Dumpable weight vs trim

[boulderjohn]

Question --(I gave up on Google-- too complicated mumbo jumbo)--
That example of 300' buoyant ascent escaping from submarine---
What pressure is the air they are breathing in the sub? 1.0 ata? If not, what?
If yes, they would probably have no fear of DCS shooting up fast from 300', no?

 

[TMHeimer]

Thanks. Very interesting. Says chances of the bends is virtually eliminated due to the short ascent time. I guess this means on the sub they have been breathing air at about 1.0 ata, not at maybe 100' down breathing from a regulator.

 

[lowwall]

Yes, subs are kept at surface pressure. Imagine the gas management and physiological issues if they were at ambient for something like an emergency dive to 300m.

 

[TMHeimer]

Yes, subs are kept at surface pressure. Imagine the gas management and physiological issues if they were at ambient for something like an emergency dive to 300m.

That's what I was thinking of course. I did read that planes are pressurized to about 8,000 feet. Thus why you should wait___ hours after diving. Wonder why they're not also pressurized at surface pressure. Probably an obvious reason.

 

[lowwall]

That's what I was thinking of course. I did read that planes are pressurized to about 8,000 feet. Thus why you should wait___ hours after diving. Wonder why they're not also pressurized at surface pressure. Probably an obvious reason.

The reason is cost and weight and efficiency. Building a strong enough structure to maintain a .8 ata difference, especially around penetrations like windows and doors, would be more expensive and make the plane heavier and thus be able to carry less. Also the pressure difference is maintained by diverting hot high pressure air from the engines, which reduces thrust, and then cooling it down a couple of hundred degrees which also takes power.

 

[CT-Rich]

In the first instance you were clearly overweighted for that dive. If you are carrying an extra six or eight pounds of air for a future dive, then you should remove that much lead to compensate. Also, even if the weight wasn't immediately ditchable, you could have had your buddy hold onto your BC while you took it off and removed the necessary weight.

As for the second situation, I don't understand why adding air to your BC wouldn't be a simpler answer. Or maybe leaving the reg in your mouth and getting horizontal if your position was causing the issue.

Of course I was overweighted, it was a full HP120. My buddy burned through air (I forget the exact reason why we ended up with such a disparity in air and had my BCD not malfunctioned, it would not have been an issue. Why any diver would create a situation where he needs a buddy to remove weight is insane. The weight belt I dropped was bought in 1980. After 35 years, I had an occasion where I thought it was better to let it go than exhausting myself on a long surface swim in the dark. I had no regrets about my weighting or my configuration. I stayed with my buddy, and we both got out of the water.

Lead is cheap. **** happens. Plenty of divers make it to the surface and drown anyway. Why not want the ability to guarantee positive buoyancy with a simple yank?

That's what I was thinking of course. I did read that planes are pressurized to about 8,000 feet. Thus why you should wait___ hours after diving. Wonder why they're not also pressurized at surface pressure. Probably an obvious reason.

The bigger the pressure inside plane, the heavier the construction has to be and the more catastrophic a loss of pressure. The Apollo space craft were at 5 psi in orbit and the Landers used 3.5 psi.

 

[lowwall]

I'm not saying you shouldn't carry ditchable weight if you want to, just that it's not necessary to have it if you are properly weighted and equipped for your configuration.

After all, you carried around a weight belt for 35 years before feeling a need to ditch it. And even then there were alternatives.

FWIW, I carry some ditchable weight when diving in warm water with an Al80 in the form of 4lbs divided between trim pockets with velcro flaps on my waist band next to the plate. But when I used an HP120 on my last trip to Coz, it didn't bother me that I no longer needed the weights. I had no problem keeping on the surface with an empty wing and I had a DSMB (and a buddy) if for some reason I needed more lift.

 

[Eric Sedletzky]

I used to be before BC’s that your one safety “panic button” or lets say not panicking but a relaxed controlled emergency ascent was initiated by dumping your weights.
Skin divers were always taught to dump their weight belt if they got in trouble. So many times we read the death reports about abalone divers perishing and were found with their weightbelts still on. It was drilled into our heads that if you feel the least bit panicked or want out you drop your weights. This though crossed over into scuba diving. The training was that you put on your S.C.U.B.A rig complete with crotch strap and the weightbelt was the last thing you put on and it went over all straps so it could be immediately ditchable.
At some point scuba became it’s own thing and moved away from it’s skin diving roots. I started to see integrated weight systems come in with BC weight pockets and trim pockets about the late 90’s. Prior to that it was poodle jackets used with weight belts. For PADI OW we had to r&r the weightbelt, learn to roll it on on the surface.
Then I started reading Internet forums and GUE came along with their tech ideas and introduced the “balanced rig” concept from cave diving where you would never have to ditch a belt because it would send you up to the cave ceiling so kind of pointless. They were all about eliminating “failure points” so a weightbelt to them could potentially be a failure point with a buckle coming undone etc. so the idea that you take all your weight you need with no intention to ever ditch it was the brainchild of a non ditchable weighted rig, perfect trim of course because in a cave you can’t touch anything and leg heavy is definitely no good with silt ups.
When I did tech diving the standard was to use a weightbelt but we used a regular nylon webbing type (no rubber belts!) and used two stainless buckles to make sure we wouldn’t lose it.
I still use a weightbelt for various reasons. I can think of several scenarios both emergency and non emergency where a ditchable weightbelt is a good thing. We dive off kayaks and to have all weight attached to my rig would be miserable. To have to drag that heavy rig off the back of the yak while I’m floaty as hell in my 7mm wetsuit trying to put it on in the water not to mention having that much weight at the back of the yak. I put my weightbelt up front further which spreads out the weight. I roll it on as soon as I get in the water which keeps be stable so I can move around and get my rig off the boat and onto me.
Shore diving. A weightbelt is nice because I can split up my weights and make hikes easier. Wetsuits can take the abuse climbing over rocks and sharp mussels on rocks without damaging a drysuit. A Drysuit being the answer to redundant buoyancy with non ditchable weight, where a ditched weighbelt would be the redundant buoyancy solution to a wetsuit. If you dump a belt at depth in a wetsuit you won’t rocket to the surface like they say. Depending on depth, you will most likely be very slightly bouyant at depth and you will gradually get lighter as you go up but you wouldn’t become a missile like an expanding BC would make you.
Wetsuit material expands slowly so lets put that myth to rest once and for all.
I would rather be alive on the surface than working my ass off trying to fin the whole works up from depth building CO2 and breathing hard just because someone told me it’s best to have all your weight non ditchable.
And some say why not just dump your rig at depth and do a blow and go, really! Lol!
Tell me the difference between “rocketing” up from depth with no rig as opposed to “rising” up from depth with your rig still on that you can get some breaths from but missing a ditchable weightbelt?

Ditching at depth, if the need ever came about I have that option. Why not swim up your balanced rig? Because maybe my leg or legs are injured, maybe I got bit, maybe I had a hell of a deal fighting a current or surge and cramped out and ran OOA and need out now, maybe there’s fishing line and I got entangled, it could be a good tool to dump the weightbelt to get light with tension on the line then cut it below you which will send you up. Maybe I might need to take my rig off to clear the line or kelp or a net, I can do that and still be neutral. Maybe I’m lobster diving and want to get crazy and take my rig off and crawl back in a hole on a hookah, with a weightbelt I can do that.
I’ve posted threads a few times before advocating the use of weightbelts and the advantage of splitting up weighting. Having everything on the rig scares me where I dive. Maybe if I was in a very controlled and steady environment it would be different but not here.
Sometimes I wonder what I’m doing here because some of the discussions are so foreign to me, and I have very little in common with the majority of posters on SB.
so many of the topics definitely don’t apply to my diving environment.
Nobody on my area dives with a “balanced rig” with no ditchable weight. They never even heard of such a thing and would consider it absolute craziness.

 

[Julius SCHMIDT]

Amazing history lesson and when I go back to colder water with double layer thick neoprene I'll be doing the weight belt thing again too. Overweighting myself for stability during rough rocky shore dives I've struggled at the surface to the verge of extinction so many time because I didn't dump weight that it's ridiculous

 

[Bob DBF]

I'm curious, for those "in favor" of ditching weights in buoyancy ascents, have any of you tried to see if you were diving a balanced rig? I.e., go down to maximum depth that you would dive, empty your wing/BCD/dry suit, and be able to ascend?

I do want to clarify that I am not in favor of ditching weights, but I will continue to configure my rig so I will have the ability to dump weight if necessary. Although I might be able to swim my rig up, under some conditions I may not have the ability in every case. Having the ability to drop weight gives one more option for buoyancy control.

The problem I have with the emergency buoyancy ascent with agencies that don't have students practice it is that will they actually be able to perform the skill if necessary?

You don't need much practice except dropping the weight, otherwise one goes at it like a CESA, only with less control. One could practice the evolution if one wanted, I would suggest from a shallow depth with a small amount of ballast. Limiting dichable weight will give positive buoyancy without going to the extreme of dropping everything.

I believe in focusing on (a) having a configuration where the diver can get to the surface without ditching. (b) ditching at the surface to remain there.

Ditching weights at the surface was one safety procedure I learned when I started diving, before the BC. Swimming up was the normal procedure for ascent, however dropping weight at depth was an emergency procedure if one cannot swim up for whatever reason.

What pressure is the air they are breathing in the sub? 1.0 ata?

It's roughly 1atm, however it can be over or under depending on events. In engineering we had a pressure gauge and altimeter to keep track. Interesting being several hundred feet underwater and looking at an altitude of 3500'. Good times.