Questions On Twinning Doubles

[tangfish]

I'm in the process of twinning up some PST E7 HP 80's. I've got a few questions for those of you who are knowledgeable and have had experience doing this type of thing (please, no advice from people who haven't actually done this).

1) Size of the bladder: Originally, I had ordered the following setup:

- OMS steel BP & Comfort Harness
- OMS 200 bar manifold and tank bands
- OMS 45lb bladder

Then, I talked to a few divers, one of whom had the same setup as I ordered, and they said that my rig would not float without me in it, even with the bladder inflated. The dive shop even said that this would be the case after I pointedly asked them about. Problem is, I add up all the weight and I should still be able to float the rig on its own. Here's my math:

bp - 6
tanks - 2x6=12
weight ~ 12 (guesstimate)


That adds up to 30 so far, leaving 15lbs for the manifold, bands and light or whatever other accessory I'll have clipped to my BC. To me, it sounds like it should float on its own. But, I've had people give me advice on both sides. Some say it will sink - but can't explain why, and others say it will clearly float. I ended up getting a 60lb bladder out of paranoia of losing my whole rig, but it's not too late to switch back to the 45lb if I can figure this mystery out. Advice please?

2) How should I go about banding them up? I've heard that you can have disastrous results if you twin tanks up improperly. Do you guys recommend me taking them to the dive shop and buying the guy a 6 pack to teach me how? I'd like to know how rather than just having them do it for me. Are there any considerations to take or decisions to make when doing this? I've seen others with HP 80s twinned up and they took off the boots because they said the bands didn't fit, but I saw one guy (the same guy who warned me about bladder size) keep the boots on and just had the tanks lower down. I also had someone tell me to put the bands over the boot so I could both have boots and have the tanks high enough to reach the manifold valve, though this sounds sketchy since I've never seen anyone put the band over the boot.

I want to do this right, but going doubles is not as simple as buying a recreational BC and strapping on a single. There doesn't seem to be a set way to do this and I keep getting conflicting pieces of advice. I hope some of you here at SB can help to shed some light on my aspirations to stay under for longer. Thanks in advance!

 

[djanni]

Hey I know you're asking a prefectly serious question here and I sure couldn't answer it myself, yet I just have to ask one... When "Twinning Doubles" are you diving with 4 tanks?

 

[PaulChristenson]

Hey I know you're asking a prefectly serious question here and I sure couldn't answer it myself, yet I just have to ask one... When "Twinning Doubles" are you diving with 4 tanks?

Geez...that's what I was going to say...

Seriously, if this is your first time, you should go to someone who has done it before and have he/she do it and you learn by watching...

 

[limeyx]

I'm in the process of twinning up some PST E7 HP 80's. I've got a few questions for those of you who are knowledgeable and have had experience doing this type of thing (please, no advice from people who haven't actually done this).

1) Size of the bladder: Originally, I had ordered the following setup:

- OMS steel BP & Comfort Harness
- OMS 200 bar manifold and tank bands
- OMS 45lb bladder

Then, I talked to a few divers, one of whom had the same setup as I ordered, and they said that my rig would not float without me in it, even with the bladder inflated. The dive shop even said that this would be the case after I pointedly asked them about. Problem is, I add up all the weight and I should still be able to float the rig on its own. Here's my math:

bp - 6
tanks - 2x6=12
weight ~ 12 (guesstimate)


That adds up to 30 so far, leaving 15lbs for the manifold, bands and light or whatever other accessory I'll have clipped to my BC. To me, it sounds like it should float on its own. But, I've had people give me advice on both sides. Some say it will sink - but can't explain why, and others say it will clearly float. I ended up getting a 60lb bladder out of paranoia of losing my whole rig, but it's not too late to switch back to the 45lb if I can figure this mystery out. Advice please?

2) How should I go about banding them up? I've heard that you can have disastrous results if you twin tanks up improperly. Do you guys recommend me taking them to the dive shop and buying the guy a 6 pack to teach me how? I'd like to know how rather than just having them do it for me. Are there any considerations to take or decisions to make when doing this? I've seen others with HP 80s twinned up and they took off the boots because they said the bands didn't fit, but I saw one guy (the same guy who warned me about bladder size) keep the boots on and just had the tanks lower down. I also had someone tell me to put the bands over the boot so I could both have boots and have the tanks high enough to reach the manifold valve, though this sounds sketchy since I've never seen anyone put the band over the boot.

I want to do this right, but going doubles is not as simple as buying a recreational BC and strapping on a single. There doesn't seem to be a set way to do this and I keep getting conflicting pieces of advice. I hope some of you here at SB can help to shed some light on my aspirations to stay under for longer. Thanks in advance!

I have a set of E7-100.

I'd recommend having the store set them up for you to begin with (but you are right, it's something that you can learn to do on your own).

I'd highly recommend getting the bands as far up the tank as possible (right at the break of the tank) as that helps you reach your valves.

I use a 40lb explorer wing with no issues (although admittedly I dont usually let my rig float on its own). My buddy uses E81-119 doubles with a 40 lb wing.

You dont really need the boots. I remove them so that no salt water gets trapped under them to caus corrosion. Think about what the boots are for: to help the tanks stand on their own. I just lay mine on the ground which is safer -- they wont be knocked over.

It would be a really good idea to get in shallow water with an instructor or mentor who is familiar with doubles and will help you get your weighting correct, trim correct and help you adjust your gear.

 

[CJ-62]

I'm in the process of twinning up some PST E7 HP 80's. I've got a few questions for those of you who are knowledgeable and have had experience doing this type of thing (please, no advice from people who haven't actually done this).

1) Size of the bladder: Originally, I had ordered the following setup:

- OMS steel BP & Comfort Harness
- OMS 200 bar manifold and tank bands
- OMS 45lb bladder

Then, I talked to a few divers, one of whom had the same setup as I ordered, and they said that my rig would not float without me in it, even with the bladder inflated. The dive shop even said that this would be the case after I pointedly asked them about. Problem is, I add up all the weight and I should still be able to float the rig on its own. Here's my math:

bp - 6
tanks - 2x6=12
weight ~ 12 (guesstimate)


That adds up to 30 so far, leaving 15lbs for the manifold, bands and light or whatever other accessory I'll have clipped to my BC. To me, it sounds like it should float on its own. But, I've had people give me advice on both sides. Some say it will sink - but can't explain why, and others say it will clearly float. I ended up getting a 60lb bladder out of paranoia of losing my whole rig, but it's not too late to switch back to the 45lb if I can figure this mystery out. Advice please?

2) How should I go about banding them up? I've heard that you can have disastrous results if you twin tanks up improperly. Do you guys recommend me taking them to the dive shop and buying the guy a 6 pack to teach me how? I'd like to know how rather than just having them do it for me. Are there any considerations to take or decisions to make when doing this? I've seen others with HP 80s twinned up and they took off the boots because they said the bands didn't fit, but I saw one guy (the same guy who warned me about bladder size) keep the boots on and just had the tanks lower down. I also had someone tell me to put the bands over the boot so I could both have boots and have the tanks high enough to reach the manifold valve, though this sounds sketchy since I've never seen anyone put the band over the boot.

I want to do this right, but going doubles is not as simple as buying a recreational BC and strapping on a single. There doesn't seem to be a set way to do this and I keep getting conflicting pieces of advice. I hope some of you here at SB can help to shed some light on my aspirations to stay under for longer. Thanks in advance!

According to http://www.huronscuba.com/equipment/scubaCylinderSpecification.html
the E7-100 is -1/-8.5 (empty/full in saltwater with valve) the isolator and bands are in the -3 to -5 range (brand dependent) and the standard plate is -6. That adds up to -27 so a 40lb lift wing WILL float your rig.

That being said, the rig will only provide 13 lbs of lift for everything else you might carry, including your skull (which I prefer out of the water when not actively diving). Only you can decide this one.

Bands should not go over boots (they shouldn't even fit over the boots if they are sized appropriately) as this detracts from solid structure and might allow the tanks to flex and break down the orings/sealing surfaces/threads.

Removing boots is along the lines of personal preference. I remove mine every third trip to clean residual salt. I also transport them standing up and strapped to the side wall of my pickup, so the boots are useful for me.

The first time you assemble your twins would best be under the mentorship of an experienced diver/tech. There are a lot of useful things, best demonstrated hands-on, that you could learn.

Band placement is also personal, someone suggested low tanks for ease of valve access. That is just the opposite of what works for me, my dry suit binds and prevents me from reaching back that far. Also your will have to play around with tank placement and weight distribution for several dives until you get it dialed in.

Just for illustration: I use 3 wings, 45, 51, and 60. I have 2 twins; Asahi HP100's and Faber LP95's. I also have single PST HP100's. The rig gets changed depending on profile. I have used the 45/LP95 setup a few times, recreational with son, but I would not if I was going to "gear up" for a more demanding dive. When carrying all the gizmos I use the 60.

Don't fool yourself, if you are going in with a dry suit, suit inflation system, sling/deco bottle, reels, cannister light, 2 backup lights, lift bag/SMB, dive tool, etc. the loss of streamling with the larger wing will not be a consideration.

Good luck with your system,

 

[matt t.]

The 45lb wing will be MORE than enough. I use a 40lb wing with double steel 100's and 2 deco bottles. Tell the LDS to do the math, and get some experience.

 

[tangfish]

Thanks for the help people. Sorry about the wording of my title, I was referring to twinning singles

To clarify my questions, I'd like to point out that I'm not worried about the rig floating me, since I'll have inherent buoyancy from the suit, etc. I'm concerned about the rig being able to float itself when fully inflated, in situations such as when removing the rig to get into a boat, etc. Yes, I know that I can clip it to a line but the downside (pun intended) is pretty catastrophic should my rig somehow get detached and end up at the bottom of the sea. A friend of mine had the same setup (45lb/twin E7 80's) and he said when he took it off it sank when fully inflated. I don't want to call him a liar, but it doesn't make sense to me unless he had some very very heavy photo equipment.

I'll scrap the idea of putting the bands over the boots (didn't sound too good to begin with) and I'll try to get the bands as low as possible on the tanks (thus making the valves higher and easier to reach). I'll also have the tech at the LDS band them up and hopefully they'll let me watch so I can learn. I guess for now I'll just stick with the 60lb bladder despite the fact that I'll never know why the math doesn't add up!:06:

 

[Divin'Papaw]

I'd highly recommend getting the bands as far up the tank as possible (right at the break of the tank) as that helps you reach your valves.

I'll try to get the bands as low as possible on the tanks (thus making the valves higher and easier to reach).

Don't you want the bands as HIGH as possible as limeyx recommended, not as LOW as possible as you indicated in your final post?

 

[rjack321]

You are going to be head-heavy in those HP80 tanks, possibly to the point where your trim sucks. You'll need to get the bands as close to the valves as possible. Tanks towards your butt.

Directions for assembling doubles
http://www.diveriteexpress.com/library/doubles.shtml

If you have the right size bands, there's no way you'd put them over boots! In fact, HP80s are so short, many boots will not fit properly once they are doubled up - there's not enough tank sticking out the bottom.

I don't understand this part of your math "weight ~12"
Do you mean your putting a V-weight on these?

If that's the case, you will likely be face down from too much weight up high.

 

[Diver0001]

Advice please?

Dive it.

but I saw one guy (the same guy who warned me about bladder size) keep the boots on and just had the tanks lower down.

.....ok.....so that worked for him.....

I also had someone tell me to put the bands over the boot so I could both have boots and have the tanks high enough to reach the manifold valve, though this sounds sketchy since I've never seen anyone put the band over the boot.

LOOOOLLLL. You need to keep this guy around for the entertainment factor......if the boots are in the way......reMOVE them!

Where you put the bands will affect your trim and your ability to reach the valves. Keep making small adjustments until they feel right. You're tanks are steel, right? I would start by mounting them as low as you can and then progressively move them up until they feel right. It's going to be millimetre work and it will take diving it to know for sure if it's right.

R..