Closed manifold, most of the time

[Polomelo]

Even though I am at least a hundred of dives away from solo diving, I have been thinking about solo configurations recently. I'm mostly interested in solo diving up to 60ft (20m) in warm or almost warm water (with a wetsuit), with a light nitrox gas (32 or 36) and no decompression stops, for dives up to 2 hours.

This is what I came up with :
- steel twin tanks, with a closed manifold and a suitable wing
- an aluminium tank, neutrally or slightly positively buoyant
- the usual gear...

The purpose of the closed manifold is that, in case of a reg or o-ring failure, you can just forget about valves and take your time to surface without stress.
The purpose of the aluminium tank is that, in case of a wing failure and inability to swim your way to the surface, you can just get rid of the twin tanks and surface with the aluminium tank

I think that a closed manifold may be better than independent tanks because you can open it from time to time underwater to make sure that there is the same amount of gas in both tanks, and close it immediately afterwards.

Please let me know what you think about it

 

[TrustMeIveGotGoogle]

Why not just sidemount then?
You're alternating regs keeping balanced tanks.
In wetsuit you can use alu so swimming up in case of wing failure isn't really a problem

 

[RainPilot]

Solo diving, side mount would make a lot of sense. Its much easier to see what is going on with your valves and you have no added manifold complexity. Also means that when you travel you can keep the same style of diving, whereas back mount doubles may not be easily available wherever you are.

The manifold technique you are talking about is called Progressive Equalisation , @Akimbo has posted extensively on this.

 

[chrisch]

You are overthinking it. From 20m how long to the surface? That's the reserve gas you need. If you use twin tanks how long reserve if you have a reg issue? For example a freeflow is the general problem most divers plan for. If you can shut down the valve this leaves the balance of gas. If you cannot shut it down how long before you are totally without gas? How long to the surface?

The problem with all complex techniques is what happens when you don't get it right or simply forget to do it? The critical aspect of solo diving is the availability of another redundant gas source to replace the buddy. That source has to be sufficient to surface safely from the planned dive with a margin of error to cover any additional issues.

A side mounted twin tank or independent twin tank back mount means that you have two times a conventional rig. In essence you carry your buddy with you. Having two tanks the same gives more gas but implies more gas planning and gas management. Having a single main tank plus an independent bailout (often called a pony rig) means the independent source is simply for emergency use and the dive is conducted as if with a buddy and all the normal protocols (surface at 50 bar or whatever you decide).

If everything fails then you need to return to the surface without gas. This implies dropping weight, something normally we try to avoid. A backplate and wing set up with manifolded twin tanks generally is used for deco diving and doesn't have ditchable weight as this is more dangerous should the weight ditch accidentally and bend the diver. With a wetsuit and failed gas supply you have no buoyant source. A drysuit rig gives redundant buoyancy as the BC feed is one side the drysuit the other.

There is no such thing as a solo diving rig. There is only solo dive planning and knowledge. Your choice of equipment will be defined by your risk acceptance and the dive that you plan. The volume of gas is decided by the depth and duration of the dive you plan. Other factors such as returning to dry land are important - are you swimming to shore, swimming to a boat, do you have a surface person and so on.

My advice is always dive the same gear you normally dive - the familiarity is a safety factor. Then incorporate the redundant gas. For me this is simply clipping on a deco tank. The deco tank has independent gas and allows me to breathe irrespective of what issues there are with back gas. I am never going to solo dive deep so I do not even need to change the deco gas from EAN50 to a lower O2 percentage for ox tox issues. Chances are the deco tank will not be needed so it goes back full and can be used for deco on another (buddy accompanied) dive.

The simple addition of a LP feed hose to the deco rig will give an alternative gas for BC inflate if you need it. Think of it as a big pony. That is the optimum for me - I dive twin tanks all the time and have a deco tank ready to go. It would be just as good with a single tank set up provided the BC has the attachment points or a single tank wing rig.

 

[beester]

Even though I am at least a hundred of dives away from solo diving, I have been thinking about solo configurations recently. I'm mostly interested in solo diving up to 60ft (20m) in warm or almost warm water (with a wetsuit), with a light nitrox gas (32 or 36) and no decompression stops, for dives up to 2 hours.

This is what I came up with :
- steel twin tanks, with a closed manifold and a suitable wing
- an aluminium tank, neutrally or slightly positively buoyant
- the usual gear...

The purpose of the closed manifold is that, in case of a reg or o-ring failure, you can just forget about valves and take your time to surface without stress.
The purpose of the aluminium tank is that, in case of a wing failure and inability to swim your way to the surface, you can just get rid of the twin tanks and surface with the aluminium tank

I think that a closed manifold may be better than independent tanks because you can open it from time to time underwater to make sure that there is the same amount of gas in both tanks, and close it immediately afterwards.

Please let me know what you think about it

We had another topic here recently of someone with no real background (in this case it was 130ft dives with independent doubles and a hot mix in one of the tanks) overthinking and rationalising a procedure that for experienced divers doesn't make sense at all.

Or you go sidemount or you go backmount but in any case (or isolated tanks on 2 sided of you or manifolded tanks on your back), that is your redundancy.

For 60-100 ft dives you definitely don't need to side sling an additional tank (pony) as redundancy because if you calculate reserve gas well you have all the gas you need on your back. That is IF you know how to use manifolded doublesets. With correct procedures and depending on your issue you can isolate the issue and safe all the gas or not isolate the issue and safe half your gas (which should be ample to get you to the surface on any NDL 60ft dive depending on tank volume of course).

Keeping your manifold closed doesn't serve any purpose and adds potential risk. If you can reach your valves closing it takes 10 seconds, you won't lose lots of gass in 10 seconds. Potential risk with a closed manifold is that you add a lot of complexity to your dive. Instead of diving with virtually 1 tank (manifolded open) you are diving with separate tanks. However you have not ingrained a procedure for switching (like in isolated doubles) and you will keep breathing from your main reg. If you don't regularly equalize, you might end up with an issue. However the biggest risk in my book is not underwater but filling the double set, with a manifold closed... specially with partial blending and nitrox.

 

[CuzzA]

If your objective is to simply add redundancy for solo dives that are less than 60 ft. why not just keep it simple and carry a small 13 cuft. pony?

I don't understand why you would want to add complexity to a dive by introducing doubles or sidemount unless your goals are to extend your dives closer to your NDL or go into deco, or in the case of sidemount, pass restrictions. Also, consider you will now have to carry twins where ever you are going, which sucks. If you are really going to stick with this idea and want to do multiple dives, you're now going to need multiple twin sets. If you aren't planning on using all of the gas in the tanks, meaning doing decompression dives, and you stick with the norm of keeping the manifold open, you'll now be paying to fill partially full tanks. Essentially wasting money.

Having seen two videos this week where the diaphragm blew out of the freakin first stage and in both instances the divers were solo, quickly bailed out to their pony, shut down their failed main tank, ascended and safely made it home, redundancy is paramount in solo diving... but as they say... KISS.

 

[Akimbo]

The purpose of the closed manifold is that, in case of a reg or o-ring failure, you can just forget about valves and take your time to surface without stress.

The manifold technique you are talking about is called Progressive Equalisation , @Akimbo has posted extensively on this.

Here is a link on Progressive Equalization with lots of photos and discussion.

Here is a discussion on the protector:
Valves up or down? Considerations...Post 47

 

[2airishuman]

Even though I am at least a hundred of dives away from solo diving, I have been thinking about solo configurations recently. I'm mostly interested in solo diving up to 60ft (20m) in warm or almost warm water (with a wetsuit), with a light nitrox gas (32 or 36) and no decompression stops, for dives up to 2 hours.

This is what I came up with :
- steel twin tanks, with a closed manifold and a suitable wing
- an aluminium tank, neutrally or slightly positively buoyant
- the usual gear...

The purpose of the closed manifold is that, in case of a reg or o-ring failure, you can just forget about valves and take your time to surface without stress.
The purpose of the aluminium tank is that, in case of a wing failure and inability to swim your way to the surface, you can just get rid of the twin tanks and surface with the aluminium tank

I think that a closed manifold may be better than independent tanks because you can open it from time to time underwater to make sure that there is the same amount of gas in both tanks, and close it immediately afterwards.

Please let me know what you think about it

Too much stuff. Either carry twins, or a pony, not both. Closed manifold and progressive equalization is an acceptable practice but one that should not be necessary if you are a) monitoring your SPG, b) monitoring the dive time, and c) have your secondary on a neck bungee so that you will notice freeflows.

I have come to prefer twins over a pony for solo dives. On the other hand a pony is practical in situations where twins aren't readily available, as when you're renting gear, or on a boat that doesn't allow/provide twins, or where it is physically difficult or impossible to carry twins to the dive site.

I carry a lift bag on some solo twinset dives, to serve as a source of emergency buoyancy in the unlikely event of a total wing failure. Keep in mind that total wing failures on wings without pull dumps are vanishingly rare. If you tear your wing on something sharp you can usually orient that portion of it down and keep the bubble in the intact portion.

 

[chrisch]

...
For 60-100 ft dives you definitely don't need to side sling an additional tank (pony) as redundancy because if you calculate reserve gas well you have all the gas you need on your back. That is IF you know how to use manifolded doublesets.

..
I have come to prefer twins over a pony for solo dives.

I dive twin tanks all the time because I cave dive and this keeps my gear familiarisation up to date. I also practice valve shut down all the time as I don't particularly want to drown in a cave . Likewise I use a deco tank for deep dives.

I think if none of this were the case I would be very inclined towards a bailout/pony for solo. I would certainly suggest to the OP that you look at both options and if possible get to try out some twin tanks (or a SM rig) before committing to the expense of buying the gear. I did a SM course which included all the equipment in the price (there is a PADI one - lots of commercial schools run it). I found it was not something I wanted to do. OK so the course was "wasted" money but the saving in buying gear was considerable.

Lots of tec instructors do a similar "intro" for twin tanks which might be worth a look.

Both disciplines (SM or doubles) require an investment of time and practice to keep your skill level up to scratch. A bailout much less so. Nothing in my opinion beats having hands on experience of the different options in help make you mind up.

 

[lermontov]

Even though I am at least a hundred of dives away from solo diving, I have been thinking about solo configurations recently. I'm mostly interested in solo diving up to 60ft (20m) in warm or almost warm water (with a wetsuit), with a light nitrox gas (32 or 36) and no decompression stops, for dives up to 2 hours.

This is what I came up with :
- steel twin tanks, with a closed manifold and a suitable wing
- an aluminium tank, neutrally or slightly positively buoyant
- the usual gear...

The purpose of the closed manifold is that, in case of a reg or o-ring failure, you can just forget about valves and take your time to surface without stress.
The purpose of the aluminium tank is that, in case of a wing failure and inability to swim your way to the surface, you can just get rid of the twin tanks and surface with the aluminium tank

I think that a closed manifold may be better than independent tanks because you can open it from time to time underwater to make sure that there is the same amount of gas in both tanks, and close it immediately afterwards.

Please let me know what you think about it

sounds like you've given this some thought and are evolving your thinking - thats a good sign - I recommend you do a some sort of a course that develops your gas planning and technique it will stimulate you mentally and give you a solid base to go further- diving up to 2 hours with no deco sounds a shallow dive so i m not sure if getting to the surface is a big concern as you get LOA
In regard to sidemount if you can find LDS that has a try out day -do it- it might send you off on a different direction that will fit your needs well