Independent doubles - hose routing and secondary position?

[Tortuga68]

Hi,

I did a search but couldn't find what I was looking for

I dive manifolded doubles but am thinking about setting up for backmount independant doubles for travel so I can use two rental AL80s with my own two sets of regs & BP/W

My main question is about hose routing and where/how to position the second stages... with manifolded doubles I use 7' primary hose and bungee on secondary but not sure how that should work with 4 second stages and 4 LP hoses? Also where you clip/route the second SPG, right d-ring or what?

Or do you just use 2 second stages, one on each tank? If so, which is primary and which is secondary, any preference and why?

I already get the switching tanks every X bar or so, but any opinions on how many X is would be good

My plan so far is to use the OMS independant doubles rig with two Apeks FST sets with a Halcyon/OMS BP & doubles wing. Naturally I would try it out and get familiar with switching tanks before going on a deco dive

Photos of hose/second stage routing would be great - or if you have any suggestions on alternate travel solutions for twins, let's hear them

Not interested in why you think manifolded doubles are better, not practical for travel. Don't think I'm interested in sidemount either but if you have a great reason why I should do it then I'd love to hear that too

edit: perhaps should have added, not planning on solo diving... well, not any more than any tech dive is a solo dive

Thanks

 

[Red Sea Shadow]

Use 2 second stages, one on each tank.

No preference which is primary and which is secondary. However, you have to switch every 5 minutes or so because the tank you use gets lighter.

 

[Tortuga68]

So, same as manifolded twins then but without the manifold. Thanks

Any thoughts on 2nd SPG?

 

[Tortuga68]

Also, does anyone turn their left tank 180 degrees so the valve is on the outside?

 

[Red Sea Shadow]

The second SPG depends on your regulators' hose routing, and whether it's coming from right or left.

If both SPGs are on your left hand side, the one of the left tank will be slightly longer than the other. If one on the right and one on the left, you might want to use a double ender to attach it to one of the stomach strap D-rings (or the wing D-rings if you have some).

Some people turn their tank so the valve is on the outside, even on single tank setup. It's doable only with DIN fittings. Personally I don't do it.

 

[Colliam7]

I dive manifolded doubles but am thinking about setting up for backmount independant doubles for travel so I can use two rental AL80s with my own two sets of regs & BP/W. My main question is about hose routing and where/how to position the second stages... with manifolded doubles I use 7' primary hose and bungee on secondary but not sure how that should work with 4 second stages and 4 LP hoses?

So, same as manifolded twins then but without the manifold.

Yes. Long hose reg on right tank, necklace on left. Difference - SPG added to right 1st stage.

I already get the switching tanks every X bar or so, but any opinions on how many X is would be good

Start on right tank; 500 psi first switch; then every 1000 psi. I tend to switch a little more often in many cases, simply to maintain the 'habit' of checking and switching.

Don't think I'm interested in sidemount either but if you have a great reason why I should do it then I'd love to hear that too.

For me, SM is perfect for travel - offers independent twin tank diving; valves are in front of you, and therefore somewhat more accessible; don't need tank bands to pair up tanks for BM; potentially easier to adjust trim / buoyancy across tank sizes and metals. If you are looking for options for twin tank diving while traveling, why NOT SM? Just curious.

Also, does anyone turn their left tank 180 degrees so the valve is on the outside?

No, not with BM, or with SM. Tried it, didn't care for the reg position when the valve was turned for BM, didn't seem to offer any benefit with SM.

 

[Tortuga68]

Thanks guys

If you are looking for options for twin tank diving while traveling, why NOT SM?

Hmm, no real reason I guess... just used to back mount singles and doubles so maybe it seems a bit unusual to me. The OMS system seemed very close to what I'm used to with manifolded twins

I could say that you need a different mounting system for SM, but that's true either way. But no tank bands needed for independant doubles. Not worried abut the trim, I dive with stages and it's ok

Maybe I've always thought of SM as a cave diving thing for restricted entries (for no particular reason, just saying)

Tell me some (more) pros?

 

[DaleC]

I dive BM ID's exclusively (except for my vintage rig) and here's what I do:

As stated the hose routing for ID's is the same as a manifolded doubles set up other than the addition of a second SPG.

I route the second SPG along the right side (the first is along the left side). This avoids confusion over which SPG reads which tank. I toyed with the idea of placing the two together but the risk of misreading one for the other seemed to outweight any benefits I might get.

I bought a lefty valve so by tanks look and act like the valves on an manifolded set up. When I use my ST72's however, I have two righty valves (both facing forward). It works fine as you don't neccisarily need to do valve shutdowns with ID's but I still prefer the left/right combo in order to be able to reach both. Actually, I can reach a righty valve on the left side but it takes some gymnastics.

No need in reality to do gas switches every 500psi or so. That is a cave diving regime. In OW I can drain a ST 72 right down on one side and still maintain trim. With my Al 80's I can drain one side down to 1000psi and maintain trim.
I base my gas switches on my rock bottom calculations for the dive and whether I am doing a repetitive dive. If my rock bottom is 1000psi that is my gas switch. If I am doing a second dive I keep 2000psi in the left tank and switch. This allows me to swap out the right tank and begin a second dive with 2000/3000 respectively.

I always begin breathing the left tank (with my longhose clipped off on the right chest D ring). I figure most OOA's will occur in the second half of the dive so that is when I want to have made my gas switch and be breathing the longhose (In order to donate it). That said, the clip is attached to my primary second stage with a piece of bicycle innertube and can be pulled apart in case a donation is needed in the first half of the dive. I tell my buddies this during our predive briefing.

 

[Cave Diver]

I dive manifolded doubles but am thinking about setting up for backmount independant doubles for travel so I can use two rental AL80s with my own two sets of regs & BP/W

If you're doing this for travel, do you think it would be less trouble to either sling the second 80, or use a sidemount config? I'm assuming (I know, I know) that you're planning to band the independent doubles together, and that just seems like a lot of extra work when there are other options open.

 

[DaleC]

Here's all the extra work you have to do and the extra gear you need to bring along: