AL tanks and diving wet

[inquis]

why couldn't that same majority kick up 20-25 lb with fins on?

It's worth trying this in a pool to see what you can actually do.

35-40 would suck but is doable

I'm skeptical. No one using a single tank should be that negative anyway. Technical divers may be getting close to that, but they would have brought redundant buoyancy rather than have to swim it up.

 

[Chavodel8en]

Have you ever swam up 25lb or 40lb?



Let's look at a "typical diver" they're 5'10" and 200lb diving in salt water and if they exhale fully they'll float with their head just awash, with 2lb of lead they'll be completely neutral in salt water with no exposure suit on.

If you now put that diver in a new high quality 7mm full suit, with a 7mm hood, 5mm gloves and booties they're likely around 27lb positively buoyant at the surface.

Then let's add a SS backplate, weighted STA they've added 12.5lb of SS to their system.

Item	Item Buoyancy	Buoyancy Sub-total
Diver	+2	2
Suit	+25	27
SS plate	-5	22
Weighted STA	-7.5	14.5
Regulators	-3	11.5

So our diver is left with about 11.5lb of positive buoyancy on the surface with no tanks.

For a AL tank

Item	Item Buoyancy	Buoyancy Sub-total
Diver, Exposure Suit and Rig	11.5	11.5
Luxfer AL80 @ 3000psi Luxfer AL80 @ 500psi	-1.5 3.4lb	10.5 (start of dive) 13.9 (end of dive)

So this diver in the AL80 needs to carry 13.9lb of additional weight to be neutral at the safety stop with 500psi in his tanks.

For a HP100

Item	Item Buoyancy	Buoyancy Sub-total
Diver, Exposure Suit and Rig	11.5	11.5
Faber HP100 @ 3500psi Faber HP100 @ 500psi	-8.4 -1.7	3.1 (start of dive) 9.8 (end of dive)

The diver in the HP100 needs to carry 9.8lb of additional weight to be neutral at the safety stop with 500psi in his tanks.


Now let's look at what the numbers look like at 100fsw where the wetsuit is likely only retaining about 25% of it's starting buoyancy.

Item	Item Buoyancy	Buoyancy Sub-total
Diver, Exposure Suit and Rig @ 100ft	-6.75lb	-6.75lb
Weight belt steel tank Weight belt AL tank	-9.8 -13.9	-16.55 (steel) -20.65 (AL)
Faber HP100 @ 3500psi Luxfer AL 80 @ 3000psi	-8.4 -1.5	-25 (steel) -22 (al)
Ditch weight belt	+9.8 (steel) +13.9 (AL)	-15.2 (steel) -8.1 (al)

So at 100ft with full tanks the diver in the faber hp100 ditching his weights would require them to swim up about 15.2lb and the diver on the AL tanks would need to swim up about -8.1lb. If we assume a full lung gives you about 5lb of positive buoyancy the diver in steels still needs to swim up ~10lb and the diver int he AL tank only needs to swim up about 3lb (30% of the weight of the steel tank)

This is the first time Ive seen all of the weighting factors laid out in detail like this. Looks like a good resource (esp since I'm about 5'10", 200 lbs, lol).

Reinforces to me that I am correct in not using a STA with my SS BP/W & thick wetsuit.

For the OP, I use a 8mm wetsuit in Califas, I prefer an HP 100 (mostly for trim reasons, as the Chairman describes above) over an AL 80, but either is fine,

I put 10-12 lbs on my ditchable weight belt, and an additional 4 lbs in trim pockets with the AL 80.

 

[inquis]

Looks like a good resource.

You'll love the spreadsheet version (a.k.a., "The Optimal Buoyancy Computer") then.

 

[tursiops]

The HP-100 in particular also trims out quite well, more so than the AL-80.

Totally depends on your size/weight/fat/gear distribution. What works for you will not work for everybody.

 

[Boarderguy]

Have you ever swam up 25lb or 40lb?



Let's look at a "typical diver" they're 5'10" and 200lb

That breakdown is fantastic and I will use it in the future. Thank you for all that.

I have swam up 35 lbs before, like I said it sucks. I routinely swim up a 10lb anchor when it gets stuck on our lake in ~20ft. That is just a mask (if I have it) or open eyes and board shorts. With fins, my 12lb belt and mask I can swim up 15 lbs with relative ease (27 lbs total) . It all depends on how you're kicking and if you can breathe. A bc failure + a reg failure is a very bad day at depth. Either one by itself is feasible with calm rational thought.

 

[johndiver999]

I dive wet with both steel and AL and adjust my lead based on which tank I grab. I'm still trying to figure out how a diver could not swim up their full kit when wet... total bc failure = ditch some weight and start kicking up. The majority of us could tread water in just swim trunks (with effort) with 10-15 lbs, why couldn't that same majority kick up 20-25 lb with fins on? 35-40 would suck but is doable especially as your wetsuit regains buoyancy. Drop one pocket and start working your way up to avoid an uncontrolled ascent. Drop the other once on the surface of you still are not floaty. Factoring in a tank's buoyancy is nice but unnecessary. If rather have the extra air and better trim from my steels than the floaty AL 80s.

LOL, you can swim up 40 lbs negative with fins...I would love to see a video of someone trying that:

Holding 40 lbs on a weightbelt wearing a bathing suit and the fins of their choice and have a snorkel and mask to make breathing easier. Just wanna see the person stay on the surface for 2 minutes.

 

[scubadada]

I dive quite a bit, all wet, mostly AL80, sometimes HP steel 100. I know the weight I need with my full 3 mm, 5 mm, or 7 mm, all with or without a 5/3 mm hooded vest. I dive 4 lbs less with the steel tank. Last year I bought a more buoyant 3 mm (Henderson Greneprene) and use 10 lbs with the 3 mm (used to be 8), 14 lbs with the 5 mm, and 20 lbs with the 7 mm and an AL tank. I dive 6, 10, and 16 lbs with the steel tank.

Do your buoyancy checks at your safety or last deco stop with just your reserve gas volume. Dive Gear Express has this nice chart that include buoyancy with 500 psi remaining

 

[Eric Sedletzky]

Dive whatever tank you want or have or can get cheap or rent.
Adjust your weightbelt accordingly so at the end of the dive you can hold your stop at 15’ with an empty wing. I dived aluminum tanks for a while before I landed some steels. Looking back it sucked but we made it work. That’s all the dive shop rented. And I am a wetsuit diver BTW.

Jesus you guys!!! I’m going to recommend to some of you to buy an electron microscope so you can split hairs even finer!

 

[Boarderguy]

LOL, you can swim up 40 lbs negative with fins...I would love to see a video of someone trying that:

Holding 40 lbs on a weightbelt wearing a bathing suit and the fins of their choice and have a snorkel and mask to make breathing easier. Just wanna see the person stay on the surface for 2 minutes.

With a wetsuit I've done 35 lbs from about 25 feet. They are buoyant and make it a lot easier. I said I seem up 27 lbs just fins and mask. Stuck anchor and my weight belt to get down their.

Edit: I said nothing about staying on the surface, drop whatever you need once safely up there and not having corked due to excessive weight drop.

 

[tursiops]

I dive quite a bit, all wet, mostly AL80, sometimes HP steel 100. I know the weight I need with my full 3 mm, 5 mm, or 7 mm, all with or without a 5/3 mm hooded vest. I dive 4 lbs less with the steel tank. Last year I bought a more buoyant 3 mm (Henderson Greneprene) and use 10 lbs with the 3 mm (used to be 8), 14 lbs with the 5 mm, and 20 lbs with the 7 mm and an AL tank. I dive 6, 10, and 16 lbs with the steel tank.

Do your buoyancy checks at your safety or last deco stop with just your reserve gas volume. Dive Gear Express has this nice chart that include buoyancy with 500 psi remaining

View attachment 739527

I think the last column in your chart is for an empty tank, not one with 500 psi in it.