Ok, a serious question about balanced rigs

My understanding is that a "balanced rig" is is either neutrally buoyant or a little negative, such that you can swim it to the surface if you lose buoyancy. In the charming thread on using an SMB as backup, a few people seem to be suggesting that given doubles and a wet suit compressed at depth, their rig would NOT be balanced and it would be impossible to swim it up.

Hmmm.

Could a doubles rig be designed with permanent buoyancy such that when full of air it is balanced? I am imagining two streamlined tubes filled with something like insulating foam strapped beside the cylinders, just large enough to bring the rig to ten pounds negative when full of air.

Another cheapo option would be a foam plate like a flutter board mounted between the backplate and the tanks, again sized to bring the rig into balance. Obviously there is some hydrodynamic resistance even if the buoyancy assistance is streamlined. But given the right construction, it could be bomb-proof.

Obviously, if diving a heavy wet suit you'd need a ton of ditachable weight to overcome the buoyancy at the surface, I get that and will stick with my dry suit for warmth and redundancy. But I'm just curious about whether this kind of thing (permanent buoyancy to make a technical rig balanced) has been tried or whether there is a huge problem I am neglecting (like the size of such a device).

Off the top of my head, more buoyancy = more weight needed up front, which seems to me like it brings you back to the necessity of ditching weight to ascend in a loss-of-buoyancy situation.

Blackwood:

Off the top of my head, more buoyancy = more weight needed up front, which seems to me like it brings you back to the necessity of ditching weight to ascend in a loss-of-buoyancy situation.

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The problem stated in another thread was that when diving doubles in a wet suit, even if you ditch all weight you cannot swim your rig to the surface from depth. The question is somewhat theoretical for me, since I dive a single and I dive dry (I added a heavy single tank adaptor to my rig to balance it).

Reg Braithwaite:

Could a doubles rig be designed with permanent buoyancy such that when full of air it is balanced? I am imagining two streamlined tubes filled with something like insulating foam strapped beside the cylinders, just large enough to bring the rig to ten pounds negative when full of air.

Another cheapo option would be a foam plate like a flutter board mounted between the backplate and the tanks, again sized to bring the rig into balance. Obviously there is some hydrodynamic resistance even if the buoyancy assistance is streamlined. But given the right construction, it could be bomb-proof.

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The usual thought process is to avoid excessively negative tanks if diving wet. Rather than double hp120s which, when combined with a steel backplate and other hardware , can well exceed 20 pounds of negative, a wetsuit diver would be better served by doubling up al 80s on an al or plastic backplate and therefore start off with less than 10 pounds of negative.

Reg Braithwaite:

The problem stated in another thread was that when diving doubles in a wet suit, even if you ditch all weight you cannot swim your rig to the surface from depth. The question is somewhat theoretical for me, since I dive a single and I dive dry (I added a heavy single tank adaptor to my rig to balance it).

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Maybe it isn't theoretical if you dive with a wetsuit and even a single a steel HP 100, for example.

Why did a diver select a steel tank? Because it took 6# off the weight belt (where it was ditchable) and added essentially nothing to the out-of-water weight of the rig. And he probably carries a little more air (HP 100 vs Al 80) so the tank is 10.5# negative at the start of the dive and 2.5# negative at the end of the dive versus -1.4 and +3.4 for the Al 80.

Great! Now, let's move to a BP/W with a SS plate. Call it 6# negative. We just removed another 6# from the weight belt (where it was ditchable).

Then maybe we add those backplate weights (8# negative) and remove yet another 8# from the weight belt (where it was ditchable).

See the pattern? We are getting rid of ditchable weight to the extent that at the beginning of the dive where we have a full tank (8# heavier than when empty but we carry lead for the essentially empty condition) and the wetsuit is compressed (maybe 16# less buoyant than at the surface), we sit on the bottom perhaps 25# heavy with only 9# of ditchable weight. So, unless we can swim up with 16# of weight, a wing failure is a problem.

Unfortunately, I don't know how to do the calculation for a drysuit. It's my understanding the suit buoyancy doesn't change as much but that you require more weight. If the weight is ditchable, no problem. If it isn't, well, maybe there is a problem. But redundant buoyancy overcomes a lot of concerns.

That 'sticky' spreadsheet over in Equipment -> BCs ... (top of list) is quite useful in evaluating various configurations.

In the end, it's just something to think about. How much lift? How much weight? How much is ditchable?

Richard

rstofer:

Unfortunately, I don't know how to do the calculation for a drysuit. It's my understanding the suit buoyancy doesn't change as much but that you require more weight. If the weight is ditchable, no problem. If it isn't, well, maybe there is a problem. But redundant buoyancy overcomes a lot of concerns.

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My experience so far is that the weight for my dry suit is driven by the fluffiness of my undergarments (as measured in kilo-bunny-tails). When I switched from my MK3 "Snowmobile Suit" to my preferred garb of two layers to underwear and a 4th Element Arctic Top, I went down eight pounds.

There is something going on as you descend, I do add air to prevent a suit squeeze and a little more to the wing to achieve neutrality at depth. But less than a heavy wet suit. And it does provide redundancy, I have done deep dives where I used the dry suit exclusively and kept the wing only as a backup and for the surface (I don't dive that way, but it is important to know how).

But I am still curious if there is a way around the heavy wet suit problem for tropical diving. Ether that or I want an excuse to paddle around Nassau in a rig with two torpedos strapped on looking like James Bond.

For all intensive purposes, i.e. a complete failure totally flooding the drysuit, figure it will have zero buoyancy. The dry suit & garments compress just like a wet suit. The difference is the amount of compression. You do not feel the squeeze in a wetsuit because the compression is even whereas with a dry suit it is not, i.e. the folds cause uneven compression - thus the squeeze.

It does not take much of a fold for something to feel uncomfortable. Think about a small fold in a sock and how that feels on your foot. Same thing.

As for balancing your rig, the conventional wisdom is that when diving wet in open water Al 80s are the best choice. Lots discussion on this so a search will be your friend. But some reasons are:

Limits your bottomtime to reasonable times for deco, which helps prevent hypothermia, changing surface conditions.

Will often require additional weight which should be ditch-able (backup buoyancy not withstanding).

Reg Braithwaite:

But I am still curious if there is a way around the heavy wet suit problem for tropical diving. Ether that or I want an excuse to paddle around Nassau in a rig with two torpedos strapped on looking like James Bond.

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Thunderbolt, eh?

Those were AL tanks btw, not steel.

I've done what you suggest in several different ways inlcuding the attachent of net floats and the custom casting of syntactic foam. So the answer is, yes ... in can be done. I have to warn you that some folks thought this to be really stupid, here're the threads:
1, 2.

Reg Braithwaite:

The problem stated in another thread was that when diving doubles in a wet suit, even if you ditch all weight you cannot swim your rig to the surface from depth.

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My simple and very effective means of providing protection against just this is by using a stacked redundant wing.....in the event of the loose of my primary wing---I can simply switch over to by back-up. And by the way I use this redundant wing while diving wet with either steel or alm doubles. My redundant wing is smaller in lift lbs. than my primary wing, but again this is for contingency use only and it will def. arrest a free decent and allow me a safe and effective ascent and reqd. stops......I picked it up used with fewer than 10 dives on it.