Question Rec cold water diver: Single, Double or Sidemount? (focus on safety)

[Wildsparrow]

This forum provides so much useful information, it's incredible. But I couldn't find anything in regards to different setups for recreational diving. I'm not sure if the question is stupid Let's try. This will be a lot of text from my side and I'm wondering how experienced divers would rate the different setups.

My scuba background:

• I'm an AOWD with about 60 dives - most of them the typical holiday/tropical dives. I did and like more advanced dives such as diving in currents, night dives, entries of a cavern (no caves). Though I enjoy diving in the "deeper" region for rec divers (let's say 20-30 meters), this is not something I pursue to dive deeper, just to be deeper as anytime before. I like taking some pictures or videos of the dives, so I usually have some additional equipment with me.

General intention:

• I want to dive (more or less) full year in local rivers and lakes. Water temperatures varies from 4°C to >20°C, of which May - October (including) are above 10°C. Only January and February are below 5°C. I have no intention to dive at those temperatures.
• Pure recreational diving. I have no intention to do extra deco stops, use mixed gases, go below 40 meters, dive into narrow caves, or start using rebreathers. I do think that all of that is spectacular and would do that in another life but diving should be fun and easy for me. This does not mean I don't want to use technical stuff for diving - in fact I love technical stuff and I'm willing to invest training, money and time just to use the technics, though not at the limit. It's like to have a decent sports car: You can accelerate and brake faster than the others and the cornering speed is higher - but you don't have to drive at the limit to have fun (i.e. 1 km/h faster and you crash). Yes, waste of money for the potential of the car, but still so much fun.
• I don't have any issues with back, knees etc., I'm tall and strong, so moving dive equipment around, regardless the configuration, is very easy.
• Safety is priority number 1. Only diving with a buddy (or in a small group), never single.

Questions:

• I wonder which are the opinions of experienced divers which setup would be "best" or which have negative sides which could be eliminated with an "upgrade":
  • Single tank. Let's say 12 liter tank. 2x valves, 2x 1st stages etc.
    • Most simple set up. If free flow occurs, closing the primary valve should give enough air to either ascend normally or maybe use a little bit of buddy's air while ascending (depending how fast the valve is closed and how much air is left in the cylinder).
    • Dives will usually be limited by air supply, not by NDL.
  • Double tank. Let's say 2x8.5 liters or 2x10 liters. 2x valves, extra valve in between (manifold), 2x 1st stages etc.
    • More "advanced" setup. May give more dive time.
    • I'm not sure if this setup will increase safety at a free flow compared to a single tank? What could happen that this configuration is superior, i.e. the extra valve between the tanks?
      If I close (let's say) the right valve, is just the exit to the 1st stage blocked but air from the right cylinder can go to the left first stage? Or is the whole right tank shut off?
  • Sidemount. Let's say 2x7 liters or 2x 8.5 liters.
    • Most "technical" setup. May give that little "extra" to diving by just using it, though not really necessary. It's like using a dedicated espresso machine + milk frother instead of a fully automatic coffee machine. The espresso machine will give the same espresso/cappuccino, but the subjective taste is superior :-D
    • This setup should result in increased safety at a free flow: Just use the other regulator. Even if the easy-to-reach valve of the affected tank is not closed - the other should provide enough air to safely reach the surface.

I think the real questions come down to:
Is a double tank configuration in any case better than a single tank configuration for rec diving?
Or will the only question be: Go single tank or sidemount. A single tank is as safe as a double tank (my assumption) but sidemount adds the technical side and improves safety.

Looking forward to your opinions and any downsides/benefits I did not mention in above text

 

[runsongas]

if you want more redundancy so you don't need to rely on your buddy:

pony bottle, al19 to al40, for shore diving where hiking doubles is going to be a pain and the entry can get rough

sidemount if entry is protected enough to clip in water or only diving relatively good conditions

doubles for boats

 

[Marie13]

Quite common in the Great Lakes region for single tank recreational divers to sling a pony for redundancy on cold water dives. Often an AL40. I did it myself for several years. Best option for those who have no desire to do tech training.

What’s the point in doing the training if you’re never going to use it?

SM not ideal for boats, depends on local customs if it is allowed or not.

 

[Imla]

Tip: If going for BM doubles, scratch the 2x10s. They are horrible to trim out. The standard in Europe are:
2x7 232 or 300 Bar
2x8,5 232 Bar (these can be difficult to trim out, but tall men usually like them)
2x12 232 Bar Super easy to trim out. In my area they are liked by all from 160 petite females, to tall burly guys.
Personally, I'd go for the smallest set of backmount doubles that felt good. Don't know where in Germany you are, but a Doubles Primer or a Gue Fundamentals would be a good start to get the knowledge you are seeking.

 

[ginti]

@Wildsparrow I am not sure what you mean by saying "safety at a free flow". If you mean that you have more breathable gas after a free flow, here you are a simple scheme:
(1) single tank with one valve and an octopus system: if you have a free-flow, you cannot stop it; whether you continue breathing from the free-flowing regulator or you need gas from your buddy (in which case it is a good idea to close the valve of your tank).
(2) single tank with two valves and separate first stages for the primary and secondary regulator: if you have a free flow, take the secondary regulator and close the valve of the primary one; you still have all your gas to come back.
(3) double tanks: see (2); to answer your question, when you close the primary valve, you can still breathe the gas of that tank from the other regulator.
(4) side-mount: as you said, however, the metaphor of the cappuccino does not fit a lot; it is not superior at all, and many advanced divers (exploration level) prefer doubles over side-mount; some others prefer side-mount. It's just a matter of personal preferences.

There are other considerations to do when diving cold. The most important is the amount of gas to return with your buddy in case of sharing gas. Personally, even for short dives, I would go at least with 15l of air, most likely in doubles; be aware that there are other options.

Also, I did not get if you want to dive all year, including January and February, with cold water or only when the temperature is higher than 10°C... sorry, my poor English is playing against me but I will be grateful if you clarify it, many thanks!

if you want more redundancy so you don't need to rely on your buddy:

pony bottle, al19 to al40, for shore diving where hiking doubles is going to be a pain and the entry can get rough

sidemount if entry is protected enough to clip in water or only diving relatively good conditions

doubles for boats

I have never seen a pony bottle in Europe, but I am not that experienced - maybe there are many. Anyway, it is an alternative, and the OP should consider it if it is his style.

EDIT: @Wildsparrow, just two further points: (1) no question is stupid (almost ) and (2) I saw many weird equipments, especially the old one, so always ask technical details to the person who is selling or renting you the equipment

 

[Wildsparrow]

Thanks for the quick and interesting replies

No boat diving here. Easy access to the dive spots. Thus hiking is no issue.
Tech training and using tech equipment is something I consider to be interesting and fun. Even if you don't use it to its full capacity (such as cave diving).

Another question regarding SM: Would you say this is as good as BM in a current in a river or is maneuverability limited with SM? (I don't think so)

Pony bottle is something I did not consider - thanks for pointing me into this direction. Honestly, I never saw that here in Germany. What would be the most common approach: Tank with one 1st stage and primary/octopus & Pony with 1st stage and 2nd stage, or tank with two separate 1st and 2nd stages & Pony with 1st and 2nd? Both options seem to me like an overkill (3 regulators and up to 3 1st stages).
Edit: Or One Tank, one valve, one 1st stage, one 2nd stage, and Pony with it 1st and 2nd stage?

GUE basis in Luzern (Switzerland) is close enough for me, will consider this.

So, the 2x10 Double is removed from my list. If double, I think 2x7 is the way to go. 2x12 seems to be way too much air which I would never use, and the bottles are considerably heavier (23.5kg a full set of 2x7 instead of 32.8kg for 2x12. And I could always rent 2x12 if needed)

@ginti Option (1) is not in consideration. Thanks for answering my question in (3). I agree, anything below 12l seems to be not enough - I would also strive to have at least 14l of air with me (though 24l seems to be too much - and then I haven't looked into 300 bar, but focused on 200-232bar). I did not say that SM is superior (in that case I would not think of going BM), I said the "technical" feeling could be something I would really enjoy

 

[formernuke]

Single tank. Let's say 12 liter tank. 2x valves, 2x 1st stages etc.

• Most simple set up. If free flow occurs, closing the primary valve should give enough air to either ascend normally or maybe use a little bit of buddy's air while ascending (depending how fast the valve is closed and how much air is left in the cylinder).
• Dives will usually be limited by air supply, not by NDL.

Are you saying have a split so you are hooking up two first stages to that one tank? If so I wouldn't as I feel you are really not gaining anything at all.

For single tank redundancy add a pony bottle setup.

For recreational diving stuff my favorite setup are my lp50's doubled with manifold. Note special training for double diving is needed. I think these would be 6 or 7 liter tanks in metric. They trim better than a large tank and are more comfortable both in and out of the water than a single large tank. I especially like them since I cave fill them for a good amount of air.

Sidemount, Sidemount has a place and I have limited experience with it. Again specific training is needed, It is more complex than backmount doubles. You said not joint issues etc and not squeezing into tight spaces I would not recommend it for you.

For me all I dive right now is backmount doubles. I use my small lp50's for rec and hp100's for tec stuff. The large doubles are very heavy and with drysuit them and a al40 deco bottle I'm overweighted by a fair amount.

Enjoy your diving, hope this helps a little.

 

[Wildsparrow]

Yes, like this:

In case of one 1st/2nd stage malfunction, I could shut this valve off and breath from the other 1st/2nd stage.

Yes, lp50 will be 7liter tanks in metric.
Thanks for your insights.

 

[formernuke]

Yes, like this:
View attachment 756046

In case of one 1st/2nd stage malfunction, I could shut this valve off and breath from the other 1st/2nd stage.

Yes, lp50 will be 7liter tanks in metric.
Thanks for your insights.

Personally that looks like a marketing scheme to me. For single go with pony.

I see nothing gained for that over a set of doubles of same or higher combined capacity.

 

[Lorenzoid]

Yes, like this:
View attachment 756046

In case of one 1st/2nd stage malfunction, I could shut this valve off and breath from the other 1st/2nd stage.

Yes, lp50 will be 7liter tanks in metric.
Thanks for your insights.

That is a variation of what is known as an H-valve and might more aptly be referred to as a Y-valve. Here is the configuration many of us have seen, which I suppose sort of resembles the letter "H" in shape: Blue Steel H- Valve - Left Hand

H-valves and Y-valves are not commonly used in the US, but I have heard they are more common in Europe, for cold-water diving. As others have said, a pony bottle is far more common in the US.

Here is a thread from 2017 discussing H-valves: What's the deal with H-Valves?