deploying lift bag or surface marker

[Jasonmh]

Ok, hopefully I can explain this in a way that will make sense. I have a smaller (3.5 feet) safety sausage/surface marker with one of the Halcyon safety spools attached. I had never tried to actually deploy it underwater until recently and I ran into a problem that I am trying to figure out. The first time I tried I was between 15 and 20 ft, got out the marker/spool, unrolled it, blew some air in to it, and it took off for the surface with me holding the spool between my fingers so that it would roll out. It reached the surface, I used the double-ender to kind of wind it back a few turns and clip it off. So i'm thinking, cool, it worked, and now the spool is floating in front of me. But then I looked up and saw that the bag was almost completely deflated and only a very small part of it was floating sideways on the surface (not standing up) with the rest hanging below deflated. Not cool. So I realized that even though the air expands as the marker gets closer to the surface, if I am only at 15 feet and only put a small amount of air in, it is not going to be full by the time it hits the surface. Makes sense. So on the second try I go to about 25 feet, and do the same thing again. This time I try to put more air in it so that it will be full when it hits the surface. So this time when I start blowing, by the time the bag is not yet half full with air, and it starts dragging me to the surface. So I grab on to the platform at 25 feet to keep me from going up, and keep blowing. This time the bag makes it to the surface and is full, but the only reason it worked was because I was holding on to something. So how do you inflate a marker at a shallow depth so that it will be full at the surface, but at the same time not put so much air in it that YOU go to the surface? It seems to me ( I have never done it, so I am guessing) that the deeper you are the easier this is to do, because a small amount of air at 80 ft is going to expand much more than a small amount of air at 15 ft. Correct?

EDIT> And one more question, I noticed that when the marker was full at the surface, it still layed on it's side unless I was actively pulling down on the spool (the weight of the spool and double-end bolt snap was not enough to keep it upright), is this normal?

 

[Soggy]

You are correct, thanks to Boyle's law, you need to fill the bag up more at shallow depths than at deeper depths.

IMO, those 3-6ft markers are only effective when you are already ON the surface, because without significant downforce, they do not stay upright and are difficult to see. The best option for a SMB is one of the Halcyon semi-closed bags. They are easy to fill, work with both wet and drysuit, stick up quite a ways on the surface, and don't require disconnecting an inflation source to inflate.

That being said, the 'proper' way to fill a CC bag is not to blow it up orally, it's to inflate it with the drysuit hose. This will provide much more rapid inflation, and as such, allow you to release it with more gas in it without starting to rise to the surface.

What buoyancy you do gain can be counteracted briefly by maintaining a slightly heads down position during the deployment of the bag. This will allow you to kick slightly against the force of the bag. If you start getting dragged to the surface, let the bugger go, though!

 

[Jasonmh]

You are correct, thanks to Boyle's law, you need to fill the bag up more at shallow depths than at deeper depths.

IMO, those 3-6ft markers are only effective when you are already ON the surface, because without significant downforce, they do not stay upright and are difficult to see. The best option for a SMB is one of the Halcyon semi-closed bags. They are easy to fill, work with both wet and drysuit, stick up quite a ways on the surface, and don't require disconnecting an inflation source to inflate.

That being said, the 'proper' way to fill a CC bag is not to blow it up orally, it's to inflate it with the drysuit hose. This will provide much more rapid inflation, and as such, allow you to release it with more gas in it without starting to rise to the surface.

What buoyancy you do gain can be counteracted briefly by maintaining a slightly heads down position during the deployment of the bag. This will allow you to kick slightly against the force of the bag. If you start getting dragged to the surface, let the bugger go, though!

Thanks. I meant to say in my original post that I don't have a drysuit. So, what is the preferred method if you don't have a drysuit hose to use? It is acceptable to use the BC inflator hose? Or is it better to orally inflate?

 

[Soggy]

Thanks. I meant to say in my original post that I don't have a drysuit. So, what is the preferred method if you don't have a drysuit hose to use? It is acceptable to use the BC inflator hose? Or is it better to orally inflate?

The acceptable method is to use an open circuit bag and keep the cc bag for drysuit diving or surface inflation.

 

[Web Monkey]

Disclaimer: I'm not DIR, but physics still works for me.

It's easier to get the bag full when filling at greater depth because the air expands as the bag rises.

Making yourself negatively buoyant before deploying it also helps.

Also, filling the bag faster helps, because your body's mass will resist the upward force from the bag. If you can get the air in and let it fly quickly, you will have moved upwards less in the water column than if you hang on to it and fill it slowly.

That said, if the water is cold, filling it quickly from your regulator may start a freeflow.

There's a nice video around here somewhere, if you want to try a search.

As for the "floppy" part, the bag will never stand upright unless something is pulling down on it a little. Typically, this would be you

Terry

Ok, hopefully I can explain this in a way that will make sense. I have a smaller (3.5 feet) safety sausage/surface marker with one of the Halcyon safety spools attached. I had never tried to actually deploy it underwater until recently and I ran into a problem that I am trying to figure out. The first time I tried I was between 15 and 20 ft, got out the marker/spool, unrolled it, blew some air in to it, and it took off for the surface with me holding the spool between my fingers so that it would roll

EDIT> And one more question, I noticed that when the marker was full at the surface, it still layed on it's side unless I was actively pulling down on the spool (the weight of the spool and double-end bolt snap was not enough to keep it upright), is this normal?

 

[jonnythan]

What I'm currently using is this: http://www.scubatoys.com/store/detail.asp?PRODUCT_ID=LargeSafety

It has an open bottom. I cut all the nonsense webbing off.

I'm able to inflate it using my regulator exhaust (learned this trick the hard way... DIRF class, I had to inflate the thing while sharing air ) enough so that it stands up a couple of feet from a depth of ~ 30'. I need to do some more playing around with it.

I've seen people orally inflate the small CC ones sufficiently from ~ 20', FWIW.

 

[dbulmer]

Jonnythan, Soggy et al - do you guys have an orange/red SMB for a normal deployment and a yellow SMB for HELP convention in the States. Over here Jonnythan's SMB would be frowned upon because of the convention in the UK of yellow indicating an emergency ie drop tank. BTW it's an unwritten convention but is more often than not the norm here among techies (DIR and non-DIR I hasten to add)or do you have a team SOP?

 

[reubencahn]

The 3.5 foot sausage is adequate if you're in fairly calm seas. If you fill it fairly full, the weight of the spool will stand it up and it is visible from a fair distance. They tested this once at Brownies and were able to see the marker from quite far away. Filling it orally works just fine in my experience. Do as Soggy recommends and fin downward while filling. FWIW, I've never shot this bag from deeper than 60 fsw.

 

[onfloat]

I was taught in DIR-F, get slightly negative, head down and orally inflate for a marker of that size.

 

[MXGratefulDiver]

What I'm currently using is this: http://www.scubatoys.com/store/detail.asp?PRODUCT_ID=LargeSafety

It has an open bottom. I cut all the nonsense webbing off.

I'm able to inflate it using my regulator exhaust (learned this trick the hard way... DIRF class, I had to inflate the thing while sharing air ) enough so that it stands up a couple of feet from a depth of ~ 30'. I need to do some more playing around with it.

I've seen people orally inflate the small CC ones sufficiently from ~ 20', FWIW.

Me ... I went the other way. I started out with a 6-foot semi-closed bag. Then I discovered that the smaller bags are a lot easier to deploy, and use those unless in a situation where a large bag is really called for (i.e. waves or chop, where a smaller bag would be difficult to see).

I've never had any difficulty inflating the smaller bag on a single breath ... but then, I've got lungs that could power a steam calliope ...

... Bob (Grateful Diver)