Question Sidemount or backmount doubles?

[tbone1004]

I am an AOW diver that wants more bottom time and thus more breathing gas. For single-tank dives, I really like my backplate & wing setup. No issues with that for those kinds of dives. But I would really love to get some more bottom time and expand my reach/range. I will definitely seek proper training to go beyond my current certification in terms of maximum depth and no-deco limits. But with which setup?

I have scoured these forums and the internet for objective pros and cons for sidemount and backmount setups. (‘Objective’ being the operative word here. Most comments seem to be very much in favour of either sidemount or backmount diving.)

Even though I will not be cave diving or doing penetrations into particularly tight spaces - for which sidemount was originally developed - there are some benefits to sidemount that look very appealing to me. Here’s what I found, or at least the major differences between the two setups.

Backmount:

• One stable unit, preferred on boats (?)
• Quite heavy to log around on dry land (I don’t have the strongest back in the world)
• Not as streamlined as sidemount (?), but adding stage bottles doesn’t hurt streamlining further

Sidemount:

• Two units, may not be as stable on boats if tanks are donned above water
• Tanks can be hauled separately
• Sleeker in the water (?), but adding stage bottles negates this advantage somewhat
• Valves are easier to reach, and visible

A few questions regarding these two lists:

• Anything I missed on either list? There are some question marks in there, any comment on those?
• Is a set of backmount doubles harder or easier to find than sidemount tanks at dive centers/liveaboards (provided I bring my own BC and regulator set)? If itineraries and schedules allow for double tank dives, is one of these configurations easier to get when traveling and renting tanks?

Obviously, there is proper training and setting-up the configuration involved in both. Investment in special gear, too (another, bigger, wing for doubles or a sidemount BC, regulator sets) and maybe in tanks. I already have two steel 12L tanks, though. I just need to put new valves on them and sidemount rigging if I would get into sidemount, or try to build a double set out of them…

Most of my comments have already been weighed in, but here goes.

First off, addressing the elephant in the room that has not really been confronted head-on. You do NOT need to be looking at doubles and sidemount at this point in your diving progression. You are still bound by no-decompression limit diving and you can always use bigger tanks if you are bumping up against your gas before you bump up against NDL. I'm travelling for work and don't have deco-planner on this computer, but at 100-110ft with a big steel bottle you're likely hitting your NDL before you hit your gas limits. If you're diving an AL80, then you shouldn't be diving that deep on an AL80 because of rock bottom issues.
At such time as you are ready to take AN/DP or equivalent to actually push those bottom times, you will have a better understanding of which configuration makes sense. It has been said here, but I will echo it. Unless you intend to dive small cave passages, doubles are the right answer. Certain physical limitations excluded, but I do also sit in the opinion that if you have those types of physical issues you shouldn't be doing those dives because of the increased risk of something going sideways. Those of us that have taken bodies out of the water because of health issues are particularly sensitive to it and I cringe every time I see someone who's shape can only best be described as globular getting into a cave because I'm afraid I'm going to have to take them out and/or putting them back in *spreading ashes sucks almost as much as removing bodies*. There are people with certain shoulder/knee/hip issues and that's why I actually started my cave training in sidemount because my knees are beat to hell and back and I knew I was going to have to go there eventually, but that time has not come yet.


Now, to address the configuration question since I was pretty blunt about it above.

I have been diving doubles since 2008 and sidemount since 2009. I took my initial cave training in sidemount over a decade ago and dove sidemount exclusively in caves until about 4 years ago when I started diving a rack mounted CCR in caves. At that point I started to dive doubles more often in caves because it meant I only had to bring one backplate/wing/regulator set and if I was doing OC dives or CCR it was just which set of gear I put the bp/w and regs on. Since then, I have primarily been diving doubles in caves for OC and using them as bailout for my sidemount CCR. Throughout all of that boat dives and teaching were always done in doubles and sidemount was only used when required for where I was going.

Sidemount undeniably easier to sort out when travelling, but anywhere that you would actually need doubles or sidemount you should be able to find doubles to rent fairly easily.

Why the change? Like I said above, it was mainly convenience driven, but even last week when I had to make 3 trips to and from the water to bring a set of sidemount bottles to the steps at the caves vs. a single trip for doubles, and that one trip actually being easier *by the strict definition of "work" being area under the curve it is actually less work to carry the doubles vs sidemount since it is a single trip. Each of the sidemount trips are less work than the individual trip with doubles but there are more of them. This is changes if you use a cart, but that's a lot of hassle IMO*. It is also significantly easier at the surface both pre-dive and post-dive, and I am a very proficient sidemount diver who can get ready about as fast as someone in doubles can, but it's still a lot of pfaffing about in comparison. Sidemount has its place, but I firmly believe that it is being oversold which is causing headaches for a lot of dive operators.

 

[Celt]

Main reason is the BOOM! a cloud of bubbles envelop you and you need to protect your remaining gas by isolating, then resolving which side's wrong. This generally brings up another common approach which is shut down the RH valve and see if that works, then open up the RH and shut down the LH valve.

But I’ll only need to shut the faulty regulator. All my gas is still available.

 

[tbone1004]

One more question...

Underwater, what CAN'T you do with sidemount that you CAN with backmount? Note that I am not going to take many deco bottles any time soon... Max two, if even that.

If we are using absolutes, then there is nothing that I can think of that you can do in backmount that you can't do in sidemount.
You CAN get off and more importantly back on any boat in sidemount that you could in backmount, but if you try to get on a 6-pack in NC that has a tuna door in sidemount with high gunwales in 6-7's then you will not only hate yourself, but the crew may well put you on the "boat's full" list.
You CAN shore dive in fairly rough surf in sidemount, but again, you may well hate yourself for attempting it.
You CAN carry more than 2 stage/deco bottles in sidemount, but it is infinitely easier in backmount both from a placement and a trim perspective *butt mounting things in sidemount without a drysuit is functionally impossible and even in a drysuit is rather annoying*.

The list goes on, but those are the big 3 IMO.

 

[NW Dive Dawg]

OK... so at the risk of all the negative comments that I am probably going to get here...... I'm going to go all the way off the "deep end" and suggest another option that is totally free... won't break the bank and will serve you well throughout your diving career.

• Work on your breathing technique. Take a solid 5 full seconds to inhale, pause for one second..... and then take a solid 5 full seconds to exhale...... then pause for a full second and repeat. Try it right now as you are reading this. With an AL80, that simple change will most likely put you into deco prior to you getting low on gas in any planned no-deco scenario.

• PS......Keep in mind that most resorts stick with AL80's for a reason.... The gas volume availability, combined with "new diver" breathing...... makes it difficult for the casual holiday resort and new divers to get into deco trouble.

• PSPS..... For local or self supplied tank diving, buy 102 Steel tanks.....or maybe a 120 if you can handle it.......and still implement the above suggested breathing technique. Just my .02... Cheers!

 

[RobPNW]

Some threads, you just know everyone will be in agreement.

 

[Wibble]

In sidemount, you can't access all of your gas if you lose a regulator. It would take multiple simultaneous failures for that to even matter. Forget a full face mask with sidemount, without a lot of extra plumbing (cough, Z-manifold). Getting a fill of a mixed gas (Nitrox) is more touchy with sidemount. If the mixer is a little off you could have a little different blend when you do a reg switch. Sometimes you might be in less than great water that you don't want to do a reg swap. Sidemount also adds clutter in the chest area. There gets to be a lot of stuff under your chin. The plumbing that would normally be behind your head is now mixed in front of you.

None of that stuff is huge. Just more of details.

But... You've 50% left and you would have factored this in to your planning. I believe the cave/overhead people call it the rule of thirds. One third in (therefore two thirds left), BOOM, now one third only left and you leave and live for another day.

If in open water it would be the same; your minimum gas would allow for the loss of one side or the other.

Clutter to the chest area? There's an elephant's trunk just like backmount but coming from one side (XDeep Stealth - others are like backmount). There's a suit inflate hose, just like backmount. Nowt else. If wearing stages they dangle just like backmount.

I use a short neclaced hose on the LHS and a longhose on the RHS which is bungeed to the cylinder. This has less crap than backmount -- no longhose routed down below the battery and across the chest. So actually it's probably neater than backmount. For donation pull the longhose out of the mouth, duck head and straight into the mouth of the receiver, then pull out the extra 3ft/1m of hose from under the bungee.

The regulators are under one's armpits, so largely away from the chest. At least there's not that mass of kit on your back to stop you from going through holes without hitting the top!

Personally I've never been that bothered about small differences with the nitrox mix. But if it were, say, 5% different, then tweak the value in the computer to either the lower value, or in between. MOD's sort of similar; would happily run it hot within reason. Actually no; I would have tested it and demanded more air if it were 5% high (e.g. for 40m/130ft I'd want 28%; if they'd supplied 33% I'd have rejected it just like any backmounter would have).


(Sorry for dealing with each in turn; it's just that sidemount isn't that difficult. I'd even argue that it's more simple than backmount with the evil valve drills. OK, tidying up the longhose would normally require the RH tin to be unhooked just like a stage cylinder.)

 

[Wibble]

And to answer the OP...

If you think your future will include some form of redundancy in your diving, e.g. backmount or sidemount, then make the move. This will be much easier if you've some friends who also dive BM/SM.

If not then you will find that your breathing rate will reduce with more experience. Couple or more reasons for this, but the main ones are that your technique will improve as your trim and finning improves so you're working less hard. Second reason is you're much happier and less stressed underwater.

Good core skills will really help you out: trim (flat), finning (without using hands to turn around, back up) and your buoyancy gets better (especially if your weighting improves).


Diving with redundancy is a good thing especially in cold water with poor visibility. The main point is you're self-sufficient should you loose buddies or even get a little tangled up on some fishing net -- you have more time to sort stuff out.

Twinsets/sidemount on recreational dives are absolutely fine.

 

[rjack321]

Underwater, what CAN'T you do with sidemount that you CAN with backmount? Note that I am not going to take many deco bottles any time soon... Max two, if even that.

A 2 deco bottle dive in sidemount (or god help you 3 deco bottles and a stage) is at least as big of a profile as in backmount doubles, and the doubles are way easier to manage.

Doubles. you fill up that nice storage spot on your back and get to add bottles onto your sides as needed. Doubles make you tall and narrow.

Sidemount fills up the best storage spots on your sides first. Then you run out of places for bottom stages or deco gas fast - that big handy area on your back is in theory unencumbered but whoopdeedoo, you are swimming around like a Michelin man of tanks. Keeping them streamlined as you use the stages/deco gas is a huge pita too. SM is a flatter profile (if you're actually good) but its also called widemount for a reason.

 

[RobPNW]

As someone with no experience with either setup, can one argument be made that SM offers a higher level of redundancy?

 

[rjack321]

IMHO, more than two deco bottles is rebreather territory.

I disagree with the comment about doubles being better for doubles. While uncommon, in my area there is a shore dive that I'd like to do (Octopus Hole) where no way would I consider backmount doubles. I wouldn't consider my rebreather either. I'd take down two cylinders separately, kit up, then walk down.

Even for long walks to/from the entry/exit, I prefer sidemount for cold water OC diving.

I remember in a similar discussion when I brought up the advantage for travel. Someone here called me lazy. I just laughed as trying to arrange in advance is a PITA and often impossible. I'd rather show up the next day after arriving, take two cylinders, and jump in the water.

You can see ALL of octopus hole on a single 100. Probably twice on a single 130.