Doubles and buoyancy in warm water?

[Banyan]

I've begun thinking, rather tentatively, about eventually migrating to doubles, and maybe taking tech courses in the future, but am unsure about my options for tanks. If I know what I should be acquiring, I could keep an eye out for deals. I'm currently diving a compact AL80 and Kydex plate, wearing a 1mm skin, with no lead.

I think doubled steels are out the question because I would be significantly negatively buoyant in the case of wing failure. Are my only options doubled standard AL80s, maybe AL63s or 72s, with a weight belt to dump in case of wing failure? All that extra buoyancy over my torso when the tanks are empty sounds like it would do awful things to my trim.

 

[TSandM]

If you are thinking about technical dives, AL80s would be the smallest tanks you would consider using.

I haven't dived them with a wetsuit, but I have with a drysuit with minimal undergarment. They're butt-light when empty; with a dry suit, I solve that by either wearing a weight belt or a half v-weight hung off the bottom bolt. You're a tad foot-heavy to start the dive, and a little head-heavy at the end, but neither is so much you can't compensate with posture. How much you can do with a really THIN wetsuit, I don't know; but steels aren't a good option.

 

[Banyan]

Thanks. I didn't even know about the minimum size thing. Shows how much I know...

 

[Pullmyfinger]

Hi Banyan,

I just left Guam. I lived there for a little over 3 years and loved it. As you already know, on Guam there are mostly compact 80's to be found. When I dove there I wore a 3mm wetsuit, double aluminum 80's (the regular ones, not the compact 80's), an aluminum back plate, 40 lb. lift wing, and an aluminum 40. I didn't need any additional weight with this rig.

I think you'd find double compact 80's to be about 8 lbs over weight. It's worth the time find a couple of the regular aluminum 80's for doubling up for warm water diving.

I had a couple of sets of doubles when I left, I shipped one set to Japan and sold the other two aluminum 80's to a friend. If you have a couple of compact 80's that you wanted to trade for his two regular 80's I could email him and ask. He dives them as single tanks, I doubt he'd have a preference between the compact or regular 80's.

If you want to get a couple of new ones, I could ask my friend there to include a couple in his next tank order. He gets them a pallet at a time, so you might have to wait a month or so to get the new ones. Either way, let me know if I can be of any help.

Take care,

Mitch

 

[Banyan]

Hey Pullmyfinger,

You wouldn't by any chance the guy who put up a huge list of tanks for sale, and somebody bought every single one in a few hours a few months back?

Thanks for listing your rig. That helps a lot. I hadn't even considered not needing weight with doubles to compensate for the buoyancy with empty. I'm going to have to sit down and do the math. I've been thinking of moving up to a 2mm as I can start shivering if I do a third dive, but 3mm seems awfully warm.

Also, thanks for the offer about tanks. I still want to get new regs before I move on to doubles, which will take a while. While I'm enjoying thinking through how to expand my diving, I really enjoy the diving I do now so am in no giant hurry. I've managed to resist the urge to buy random tanks that appear on Craigslist. I don't think I've ever seen standard 80s at MDA, but GMI had some last time I wandered in. Jim even sells them for less than compacts because of lower demand.

 

[Tortuga68]

I dive double standard AL80s with an SS backplate... don't need any extra weight in a 3mm shorty. If I wear a steamer or my 5mm hooded shorty I add a pound or two

 

[cwkline]

Kirk,
Next time you're in town I'll let you try a set of LP 72's. I have a wing you can use, as well as regs. It'll give you an idea of weight and trim.
Charlie

 

[Pullmyfinger]

Hey Pullmyfinger,

You wouldn't by any chance the guy who put up a huge list of tanks for sale, and somebody bought every single one in a few hours a few months back?

Thanks for listing your rig. That helps a lot. I hadn't even considered not needing weight with doubles to compensate for the buoyancy with empty. I'm going to have to sit down and do the math. I've been thinking of moving up to a 2mm as I can start shivering if I do a third dive, but 3mm seems awfully warm.

Also, thanks for the offer about tanks. I still want to get new regs before I move on to doubles, which will take a while. While I'm enjoying thinking through how to expand my diving, I really enjoy the diving I do now so am in no giant hurry. I've managed to resist the urge to buy random tanks that appear on Craigslist. I don't think I've ever seen standard 80s at MDA, but GMI had some last time I wandered in. Jim even sells them for less than compacts because of lower demand.

That wasn't me that listed tanks for sale, I shipped all of my tanks to Japan except for the 2 aluminum 80's I mentioned.
You are correct on the 3mm, it's more than you need for Guam. I had a 1mm suit but it being so thin it didn't provide enough support to hold the pockets I installed. The 3mm was a better choice for that, and it wasn't too warm during the dive.

You already know the guy to see when it's time to get tanks.

MDA only gets the compact tanks, everybody seems to want those on Guam.

Take care,

Mitch

 

[TSandM]

72s are pretty marginal tanks for tech diving, at least for anybody who doesn't breathe like a bird.

They hold 144 cf at plus rating, so the tank factor is 6. If you don't want to take them below 500 psi, that's 30 cf that you can't use, leaving you with 114 cf. If your SAC rate is a typical male .7 cf/min, at 150 feet you are using almost 4 cf/min. In 28 min, you are down to 500 psi . . .and you have no reserve to get YOU to your gas switch, let alone you and a buddy. If you put that much aside, you have about 15 minutes at 150, at MOST, and you'll be running right smack up against all your reserve volumes.

I can get two respectable deeper recreational dives off a set of 72s (although I'll gas limit on the second one) but even I wouldn't tech dive with them.

 

[Centrals]

Twin 10L steel is fine with me if I keep the bottom time to around 20mins with max depth around 54m(air). The deco starts at 21m with 50%. I normally still have 80-90 bars of back gas left when I surface.
SAC:12L per min