Single and doubles

[rrweather]

I am currently in the market for tanks (obviously). One of the LDS has pretty good deals on the HP steel tanks. I am trying to decide on a size that will fill my needs for both singles (now) and doubles (in the future). The two guys I know that dive doubles (friends) are both out of town so I can't pick their brain yet. I am a fairly big guy (5'11 230 ibs.) so I can handle the weight. I also tend to consume air quickly (hoping the slow weight loss will help that) so I am looking at the larger tanks (100, 119, or 130). I jut don't want to get something so large that doubles become too much and I have to start looking for more tanks. I am going to be taking the rescue course through the same shop in a few weeks so I am going to see what they have that I can try for the sake of trim and comfort. I just wanted to pick the brains on here to see what size tanks people are using in a doubles setup. Thanks.

 

[Doc Harry]

Do a search, there was similar discussion here at Scubaboard not too long ago.

FWIW, twin steel 130s are really heavy and take a lot of practice to master.

I am currently in the market for tanks (obviously). One of the LDS has pretty good deals on the HP steel tanks. I am trying to decide on a size that will fill my needs for both singles (now) and doubles (in the future). The two guys I know that dive doubles (friends) are both out of town so I can't pick their brain yet. I am a fairly big guy (5'11 230 ibs.) so I can handle the weight. I also tend to consume air quickly (hoping the slow weight loss will help that) so I am looking at the larger tanks (100, 119, or 130). I jut don't want to get something so large that doubles become too much and I have to start looking for more tanks. I am going to be taking the rescue course through the same shop in a few weeks so I am going to see what they have that I can try for the sake of trim and comfort. I just wanted to pick the brains on here to see what size tanks people are using in a doubles setup. Thanks.

 

[rstofer]

It seems to me there are at least five things to consider:

1) Assuming no-deco diving, how much air do you need on any one dive to get to the NDLs. In warm water, diving a square profile, I could hit the deeper NDLs with an Al 80.

2) Using Nitrox extends the NDL, how much more air do you need? Are you going to have a lot more air or NDL than your buddy? If so, why? Right now, my grandson dives with Al 50s. Even though his SAC rate is fairly low, he still runs out long before I exhaust my HP 100. I could make a good case for using a smaller tank.

3) If your rig is massively negative at the start of the dive then if you ever get turned sideways, you will tend to turn turtle. I really notice the difference between an HP 100 (-10.5#) and an Al 80 (-2#). The tank on my back becomes quite noticeable. I imagine doubles would be even worse. The tradeoff, of course, is that I can remove weight from my harness. Someday I'll reconsider whether it's a good tradeoff. Conventional wisdom says it is. The problem with conventional wisdom is that it's often wrong (for any one individual).

4) Inertia of the tanks is related to their mass, not their buoyancy. It takes energy to accelerate a mass. The old F = MA thing. Do you get enough additional bottom time to make it worth the effort (literally)?

5) How much weight can you hump from the car to the beach entry? This is THE limiting factor for me. I am getting old and my back just won't carry the weight. Then too, some entries are easier to reach than others. That said, I plan to put together a pair of Al 50s for my double hose regulators. Mostly for the coolness factor. That and I can't hump double LP 72s.

Richard

 

[TSandM]

If your gas consumption is high, HP130s are wonderful single tanks. And as your consumption falls, they're still great single tanks. But they are heavy beasts as doubles. At fewer than 50 dives, you're probably still in the realm where you can expect further significant decreases in your gas consumption, especially if you work on your buoyancy control and your trim, and get very accurately weighted.

HP100s are fantastic tanks. They are lighter than LP95s and hold more gas. I love my husband's doubled 100s -- they trim out well, and I can get them in and out of the car by myself. They hold plenty of gas for any Tech 1 type dive, and I can get a deeper recreational dive and a second, shallower dive out of them while maintaining safe gas reserves.

It's always great to have more gas than you need, but when you get to doubles, you really have to start considering the weight you are carrying -- not just whether you CAN carry it, but whether you want to fight with it on a pitching boat, or coming up the ladder, or doing longer hikes to shore diving sites. A compromise on a set of tanks that will give you enough gas but still be manageable to carry is often a good strategy.

 

[SparticleBrane]

They are lighter than LP95s and hold more gas.

Note that this is only at rated pressure.

 

[rrweather]

Thank for all the help. This is exactly the discussion I was hoping to read. Thanks again.

 

[TSandM]

Note that this is only at rated pressure.

Not all of us live in Florida, Sparty.

 

[dannobee]

Note that this is only at rated pressure.

True.

One more thing to consider with the HP tanks is that you could have problems with getting them filled to rated pressure, negating some of their capacity. With LP95's you'll seldom have that problem. Some shops will overfill LP tanks, sometimes to the rating of the HP tanks.

I never got full fills with my HP tanks until I bought my own compressor.

.

 

[coyoteblastin]

I'm 5' 7" weigh 150 lbs soaking wet and I dive hp 120's. Dannobee is right about having problems filling them. I've run into this myself. I am actually thinking about getting some hp 100's because I feel like these tanks are as big as i am. The only reason I got them is cuz my instructer told me that's what I needed.

 

[lowviz]

...HP100s are fantastic tanks. ... I can get a deeper recreational dive and a second, shallower dive out of them while maintaining safe gas reserves. ...

I'm in the 190# range with an average cold-water RMV.

I bought a set based on gas management calcs and no-deco limits. Back then I was expecting to move up to larger tanks. I didn't, mainly because of weight and balance, now I have more sets of 100's.

-There is a place for the larger tanks, I'll be heading there with an upcoming IANTD deep diver course. But I'm not buying anything until I find out...