Lifting a Shot Line [Archive] - BSAC Scuba Diving Forums

Drydiver

06-03-2006, 15:40

I was teaching a Sports Diver the lesson DO4 Shot Recovery by Simple Lift at Stoney Cove on Sunday.

After successfully demonstrating how to attach the Lift Bag and to inflate using the Octopus so that the shot could be repositioned I emptied the bag and allowed the student to practice the skill. The student attached the Bag and began to fill it using her Octopus. At this point the regulator began to freeflow due to freezing in the cold water. As it would only have got worse the student took my Octopus and we made a safe AAS Accent.

The questions are as follows.
Should I have used a Blow Gun to inflate the Lifting Bag?
If so what should I attach it to? I don't have any spare LP ports on the 1st Stage for another hose so would I detach my BCD or Drysuit for the inflation. Also even if I did fit another hose using an LP T joint how would the student fill the bag?

Just looking for other peoples views on this and how they would have run the lesson.

James

MattDuke

06-03-2006, 16:02

Sean Gribben

06-03-2006, 16:02

Use a pony cylinder with separate DV and blowgun on it.
You can detach and have it lying on the deck next to the object that needs to be lifted.
Both you and student can easily use the same device.

Sean

Andy Nye

06-03-2006, 16:39

I use a detatchable blow gun, which i can use from either the direct feed to wing or dry suit hose.

padi paddy

06-03-2006, 17:06

I use a detatchable blow gun, which i can use from either the direct feed to wing or dry suit hose.

I agree with that a blow gun is a couple of quid and saves a lot of bother !

:)

Paul Morris

06-03-2006, 18:08

I agree with that a blow gun is a couple of quid and saves a lot of bother !

Couple of quid? Please tell us where? The cheapest I've seen them is £10-15 :(

Gareth

06-03-2006, 18:30

I have to say. You gave an excellent demonstration of the hazards of cold water diving!

Nicely emphasising the:
wisdom of an independant air supply.
wisdom of a dedicated air supply for the lifting of objects.
risks of freeflows with high flow rates on regulators in cold water.
wisdom of 'cold water' rated regulators.

The potential problem with an air gun is that you still have a high flow rate through the first stage (& the air gun) - thus still a risk of the first stage (or air gun) icing in cold waters!
At least with a dedicated air supply you can shut it off at the pillar valve.

In cold conditions I would follow Matt's suggestion of small purges (Octopus or air gun), with a good dwell between them!

Safe Diving

Gareth

Drydiver

07-03-2006, 11:38

Thanks for the advise.

In hindsight a pony dedicated for the lift is fairly obvious.

Still wouldn't want to disconnect a hose from my bouyancy device to attach the blow gun to.

John Williams

11-03-2006, 16:17

Thanks for the advise.

In hindsight a pony dedicated for the lift is fairly obvious.

Still wouldn't want to disconnect a hose from my bouyancy device to attach the blow gun to.

I agree that an downstream gun is the best option...if it fails - it fails shut and does not lose you all your precious air!

but ....here's a thought (just to play devil's advocate)

What's a pony for?
Is it an emergency bale out? - a source of something to breathe when all else fails? Something to get you back to the surface before you drown when your primary fails?

So the air in there is the most precious air you hope never to use?

But what if you've already used it to do lifting exercises?
What if you've put your pony down (to make it accessible to both your trainee and yourself during the lifting exercise) and they run out of air and bolt for the surface?
Now your (depleted) alternative air source is on the bottom and not where you need it!

Of course if it is a spare pony - taken down just for the exercise then there's no problem!

Or did you grab it and tuck it under your arm whilst you try to wrestle with your bolting trainee?

Or do we need to carry pony AND octopus (AND stage cylinders)
...though you probably should not be teaching lifts on a dive involving staged deco!)

next Q:

Should a pony have a "line-of-sight" pressure guage?
If you are going to use the contents for other stuff then you surely need to decide at what point it is depleted sufficiently to not count at an AAS? Where would that be? 150bar? 100bar? 50 bar?
If you keep the pony for emergencies only (and not for lifting exercises etc) then one of those button guages (just to check it is full before the dive) would be sufficient...you don't need to check it again during the dive if you have not used any air from it!

I thought we advocated KISS...how does KISS work with
1) two pressure guages in sight (that could get confused - remember to make then VERY different in appearance...colour is no good at depth/in the dark!)
2) Mouthpeices for
a) You
b) Octo
c) Pony
d) stage (s)
(that could also get confused - remember to make then VERY different in appearance/feel...colour is no good at depth/in the dark!)

Now...I like shiny diving stuff as much as the next guy...but what I don't want is a decision to take about which to use in an emergency...I want it to be bloody obvious...and I want the bloody obvious choice to be the FULL one!

as the advert for AOL says:

/discuss....
(says he as he lights the blue touch paper and stands well back!:D )

John

Garry Whyke

11-03-2006, 18:41

Interesting one.

Must admit, whenever I've been diving with a view to potentially lifting an object I always set up a gun in my config. Although we do teach the use of AAS with lifting bags I find them too severe a discharge, and in cold water (even with small bursts) they appear more prone to free flowing than a gun (I presume this is due to the rate of discharge of an AAS compared to a gun). In such cases (at least over the last 4 - 5 years) my set up has always been twin sets.

BUT: Even then in my pre-dive plan I calc the amount of air to lift an object at the given depth (takes a few seconds), so I know the implications on my air source.

For the very reason John highlighted, if you are diving with a single cylinder again understanding the impact on your air source needs to be determined and built into the air calc plan. Using a Pony is fine BUT would there be enough left to get you to the surface. Take into account that a 3ltr could only just get you to the surface from 30 mtrs IF you are only talking a couple of minutes of deco (and assuming a higher breathing rate), any more you're risking it.

So, here's a twist. When I dived on a single and 3ltr pony quite a few years ago I would feed the dry suite or BC from the main cylinder, and the other from the pony. This opens up a port on the main cylinder where I would connect a hose for the gun ( I have thought of using the dry suit hose if / when I needed a gun, but havn't decided to go down that route), I do like the seperate hose, and just clip it out of the way.

Yes this does mean that the pony is now being used for buoyancy, so an understanding of consumption does need to be understood. BUT, you do have buoyancy from a seperate source now.

As the gun would be on the main cylinder, again its implication would need to be understood, but it would have a reduced impact in relation to the percentage of pressure drop in the cylinder.

Nevertheless, with all of this, the max depth I would consider using a main cylinder and pony (3 ltr) would be approx 25-30 mtrs. Lots of variations such as consumption, available bail out etc could also impact this view. You just need to appreciate that there is an impact on available gas and this may limit the depth you can safely go to. Personally I would prefer to be back on a twin set.

My view anyway.

Cheers

............ Garry

Neil R

11-03-2006, 20:16

Couple of quid? Please tell us where? The cheapest I've seen them is £10-15 :(

Hi paul ,
if you have a local decathlon store there blow guns are about £5 , but most of there dive kit is reasonably priced :)
They also have have a free notice board where you can advertise your club .;)

Janos

11-03-2006, 21:34

I thought we advocated KISS...

I certainly do!

Janos

John Williams

12-03-2006, 11:20

I always set up a gun in my config. Although we do teach the use of AAS with lifting bags I find them too severe a discharge, and in cold water (even with small bursts) they appear more prone to free flowing than a gun (I presume this is due to the rate of discharge of an AAS compared to a gun)

The things you breathe off are downstream valves...they are designed to fail open (so that you can still breathe from them as they freeflow)

Guns are upstream valves ...designed to fail shut (so that they don't lose all the air you need to breathe)

In a nutshell downstream valves push the valve open in the direction of air flow (downstream) ...so if they get stuck (e.g. with ice preventing the valve shutting) they stick open.

Upstream valves are opened by forcing the working parts against the flow (upstream) - so if the flow gets excessive there is more pressure to shut the thing and protect your air supply.

This is why guns are far less prone to free-flow.

Think like a bulkhead door...on a sinking ship - they slam shut if they are opened against water flow (and cannot be opened again because of water pressure). That's because you cannot force the door UPSTREAM ...against the flow.
This is why an air gun fails shut!

However - in the films the star always wants to come through the door in the same direction as the water (downstream) and then shut it behind them ...cutting off the flow (very difficult! ...except against a trickle). This door then needs locking and securing if the catch is not to be blown off by the increasing pressure behind it.

Your D-V has no locking/securing mechanism ...so it automatically fails open!

HTH

John

Gareth

12-03-2006, 12:16

John

The risk with a gun, is if the failure occurs in the first stage the Intermediate pressure will rise to the cylinder pressure, At somepoint something will let go!
If a second stage is connected to the system the failure point should be the second stage.
If there is no second stage, but an inflator is connected, it will let go at the inflator - not good.
The alternative is to fit an overpresure valve designed to let go at 15bar (approx).

The above configuration would be very unusual. (Gun Only.) But we do need to be aware of the risks with Upstream valves.
(Posieden get round this by building an overpressure valve into the hose connection on the Jetstreams & Xstreams).
It is also true that most failures START at the 2nd stage, they may later progress to the first stage!

I suggested a seperate cylinder specifically for the lifting. I agree this is outside the 'meaning' of lift & move a shot.
It is good practice if we are looking at lifting, i.e. A seperate air supply that is specifically for the lift, not part of the air calculation, or emergency air provision.

If we are talking about lifting & moving a shot during a dive, this may occur at two different times. The start of the dive (relocate the shot for the team, or remove the shot once the last pair is down), or, at the end of the dive (making the shot easy to remove from the wreck, i.e.only slightly negatively bouyant).
In both of these cases it is better to do this if you are carrying an independent bailout (twinset or pony).
At the start of the dive you should have more than enough air to bailout if you need to on the independent bailout. Potentially a shutdown would be sufficent to stop the freeflow, & the dive could continue, air permitting!
At the end of a dive you should still have more than sufficent air to make a controlled ascent including all the decompression on your bailout - if not someones air calculations & dive practice need looking at!
If you have had a problem, & get back to the shot with a compromised air supply, I suggest that lifting a shot is no longer a priority!

I do think the original question highlights some good points:-
cold water diving - independent bailout very advisable
'working' underwater (using air for a task) - independent bailout very advisable.
Relying on a single air source in adverse conditions, or, when that air source is also being used for other tasks underwater (liftbags) is not advisable!

It also points out that understanding the limitations of the equipment is advisable, high flow rates in cold water is not advisable. This includes purges & panicking divers!

Just my thoughts,

Gareth

John Williams

12-03-2006, 14:08

Just my thoughts,

Gareth

Good ones at that!

(as I said when I joined in...I was playing "devil's advocate" - just to get people thinking this sort of thought!)

Cheers

John

Ant Slegg

29-03-2006, 16:30

Firstly my apologies if this is stating the obvious...

If you are talking about lifting a shot weight rather than general lifting exercises bear in mind that all you are trying to do is offset some of the weight of the shot for the person who will be lifting it - i.e. you are not trying to lift the weight immediately just make it lighter but not so light that it drifts/drags in the current and gets lodged somewhere - into the wreck for example.

You also might want to ascend the shot and as the last pair might have to hold onto the shot during deco' as the current increases. If you've made the shot too light then you could drag the shot yourself. The better alternative is to inflate the shot weight lifting bag leaving the lot in-situ and then bag-off your D-SMB(s) well away from the shot and leave the recovery for when you are back in the boat.

With this in mind a small lifting bag and a few litres of air added in small bursts will be enough. Later, once the weight is clear of the bottom, (might require an initial strong heave from someone in the boat) the pressure drop/volume increase will do the heavy work for you.

Only if you initially put too much air in will you have a problem as the weight rockets to the surface dumps air and maybe sinks. If your technique ends up with a buddy pair sitting on the bottom watching the weight head to the surface then there'll be a minute or so of wondering if the thing is heading back in your direction and trying to figure out which is the best way to swim (generally into the current).

One final comment - the D-SMBs with small aluminium bottles (like the Buddy one) work very well in this application as long as you don't crack the bottle open for too long.

Ant S

MattS

30-03-2006, 10:49

Or do we need to carry pony AND octopus (AND stage cylinders)Kiss means many things to many people, as does redundancy.

Personally, to move a shot in cold water I would use exhaled breath to inflate a small bag.
+ you are not pressing purge buttons
+ you are not wasting gas
+ entrapment danger is minimal (the shot should be staying on the bottom)

There are a couple other options.
+ in shallow water you could drag it
+ leave it where it is, shot weights are disposable

Should a pony have a "line-of-sight" pressure guage?
If you are going to use the contents for other stuff then you surely need to decide at what point it is depleted sufficiently to not count at an AAS? AFAIC a pony is only sufficient to provide a redundant reserve for the main cylinder and should only be used for the critical functions you would use a main tank reserve for (escapeing, not inflating lift bags). If you are going to use a blowgun or purge button, connect it to the larger main supply. Swap to the pony before inflating the bag. If something does go wrong you are already on your alternate, your buddy is breathing their main, and you can get the heck out of Dodge, knowing you have enough gas in the pony because you worked out the ascent requirement beforehand.

Where would that be? 150bar? 100bar? 50 bar?You calculate the ascent requirement. You add a reserve. You take that away from the contents and the figure you get is the minimum acceptable pressure.

If you keep the pony for emergencies only (and not for lifting exercises etc) then one of those button guages (just to check it is full before the dive) would be sufficient.There is an argument along the lines that if you are going to fit a pressure guage, with it's assosciated failure points, make it a full size one. You then have a chance of spotting a leak. Personally I view SPG swivels as the Devil's work so would consider a button guage or no gauge at all.

I thought we advocated KISS...how does KISS work with
1) two pressure guages in sight (that could get confused - remember to make then VERY different in appearance...colour is no good at depth/in the dark!)KISS would lead to working out your gas requirement and not using a guage. At the time of escape either the cylinder contains enough gas or it doesn't - so no point having a guage. Personally I think you can afford to consider what the effect of not knowing contents might do to your breathing rate and compromise accordingly.

The flavour of KISS I subscribe to* demands that life critical equipment is always stowed in the same place regardless of the specific set you happen to be wearing. So I would stow the SPG from the pony in the same position I would stow a second SPG on indis (main left, second right). You can use colour to differentiate by choosing two contrasting colours (white and black).

2) Mouthpeices forYou only ever need two 2nd stages on the main set (single, pony, dual outlet, twins) and they are always stowed in the same place. Stage cyllinders containing deco mixes are locked out with an ORG** and the valve is turned off.

(that could also get confused - remember to make then VERY different in appearance/feel...colour is no good at depth/in the dark!)There are various ways to differentiate different systems. I tend to use left and right. My regs are Jetstreams, the 2nd stages can be swapped underwater fairly easily.

Now...I like shiny diving stuff as much as the next guy...but what I don't want is a decision to take about which to use in an emergency.The fact it's a pony makes no difference to my decision making. It's mounted the same place I would mount the 2nd cylinder of a twinset. The regs are stowed in the same place. The valve is left switched on the same. Its plumbed into a second buoyancy device the same - controversial perhaps but personally I don't want to be faffing with oral inflation when I could be ascending to a shallower depth where the limited reserve will last longer. The only decision I have to make is whether a 3Ltr pony is an adequate reserve for the dive in question and that's pretty similar to deciding between my 7s and 12s. Simple enough?

* It's important to have a cool acronym these days. Mine's, All the Right Stuff for the Environment. It's very flexible :)

** Oxygen Regulator Guard - a bit of bungee over the mouthpiece.
:D