Using SMB For Backup Flotation

[Indy Diver]

An addendum to my previous post:

Mempilot makes some excellent points.

The bag I use has an open bottom, because I don't care about whether or not it spills at the surface. I really only need it to get off the bottom and control my ascent rate, as the wetsuit expands near the surface it becomes un-necessary. Also with a HP100, I have enough ditchable weight to stay on the surface with no effort on my part, even with a full tank. I didn't think about it before, but if you are diving double steel 120's, an open bottom lift bag could turn out to be a very bad idea.

The whole lift bag thing is harder than it sounds. It took five ascents from the 40' platform for me to get it to work half-way smoothly. The first time, I over-inflated it and ended up letting go of it because it was dragging me to the surface pretty quickly.

 

[TSandM]

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).

If you are diving a single tank and are reasonably fit, you don't need a whole lot of additional lift to get off the bottom. And a wetsuit will begin to expand as you go up, so you need even less additional lift as you ascend.

Losing all the lift in your wing and all the lift in your drysuit is two catastrophic failures. You can plan for that if you want to, but the likelihood of it happening is so tiny that you'll be encumbering yourself to deal with a extremely rare event.

One of the things I don't remember anybody mentioning is that, once you get to the surface, you have to stay there. This is the place where the person in heavy neoprene has an advantage, because he's probably carrying ditchable weight. If you're diving in light exposure protection, where you aren't getting much additional buoyancy from wetsuit expansion and you don't have any ditchable weight, you might be much more comfortable and safer with an auxiliary lift device, and it should have enough lift to be able to rest on it while working your way back to the boat, or awaiting rescue.

 

[Web Monkey]

This is the problem you envision, yet the solution you've landed on is to attach the line to yourself?

I'm really not sure why this has become such a complicated thought process.

1. Shoot a bag
2. Roll the line back up on the spool until you're at the surface (works regardless of whether or not your BC holds air)
3. Ditch equipment until you float.

Terry

 

[Reg Braithwaite]

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.

...

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.

To be honest, this makes me think that if you choose to dive wet, cold and deep, you really need to think through the BC failure scenario very carefully. Your story (not quoted) of a student and instructor dying in this configuration scares me silly.

I don't know if a dual bladder is overkill, but I would say that whatever a diver chooses for alternate lift, (s)he ought to have practiced using it under actual diving conditions, i.e. deploying a lift bag from 100' and making a safe ascent all the way to the surface.

I am not a particularly experienced diver, but I will say that when I got my dry suit I practiced using it exclusively for buoyancy with the wing for backup as well as using the wing for buoyancy and managing the suit to keep the squeeze off and no more.

 

[TSandM]

To be honest, this makes me think that if you choose to dive wet, cold and deep, you really need to think through the BC failure scenario very carefully.

Yes. The DIR answer is not to dive heavy neoprene exposure protection deep. A dry suit gives you redundant buoyancy AND superior insulation.

 

[rstofer]

Yes. The DIR answer is not to dive heavy neoprene exposure protection deep. A dry suit gives you redundant buoyancy AND superior insulation.

If it wasn't for the cost... Times 4 for our small herd...

Richard

 

[Splitlip]

Well, sure! The SMB is ascending, has as much as 50# of lift, hasn't reached the surface and somehow the line gets tangled in the reel. I don't think there has ever been a line that is played out from a reel that doesn't jump the flanges at some point. Once it jumps the flange, it is now wrapped around your finger. But the SMB is still pulling. Hard! That's going to hurt...

By definition, you can't be controlling the speed of the SMB ascent because it has a bunch of lift and you are only 12# negative. If you aren't ascending with the SMB, you are only slightly moderating the speed. If you try to increasingly moderate the speed, that reel is going to smoke your gloves. In fact, if you wanted to moderate the speed, and I don't know why you would other than to keep tension on the reel, a slight bend around the carabiner might be a good thing.

I think these things need to be evaluated by testing. There's just so much that can be discussed and sooner or later it comes down to implementation. Just keep a knife nearby should it become necessary to cut the line when the test fails miserably.

Richard

Holy crap! That is the point of NOT running the line through the carabiner. A bird nested reel and 50# of lift will take your scrawny 12# for a ride you won't believe.

Maybe that is the desired outcome. I just suggest you SCREAM on the way up.

BTW, you won't have time to get a cutting tool into play.

 

[battles2a5]

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.



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.

If you are on a wreck in current and blow a bag you are going to have a hard time getting to an anchor line. And if you get there it is going to much more difficult to control your ascent up the line without fouling your line and/or everyone else on the anchor. The way we dive in NC I can't imagine using a liftbag on the surface to as backup bouyancy. The risk of entanglement which would then render the lift bag useless are too great.

 

[RJP]

If you are on a wreck in current and blow a bag you are going to have a hard time getting to an anchor line.

If I'm on a wreck in a current I could/would crawl across the wreck to the anchor line and pull myself up.

Though the fact of the matter is, diving dry I've already got redundant buoyancy so at some point much of this discussion is mental masturbation.

 

[mempilot]

I'm really not sure why this has become such a complicated thought process.

1. Shoot a bag
2. Roll the line back up on the spool until you're at the surface (works regardless of whether or not your BC holds air)
3. Ditch equipment until you float.

Terry

Imagine this:

You are diving a deep wall off Cayman in a 3mm wetsuit with double AL80's. Your wing fails at the threads between the inflation hose and the bladder making maintaining bouyancy with the wing virtually impossible. Any air added just easily escapes out as you add it. All this is happening while you are kicking feverishly to maintain depth due to being negative from the doubles fairly early in the dive. You are sinking against the kick initially at a rate of 30 feet per minute as you deploy your bag. Instead of clipping the snapbolt to your crotch d-ring, you decide to attach it to your reel and blow it to the surface. The bag rises above you and the line jumps the spool, tangling with the force of 50lbs pulling against your mass.

What do you do?

1. Go for a ride and get bent?
2. Cut the line/let go of the reel, and start your descent into the abyss?
3. Did you bring a backup bag and reel to replace the primary in such an event?

None of these are good options in this scenario, which is not fantasy. The appropriate way to use a lift bag to control bouyancy is to handle it the same way you would your other forms of bouyancy. Keep it close to the body so you are in control at all times. A proper 50lb lift bag will have a stainless steel snap bolt at the bottom of the lifting strap. You clip it to the crotch d-ring, add enough gas to it to stop the descent, then gather your wits. At this point, you will not need to add any more gas to the bag, as Boyle's Law will take care of the rest. You slowly give a few kicks to rise just a few feet in the water column, just as you would if you still had use of your wing; all while keeping the bag close to your chest, anchored at the crotch d-ring, and one hand stabilizing the top of the bag and the other hand on the OPRV at the top of the bag. As you rise a few feet, you burp the OPRV, and repeat with a few kicks.

This is any easy task with practice. I've had to do it for another reason I will explain in another post if anyone wants to hear it. Shooting the bag to the surface and reeling yourself up is not an option. Try it, and you will see that you are not going to be able to turn the spool against all that mass, even while kicking your heart out. You will very quickly tire. You need the gas in the bag to lift you, not your arms and fingers on a tiny line and spindle.