Double Aluminum 80's

[darylm74]

Being a Northeast diver, all I have heard about was double steel tanks. When I was in Key Largo, I heard quite the opposite. Everyone seems to be diving double Aluminum 80's? Why? I was told it was because they weren't diving with a drysuit. That led to other questions about redundancy, but that is for another thread. I have a set of 95's taht I have bands and a manifold for but havent' gotten them doubled yet. Should I be looking a second set of doubles?

 

[jonnythan]

Steels are, in general, negative when empty. When you have two steel tanks and doubles hardware on, you can be seriously overweighted when wearing a lightweight wetsuit.

A set of Al80's, when empty, is several pounds positive when empty, and when you have the bands, valves, regs, backplate, etc, you have a much better shot of being in balance and not being overweighted.

I have a set of steel tanks I use when diving with my drysuit, and I use some double 80s when diving in my wesuit.

 

[wedivebc]

When I did my cave training in Mexico I used a 7mm wetsuit, dual al 80s a SS BP and no lead whatsoever. For the shallow low flow caves 80s are the perfect size. When I go to Florida I will probably rent larger steel tanks due to the cooler, deeper water and likelyhood of swimming against current.

 

[mike_s]

Just before I read this thread, I was watching an older episode of Deep Sea Detectives on my TIVO about the japanese fishing boat the USS Greenvile hit in Hawaii.

While watching the navy divers, I noticed that the ones diving on scuba (and not surface suplied air hoses), that several of them seemed to be diving AL 80's set up in doubles. This surprised me some too. Of course, like you noted about exposure suits, these divers were wearing wetsuits. Some of them shorties or two piece wetsuits tops (like the top of a 5mm long sleeve). (In case you're wondering how I knew for sure they were Aluminum's, they had flat bottoms on them.) Just FYI to add because I thought it was interesting that they were diving Aluminum doubles.

 

[WarmWaterDiver]

When we travel to dive destinations, the rental tanks are almost always aluminum once we get there. I have often dove with doubled aluminum 63's and 80's. Not necessarily manifolded though. And not always from boats. Bonaire is one good example that springs to mind.

 

[double80s]

When I did my cave training in Mexico I used a 7mm wetsuit, dual al 80s a SS BP and no lead whatsoever. For the shallow low flow caves 80s are the perfect size. When I go to Florida I will probably rent larger steel tanks due to the cooler, deeper water and likelyhood of swimming against current.

When you go to Florida (Ginnie) you'll have no choice but to rent steel doubles.

I dive AL 80's wet here in California. I take my AL BP when I go to Florida cave country, otherwise, I'm way too overweighted in my 7mm. You usually only find double 95's or larger to rent. Rich at Cave Excursions can hook you up.

 

[darylm74]

When we travel to dive destinations, the rental tanks are almost always aluminum once we get there. I have often dove with doubled aluminum 63's and 80's. Not necessarily manifolded though. And not always from boats. Bonaire is one good example that springs to mind.

....steel 85's. I did not get the chance to dive doubles however I was told that most tech divers dive aluminum 80's down in Florida Keys area. They had a few pairs and Diver's City and it prompted a whole lot of questions between my friend (and instructor) over a few beers and rounds of tequila. Bob at Diver's City left us thinking about the differences between diving the cold freshwater dives we were used to and the warmer dives in the Key's. He didn't give a thorough explanation on why so I figured I would ask here.

 

[Hoyden]

The idea behind double AL80s comes from the days when all steel tanks were very negative (kind of like the current Faber MP72s or Faber HP100s). The logic doesn't hold up when looking at steel tanks like Faber LP 85s. Even folks who preach Al80s as the only doubles for openwater admit that it is for "team unity."

To compare the numbers -

Luxfer AL 80 - 7.25" in diameter, weighs 31.38 lbs without the valve, is 26.06" tall without valve, is 4 lbs positivly bouyant when empty and -1.4lbs when full

Faber LP 85 - 7.25" in diameter, weighs 31 lbs without the valve, is 26" tall without valve, is dead neutral when empty and -6.7 lbs bouyant when full

Faber LP 95 - 8" in diameter, weighs 37.2 lbs without the valve, is 23.8" tall without valve, is -1.2 bouyant when empty and -8.325 lbs bouyant when full.

So I need to add 8 lbs of lead to account for the gas swing in double AL80s and can remove 2lbs of lead if I dive double 95s - Lead is not a factor at all when diving 85s (okay, I have to account for the weight of my manifold and regs) - I can swim both my 85s and 95s up with no lift, but I shouldn't have to since I will never be without some form of redundant bouyancy.

Jackie

 

[Hoyden]

Faber 85s are 7" in diameter, not 7.25" - Typo on my part.

Jackie

 

[Mambo Dave]

I'm really new to doubles in that I have two AL80's that I may double up. Does any company make tank bands that are heavier to offset the buoyancy of twin AL80's?