Hydrodynamics - backmount vs sidemount

[RN]

Back to real world scenarios....I can think of at least 4 deaths in the past 2 years where getting turned around for one reason or another lead to death. I can think of 0 where diving 1/3rds killed someone.

And how many of those 4 might have had a chance had they reserved more gas?? No need to answer because no one knows. However, had those divers cut back turn pressure by 200psi, they would have had an extra 600 psi. That extra 600psi would either get them out alive or, as you state, prolong death. I'll choose the extra chance of getting out alive.

Your dismissive to jj1987:

No, James and I have had this discussion before. He knows where I stand. I know where he stands. No point in going over it all over again.

Just how did YOU plan to "salvage" it? If you're not talkin' about reg switches or valve breathing, just what EXACTLY are YOU talkin' about?!! Maybe I'm ignorant, but you must think I'm stupid that I can't follow your discussion in this thread.

I won't bother repeating what others have already posted. Go back and read Jay's, DA's, Gary's, etc, posts. My argument was not that you wouldn't lose half your gas supply in sidemount, it's that you will likely lose MORE than half your gas supply in manifolded doubles.

[phillip1]

In reality I could not care less what people argue this BM vs SM, I prefer SM because I have dove both extensively and I dive almost exclusively exploration dives with some really adverse conditions, some sumps and some very long multi stage dives too, some caves are so tight they seems impassable some so big you could go by submarine, SM does them all perfectly with the identical setup.
In all the diving I have done so far I have not found even the slightest advantage to dive BM, really and honestly I think SM has only advantages over BM (at least in my experience)
After diving both and gaining enough experience SM not just a few dives, but at least a few years I can safely say that IMHO SM is far better in all aspects of my diving, be it safety, logistics, comfort and last but not least fun.
I think many people formulate an opinion of SM knowing little or nothing about what SM entails etc.. SM is very different than BM and a few dives will not really open your eyes to the advantages/disadvantages of SM.
If a diver with several hundred dives starts to tell me he or she prefers BM, no problem I will listen and respect that opinion and maybe learn something out of it, but it appears that many critics (I may be wrong so forgive me in advance) of SM know little or nothing about SM other than maybe a few dives in a badly setup Nomad or what they read about SM on the internet.

Some of the most highly experienced divers I have met in both BM and SM choose SM almost exclusively for all they're recreational cave diving and exploration. I have listened tried and learned and I agree.

Granted if you have been BM your whole life switching to SM is not the easiest thing and it will take a while to get it right but all things being equal, safety wise, SM is far more comfortable, flexible, and yes I admit it waaaaaaay more fun.

As for thirds I have never done a single dive were I get to thirds, I always have more, I think thirds is very unrealistic even in a high flow cave, you can never assume that even with flow the exit will go as smooth as the start of the dive, especially if you are in an emergency, some find my gas management overly conservative.
No matter what you will always be better off with more gas, even just a bit more 300-400psi more, it may not be enough to save your life but then again it might and in a situation like that I would rather have that extra 300psi than be empty.
I think there have been a few accidents were the divers ran out of gas 3-5 mins from the entrance, maybe in one of those 300psi would have made a difference, maybe not, either way I will bet my money on having more gas.

I think a SM vs BM race would be interesting and is a good idea, not to get people to change they're minds, everyone should dive how they feel comfortable, but nevertheless interesting to compare drag, maybe there is an even better way to streamline gear, maybe not, either way this sounds like it would be really fun to do, and isn't that why we all dive in the first place?

[diveongas]

I won't bother repeating what others have already posted.

Good, there is no need.

Go back and read Jay's, DA's, Gary's, etc, posts.

Okay. Jay's, DA's, Gary's, etc. collective posts are logical, acknowledge competing view and are very informative. They know EXACTLY what they're talking about.

My argument was not that you wouldn't lose half your gas supply in sidemount, it's that you will likely lose MORE than half your gas supply in manifolded doubles.

Okay, it's a good argument supported by many. Good clarification, thanks. I guess we're all good now.

,

[SuPrBuGmAn]

We won't have to listen to "Backmount is so much more streamlined than sidemount" and "Sidemount is so much more streamlined than backmount." Either one or the other is, or it's a tossup.

It's kind of like the commercials where the gas company tells you how much cheaper it is to heat your house with gas, and the electric company tells you how much cheaper it is to heat your house with electricity. They can't both be right.

Sure they can... cause there's too many variations to really make a definitive answer for such broad configurations. One SM configuration could be rigged up to cut through water like a semi-truck, while someone else might have there rig ALOT more streamlined. They're both SM, so?




When its all said and done, the SM guys still have more cave to dive

[Bob Cree]

I think there is merit to Kelly's point re. BM being more streamlined than SM. Sure you can throw math at it, but the point missed in my opinion is trim. How many people do you see truly horizontal in the water. I have seen only one. When you see it, your jaw will drop and you'll have to catch your reg. Don't kid yourself, it doesn't happen very often.

Take just a bottle. As others have pointed out, drag is proportional to frontal projected area. "IF" you were horizontal, ONLY the top of the bottle would present itself. OK - lets say 8 inches in diameter and 24 inches long. True horizontal, the frontal projected area is 50 in^2. Now go to 15 degrees up angle on the diver...that doubles the frontal projected area to roughly 100 in^2. 30 degrees, it is 150 in^2. 60 degrees - ok, now we are getting silly. Point is - you gain the most from trim. Problem is, most people don't realize this and their trim sucks, and it is magnified by the WIDTH of the suckee!

Unfortunately, the width of SM divers is greater than BM divers (roughly twice)...so IF your trim SUCKS - a SM diver will suffer (2X) MORE than a BM diver....proportional to that width difference...

The moral is, IF you truly have perfect trim - it does not matter. If you are mortal, BM has less drag than SM because most of us, well, our trim sucks...work on technique, and you will have the biggest effect no matter the configuration.

[Herbie]

When its all said and done, the SM guys still have more cave to dive

And the no mount(NM) guys have even MORE caves to dive ! Hydrodynamics is what this thread is supposed to be about but I gotta admit its interesting to see the rivalry between cavedivers. Can't we all just get along and dive...dive....dive...dive...dive...dive...even though the backmount guys do have better hydrodynamics What?

[Rich]

I just want the the time back that I spent reading this.......

Safe diving,

Rich

[gearhound]

If you all are really worried about absolute efficiency and streamlining, you should reduce the size of the biggest part of you in the water...for some of you, your ass or gut. Get off the computer and run some laps son!

[DA Aquamaster]

It's kind of like the commercials where the gas company tells you how much cheaper it is to heat your house with gas, and the electric company tells you how much cheaper it is to heat your house with electricity. They can't both be right.

They both lie. Coal is way cheaper than either gas or electric heat. Of course...a neighbor of mine when growing up used geothermal heat - he was a little different but brilliant - and that was basically free except for a few periodic plumbing repairs.

[RN]

I think there is merit to Kelly's point re. BM being more streamlined than SM. Sure you can throw math at it, but the point missed in my opinion is trim. How many people do you see truly horizontal in the water. I have seen only one. When you see it, your jaw will drop and you'll have to catch your reg. Don't kid yourself, it doesn't happen very often.

Take just a bottle. As others have pointed out, drag is proportional to frontal projected area. "IF" you were horizontal, ONLY the top of the bottle would present itself. OK - lets say 8 inches in diameter and 24 inches long. True horizontal, the frontal projected area is 50 in^2. Now go to 15 degrees up angle on the diver...that doubles the frontal projected area to roughly 100 in^2. 30 degrees, it is 150 in^2. 60 degrees - ok, now we are getting silly. Point is - you gain the most from trim. Problem is, most people don't realize this and their trim sucks, and it is magnified by the WIDTH of the suckee!

Unfortunately, the width of SM divers is greater than BM divers (roughly twice)...so IF your trim SUCKS - a SM diver will suffer (2X) MORE than a BM diver....proportional to that width difference...

The moral is, IF you truly have perfect trim - it does not matter. If you are mortal, BM has less drag than SM because most of us, well, our trim sucks...work on technique, and you will have the biggest effect no matter the configuration.

You forgot one key element - a properly trimmed sidemount diver doesn't have as much cylinder surface exposed to forward movement. At least 1/3 of my cylinders are shielded by my shoulders, which are there even in backmount .