Diving Twins

This forum is provided for the further edification of our club members seeking to improve their knowledge and diving skills. (recreational diving only)
Post Reply
User avatar
Tom Nic
I've Got Gills
Posts: 9368
Joined: Mon Apr 10, 2006 6:26 pm

Diving Twins

Post by Tom Nic »

I notice several folks on this board that dive twins...

As I've talked with folks at different dive shops I get positives and negatives... Because of the way I can snarf a steel 100 :pale: I've been thinking about twins.

I would love to hear from some of you both the why's (and I'm assuming it's all about the bottome time!), and the HOW'S... what to consider in your purchases, what to avoid, pro's and con's, safety issues, etc.

Thanks for sharing your knowledge! :salute:
User avatar
Grateful Diver
I've Got Gills
Posts: 5322
Joined: Mon May 15, 2006 7:52 pm

Re: Diving Twins

Post by Grateful Diver »

I'm mostly a singles diver, but I do own and dive a set of E8-119 doubles.

Why? Because it was something different to try, and I wanted to have the skills to do it for when a dive profile mandated doubles as a better alternative.

How? Same way as singles, although the trim takes some getting used to. When I started out I kept going head heavy ... looking something like a lawn dart heading toward the bottom. It took a few dives to make the subtle adjustments necessary to dive them properly.

What to consider? Well, you have to justify the cost. My doubles rig ran me about $1,200 ... and you can buy a lot of singles gear for that kind of money. Also consider the size of cylinders you want (usually will want to match what your buddy is using to make gas planning easier), and an appropriately sized wing (large wings are harder to dive, but necessary if you're going to be carrying stages or deco bottles).

Pro's? Well, no need to swap tanks between dives ... no weight belt ... and after you've done a few dives with a doubles rig on your back, a singles rig will feel like a toy.

Cons? Cost and weight ...

... Bob (Grateful Diver)
User avatar
Tom Nic
I've Got Gills
Posts: 9368
Joined: Mon Apr 10, 2006 6:26 pm

Post by Tom Nic »

Thanks Bob! Just the kind of input I'm looking for.

Twin 119's?!?! :prayer: Wow! :naka:

Just curious, what brought the bill to 1200? I'm assuming that a little more than half of that was the tanks?

I look forward to hearing more from others...
User avatar
Ken G
I've Got Gills
Posts: 1486
Joined: Sun Apr 02, 2006 10:07 pm

Twins

Post by Ken G »

I have not started diving doubles but the idea of redundancy is appealing.
User avatar
sparky
I've Got Gills
Posts: 1269
Joined: Thu Jan 05, 2006 4:54 pm

Post by sparky »

I too plan on putting my Al 80s to use as doubles .
Im just not big enough to carry around two 119s at the same time. :prayer:


But i am not in any big hurry to go that route just yet.

I have decided there is some more important gear I needed first

like a Drysuit ( thanks to Diver Down ) I think I have that one out of the way.

A good Light still diving the llittle flash lights i started with
going to go with the GreenForce light sold at Tacome Scuba in a month or so

and I need a wing getting that next month
then we will start thinking about doubles a little more

but I too like the idea of diving to say 75 feet for 30 min and haveing the air to stay there for the weekend comeing up just long enough to eat some of good BBQ going on at the Meeting place. LOL

Sparky
A Smart Man
Learns from his mistakes

A Wise Man
Learns from the mistakes of those that have gone before him
User avatar
Grateful Diver
I've Got Gills
Posts: 5322
Joined: Mon May 15, 2006 7:52 pm

Post by Grateful Diver »

Thanks Bob! Just the kind of input I'm looking for.

Twin 119's?!?! :prayer: Wow! :naka:

Just curious, what brought the bill to 1200? I'm assuming that a little more than half of that was the tanks?
Nope ... that didn't include the tanks ...

Regulators - $400
Backplate/harness - $150
Bands - $100
Manifold - $225
Wing - $325

... Bob (Grateful Diver)
User avatar
RSdancey
Avid Diver
Posts: 68
Joined: Fri Jun 23, 2006 6:46 pm

Post by RSdancey »

I have 3 sets of doubles:

AL80 doubles (like 'em, but they're tricky because they're positively bouyant when mostly empty)
Steel LP95 doubles (love 'em)
HP120 doubles (diving them for the first time tomorrow)

Making a set of doubles:

You want to get an "isolating manifold". That's a manifold that has a valve in the middle that you can turn off, which separates the tanks (making them act like independents instead of twins). Also, it should have DIN valves, the knobs should be rubber, and the manifold should use "barrel o-rings". The Halcyon manifold is popular, and very well designed.

You also need a set of bands; the metal components that you use to connect the two tanks together, and that hold the bolts you use to secure it to your rig.

On eBay, or from friends, or with a good deal with a local store, the two together should not cost more than $400.

You can set these up yourself. Here's a link with good instructions:

http://www.diveriteexpress.com/library/doubles.shtml

You need two regulators. They should be DIN regs, not yoke. In addition, you need two secondaries; one for each primary. A good mid-range reg from any of the top manufacturers (Scubapro, Apex, Zealge, AquaLung) will do. No need to get super fancy right out of the chute. If you want to rig "DIR" style, you'll also need a submersible pressure gauge (SPG) and the right hoses.

Figure spending about $300-$400 per reg.

You will need a rig to mount it all on. I use a backplate & wing system, set up in the "hogarthian" style with a continuous peice of 2 inch nylon webbing. This rig is the cheapest option for doubles, and it is very configurable. Some people use a "tech rig" like the OMS Transpac system. There are downsides; but that's another topic altogether.

You should be able to get a good rig for less than $500, including all the hardware (buckles, d-rings, etc.)

Here's the good news: Once you've got the regs, and the rig, you can use them on as many sets of doubles as you may acquire; you only need to buy that stuff once. If you're handy with an allen wrench and don't mind working on your regs, you can easily configure a reg for single tank use (and vice versa), and there are fairly inexpensive adapters that will let you use the rig with a single tank too. Depending on the reg you already have, it may be suitable for this setup, meaning you only need to buy one additional reg.

===============

Ok, enough about the "how", now here's my answer for the "why":

1) Bottom time. Like you, I have a pretty high air consumption rate. While there's not a lot of deep diving to do here locally, we do occasionally get down to 100fsw, and there are a couple of places we could go deeper. With a single AL80 tank, with proper gas management, my bottom time at those depths is about 10 minutes. Even shallower, when using EAN32, my bottom time by gas is much less than my bottom time by NDL. Doubles frees me from this limitation and lets me dive pretty much as long as I want to.

2) Safety. Manifolded doubles, configured "DIR" style, are redundant, and very safe. Once you get some basic instruction on how to do a "valve drill", you'll have the necessary tools to use the rig to its maximum redundancy. I could deal with a catastrophic failure underwater, up to and including having a cylinder physically fail, and still be able to use half my gas supply to make a safe, controlled exit. I also do most of my diving with people diving singles. In the event that THEY had a catastrophic problem underwater, I would have enough gas to donate, and make a safe, controlled ascent. I'm like a big gas reservoir available to the whole team in the event of a disaster.

3) Advanced diving preparation. I intend to move into staged decompression diving after mastering basic skills. The classes I intend to take require the use of manifolded doubles. Getting that experience now, as I'm budiling fundamental skills, will help me make the transition to more challenging training without also having to deal with a big gear configuration change too.

Overall, I found strapping on the doubles to be fun, easy, and other than that initial feeling of OH MY GOD THEY'RE HEAVY the first time you stand up, relatively painless.

Good luck!

Ryan
User avatar
John Rawlings
I've Got Gills
Posts: 5781
Joined: Sat Feb 25, 2006 8:00 am

Post by John Rawlings »

Overall that was a GREAT post, but I do disagree with the following statement:

"While there's not a lot of deep diving to do here locally, we do occasionally get down to 100fsw, and there are a couple of places we could go deeper."

?????? There are plenty of deep dives around Puget Sound, the Strait of Juan de Fuca, the San Juans, and British Columbia - wrecks, walls and slopes - in both salt water and fresh.

- John
“Don’t pick a fight with an old man. If he is too old to fight, he’ll just kill you.”

Image

http://www.advanceddivermagazine.com
http://johnrawlings.smugmug.com/
Tangfish
NWDC Mascot
NWDC Mascot
Posts: 7746
Joined: Fri Dec 30, 2005 2:11 pm

Post by Tangfish »

Tom Nic, one thing you'll want to consider is that you'll want to be very, very comfortable with your buoyancy and maneuverability with single cylinders ahead of going doubles. It's a bit like going from diving a midsize car to driving a large truck. There's a bit of a learning curve but as the fellows have so kindly informed you here, there are some benefits.

I'm switching from E7 HP80s to LP85s today, mostly because of trim and gas volume issues. I just can't lift anything bigger on land (or I don't think I should). I might also pick up some LP 102s UWS has in stock to dive as single cylinders.
User avatar
Tom Nic
I've Got Gills
Posts: 9368
Joined: Mon Apr 10, 2006 6:26 pm

Post by Tom Nic »

Great Advice everyone... practical and very helpful! Thanks Ryan! :prayer:

Thanks for taking the time to share your knowledge and experience.

My main reason for going doubles will be my humongous air consumption. It's getting better, even though I'm only around 40 dives.

Good advice as well, Calvin. I'm not in a huge hurry, just gathering all the information and advice that I can well in advance. I know I'm not the only information hog on this board! :book: Though I think most divers tend to be that way by nature.

Thanks again to all, and please continue to weigh in as you are able.

Tom Nic
User avatar
Maverick
I've Got Gills
Posts: 2517
Joined: Wed Mar 15, 2006 8:57 pm

Post by Maverick »

Tom my only point I can give you is don't buy High pressure tanks for twins, buy Low pressure tanks. I will get into it with you next week end at hoodcanal.
Maverick

Diving. . . is an active physical form of meditation. It is so silent- You're like a thought.

SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR
ANYTHING, BUT THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE
STAIRS.
User avatar
sparky
I've Got Gills
Posts: 1269
Joined: Thu Jan 05, 2006 4:54 pm

Post by sparky »

Maverick wrote:Tom my only point I can give you is don't buy High pressure tanks for twins, buy Low pressure tanks. I will get into it with you next week end at hoodcanal.
This sounds like a good topic to bring up during the BBQ FEED so thouse of us thinking can all benafit from the infermation .

As I said I also am planning to go to a set of doubles. and would be most grateful for any helpful infermation.


Ryan:
would you please expand a bit on the down side of diving a Trans Pack with doubles as that was my intention I have a dive rite TRans Pack and will be ordering my Golem Wing next week some time
for diving singles.

I was also planning to dive the Trans Pack with a back plate when diving doubles and would be most intrestead in your input on the down sides of this idea?

Sparky
A Smart Man
Learns from his mistakes

A Wise Man
Learns from the mistakes of those that have gone before him
User avatar
RSdancey
Avid Diver
Posts: 68
Joined: Fri Jun 23, 2006 6:46 pm

Post by RSdancey »

Re: Transpac system:

1) The quick-release buckles are a point of potential failure. With a properly fitted web harness you should be able to chicken-wing your self out of the rig without needing releases. On the other hand, if you were to crack one (coming up the ladder on a boat, or bashed into rocks in the surf, for example), you're most likely done diving for the day.

2) The chest strap is an indication that the overall fit of the rig will be positioned incorrectly to bear its own weight. With a properly fitted web harness you don't need a chest strap (indeed, such a strap would just add clutter to your front and create an unnecessary entanglement hazard. If you dive with a necklaced backup, having that chest strap there is just an invitation to get the bungee tangled, or to mis-clip the strap and trap the bungee under the clip; creating a potential disaster if you had to go to the backup without warning.

3) Too many D-Rings. every D-Ring you add is a potential mis-clip (putting something in the wrong place on accident), and adds clutter. You only need 5 total; 2 on the chest, one on the left side waist belt, and 2 on the crotch strap. Everything else is superfolous.

4) No crotch strap. (It's optional, but if you didn't know you needed it you might not get it when you configure the system). The crotch strap is an integral part of keeping the backplate situated correctly on your back, and creating a "firm" fit of the rig, so you don't feel "sloppy" as you swim. It will also assist in keeping all your gear properly organized when you're vertical on the surface; it keeps the BC and tanks from riding up.

5) The backplate is plastic. This creates several issues. First, it could crack ending your dive. Second, if you use a metal back plate you can move weight off your belt, and onto your rig, where it aids in trim and boyancy control.

For about 2/3rds the cost, you can get a backplate rigged custom fitted for you, and a wing (the wing is extra for the Transpac - like $400 extra!) It packs into a tiny space for travel, and can be adjusted if you gain or lose weight. You'll need no extra equipment to attach doubles, and depending on the plate you buy, you may need nothing more than tank bands to attach a single tank if that option is useful.
Post Reply