Redundant Buoyancy

[MichaelMc]

AL plate is better than being negative with SS, just as starters.

What exactly is your kit??
-7 w/ AL plate seem a lot for just the rig.

You likely have a bit of positive buoyancy yourself.

 

[seeker242]

To those who mentioned shedding weight, How could I do that? I don't seem to have much extra anything besides the SS plate

That's probably the bulk of your weight. What other gear are you carrying that weighs another 3 lbs? 3 lbs of extra gear somewhere, sounds like a lot of extra unnecessary stuff.

 

[tmassey]

An excellent question: I'm impressed that someone with so few dives is thinking carefully about having a properly balanced rig!

Keep in mind that almost all rec divers dive with non redundant bladder BC's.

But they have ditchable weights...

To the OP: You're correct: You added up the buoyancy of each of those items, and those items together will be 15 pounds negative. And that would be a problem if that were it. But what about the rest of the items you're diving with: your wetsuit and *you*! Those should both be positive -- *very* few people are truly negative, and you might be quite positive. It's entirely possible you'll actually need to *add* weight (which you could easily make as ditchable!) in order to be properly balanced.

I think you're going to find that you're within 6 pounds of neutral either way. And that won't be nearly as much of a problem!

 

[doctormike]

It's pretty rare to really need redundant buoyancy unless you are diving steel doubles in a thick wetsuit. The OP is in a 3 mm suit, and I'm assuming that they are diving single tank.

Remember, just because your rig is 15 lbs negatively buoyant it doesn't mean that you need to swim up 15 lbs in case of wing failure. Most human bodies are positively buoyant. Even if your wetsuit is compressed and your wing has failed, a reasonably fit diver should be able to swim their gear up from depth.

Ditchable weights are for ditching at the SURFACE, in case of a rescuing a compromised diver who can't achieve positive buoyancy for whatever reason (exhausted, unconscious, wing failure, etc..). There really shouldn't be a scenario in recreational diving where you would need to ditch weights at depth.

You should be weighted so that with an empty wing and a near empty tank, you will be close to neutral at safety stop depth. The gas in your wing compensates for two things - the weight of gas used during the dive and the buoyancy loss of a wetsuit at depth. With a single tank and a thin wetsuit, most divers should be able to swim up that amount of extra weight in case of wing failure. Remember, it gets easier as you ascend and your suit expands.

But everyone should have an SMB, and that's a source of redundant buoyancy if you really feel that you need it.

 

[Zef]

An often overlooked area when it comes to BCs, Wings, etc., is checking to see that your dump valves are screwed on tight.

I was discussing with a member of one club I am in about an incident that happened with a member of a different club I am in where the diver panicked and fell unconscious while struggling to swim up because one of their valves was so loose they their bc would not retain air. We were standing by the pool while having this discussion and while speaking I reached up and checked the opv/dump valve on his shoulder and sure enough it was loose. I then check the one by his hip and that one was loose too....it would be wise to make it a consistent part of ones personal pre-dive check and a part of the buddy check process just as one might check that their buddy's tank strap(s) are properly tight.

-Z

 

[Divectionist]

I think once in the water, this may be a non-issue.

My bp/w weights on land:
backplate ss 5.3lbs
STA 2.2lbs
= 7.5lbs, call it 8 or 9 with the other metal hardware bits on the bp/w, similar to yours.

Add the pony with reg which sits around -4.5lbs full, negative fins, torches, and we easily are at your 15lbs mark without any added lead.

My notes specify that with an AL80 and the above, with a 5mm wetsuit only, I am adding 0 to 1lbs to be neutral at 50bar/5m. Add a 2.5mm hooded vest and I require 2-3lbs in lead total. A trilam drysuit with thin undergarments and it's 8lbs total.

Due to the way the lead is dialled in to be neutral at the safety stop near the end of the dive, I consider this 'balanced' and also have no problem at all swimming it up, at the beginning of a dive, with no air in the wing.

I am going out today to test the wetsuit setup (it will be 5mm+2.5mm hooded vest) with my new 10.5l steel tank (buoyancy specs here are different from the US tanks, they are a bit more negative), which is probably a good simulator of how the above weights feel in just a 3mm suit in your scenario.

At this shore dive I can only go to 10m but the purpose is to see how heavy I feel with the steel tank so I'll swim the rig up and will report back here to give you one more data point.

 

[OmarM]

First I would like to thank everyone for taking the time out to help me be a safer diver! Second I appreciate you all recognizing that I am new to this sport, and that makes the communication a little less clear on my part.

The general consensus I am getting is that between my buddy, a DSMB and my ability to swim up some weight I should be in a good ball park to do some dives and dial things in. On the bright side, my next couple of dives will all be in the accompaniment of an instructor who should be able to help me with that.

 

[aviator8]

Discuss your setup with your instructor. They should show you how to do a weight check, which should get you dialed in. As stated earlier, you will probably end up carrying a few lbs of ditch-able weight on your waist.

 

[jgttrey]

You're thinking about the right stuff.

The biggest unknown about your situation, pointed out by others, is that looking at the weight of the rig only is irrelevant except for the entirely different situation of needing to be sure your wing will support your rig when you aren't in it so you can ditch and don at the surface. That isn't the question of a "balanced rig."

What matters 99% of the time is the buoyancy of the entire system, including the diver. You are buoyant. My steel BP and AL cylinder, like yours, is significantly negative by itself. But, my body is significantly buoyant (more than it should be, unfortunately). Together, we make a balanced rig.

Separately, a comment on some of the other feedback:

Let's assume you are in fact -15 even when accounting for your body. I'll take issue with the notion that a rig that leaves you (you + rig) at -15 is okay. That's sheer nonsense. I'll say right now that bringing up 15 pounds net negative is horribly unsafe. You cannot sustain that for long at all, particularly if the reason you can't fill the wing is that you've gone OOG and also don't have anything to breath. See how many laps you can swim holding not just 15lbs, but enough lead to make you, overall, -15. My bet is maybe 1 or 2.

The other reason that -15, or -10, or -5 is undesirable is that it requires you to have significant gas in your wing to carry all that weight. That volume of air in your wing requires constant BCD adjustments as you change depth and creating more drag.

The goal of a balanced rig is not just so you can swim it up, but so you can do much of the dive with little to no gas in your wing. In a single and wearing a rashguard, after I get below about 1500 psi, I have zero gas in my wing for the remainder of the dive. At most, at the beginning I have a couple of pounds worth of gas in there - almost nothing. If I were in a wetsuit, I'd carry a tad more weight so I could hold my stops, but the goal is to have as little gas in the wing during the dive as possible.

 

[aviator8]

I don't think swimming up 15lb with fins presents much of an issue. I have had to do surface tread tests holding that much weight over my head with no fins. Also remember that your tank is going to go from -3 to +3 lbs over the course of your dive. Between a buddy, a DSMB and your setup I would say you are good diving over a hard bottom.

You're thinking about the right stuff.

The biggest unknown about your situation, pointed out by others, is that looking at the weight of the rig only is irrelevant except for the entirely different situation of needing to be sure your wing will support your rig when you aren't in it so you can ditch and don at the surface. That isn't the question of a "balanced rig."

What matters 99% of the time is the buoyancy of the entire system, including the diver. You are buoyant. My steel BP and AL cylinder, like yours, is significantly negative by itself. But, my body is significantly buoyant (more than it should be, unfortunately). Together, we make a balanced rig.

Separately, a comment on some of the other feedback:

Let's assume you are in fact -15 even when accounting for your body. I'll take issue with the notion that a rig that leaves you (you + rig) at -15 is okay. That's sheer nonsense. I'll say right now that bringing up 15 pounds net negative is horribly unsafe. You cannot sustain that for long at all, particularly if the reason you can't fill the wing is that you've gone OOG and also don't have anything to breath. See how many laps you can swim holding not just 15lbs, but enough lead to make you, overall, -15. My bet is maybe 1 or 2.

The other reason that -15, or -10, or -5 is undesirable is that it requires you to have significant gas in your wing to carry all that weight. That volume of air in your wing requires constant BCD adjustments as you change depth and creating more drag.

The goal of a balanced rig is not just so you can swim it up, but so you can do much of the dive with little to no gas in your wing. In a single and wearing a rashguard, after I get below about 1500 psi, I have zero gas in my wing for the remainder of the dive. At most, at the beginning I have a couple of pounds worth of gas in there - almost nothing. If I were in a wetsuit, I'd carry a tad more weight so I could hold my stops, but the goal is to have as little gas in the wing during the dive as possible.

I think you are referring to my post above. I did not mean to imply to anyone that a -15 situation is good. I was viewing this in terms of the rig he described, on him, with an Al80, in the water. That total system if his BPW is truly 15lbs negative would end up being less negative as an entire system, and thus he could swim it off the bottom in a wing failure.