Choosing gear, weight, and buoyancy

Reg Braithwaite · Feb 22, 2009

From another thread:

cool_hardware52:
Start with the *Minimum Buoyancy* of your dry suit.

What is the minimum buoyancy of your suit? It is the amount of ballast you need to get neutral if you were wearing only your undergarment and drysuit, in neck deep water with an open exhaust valve.

Let's say you test your suit and find that it takes 24 lbs to get neutral with only your undergarment and drysuit on.

What is the goal for your total weighting? To have your total ballast equal to the minimum buoyancy of your suit (+ 1-2 lbs) with empty tanks.

Why? If you need to hold a shallow stop while you breathe down your backgas to zero you need enough ballast to offset the buoyancy of your suit. Pretty simple.

If your "rig" i.e. back plate +harness + empty tanks + bands and manifold + regs + can light provides more than ~26 lbs. (24 +2) then you need to change components, lighter plates, lighter tanks etc. until it does.

If your rig provides less than 26 lbs you need to add ballast, or you will not be able to hold a shallow stop with empty tanks. Different plates, and or adding ballast to the rig or using a belt.

Now if your rig provides ballast equal to the minimum buoyancy of your suit +2 lbs with empty tanks how negative will you be when you have full tanks?

The weight of your back gas + 2 lbs.

Do you ever **need** to more negative? No. If not why select components that increase the problems a diver will face if they suffer a buoyancy failure?

Carrying more ballast than is required to hold a shallow stop with empty bottles offers no advantage, and increases the risks for the diver.

Over weighted + a larger wing is simply ignorance in action.

Summary: It is not necessary to be overweighted. This seems correct for my recreational setup: For warm water I am diving a 3mm wet suit, AL80, steel BP, and need only 2lbs. of weight to be neutral with an empty wing at 10'.

I will have to play with my dry suit and see how things work out for my just-purchased HP-130s. Maybe I can keep the steel BP, maybe I need even more weight to compensate for the undergarments' buoyancy.

All that being said, what about choosing a wing capacity? Although things can balance out nicely in the normal case, in my n00biditrudinous mind I am thinking you need a wing with enough lift to handle the worst case. For a wet suit, that is full compression at depth. For a dry suit, would that be a suit flood at depth with all tanks full of air? I am assuming that the undergarments will lose some of their buoyancy if flooded, and you would need to add enough air into the wing to make up for the suit flood.

Is this right? Or is the loss of buoyancy negligible when the suit floods?

TSandM · Feb 22, 2009

You don't lose all the buoyancy when the suits floods (she says, from experience) and it's rare to have an issue such that you can't put any gas in the suit. More often, it's a leak that floods the suit, but you can still introduce some air.

Wetsuits compress in a rather predictable fashion, which is why some folks argue against deep diving with thick wetsuits and steel tanks.

If you are diving cold water, you don't ever want your total buoyancy (you and your gear) to be more negative than what you can swim up. If your total potential negative buoyancy (suit compression and gas and ballast) is more than you can swim up, you need some weight you can jettison in a really urgent situation.

A flooded drysuit is not as negative as a compressed, thick wetsuit, at least in my experience.

DA Aquamaster · Feb 23, 2009

Having at one point in time jumped in with my dry suit unzipped, I can confirm that you do not lose all the buoyancy with a flooded dry suit.

I think some peopls go too far in terms of small wings under the premis that smaller is lower drag and in some way much better. You need enough lift to float your gear if you get out of it, so at a minimum you need enough to float the full tank, plate, regs, and any weights, lights, reels, etc that may be attached.

You also need enough wing to get your head fully out of the water. The average human head weighs 15 pounds, so you need that over and above what it takes to get you and your gear (with full task) neutral at the surface. In my opinon, that means no less than a 30 pound wing.

TSandM · Feb 23, 2009

Well, a five pound backplate and empty Al80 together are almost neutral, so a 17 or 20 lb wing should be able to get your head out of the water (and that's been my experience).

A 30 lb wing works great for single tank, cold water diving, and is certainly also useful in warm water, if you only want to buy one wing.

The biggest advantage of the small wing is simply the ease of venting. I don't notice that much difference in swimming resistance (but then again, I have never gone directly from one wing to the other), but the 17 lb wing is delightful, because the air is always right there to exhaust -- no tipping, rolling or anything else to move it around.

But if budget is a concern, the 30 lb wing works.

SailNaked · Feb 26, 2009

I was noodling this same question when thinking about my new doubles, with my 3 mil wetsuit and single tank and wing I am very negative with 4# of weight,

my tanks are ~2(-) full and 3(+) empty so I need 6# to hold them both down at stop depth.
my suit by the above point of reference is ~ 6#+

so if I placed the Al80 doubles on my back, I would need another 2-4# for when they are both empty. my total negative weight with full tanks and compressed wetsuit at the start of a dive would be 12# unless I did not add the right things together.

I do not see the need for a doubles wing when my single wing already has about 20+# of lift (OMS). assuming my tanks were full, and I needed to be on the surface for a bit, I would still have 14# of lift for my head.

but that is the pleasures of warm water diving not for dry suits I expect. and maybe I added or subtracted when I should have done the reverse.

TSandM · Feb 26, 2009

Well, the big problem with using a single tank wing for doubles is that the center panel of a single tank wing is narrow, and the double tanks exceed that width, and compress a significant amount of the bladder. Thus your lift is not what the rated lift for that wing is, and sometimes by quite a significant amount.

If your tanks are double Al80s, the weight of the manifold, bands, and two first stages makes them just about neutral when empty. You don't end up having to add another 3 or 4 pounds for the second tank.

JeffG · Feb 26, 2009

DA Aquamaster:
Having at one point in time jumped in with my dry suit unzipped, I can confirm that you do not lose all the buoyancy with a flooded dry suit.

Totally dependent on what kind of underwear you are using. Using DUI 400gm (or similar) underwear, you lose very little buoyancy. Some flavors of fleece are not very good when flooded though.

SailNaked · Mar 2, 2009

Thanks, tsandM, I had not considered the weight of the manifold. I actually got in the water with my new wing this weekend and discovered that I am negative bouyant with no weight at all and a 3mm Suit. I think maybe the borg have implanted steel in my brain.
I plan to purchase a 2x Wing shortly because I doubt my course instructor will let me do the course without one. Since I am a warm water diver I guess being over weighted will never be my problem.

Choosing gear, weight, and buoyancy

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Reg Braithwaite

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