Do you need ditchable weight?

[FishWatcher747]

I have searched this topic but haven't seen what I am after.

First some feedback for those that have read my recent threads about a first year diver struggling with being foot heavy in a jacket BCD. I switched to a HOG Stainless steel backplate with a 32# wing and have 20 dives in this configuration. Easy to be perfectly horizontally trimmed. In an XL 7mm wetsuit boots and hood I use 20# of weight. After some experimentation I ended up with 2# on each side of my harness belt in ditchable trim pockets and 8# in each upper cam band trim pocket.

There is no way I could have gotten trimmed in my jacket BCD. I would have had to have virtually no weight at the waist in a BCD designed to put the vast majority of the weight in integrated waist weight pockets.

So when I descend to a 30 foot reef I just put a few squirts of air in the wing. When I breathe down most of my air I virtually have no air in wing but can still hold a safety stop.

I also did 3 deep wreck dives in Key Largo, 2 on the Spiegel and one on the Duane. When descending on the mooring line to 90 feet with an empty wing and I let go of the line I needed a surprising amount of air to get neutral.

So my question is I now have almost no weight on my harness belt. In the event of a wing failure, puncture whatever I would be quite negative on a deep recreational wreck dive of 90-110 feet. I'm not sure ditching 4# of weight would be enough. I can reach my upper trim pocket on the left fairly easily and if I changed that trim pocket to a ditchable pocket I could ditch weight there. Not so easy to reach on the right because of prior Right shoulder issues.

When I get to the Keys or caribbean in warm water and am not wearing a wetsuit I might only have 6 # total in the upper cam band trim pockets to work with if I go deep.

On the other hand I wouldn't want to ditch so much weight that I would induce an uncontrolled ascent. So how do you address the unlikely event of a wing failure?

 

[kelemvor]

A lot of folks will say yes. However, I've done plenty of dives with none. When diving with a steel Worthington and alu plate, I'm negative at 500psi. If I found myself in the open ocean with a completely blown out wing that would hold no air, I guess I'd have to ditch the whole rig.

I've never had to ditch weights outside of OW class.

Make sure you practice orally inflating your BCD. If you ALWAYS orally inflate (on the surface) then you can save quite a bit of air and have longer dives. You can orally inflate underwater but I usually don't bother. That way if you find yourself on the tagline and OOA (I've seen that many times) then you have no concerns about buoyancy.

Generally the formal answer is yes, unless you have redundant buoyancy (drysuit or dual bladder wing).

I did buy a dual bladder wing a few years back, but it's still new in the package. Maybe I should resell it.

 

[Celt]

Not having positive buoyancy on the surface would be a real problem, bring a small lift bag.

 

[Steelyeyes]

I'm a fan of having ditchable weight. Four of us were diving in Hawaii many moons ago. One of us and myself got snatched up in surging current. The other guy took the brunt of it and came away with a head injury, laceration to the knee, a broken dump valve on the BCD, ran through the washing machine and spit out after relieving himself of his stomach contents due to swallowing water when his regulator was pulled from his mouth in the tumble. He made it to the surface but barely.

It took time to locate him and when we did he barely had his mouth above water. He thought he'd ditched his weights but hit his tank buckle instead the now empty tank and his shorty wetsuit were his only buoyancy. Dumping his weights made a huge difference. Had he managed to do that the first time he'd have been far better off.

I have never, knock on wood, had to dump mine but I'm sure it would be a benefit it things ever get in a bad way.

 

[James79]

Real question to me is "why were you so negative"? If it was due to still having your "heavy wetsuit" amount of lead, then first address that and see if you can still get in trim without being over weighted. If you can, then you shouldn't need much of the weight to be ditch-able to achieve positive buoyancy at the surface..... and if you can't, then you might want to look at a "warm water plate" (aluminum or plastic) which would require a little more lead, and therefore allow placing the weight where you want it.
My rig is somewhat negative, and I'm using no lead with a 3mm in freshwater to get me and the rig neutral... in a true emergency, I'll ditch the whole rig if I need to. Realistically, my DSMB would just become a glorified pool noodle to give me the lift I needed.
I dive BPW that I make myself from scratch... the learning curve making the wing resulted in a couple of "catastrophic" wing failures (bladder separated from elbow flange, for example). Due to proper weighting, it was just a case of signaling my buddy that I was thumbing the dive, and swimming to shore. If I had been a few pounds more negative, I would have just busted out the DSMB.

Short version: Ditchable weight is good, but proper weighting and alternate means of lift is almost as good.

Respectfully,

James

 

[lairdb]

"You should always be able to swim up your rig." (For certain values of always.)

This is a drastic oversimplification, but: First, start with being reasonably weighted, not drastically overweighted. Second, remember that buoyancy compression as a percentage is less the deeper you get.

Let's say your wetsuit has 7 pounds of buoyancy, so you wear 7 pounds of lead. (Simplified.) When you descend from 1ATM to 2ATM (33fsw), that's 100% additional pressure, so let's say 3 pounds of that wetsuit buoyancy get compressed out -- now your suit is +4 and your weight is -7. You add 3 pounds of BCD buoyancy, and are neutral.

Now descend to 3ATM (66fsw). That's only 50% additional pressure, so only 1.5 pounds of buoyancy are compressed out of the wetsuit; and 1 pound is compressed out of the BCD. Compared to the surface, you have +2.5 of wetsuit and -7 of lead, and you balance with your BCD.

Now descend to 4ATM (99fsw). The wetsuit is compressed further -- it would be 0.75 pounds compressed out, but the wetsuit is reaching its limit of compression, so you only drop 0.5. Now, compared to the surface, you have -7 of lead, and +2 of wetsuit, so you're compensating for -5 with your BCD.

Now you have a total air cell failure. Now you are -5 at 99fsw. You can swim up -5 pounds. That's probably even a better choice than ditching 7 pounds and ending up uncontrollably positive as you ascend.

 

[kelemvor]

"warm water plate" (aluminum or plastic)

FYI: I've got 7 plates now. Two are plastic. They're fairly thick and have almost exactly the same buoyancy as an alu unfortunately. At least that's the case for mine.

Keep in mind, most "wing failures" are really just a leak that is manageable. I've had that happen. It's really no bother other than you waste a little air. I have seen someone else's exhaust elbow come unscrewed. A competent buddy can fix that in a jiffy. That could have been a problem on the surface in deep water.

 

[scubadada]

At the beginning of a dive you will be at least as negative as the amount of gas you will consume, so that you will be neutral at your SS or last deco stop and will then be able to make a controlled final ascent. For an AL 80 this is about 5 lbs, more for larger cylinders. If you a weighted correctly, the weight of the air is the most you would have to swim up. It might be a bit more if your wet suit is compressed at depth. You should easily be able to swim this up, even without ditching weight. You should be carrying an SMB. Most SMBs have a buoyancy of something like 15-25 lbs. You could always use this at the surface if you were in the position of waiting for a pickup

Personally, I dive with some ditchable weight, have never ditched it.

 

[FishWatcher747]

"You should always be able to swim up your rig." (For certain values of always.)

This is a drastic oversimplification, but: First, start with being reasonably weighted, not drastically overweighted. Second, remember that buoyancy compression as a percentage is less the deeper you get.

Let's say your wetsuit has 7 pounds of buoyancy, so you wear 7 pounds of lead. (Simplified.) When you descend from 1ATM to 2ATM (33fsw), that's 100% additional pressure, so let's say 3 pounds of that wetsuit buoyancy get compressed out -- now your suit is +4 and your weight is -7. You add 3 pounds of BCD buoyancy, and are neutral.

Now descend to 3ATM (66fsw). That's only 50% additional pressure, so only 1.5 pounds of buoyancy are compressed out of the wetsuit; and 1 pound is compressed out of the BCD. Compared to the surface, you have +2.5 of wetsuit and -7 of lead, and you balance with your BCD.

Now descend to 4ATM (99fsw). The wetsuit is compressed further -- it would be 0.75 pounds compressed out, but the wetsuit is reaching its limit of compression, so you only drop 0.5. Now, compared to the surface, you have -7 of lead, and +2 of wetsuit, so you're compensating for -5 with your BCD.

Now you have a total air cell failure. Now you are -5 at 99fsw. You can swim up -5 pounds. That's probably even a better choice than ditching 7 pounds and ending up uncontrollably positive as you ascend.

So this is what I am getting at, understanding you are just oversimplifying. Maybe just keeping 4# total in ditchable weight pockets in harness belt is the right amount to ditch then swim the rig up and safely surface. At the surface dump the other weight from the upper cam trim pockets via ditchable pockets or remove rig to access trim pockets to dump weights if needed.

 

[OTF]

At least some of your weight should be ditchable. Doesn't have to be all of it. There are lots of ways to carry weight, you might as well choose one that lets you ditch it.

That doesn't need to mean quick-release pockets, which sometimes release too easily. I wear a weight belt, it goes under my crotch strap. I've often heard of this setup referred to as "unditchable" weight. But it is trivially easy to ditch by dropping the belt, then releasing the crotch strap. That could be done on the surface or underwater with only a little more effort than quick-dump weight pockets. In fact it's a nice setup because if the weightbelt does come off unintentionally the crotch strap can catch it before I lose it and rocket to the surface. Very different from a weight that is bolted to the backplate, which truly is unditchable underwater.