Recreational doubles

[2airishuman]

As for myself what I really like on the advantages from what I have gathered is the not only is are the tank closer to you and helps with the center of gravity. Not only is it lower profile, But tank length is much shorter! That actually is a big deal for my wife. She has to put that aluminum 80 all the way down to avoid hitting her head. She really does not like that at all.

The standard solution where tank length is a problem is to use an AL63 or an FX80.

 

[stuartv]

Ideally one way to reduce the weight factor would be to switch over to a dry suit vs my 7 mm (less lead to carry)

I don't use less lead with my dry suit than with a 7mm. Does anyone?

 

[stuartv]

As for myself what I really like on the advantages from what I have gathered is the not only is are the tank closer to you and helps with the center of gravity. Not only is it lower profile, But tank length is much shorter!

Doubles are not as streamlined in the water. They take more effort to move around when you're kicking. You present a bigger cross section in the water to create more drag, plus the extra weight means more inertia, so more force required to propel yourself. Also, I've been out on some charter boats that didn't allow doubles. One told me they just banned them because someone with doubles slipped and fell and broke another diver's foot with their tanks. When I'm on a boat in rough seas, I'd definitely rather be moving around the boat with just a single on my back.

I have singles and doubles. I'd always rather dive my single 100 or 120 with a 23# wing than dive my double 100s or 120s with my 45# wing. If the dive is suitable for diving with a single tank. The difference in balance and closeness of the center of gravity doesn't affect me in any way that I notice. The more drag in the water does.

As mentioned, doubles is also twice as expensive for annual VIP, plus hydros, if you're replacing one single tank with one doubles set. For me, it would be 2 x singles versus 1 x doubles set, so VIP and hydro is more or less the same.

 

[Basking Ridge Diver]

I don't use less lead with my dry suit than with a 7mm. Does anyone?

No one that I know of uses less lead with a drysuit than a wetsuit or semi-dry.

 

[Storker]

Doubles are fricking heavy and awkward above the surface.

I'm pretty certain that there's a difference across the pond about this. I have a strong impression that US steel tanks are bigger and heavier than European tanks. Normal hydro pressure here is only 1.5x working pressure.

Those small D6, D7 or D8.5 liter sets aren't that much heavier than, say, a single 12x300. And I'd rather lug a D7x300 than the 15x300 I sold a year or two ago.

 

[Storker]

Another fact to consider is that you do need a BP/W setup and have to choose the wing carefully.

Tell that to my buddy on that dive. He dives a jacket BCD made for doubles. Just like a couple of my clubmates.

 

[george_austin]

I dive a double set of Catalina AL45's (3000psi) on occasion because their buoyancy characteristics most closely resemble a single steel 72. Each 45 is +2.8 when full and +1.3 at 500 psi.
They're pretty fun to take out once in a while because they do look pretty cool with a cotton harness, no wing and a double hose regulator.
In the summer in Southern California I'm just in a zippered sleeveless 3 mil vest and swim trunks so maybe I'll put 4 lbs of lead on a belt and that is a nice dive rig right there - too heavy and awkward lugging around topside though but the flat bottom on those tanks are pretty nice for stowing along the gunwales.
I can say I paid a hell of a lot less than 709.00 for them . . .
Really, 709.00? Wow

 

[george_austin]

I meant doubled up they are almost just like a steel 72 is as a single

 

[Z Gear]

I don't use less lead with my dry suit than with a 7mm. Does anyone?

I was assuming that the 7 mm wet suit would add a significant amount of buoyancy compared to a dry suit. Is this not correct?

I have no idea just guessing.
Frank G

 

[Z Gear]

Doubles are not as streamlined in the water. They take more effort to move around when you're kicking. You present a bigger cross section in the water to create more drag, plus the extra weight means more inertia, so more force required to propel yourself. Also, I've been out on some charter boats that didn't allow doubles. One told me they just banned them because someone with doubles slipped and fell and broke another diver's foot with their tanks. When I'm on a boat in rough seas, I'd definitely rather be moving around the boat with just a single on my back.

I have singles and doubles. I'd always rather dive my single 100 or 120 with a 23# wing than dive my double 100s or 120s with my 45# wing. If the dive is suitable for diving with a single tank. The difference in balance and closeness of the center of gravity doesn't affect me in any way that I notice. The more drag in the water does.

As mentioned, doubles is also twice as expensive for annual VIP, plus hydros, if you're replacing one single tank with one doubles set. For me, it would be 2 x singles versus 1 x doubles set, so VIP and hydro is more or less the same.

Different points of view to consider.

On the one hand its great that the tanks are closer to you and keeps the center gravity closer than a larger single tank. Which should help overall balance.
But on the other hand I have a larger cross section to deal with and now I created more drag. Plus I have increased my overall weight and now I have to work harder. That doesn't sound to good.