Sidemount VS Backmount

[Gary]

No need for a crossbar on doubles at all. Just a 2nd pressure guage and dive them independents - same gas methods as for sidemount.

I dive sidemount or backmount (independent). I prefer backmount - I find it more comforable and more streamlined - and I prefer to reduce my last trip to the water (and first load out) as a massive two tank haul. I know others who prefer sidemount. I dive sidemount when it is advantagous for the dive - which depends on the cave.

[phillip1]

So don't use one. Half the people I dive with, dive BM without a manifold valve (just an open crossover). The reason is that the isolator adds failure points and only is required if you have a failure on the tank side of the post valves. There is not much that can fail on the tank side. Other than the blowout plug - which if it is "properly" fortified, is not an issue - the failure will be on the reg side. For everything else, you do have a buddy (or buddy bottle).

This is a weak point for SM. Failures do occur in the reg and without a crossover, the gas is not nearly as accessible as with a crossover. I know you can feather a valve or swap regs underwater, but you are going to lose some precious gas and just as or more importantly you will lose time. With a crossover, you don't have to think because the gas is automatically there.

Another weak point for SM is that most do not rig a long hose, (or if they do, it looks real ugly). This means the diver is thinking only of #1 and the heck with other divers. I do not think this is a good attitude. Hose routing is just easier and cleaner with BM.

Staging is easier with BM because the bottles are in front of you.

There seems to be less drag with BM. Take a diver configured properly in SM and BM and take their picture head on - side by side. There is about 30% more cross sectional area for the SM, so that would explain it. I have dove with SM's several times and usually end up waiting on them.

I disagree and this is why;
I do 99% of my diving exploration we are a team of two sometimes three, all sidemount. Every member is 100% independent in sidemount configuration making it a way safer and a more solid and flexible team. When you dive backmount you are relying on your buddy in the event of air loss, hence the long hose. There are several possible situations were you can loose all your air before you could isolate in backmount, so you are not independent as you would be in sidemount.
This does not at all mean I am diving thinking only of myself that is completely ridiculous, we are diving as a team and should something happen I am there to help and vice versa.

As for the regs etc.. in sidemount you have immediate access to the valves & regs and can spot a problem in an instant, if you need to feather the valve with a free flowing reg it is so easy that you really do not loose much gas at all, it happened to me at Jailhouse and although I should have I did not even call the dive it was such a non issue, had it been in backmount I would have called the dive, you would have a real hard time feathering the valve backmount.

As for gas sharing let me give you a worst case sidemount & backmount scenario, I am diving with another person sidemount, that person looses all the air in both tanks (very very improbable), I can either share with my right side reg which is 4ft long or I would simply hand them off one of my tanks. I know I am giving up my redundancy but if my buddy's life depends on it I will take my chances and do it, but you know so are you in backmount and in a much worse way, so now (backmount) you are both air sharing with a long hose and all of a sudden your burst disk blows you isolate but loose that tank, your buddy has no air in his tanks but you have enough in one tank to both get out but the long hose reg starts to freeflow, now you have to buddy breath of the backup reg all the way out, but it gets worse there is a major 100 foot long restriction ahead of you that you cannot go through side by side, would you rather be in sidemount or backmount in this situation?
In the above case in sidemount at least you could feather the valve or breath of the valve directly with very little trouble and still be independent of each other although not air redundant, if no other reg failure occurred you would get through the restriction very quickly (lower profile of sidemount) and exit.
Now say that just before getting to the restriction all the air in my tank is lost, since we have been using thirds we still have enough gas for both of us in the other persons tank to both exit buddy breathing of the one reg, and although awkward we can move that tank in between us in the restriction while buddy breathing of the one reg and make it through the restriction and exit. I know this would be difficult and very stressful but you have much more of a fighting chance than in the backmount scenario as you would loose no valuable time at all uncliping the tank and pushing it through between you as you are already configured to do this in sidemount, however in backmount not only do you have to take of your rig maybe loosing buoyancy control, stow the long hose, deal with light canisters and cables etc.. but now you have to share air and push a set of doubles through between you too, add to this the fact that you probably have to hold the line too as it would be a low viz situation.

As for stages, it is way easier having them in sidemount you don't even get off balance and you are still fairly streamlined, it is much more comfortable that with doubles and stages.

This is my personal opinion but this notion of buddy cave diving is a false one, first off I think you should never dive relying on a buddy for safety, there are many times in a cave that you think you are with a buddy but really you are solo, such as a complete silt out, you are wandering off too far back, separation etc.. should an emergency happen then and you need air asap I think that you might be in trouble, so I personaly much prefer an independent setup.

There is also the matter of cave conservation, for example in Cenote Calimba and all other similar lower ceiling caves for example, although totally divable backmount, people tend to hit the ceiling way more than if they were in a sidemount configuration.

As for more drag, I don't think so, what you do gain in lateral drag you would have on your back anyway so I think it is the same.

[Bob Cree]

LOL - It was beginning to sound like the sidemount glee club for a while there. Nice responses all.

On the gas loss side, Forrest, you made an interesting statement that I have not been able to get anything substantiated on - that you have experienced total gas failures due to tank side problems. I would be truly interested to hear what happened with those. I would also be very interested in your opinion of the probability of having a high flow gas loss occur on the tank side versus the reg side (1:100 5:100???). On the blowout plugs - IMO they should be non-existent in a cave and therefore a non-problem.

Hose routing...glad to hear SM's are taking this seriously. It is hard to improve on BM and IMO - I have not seen anything better, only worse with folks diving SM which is why I am of the opinion that BM wins this one. Take just the SPG's, many folks have them dangling in front + there are 2.

Staging. BM, stage #1 goes under the arm, right where your left SM bottle goes. I will only point out that this was the ideal place for a bottle to be in the beginning of this thread - as opposed to on your back. So what changed? Ok - from the other point - placing the first stage when SM underneath you, well is clearly worse than under your left armpit like stage #1 when BM. IMO - in this case, either you see the logic or you just choose to ignore it.

Forrest, on the drag side - another good data point. But you are also stating the assumption that both are very well streamlined. I am basing my statement on what I see from the general population of SM divers...just measure how far down below and above the body most SM'd tanks protrude. Add the head sticking up in the middle. Let's say that the total frontal area on the tanks is very similar to BM tanks. Now the head is extra (like a 3rd tank). The head in BM uses part of the same area as the tanks. Increase the area, increase the drag = slower diver.

The last SM diver I dove with, I had to wait for both out of the water and in the water...I promise Bruce, no names... Lol, the out of the water part didn't have much to do with his SM configuration though...Now I understand that SO-Cal means SlOw-Cal. Couldn't resist it Bruce - had fun.

Bob

[phillip1]

the thing about sidemount is that you have to experiment with different hose routings, lengths etc.. when I first tried sidemounting I had to learn from photos and posts on this site and eventually after many dives got it streamlined and were I like it. I think the main difference is that in backmount there really is a standard tested method of hose routing that everyone uses which is very good and streamlined and taught in every school, but in sidemount it is really to each his own, and like anything some people are fast & some are slow.

[FW]

.....On the gas loss side, Forrest, you made an interesting statement that I have not been able to get anything substantiated on - that you have experienced total gas failures due to tank side problems. I would be truly interested to hear what happened with those. I would also be very interested in your opinion of the probability of having a high flow gas loss occur on the tank side versus the reg side (1:100 5:100???). On the blowout plugs - IMO they should be non-existent in a cave and therefore a non-problem.....

Well, I have only had two problems out of well over a thousand dives. Add to that the modern manifolds are tougher, so the odds are more like 1:1000. I am just saying that don't kid yourself that there is no chance of a problem.

FWIW, I thought I listed those dives in the IRAP forum, but I don't see them. I will write them up, and post them.

As for drag, streamlining is much more important than configuration. The worst drag I ever had was in sidemount on a DPV, because the bungies were too weak, and the tanks "blew" out to the side, and increased frontal area about double.

[atedeschi]

LOL - It was beginning to sound like the sidemount glee club for a while there. Nice responses all.

On the gas loss side, Forrest, you made an interesting statement that I have not been able to get anything substantiated on - that you have experienced total gas failures due to tank side problems. I would be truly interested to hear what happened with those. I would also be very interested in your opinion of the probability of having a high flow gas loss occur on the tank side versus the reg side (1:100 5:100???). On the blowout plugs - IMO they should be non-existent in a cave and therefore a non-problem.

Hose routing...glad to hear SM's are taking this seriously. It is hard to improve on BM and IMO - I have not seen anything better, only worse with folks diving SM which is why I am of the opinion that BM wins this one. Take just the SPG's, many folks have them dangling in front + there are 2.

Staging. BM, stage #1 goes under the arm, right where your left SM bottle goes. I will only point out that this was the ideal place for a bottle to be in the beginning of this thread - as opposed to on your back. So what changed? Ok - from the other point - placing the first stage when SM underneath you, well is clearly worse than under your left armpit like stage #1 when BM. IMO - in this case, either you see the logic or you just choose to ignore it.

Forrest, on the drag side - another good data point. But you are also stating the assumption that both are very well streamlined. I am basing my statement on what I see from the general population of SM divers...just measure how far down below and above the body most SM'd tanks protrude. Add the head sticking up in the middle. Let's say that the total frontal area on the tanks is very similar to BM tanks. Now the head is extra (like a 3rd tank). The head in BM uses part of the same area as the tanks. Increase the area, increase the drag = slower diver.

The last SM diver I dove with, I had to wait for both out of the water and in the water...I promise Bruce, no names... Lol, the out of the water part didn't have much to do with his SM configuration though...Now I understand that SO-Cal means SlOw-Cal. Couldn't resist it Bruce - had fun.

Bob

1) Yes the chances of a manifold failing are slim but still there. You should def have an isolator not just a straight crossover, because if you do have a failure on the tank or manifold you can shut it down. With you tanks in front you can see the issue and shut them down quickly.

2) Streamlineing is easy people just have to stop trying to make it so difficult. A SM unit can be very neat and clean just like BM. As far as SPGs there should be no SPGs hanging down. Mine point straight out and my body would come in contact with the ground before them. Most SM divers I see have a long hose so I am not sure were you got that notion.

3) Drag- i dont know how you say there is more drag. if the tanks are tucked in under the arm pits and even with the body then they are in the slip stream. Even if they are alittle off they are still more in the slip stream then the double on the back are. As far as a stage they still have the same amount of drag as a normal stage in BM.

[phillip1]

1) Yes the chances of a manifold failing are slim but still there. You should def have an isolator not just a straight crossover, because if you do have a failure on the tank or manifold you can shut it down. With you tanks in front you can see the issue and shut them down quickly.

2) Streamlineing is easy people just have to stop trying to make it so difficult. A SM unit can be very neat and clean just like BM. As far as SPGs there should be no SPGs hanging down. Mine point straight out and my body would come in contact with the ground before them. Most SM divers I see have a long hose so I am not sure were you got that notion.

3) Drag- i dont know how you say there is more drag. if the tanks are tucked in under the arm pits and even with the body then they are in the slip stream. Even if they are alittle off they are still more in the slip stream then the double on the back are. As far as a stage they still have the same amount of drag as a normal stage in BM.

Yeah!

[Sludge]

if you do have a failure on the tank or manifold you can shut it down.

Two possible reasons for this scenario: extruded cylinder neck o-ring or burst disk failure. Chances of one of these happening to properly-maintained doubles: one in a bazillion.

If it does happen, share gas out of the cave.

I have isolators on all my doubles, but they point down, out of the way. Far less chance of damaging the cave or the manifold.

[atedeschi]

not sure what you are trying to state or if i was unclear, but i agree with you. i do not believe in the straight crossover which i believe the OP was refering to.

[Sludge]

Actually, my point is that closing the isolator is just about the most useless skill that is practiced regularly by cave divers. I've known of three cases where divers had an incident and automatically closed the isolator, and in all three cases it was the wrong thing to do.