OMS wings vs Apeks wings and LP vs HP tanks

[cool_hardware52]

For doubles the minimum wing lift is:

Weight of the back gas + the minimum buoyancy of the Dry suit + 2~3 lbs.

In cold water the buoyancy of the tanks used is almost never a factor, as the buoyant drysuit will require ballast in addition to the tanks, plate, regs, can light, bands, manifold etc.

The minimum ballast the diver requires is:

Buoyancy of the drysuit with minimum gas + 2~3 lbs. This allows the diver to maintain a shallow stop, with near empty backgas tanks, and be able to add some gas (2~3 lbs) to their suit.

To determine the minimum suit buoyancy put on your undies and drysuit and get into neck deep water with a big bag of ballast. Vent all the gas you can from the suit.

Remove lead until neutral, weight the bag of lead.

Example:

Tanks........HP 100's (200 cu ft of air or nitrox =16 lbs)

Exposure suit 26 lbs positive with minimum gas.

16 lbs (weight of back gas) + 26lbs (min suit buoyancy) + 3lbs = 45 lbs.

Required ballast = 26 + 3 = 29.

Medium SS plate & Harness = 6 lbs
Bands and Manifold = 4
Dual regs = 4
2 x HP100's (empty) = 4
Can Light = 2

Total 20

Diver will need ~8-10 more in a belt or in a V weight or soft weight between the wing and plate.

If all the ballast is mounted on the rig it will be 29 negative with empty tanks and 45 lbs negative with full tanks.

A wing in the 49-50 lbs range is a reasonable choice.

How much gas would a diver need to carry, and how buoyant would his drysuit need to be to require a 100 lbs lift wing?

Tobin

 

[Thadmn]

The inflator hose comes out of the left front on the OMS 60# wing which is a little different.
I have the banded one. I've never had a problem with trapped air or snagging. I happen to like the bands myself even though the standard reponse is that they will get snagged. It wouldn't take much to break the band/bungee if you did get stuck. One reason I decided to go with the banded model is that if you decide that you don't want them, you can always remove them, but you can't add bands to the non-banded version.

 

[rjack321]

Example:

Tanks........HP 100's (200 cu ft of air or nitrox =16 lbs)

Exposure suit 26 lbs positive with minimum gas.

16 lbs (weight of back gas) + 26lbs (min suit buoyancy) + 3lbs = 45 lbs.

Required ballast = 26 + 3 = 29.

Medium SS plate & Harness = 6 lbs
Bands and Manifold = 4
Dual regs = 4
2 x HP100's (empty) = 4
Can Light = 2

Total 20

Diver will need ~8-10 more in a belt or in a V weight or soft weight between the wing and plate.

If all the ballast is mounted on the rig it will be 29 negative with empty tanks and 45 lbs negative with full tanks.

A wing in the 49-50 lbs range is a reasonable choice.

How much gas would a diver need to carry, and how buoyant would his drysuit need to be to require a 100 lbs lift wing?

50lbs "extra" lift available with the 100lb wing.
50/8lbs per 100cf of air = 6.25 units of 100cf
So to "need' that capacity you would have to have roughly 625cf more air or nitrox, or 825cf total

So add 8 AL80 stages of air or nitrox to those double hp 100s and you're in the ballpark of 100lb wings. You'll also need lead unless you're ditching them.

 

[cool_hardware52]

50lbs "extra" lift available with the 100lb wing.
50/8lbs per 100cf of air = 6.25 units of 100cf
So to "need' that capacity you would have to have roughly 625cf more air or nitrox, or 825cf total

So add 8 AL80 stages of air or nitrox to those double hp 100s and you're in the ballpark of 100lb wings. You'll also need lead unless you're ditching them.

I know you are just playing along and I won't quibble with your math, just your assumptions.

Stages are ditchable, and should not impact either the minimum wing required, or the divers ballast needs.

A full rigged al 80 is about -4 lbs, and empty is about +2.

In my example above the diver is using a ~50 lbs wing, and 2 x 100 cuft back gas tanks, and if the drysuit is intact he has 50-16-3 = 31 lbs "excess" wing capacity.

31 / 4 = ~8. In theory the diver in my example above could carry almost 8 full nitrox or O2 80 cu ft alum tanks before they "run out of wing"

Tobin

 

[elan]

my 2c , simple math, each 13 cuf weights 1 lb approx. So to offset the double 130s at the beginning you need 20lb lift only for the air + deco bottles say you get 2 extra Al80 - ~ 11lb if 4 - 22 lb so we get 44 lb in the worst case for the air then should you need extra lift from the beginning you add that + 20% as a safety margin , 100lb looks like an overkill

 

[rjack321]

I know you are just playing along and I won't quibble with your math, just your assumptions.

Stages are ditchable, and should not impact either the minimum wing required, or the divers ballast needs.

Well sorta. If you are retaining enough gas as weight to stay down you just dive with them. e..g diving only stages in the cave with backgas reserve. And if you lost backgas you obviously ditch them.

But in cases where I want to actually use alot a chunk of my backgas and a stage. e.g. for a ~45 min dive at 160ft using double 100s and a bottom stage I need 65-70cf of backgas as rock bottom and ~160cf to do the dive at a SAC of 0.6cf/min. That presents a problem because you will probably be too light if you completely subscribe to the "stages are ditchable" concept and just use the same weighting as you'd dive without the stage. You are now in a position requiring the ditching of stage(s) to help you stay down.

Not a very cost effective plan in the ocean. So practically speaking you end up needing about 3lbs extra lead per AL80 if you use stages in the ocean. AL40s are alot closer to neutral and generally only need 1lb extra to be comfy with minimal gas for shallow stops. Trying to purge every last molecule of gas from your drysuit when you added a bottle for a long dive and have a chunk of time left to do shallow really sucks.

Most people are probably overweighted already, so this shouldn't be interpreted as license to pile on the lead.

 

[cool_hardware52]

But in cases where I want to actually use alot a chunk of my backgas and a stage. e.g. for a ~45 min dive at 160ft using double 100s and a bottom stage I need 65-70cf of backgas as rock bottom and ~160cf to do the dive at a SAC of 0.6cf/min. That presents a problem because you will probably be too light if you completely subscribe to the "stages are ditchable" concept and just use the same weighting as you'd dive without the stage. You are now in a position requiring the ditching of stage(s) to help you stay down.

If you are weighted so you can use 100% of your backgas and still be 2-3 lbs negative, as I stated in my example, a single stage is not a problem. In the unlikely event that you need to use all of your back gas and all of your stage you will be about neutral. Lungs + min gas in the suit if necessary.


Tobin

 

[RJP]

Stage gas, by definition, implies the same mix as backgas.

By definition, "implication" is not the same as "definition".



By definition, stage gas is any gas that you stage. And you might stage gas for one of two different reasons:

1.) You need more gas volume
2.) You need a different gas mix

By inference, it seems your post assumes one would only stage gas to extend a dive from a gas volume perspective.

Of course it's often desirable to switch gases to extend a multi-level dive. Especially if you want to do a longer multi-level dive while staying within no-deco limits.

Consider a wreck dive here in NJ on the USS Algol where you might want to do 15min at 130' in the holds, or out in the sand looking for scallops on 28% and then switch to 40% upon ascending to 70' and spend 25 min exploring the superstructure and maybe shooting a fish or two.

With a stageg bottle of 40% that dive is a 47min no-deco dive, requiring only a 3min safety stop.

The "implication" that the stage gas is the same as back gas turns that same dive into a 59min deco dive with required stops of 3min at 20' and 10min at 10'. Don't know about you, but I wouldn't be thrilled with 13min of deco in 40deg water, trying to hold a 10' stop for 10min in the typical 4'-6' seas we run into here.

 

[PerroneFord]

Ok RJP. You are right. I wouldn't consider switching gas on a recreational, non-deco dive to try to stay out of deco. Not sure what OW class covers that either.

I will say that I cannot fathom ANY circumstance where I would be carrying multiple stages to keep from doing deco, nor would I EVER try to do a 10ft stop in the open ocean. Especially a rough one.

 

[rjack321]

I will say that I cannot fathom ANY circumstance where I would be carrying multiple stages to keep from doing deco, nor would I EVER try to do a 10ft stop in the open ocean. Especially a rough one.

Here in the technical diving forum we always carry 3 or even 4 mixes in LP steel stage bottles to create NDL dives and avoid hanging on anchor lines with our bungied OMS wings.