Using SMB For Backup Flotation

[mempilot]

While I used to dive double steel 98's prior to the rebreather, I never did so without backup flotation. The drysuit is my first choice, oral inflation of the wing (bladder not compromised) being my second choice, but a LB makes a good third alternative. As stated above, the LB must have a top mounted dump, and you will want to attach the strap low on your body around the waist area, so that the top of the bag is accessible to you (keeping it close to the chest area for control). The best way to utilize the LB for flotation is to only get put enough gas in it to still require a slight swim up, dumping gas as you go. You do not want to fill it to where it starts floating you in the water column, because it will very easily accelerate past the ability to dump gas fast enough. You have to stay ahead of it, and swim up.

I use a Halcyon Closed Circuit LB so that there is no chance of inadvertantly spilling the gas at the surface and decending like a rock again. This could have dire consequences. I have swum up some heavy stainless hardare using my bag and deflating my wing completely. It takes practice to do this safely, so if you choose to go this route, practice it as a skill on a shallow dive so you are aware of what will happen when the skill is really needed.

A few months ago on a trip to Bonaire, I watched a guys inflator come clean off the corregated hose, leaving his wing unuseable even via oral inflation. Luckily, he could swim the rig up, as it was just a simple recreational setup. If we had been deeper with doubles, he would have been in trouble with a some sort of backup.

 

[Gombessa]

A few months ago on a trip to Bonaire, I watched a guys inflator come clean off the corregated hose, leaving his wing unuseable even via oral inflation. Luckily, he could swim the rig up, as it was just a simple recreational setup. If we had been deeper with doubles, he would have been in trouble with a some sort of backup.

I've never given much thought to this particular failure, but couldn't you just point your butt up and exhale straight into the corrugated hose?

 

[mempilot]

I've never given much thought to this particular failure, but couldn't you just point your butt up and exhale straight into the corrugated hose?

He attempted to exhale into the hose and then pinch it off. You'd be amazed at how that gas wants to escape. As for an inverted ascent...Well, can I be there with a video camera when you try it for the first time?

I suppose anything is doable in theory. But when practiced....

 

[Web Monkey]

He attempted to exhale into the hose and then pinch it off. You'd be amazed at how that gas wants to escape. As for an inverted ascent...Well, can I be there with a video camera when you try it for the first time?

I suppose anything is doable in theory. But when practiced....

If you have a regular BC or wing, there should be no problem keeping air in it as long as the hose/hole isn't a high point.

If you have the Bunigeed Wings of Death, that's another story.

Terry

 

[Gombessa]

He attempted to exhale into the hose and then pinch it off. You'd be amazed at how that gas wants to escape. As for an inverted ascent...Well, can I be there with a video camera when you try it for the first time?

I suppose anything is doable in theory. But when practiced....

Actually, I've done one before! You'd need to talk to my buddies to see how hilarious it looked, but when I was first starting, staying butt-up, heads and feet down, with my hand on the dump valve string was the only way I could ascend without going vertical and venting from the inflator hose. Yes, it would have been great with a video camera there No, I've never tried it with a broken corrugated. But it does sound like you can trap a good amount of air this way if you keep the hose low (i'm willing to bet that the person you witnessed went upright was he was trying it, in which case it's not surprising that all the air came out).

 

[battles2a5]

Of course you don't want it attached to you. You want it attached to a line, which would be attached to a reel or spool, so when you inflate it it goes to the surface and then you ascend on the LINE.



Umm, I though you didn't want the bag attached to you? (PS - note they aren't STRAPS.)

It wouldn't be attached to you. If it gets away from you, you put your arm straight up and away it goes. Not that this should happen since you have the dump right there. Sending one up on a line means you can only go straight up. Doing it the way I described gives you the option of swimming back to the anchor line (or any other horizontal distance) which can be pretty handy.

 

[OH-JJ]

ok First I will + what ever we are up to on not using your DSMB for floatation. you cannot control it so go ahead and just attach it to your line and shoot it up.

the SHTF flotation device is your lift bag. it need to have a top dump and a string down to the bottom. As to it's use. go practice lifting stuff with it first. the Idea being that you want a controlled accent, and not simly shooting it to the top.

Once you can lift an object slowly in a cotrolled mannor, then you are good to go. Simply treat yourself as the object being lift. make your stops as needed and stay calm.


I always carry my lift bag, weither I dive wet or dry.

 

[RJP]

It wouldn't be attached to you. If it gets away from you, you put your arm straight up and away it goes.

It would be attached to you until it wasn't, and the likelihood of it getting caught on something when you tried to get your arm out is too great and not worth the risk. Especially keeping it that close to your body. Hold it with your hand, out at arms length, OK. But I wouldn't put you arm through "the straps" but maybe that's just me.

Sending one up on a line means you can only go straight up. Doing it the way I described gives you the option of swimming back to the anchor line (or any other horizontal distance) which can be pretty handy.

Of course that's not even close to being true in OW. Yes, the BAG can only go straight up, but once it's on the surface you can swim all over God's green apple while pulling the bag along with you. I've done so many times in the past few weeks myself as part of a Tech course, where not surprisingly, the way we were taught to use a lift bag as back-up buoyancy is to shoot it to the surface and ascend on the line.

 

[Reg Braithwaite]

I'm still working on my skills, so I confess that a few times when sending up my SMB on a finger spool I have dumped air to be slightly negative and then climbed the line by winding myself up the spool.

Of course, I now know that the correct thing to do is to stay in trim with proper buoyancy and not get so wrapped up with the line that I forget to dump air as I rise. My bad!

But it does make me wonder whether this would be a reasonable option if I lost my wing AND my dry suit. After all, I don't need 100% lift, I would still swim upwards, but would winding up the line be a reasonable way to use an SMB that doesn't have a dump valve?

(I have a fairly balanced rig, so this is a theoretical question, but still... I would like to learn from your suggestions).

 

[Indy Diver]

Alternatively, bag or sling a pony, so in a situation like this you could ditch all your gear and ascend using only the pony. Won't work if the pony is hard-mounted to your tanks, which is why I say bag or sling it.

Also, I would think that, as long as you had a spool of some sort along with your SMB, you could shoot the bag normally and kind of crawl up the line once it's deployed and floating (like everyone has said, you certainly wouldn't want to attach it to yourself on the way up!).

>*< Fritz

I just want to set the record straight - the boyancy variances with doing deeper diving with a wetsuit, especially a 7/8 mm wetsuit, really have nothing to do with steel tanks and backplates or doubles. It is really related only to the wetsuit and its compression.

It dosen't matter where you put your weight, at the end of your dive you should be able to maintain neutral buoyancy all the way to the surface with 500psi in your tank. So the minimum weight you can carry makes you neutral at or near the surface with a near-empty tank and an empty BC baldder. That weight can be in tanks and backplates, integrated BC pockets, or it can be on a weight belt.

At the start of the dive, you have an extra 6 or 7 pounds of air in your tank (assuming a single AL80 or HP100 tank), so you are a minimum of 6 lbs negative at the start of your dive on the surface.

Now comes the important part relating to wetsuits - all 6 pound negative buoyancy is not created equal. If you are diving in a bathing suit in the caribbean, you are six pounds negative at the surface and you are 6 pounds negative at depth. This is not the case with a wet suit.

I dive a 7mm fullsuit with a 3mm vest/7mm hood combo in colder water. That combo is about 23 pounds buoyant at the surface, so I need to add 23 lbs of extra (relative to the bathing suit guy) weight somewhere to offset it. The bad part is, the wetsuit is only about 7 pounds buoyant at 100 feet. (That nice 200% stretch neoprene really compresses nicely)

That means that in order to be neutrally buoyant at the surface at the end of my dive, I am a minimum of 22 pounds negative at the start of my dive at max depth. This minimum negative buoyancy is always equal to the loss of buoyancy from wetsuit compression + the weight of my backgas, and has nothing to do with other equipment configuration.

Where steel vs aluminum tanks and steel backplate vs aluminum backplate come into play is, what is the rescue scenario if there is a total bladder failure. I know this is very rare, but look at the DAN database - people have died this way. Including a student and the instructer trying to rescue him. The student had a BC failure diving double steel tanks / steel backplate.

If you are diving heavy steel tanks and packplates, the only solution is to have redundant lift capability, like a lift bag or double bladder (or of course get a drysuit!)
The solution of carrying a pony bottle and ditching your heavy steel rig does not work because, as you go up breathing off the pony, your wetsuit picks up 16 pounds of buoyancy (in my case) and you are in runaway ascent mode. I would ditch the rig if it came to that, because being bent is better than being dead, but I certainly wouldn't intententionally configue and plan for it.

If you are diving a lighter rig and have the weight in a ditchable location, then you could always ditch weights to get off the bottom, but you can't ditch all your weight. You still have to kick up from the bottom negative enough that you don't go into runaway ascent mode as you get near the surface. I my case, with a wetsuit that gains 16 pounds of bouyancy on the way to the surface, I would have to be able to kick up from the bottom at 100 feet being 13 pounds negative at the start in order to be able to hold my safety stop at 15-20 feet. Of course, the exact amount of weight to ditch depends on the amount of the 7 pounds of backgas I have consumed already. And what if I was at 80 feet or 120 feet when I started? All of this is too much to manage in a crisis, so I am back to the only solution for this scenario is a redundant lift capability. I carry a lift bag because I think it is easier to deploy and manage than an SMB, and mine has a dump valve on the top and pull cord for it coming out the bottom. I think a dual bladder BC is a bit of overkill for a guy diving a HP100 and an AL19 pony.

Bottom line, I never dive in my 7mm wetsuit without carrying my lift bag. I have 50lb model available from Scubatoys that I highly recommend as an inexpensive piece of safety gear.