15 replies to this topic

[BubbleBoy]

I just got a nice new SMB that can double as a 30lb lift bag. I don't dive tech , so I rarely deploy these things except for practice or emergency.

I got to thinking though (look out, he's thinking again) what happens to your buoyancy control while you are shooting the bag from underwater? If you are shooting the bag from your reel, so that it's only attached to you, don't you start to get much more positive as the bag inflates? How do you maintain neutral buoyancy and depth as you are filling the bag?

My SMP has three fill methods: oral, reg, and LP hose. All of these ultimately use gas from my tank. This increases my total buoyancy as the gas goes into the bag, just as if the gas were going into my BCD. I was wondering if it makes more sense to start filling the bag with my BCD vent first. That way gas from my BCD goes into the bag and my total buoyancy stays neutral, at least until my BCD is drawn down to zero. Once I start releasing the bag to the surface, I can refill my BCD as I loosen the tension in my line. This seems like it would be a lot easier to do than trying to vent my BCD to the ambient while filling the bag.

Any thoughts on this from divers with experience?

[Racer184]

SMB = SSD = SMST

Edited by Racer184, 04 February 2007 - 10:23 AM.

[ScubaDadMiami]

People do it different ways. Many will use the longer hose regulator second stage in order to keep the bag away from the body, and from becoming potentially entangled in the diver. Some will hold the bag above the head, exhaling into it. I have also heard of people using gas from the wing since, as you mention, it offsets the gas added to the SMB for the most part. (Then, they add gas to the wing after releasing the bag.) For CCR, I have a hose with an inflator nozzle attached to my offboard tank, and I just pull that out to fire some gas into the bag. The great thing about days of practice is that you can play around with lots of different ways to see which works best for you without having to do it in a real life situation.

No matter which method you use, the main thing to consider is that Boyle's Law will come into play. So, even if you put just enough gas into the bag to barely get positive buoyancy from the SMB at significant depth, by the time your bag hits the surface, it will be quite full and will stand up well. You do not really want to put so much gas in the bag that it drags you to the surface. You just want to get it to start up toward the surface, and then you let Boyle's Law go to work.

Of course, this assumes that you are shooting your bag from depth. Some believe that one should shoot the bag from a shallower stop. (This does not work well in my local diving area because we have strong prevailing currents. If I were to shoot my lift bag after reaching my shallower stops, there is a good chance that the dive boat would not see me because my bag would reach the surface when I am very far away from the boat. So, I shoot my SMB as soon as I clear any potential wreck structure on the bottom.) Even if you are on a shallower dive, the volume you put into the bag will double from 33 feet (salt water) to the surface.

When I do get ready to send my bag up, I make sure I am slightly negative so that I do not start upwards the second I add gas to the bag. Another really important thing to remember is to keep the bag and the line from your reel from becoming entangled in your gear, which will then drag up up to the surface. If the reel should jam, let the whole assembly go. Pull out your second bag and reel (you do carry two, don't you? ), and start again.

[BubbleBoy]

.. The great thing about days of practice is that you can play around with lots of different ways to see which works best for you without having to do it in a real life situation...

Good comments. This obviously gets a bit tricky as you get a larger capacity lift defice. I never had to worry about it much with my old safety sausage, since it only generates about 8 lbs of lift when fully inflated. I'm definitely going to practice with this new one a few times under controlled conditions.

[Twinklez]

SMB = SSD = SMST

Surface Marker Bouy :-)

No matter which method you use, the main thing to consider is that Boyle's Law will come into play. So, even if you put just enough gas into the bag to barely get positive buoyancy from the SMB at significant depth, by the time your bag hits the surface, it will be quite full and will stand up well. You do not really want to put so much gas in the bag that it drags you to the surface. You just want to get it to start up toward the surface, and then you let Boyle's Law go to work.

That little tidbit about Boyle's law is so true. You don't have to worry about filling the bag all the way.

Good comments. This obviously gets a bit tricky as you get a larger capacity lift defice. I never had to worry about it much with my old safety sausage, since it only generates about 8 lbs of lift when fully inflated. I'm definitely going to practice with this new one a few times under controlled conditions.

Remember, if using it as a lift bag, you've probably got something heavy attached. You only put enough air in to cause the object to rise gently and slightly. You keep hold of the deflate string or whatever mechanism it has to let air out. Start swimming up slowly while lifting and controlling the object. If you start rising too fast, let just a little air out...like you would your BC. Too much air out and you'll sink again. Fix yourself up a 14# weight belt and practice taking it down and bringing it up - heck, swim around with it a little until you're comfortable going up and down, then find yourself a 25# boat anchor and practice a little more. Then from a skills platform or something similar where you can steady yourself, practice using your new toy as an SMB. See how much air it's going to take to get it to rise and remember what Howard said...at a greater depth Boyle's law will cause the air to expand as it rises so you'll need less.

[JimG]

For starters, you do not ever clip the bag to your person once it has been deployed. Clip it to a spool and allow the spool to unwind by holding lightly between your fingers. With a Delrin spool, you can even let go, and allow it to unwind all by itself - most times it will stay right in front of you and just spin away. Even if it does go up a little, it will drop back down again. The main thing is not to have any part of the SMB or spool in a position where it can catch on you or your equipment.

To inflate the SMB, you do not need that much air - just enough to make it "stand up". Boyle's Law will take care of the rest as the bag ascends. The buoyancy issue is not really that much to worry about. If you inflate the bag by exhaling or "donating" from some other piece of equipment (BC or drysuit), then the buoyancy shift is pretty well balanced - the (already expanded) air simply goes from one place to another. If you fill from your second stage, then you can time it with an exhalation to offset the increase in buoyancy. In reality though, the amount of positive buoyancy that is created by blowing a burst of air into a lift bag is not that much, and most people can deal with it pretty easily.

One other important consideration is body position - you want to be level in the water while you are deploying the bag. This presents a larger profile in the "up" direction and creates more drag, which helps reduce the buoyant effect of inflating the SMB. It also gives you more leverage for controlling the SMB, or if you have to pull it back down for some reason (note that "pulling down" only works for small bags - it would be difficult to impossible to do that with your 30 lb bag).

Try to find someone who understands the mechanics of bag deployment to give you a quick demo. It's really not that difficult once you get the steps down. And of course you need to practice, practice, practice until you can do everything smoothly.

-JimG

[Dive_Girl]

Try to find someone who understands the mechanics of bag deployment to give you a quick demo. It's really not that difficult once you get the steps down. And of course you need to practice, practice, practice until you can do everything smoothly.

Great advice! I am lucky my "tech" instructor didn't drown himself laughing while watching the first time I deployed my lift bag in training...

[seafox]

Here is my suggested methodology. I am not suggesting that this the only way.
It's just my way!

Suggested procedures for deployment

A lift bag may be used in several ways and is a useful underwater tool; however, perhaps its most common use is as a signal marker to show surface support -- such as a pre-briefed boat captain -- the dive team's position in the water during free and drifting ascents and to aid in the decompression procedures. It is this use that the following procedure will outline. This procedure will be taught to you as part of your Technical Diver Training program.

Step-by-step procedures (Assumes use of a lift bag type marker connected to open-faced spool or reel containing more than 70 feet of #36 braided nylon knotted every 3 meters or ten feet)

A diver alert marker or sausage-type is the most effective way to signal a team's position in the water during an ascent away from a fixed ascent line in still water or during a drifting deco. The sealed or semi-sealed bags are preferred. Bag should be brightly colored and should be marked to conform to local regulations. In addition, it helps when diver's name is added to the bag in large letters with a Sharpie-type marker.

Team deployment single marker

Unless you are doing a skills session as part of your in water assessment, it's usual to deploy only one marker per dive team. This is often done when the team has reached relatively shallow water; perhaps just prior to the 70-foot gas switch.

Dive leader signals "Deploy Marker/bag" and team members confirm. Each member should carry a lift bag and a spool but part of the dive briefing will have been the selection of "whose" bag and spool will be deployed! This team member will remove her/his spool and bag from her/his pocket or pouch and display it for team to see. If the spool and bag are not pre-attached, she/he will do so and then hand the spool to her/his dive buddy. She/he will confirm that the line from the spool is firmly attached and give her/his buddy the "OK' signal. She/he will confirm this signal. After a final check to see that the line is not fouling any equipment, she/he will begin to inflate the marker. When it has sufficient gas to rise towards the surface she/he will hold the bag away from her/his body and in the center of the buddy circle and her/his team members will give the "OK' signal and she/he will then release the bag. The spool may be held lightly with the fingers or may be left to unroll itself freely in the water column. When the bag reaches the surface, the line is tightened and re-clipped to prevent the spool from dropping into the depths.

The spool may be left in the center of the buddy circle providing a good visual reference. The spool's owner is usually responsible for rewinding line as the team continues its ascent.

Team deployment multiple markers

Putting more than one bag and line up usually means the exercise is part of a skills session. In this case, deployment is done individually (see procedure below). However, each diver waits her/his turn to deploy her/his bag. DON'T try to throw several bags to the surface at once. You'll simply end up with a bird's nest of tangled lines.

Individual Deployment

Take spool and bag from pocket ensuring that line is firmly attached to bag. Hold spool in right hand and bag in left and show to buddy. They should confirm they have visually checked that you are clear to inflate. Begin to inflate bag until it is pulling lightly for the surface. Hold line andbag in front of you making sure no equipment is fouling the line. Watch for your buddy to give the "OK" signal and allow the bag to ascend.


Further notes:
A common mistake is over inflating the bag so that it is impossible to control at depth. Remember Boyle's law.

It's vital that divers break surface no more than three meters from the bag especially where surface traffic or heavy seas may be a factor.

Diver alert markers/lift bags can also be used to signal surface support that there is a problem with the dive team. Some advocate the use of different colored bags for this... I am not entirely comfortable with that option. I prefer instead the practice of sending a second bag up the same line. Naturally, whichever practice you opt to use, it is necessary to discuss this with your surface support prior to EVERY dive.

One last tip: knotting the line on a spool (say every ten feet or so) can help you measure things like the length of a hatch cover or how far you are from the surface!

Hope this is helpful!

Cornel

[ereediver]

Reading these posts, I get the impression that finger spools are the preffered spool for deploying surface marker bouys. If I am reading this right, Why is that. or does it not really matter. I did pick up a marker and a dive rite safety spool this winter (90 feet of 24 line if I remember right) thinking that would work well as a start for navigation and SMB if needed. So I am interested if that should be regulated to nav duties only. It does clip nicely to my new back plate thought.

[PerroneFord]

Reading these posts, I get the impression that finger spools are the preffered spool for deploying surface marker bouys. If I am reading this right, Why is that.

They are light, small, easy to carry, and never jam. Trying to shoot a bag from 80ft and having the line jam in the reeel after 30ft has spun off is a real bummer.

Of course, you can't easily use a finger spool from depth if you're a mix diver or on deep air. Spools get unweildy beyond about 100-150ft. Great for your EAN50 stop, not so great if you're on deco with 21/30.

[JimG]

Reading these posts, I get the impression that finger spools are the preffered spool for deploying surface marker bouys. If I am reading this right, Why is that. or does it not really matter.

Spools are definitely preferred for this. Reels jam, and typically do not deploy line as fast as a spool will, due to the inherent friction of the hub assembly. Spools are simpler (no moving parts), easier to stow (fits in a pocket), and more versatile, as they may used for multiple purposes.

[ScubaDadMiami]

I used to carry spools for deploying my SMB on shallower dives, and for using for jumps while cave diving. However, it can take a while to unclip and retrieve the loop in total darkness such as one will find in cave diving (with light failure).

I now use two smaller reels (Dive Rite Side Winders) for the spools I had been carrying. I have a safety reel with 140 feet of line (which is good for shooting SMBs in shallower water), and another jump reel with 50 feet of line on it. I find these superior to spools.

[JimG]

I used to carry spools for deploying my SMB on shallower dives, and for using for jumps while cave diving. However, it can take a while to unclip and retrieve the loop in total darkness such as one will find in cave diving (with light failure).

I have a "Woody" on all my spools, so finding and pulling the loop by feel is pretty easy. In an actual lights-out exit however, I would opt to leave them in the cave, rather than waste time retrieving them. You can always come back later and get them (at least I hope so ).

I now use two smaller reels (Dive Rite Side Winders) for the spools I had been carrying. I have a safety reel with 140 feet of line (which is good for shooting SMBs in shallower water), and another jump reel with 50 feet of line on it. I find these superior to spools.

I used to have one of the DiveRite "blue reels" as a safety. It jammed on me twice during a lights-out drill in my Full Cave class. I somehow managed to unjam it both times (in total darkness) and eventually found the main line. After that dive I pitched the reels and have been using spools ever since. That was over 11 years ago, and I have never regretted the decision.

Reels jam. Spools don't. That fact alone (in my opinion) makes spools a far better choice in almost every situation.

And don't even get me started on the "exploding gap reel" story.

[PerroneFord]

After fooling with the Dive Rite safety and gap reels in my cave class, I'm a spool man for life.

I do like my Salvo primary though.

[ScubaDadMiami]

The Sidewinders are not like the Dive Rite reels of old. I've shot my larger, Halcyon reel from near 200 feet (and many times shallower) without incident. If it jams, I just let it go, pull out the smaller reel, pull out the lift bag, and do it again.