoulders. Again, the surface area is canceled out by the cylinder. I also use a 7' hose, tucked along my right cylinder between the cylinder and my body, again, no added surface.

Any change in forward surface area by having the tanks at any slight angle will necessarily change the resistance negatively.

You are correct, which is why I'm so particular with my students and getting their cylinders perfectly in line with their bodies.

RN said:
"How about having the valves and 1st stages where you can see them and they are more protected? Being able to reach your valve knobs to shut one down without having to contort your body."

Reaching behind my neck is hardly an impossible contortion.

Lucky you. I'm also lucky enough to be able to do it quite easily, but I also demonstrate this skill to my backmount students on a regular basis. However, most of my backmount students have a very difficult time trying to do valve drills. Most of them end up in sidemount.

I would theorize that the amount of protection afforded to the valves would be identical to back mounting. The only difference is that instead of the possibility of hitting the ceiling, one would be more likely to hit the floor instead. The regs will still be positioned toward the center of the body either way. A key difference might be that since your head is right there next to the valves, a natural result will be that since most divers (and people in general) take care to protect their head more than any other body part, the ancillary benefit is that the diver will (sub)consciously avoid hazards likely to affect that area and the nearby valves.

If you position the cylinders with the 1st stage in towards your body they snug up between your arms and your body. I don't see that happening with backmount. And properly positioned cylinders have the valves slightly higher on the plane than my dry suit inflator.

RN said:
"Moving the weight mass from high on the body closer to the center of gravity on your body so you are more stable in the water. Planing out your gear so you are more streamlined in the water (Waiting for Kelly to post it's not as streamlined but I think those divers weren't trimmed out properly ). "

That movement of mass also spreads the tanks further apart, giving even greater stability, but increases the lateral profile. Sidemounting gives you greater freedom to navigate awkward passages but to consider it a Panacea would be to neglect the fact that manifolds are pretty robust and no one ever died from their failure. That's why I brought up Bill Gavin's chapter in the book. Out-of-air situations with each configuration that he describes are particularly interesting.

Panacea is your word, not mine.

[Unregistered User]

RN, your comments are certainly valid and well thought out. I am sure that you (as an instructor) must be able to discern and then apply the proper configuration for each student's individual needs: an unenviable task if ever there was one.

I mentioned Bill Gavin's article for one reason which I will describe later. Here is a truncated excerpt (hope I'm not violating copyright law by this) from the book:

"If cave divers...went to the trouble of inventing...the dual valve manifold..., then maybe they had some good reasons...[It] solved a lot of problems without creating a lot of new ones, which is not the case with independent setups.
If cave divers were perfect automatons that never made mental errors then the independent arrangement might be safer than the dual valve manifold, but cave divers do make mistakes and that is what many of these valve analyses fail to take into consideration...The dual-valve manifold has none of the task loading problems that plague the independent valve configuration...It makes no sense to switch to a more complex system because of a failure that rarely occurs and has never cost a life."

Of course, Mr. Gavin is not infallible and my use of the word "Panacea" was not to imply that it was your intention to describe sidemounting as being so, merely that some approach it from that angle. You have clearly demonstrated that is not necessarily the case with your excellent posts regarding the matter. It just seems that the potential problems that sidemounting can create vastly outweighs the benefit of its use (ONLY for caves that can be otherwise dived with backmounted doubles). Surely, you have read his chapter in the book as he is a quite accomplished diver and diving innovator and the book, itself, is an authoritative and historical reference for the sport of cave diving?

[RN]

Gavin was referring to independent backmounted cylinders. I wonder what his thoughts are when comparing backmounted manifolded cylinders to independent sidemounted cylinders.

[FW]

Gavin was referring to independent backmounted cylinders. I wonder what his thoughts are when comparing backmounted manifolded cylinders to independent sidemounted cylinders.

Good answer!