Balanced Rig: AKA "How much Lead do you REALLY need?"

[onepointfivethumbs]

I dive in cold, fresh water (great lakes and quarries), so "you don't need weight" responses are unhelpful.

When I did my OWD the shop gave me about 30lbs of lead, I did my checkout in a jacket BCD, 7mm suit, hood & gloves. I did the "eyebrows weight check" but even then I felt heavy, when we were doing follow-me drills at about 40FFW my BC was about 60% inflated.

I admit that I am not svelte in any sense of the word, however I still sink when I fully exhale. My understanding is that it takes 2lb per millimeter of suit thickness, so a 7mm suit would need 14-15lbs of weight. If the bp/w assembly weighs 6-7lb, and assuming everything else is functionally neutral, I would only need to find another 7lb of weight. So where does this other 15lb come from?

My understanding is that DIR promotes the use of a "balanced rig", properly weighted so that you can swim up an empty tank and only have to ditch a minimal amount of weight for a full tank. If you dive dry you can dive steel, which is negative empty and full, and you can make up the difference with P-weights or V-weights.

For starting out in a steel backplate and an STA, how much weight should I really be looking at carrying?

 

[Hartattack]

I dive in cold, fresh water (great lakes and quarries), so "you don't need weight" responses are unhelpful.

When I did my OWD the shop gave me about 30lbs of lead, I did my checkout in a jacket BCD, 7mm suit, hood & gloves. I did the "eyebrows weight check" but even then I felt heavy, when we were doing follow-me drills at about 40FFW my BC was about 60% inflated.

I admit that I am not svelte in any sense of the word, however I still sink when I fully exhale. My understanding is that it takes 2lb per millimeter of suit thickness, so a 7mm suit would need 14-15lbs of weight. If the bp/w assembly weighs 6-7lb, and assuming everything else is functionally neutral, I would only need to find another 7lb of weight. So where does this other 15lb come from?

My understanding is that DIR promotes the use of a "balanced rig", properly weighted so that you can swim up an empty tank and only have to ditch a minimal amount of weight for a full tank. If you dive dry you can dive steel, which is negative empty and full, and you can make up the difference with P-weights or V-weights.

For starting out in a steel backplate and an STA, how much weight should I really be looking at carrying?

When we factor in proper weighting and buoyancy control, we take this slightly further by evaluating fair weighting distribution over the entire diver. E.g., counteracting a neoprene suit's positive buoyancy compared to a dry suit, dive cylinders becoming lighter due to gas consumption, and the need to manage these aspects alongside changing pressures through deep and shallow water. So, with that said, let me ask you a few questions:


What is your exposure protection?
What is your tank(s) of choice?
Are you diving single or doubles?
What regulator(s) are you using?
Do you have a cannister primary light, if so which one?
If single tank, is your STA weighted or not?
What Fins are you using?
What does your current rig weigh?

 

[James79]

Depending on how much you want to nerd out on it... I like the spreadsheet found here: Optimal Buoyancy Computer

Simple version:
Buoyancy can be looked at in 3 chunks;
1) Individual (are you as a human positive or negative, and by how much)
2) Exposure protection (wetsuit/drysuit buoyancy, which can compress and reduce at depth)
3) Rig buoyancy (both the positive or negative of the tank/bcd combo, and it's lift capacity).

Number one can be figured out in a pool. Number 2 does follow a rule of thumb (the 2lb per mm), but varies with brand and age of suit). And number 3 varies completely by the rig, from poofy poodle jackets that can need significant lead by themselves to steel BPW with a steel tank that are significantly negative even when empty (but that can also be checked at the pool).

So some of the "extra 15 lb" was just to sink the jacket BC. Some could have been intentional overweighting (some instructors do that... right wrong or indifferent). Some could be due to the fact that when we aren't comfortable in the water, we tend to breathe off the top of our lungs, instead of a natural breathe (part of the reason people actually do need less lead with experience). I would probably start with with the "extra" 10 lb, and fine tune from there.

This subject warrants an entire dissertation, lol.

In a perfect world, I would dive a truly balanced rig.... the rig without me in it would be neutral with an empty tank, and I would wear weight to be neutral independent of the rig. So I would only be approximately 5 lb negative (weigh of the air in the tank) at the start of the dive, plus any wetsuit compression (a few pounds for the thin suits I use). So even at the start of the dive, if I had a catastrophic wing failure I could still swim up 8 lb or so of negative buoyancy... then decide at the surface if I need to ditch lead to maintain positive buoyancy. In reality, my rig is negative, and I'm positive and I dive with no lead for the same scenario... and if I had to, I would ditch the rig. More likely, I would use my DSMB as an alternate lift source.

My advice is always worth what you paid for it....

Respectfully,

James

 

[onepointfivethumbs]

When we factor in proper weighting and buoyancy control, we take this slightly further by evaluating fair weighting distribution over the entire diver. E.g., counteracting a neoprene suit's positive buoyancy compared to a dry suit, dive cylinders becoming lighter due to gas consumption, and the need to manage these aspects alongside changing pressures through deep and shallow water. So, with that said, let me ask you a few questions:


What is your exposure protection?
What is your tank(s) of choice?
Are you diving single or doubles?
What regulator(s) are you using?
Do you have a cannister primary light, if so which one?
If single tank, is your STA weighted or not?
What Fins are you using?
What does your current rig weigh?

For the sake of argument:

Exposure: 8/7 Hooded Semi Dry
Tank: AL80
Rig: Singles
Regs: TBD but let's say Scubapro MK25
Light: No canister, handheld
STA weight: Let's say no because the Halcyon one is $250 for some reason?
Fins: Mares Avanti Quattro
Rig Weight: (Steel BP + Harness + Wing) maybe 8lb?

 

[Hartattack]

For the sake of argument:

Exposure: 8/7 Hooded Semi Dry
Tank: AL80
Rig: Singles
Regs: TBD but let's say Scubapro MK25
Light: No canister, handheld
STA weight: Let's say no because the Halcyon one is $250 for some reason?
Fins: Mares Avanti Quattro
Rig Weight: (Steel BP + Harness + Wing) maybe 8lb?

While this is an excellent recreational rig, you lose a lot of your weight due to your positively buoyant semi-dry and AL 80 tank. My recommendation would be to go with an LP 85 or HP 100 tank and add trim pockets with 3lbs each. You want the pockets as close as possible to your BP and also over your center of gravity. You could test out this configuration first and see how it feels; after that, you could add a weight belt if needed. With all of this said, feel free to PM me, and I can assist you further as I also live in the Midwest. I would be happy to work with you on this.

 

[kmarks]

You say you sink when you fully exhale? But you aren't made of neoprene. As you go deeper, your neoprene compresses, thereby losing buoyancy, but the amount your body compresses is minimal to zero. So even if you start to sink upon fully exhaling, you might pop back up when you actually have a little air in your lungs. In fresh water with no need for an exposure suit (aka a pool), I am personally very negative to the point that I sink without full lungs and can't float on my back to save my life, but I just did a Try Scuba with two guys over the weekend who were each a little over 6 ft and 280 and I had to put 16 pounds on one and 14 on the other to keep them from bobbing back up. Part of that, as has already been mentioned, is that new divers don't do a great job of fully exhaling even if they are 100% certain that they did.

Your calculation of 2lbs/mm of suit thickness is a nice starting point, but it's not very accurate. Taller and larger people have a lot more neoprene in the same thickness than shorter or thinner people do, and different brands have more or less buoyancy than others. For the record, I am 5'9.5", weigh just under 180, and in a full 7 mm, hood, boots, and gloves, 11-12 pounds will sink me in fresh water with either my aluminum BP/W or my Stiletto.

Your steel BP is probably 6 lbs underwater and your harness and wing will be neutral to slightly positive, so don't count on those. Your semi dry might require more weight than you think because of the way it is designed to not allow water, and therefore air, to flow through it.

 

[onepointfivethumbs]

So I guess the big question is should I get 15-20lb pockets so I can play around with it, even if I only need to drop 5lb to start to become buoyant?

 

[Hartattack]

So I guess the big question is should I get 15-20lb pockets so I can play around with it, even if I only need to drop 5lb to start to become buoyant?

That depends. Do you want a balanced rig or the system you learned from? I'm assuming from the thread that the original system of weighting is not working.

 

[onepointfivethumbs]

The goal is a balanced rig

 

[elgoog]

@onepointfivethumbs When I first started diving locally, I had pretty much the same setup you described above - I used 22lb with an AL80 and 16lb with an HP100. The latter was where I ended up after Fundies. I had 8lb weight plates on my backplate (you could get an STA weight of the same) and the rest on a weight belt.

I didn't dive this much because I got a drysuit pretty soon after but it didn't feel like I was off by a lot. I'm 5'11" and weighed maybe 160lb back then.