Aluminum doubles

[Scott L]

They dominate tec diving in these parts...

I don't know what to tell you other than call Chris Bown at Slient World in Key Largo and Oliver Paoli at Avid divers in Pompano for their thoughts.

 

[GrumpyOldGuy]

Wrong...

I wear an Akona 5mm Suit or a Harvey's 7mm Suit or a Tri-Lam Drysuit
With a complete wing failure in fresh water, I cannot swim Double 104's to the surface in Open Water. How negative are Aluminum tanks underwater? Not that much. How negative are LP104's underwater, empty or full, they weigh a ton underwater. I haven't worn added weight in about a decade even with my drysuit.

Too many things to consider. Are you flat or fluffy, muscular or overweight. How old is your wetsuit. What kind of fins are you wearing. Do you float like a cork or sink like a rock. The whole purpose in redundant buoyancy is because sometimes it's impossible to swim a set of steel tanks to the surface.

However, I'm pretty sure (I've never tried it) I could swim Double AL80's to the surface with a single fin.

You are over weighted with double 104s, plain and simple. Not due to the lead you don't need, but due to gear selection.

My statement was qualified with the words "Properly Weighted". The best definition of this is to be neutral with a near empty tank just under the surface. With the 104's you are essentially a boat anchor. If you need or desire to do so, then you need to take the proper precautions (redundant lift) which I assume you do. But that still does not make you properly weighted, it makes you over weighted with gear to compensate.

If you take a more rational approach (at least for outside cave country), a set of double 100/119/120 can be properly weighted and the result is the extra effort to swim up the diver is 5-8lbs. Of course this is on top of the 25lbs or so from the wetsuit and first tank, so it is not trivial.

 

[Superlyte27]

I don't know what to tell you other than call Chris Bown at Slient World in Key Largo and Oliver Paoli at Avid divers in Pompano for their thoughts.

Dominate would imply (to me at least) that there were considerably more Double AL80's than any other configuration. And on Chris's boats, that's simply NOT the case. Not even close. In fact, most tec divers (diving doubles anyway) on the Silent World I, Silent World IV and the Get Wet are diving steels (i'd guess 90 percent of the time to be safe). I can't speak about Oliver Paoli because I've never dove his.

 

[sabbath999]

I agree.

An LP104 holds more air at 3600psi than a set of AL80's. If you want the safety factor, by an H-Valve. It's alot easier to dive than Doubles and has bettery buoyancy characteristics. Oh, and it'll be cheaper.

Yeah, and if you pumped those tanks that are supposed to be at 2400PSI on up to 5000PSI, you would have a LOT more air in them.

You could pump the AL80's on up to 5000 and get more air in them too... just double up the safety blowout things and pump em to the moon....

Yes, I am kidding.

Recommending that somebody do an overfill of 150 percent of what the tank is rated for and using that in comparison to a tank system that is appropriately filled is... IMHO... not really all that good of basic scuba advice.

10 percent overfill on a plus tank? Fine. They are made for that... 150 percent of capacity? Not so much.

 

[Scott L]

Dominate would imply (to me at least) that there were considerably more Double AL80's than any other configuration. And on Chris's boats, that's simply NOT the case. Not even close. In fact, most tec divers (diving doubles anyway) on the Silent World I, Silent World IV and the Get Wet are diving steels (i'd guess 90 percent of the time to be safe). I can't speak about Oliver Paoli because I've never dove his.

When the cave crowd visits I am sure they are diving dry w/steel doubles as you say. I am speaking for the rest of the diving community but dominate was perhaps not the best term to use...

 

[wrybosome]

Recommending that somebody do an overfill of 150 percent of what the tank is rated for and using that in comparison to a tank system that is appropriately filled is... IMHO... not really all that good of basic scuba advice.

Not quite 150% overfill, but I can usually get 3400 psi on an LP95. Actual 150% overfill is normal for cavers, right? That'd be...3600 psi on a LP tank. That's still a >25% safety margin from the hydro test pressure. I haven't heard of too many cavers exploding down there...

I don't see too many people here sticking to 2640 psi.

 

[sabbath999]

In this part of the country, NOBODY will fill over 2640. Period.

I have trouble getting fills to 2640 in a lot of shops, two of em absolutely refuse to give me the final 240 so I don't fill there any more.

Yeah, when I go to cave country they ask ya how much you want... but then again, cave fills and cave diving ain't exactly basic scuba IMHO, and I am told by people I trust (including a friend who owns a hyrdro business) that overfilling shortens the lives of the tanks.

Cavers don't care... having to replace tanks more often is better than running out of air 1000 feet in.

 

[sabbath999]

Not quite 150% overfill, but I can usually get 3400 psi on an LP95. Actual 150% overfill is normal for cavers, right? That'd be...3600 psi on a LP tank. That's still a >25% safety margin from the hydro test pressure. I haven't heard of too many cavers exploding down there...

I don't see too many people here sticking to 2640 psi.

But if you are going to give an overfill on the steels in this discussion, you gotta give an overfill on the Aluminums too. Fair is fair. I have strapped on rental AL80's that had 3800 in em in the shade in Kona.

Not that I am recommending aluminums over steels. I dive steel 120's.

 

[vjanelle]

The theory goes that steel tanks will hold out better than AL tanks due to the structure of the materials. AL tanks don't handle being stretched out farther than their rated pressure as much as steel does.

 

[Superlyte27]

Yeah, when I go to cave country they ask ya how much you want... but then again, cave fills and cave diving ain't exactly basic scuba IMHO, and I am told by people I trust (including a friend who owns a hyrdro business) that overfilling shortens the lives of the tanks.

.

I used to hydro literally thousands of steel tanks a couple of times a year. I'll agree with the Department of Transportation that says a LP Steel tank should survive 10,000 Hydro Cycles. 2640 x 5 / 3 = ???

Anyone here gotten 10,000 dives on their same set of tanks? Me neither. Anyone ever heard of an LP fatality? Me neither.

And in my arsenal of Steel 95's and 104's I have sets of tanks that are over 20 years old. Never a fill less than 3400. Exactly how long should a tank last?