Alternate lift device

TobyFish · March 20th, 2007, 11:36 PM

All,

Well, my car just blew up, so my DIR kit and training are gonna have to wait a bit longer. But I'm still interested in all aspects of procedures and techniques.

I've been thinking about redundant buoyancy. I understand why DIR doesn't advocate dual bladder wings. And I understand how the drysuit is the first-line redundant buoyancy in the event of a wing-failure. But people talk about carrying a lift-bag as a redundant lift-device. I assume this is even more important on a wetsuit dive.

So I'm curious how you use the lift-bag as buoyancy in the event of all other buoyancy failing.

Do you hold on to it and fill it enough to establish neutral buoyancy then "fly" it to the surface, dumping air from it to stay neutral?

Or do you send it to the surface and winch yourself up to it using your reel?

Or what?

Every day's a school day

Toby

*David Martin* · March 21st, 2007, 01:31 AM

Caveat - I don't know what the official line is, nor have I ever needed to do it for real...

I would go for the second option (but replace "reel" with "spool", since that's what we carry). Deploying the DSMB/lift-bag and holding the line is a variation from a standard skill (deploying the DSMB); trying to ride a part-inflated DSMB/liftbag is a very different and rather more complicated skill.

Trying to hold onto a moderately buoyant DSMB/lift bag and dump from it would be extremely difficult. Controlling a lift bag when attached to something other than you ascending/descending is relatively involved, but has the advantage that you can chose your height relative to it, to be near the dump valve. (Hence why when using a lift bag, to retrieve something (eg the shot) the usual option is to fill it until bag+load is just positive, ensure everything is out the way and then let go.) If the lift bag is pulling you up, the dump would probably be a significantly above from you. Using a DSMB is even worse, as the dump is at the bottom, with the gas at the top - a recipe for gas to be undumpable. If you couldn't control the bag, you'd be left with the options of letting go and sinking, or holding on and ascending uncontrolled to the surface.

Consider deploying the DSMB/lift-bag. Assuming that the bag is fully, or semi-closed, it will stay inflated on the surface, provided that you inflated the bag sufficiently (ie you+bag were neutral before you launched it) the bag on the surface will have more than enough buoyancy - but importantly, not too much. By varying how hard you pull on the line, you can offset the correct amount of lost buoyancy. Obviously you need sufficient line to go from your current depth, rather than the depth at which you'd normally deploy.

If using a balanced rig, the amount that you're negative with any kit failure should be a relatively small amount and you should be able to reel the spool in without any major issues. Also, it's a rare failure that will completely remove the lift capacity of your wing/drysuit, by altering your trim (to put any hole slightly downwards) you should be able to retain a significant amount of the original lift. This is one of the reasons in favour of non-bungeed wings.

David

lizardland · March 21st, 2007, 02:38 AM

Assuming you are diving from a boat.

There is a simpler option if you are shore-based (for example cave diving), swim along the bottom back to land. A very disgruntled Stoney Cove employee wasn't overly impressed by that answer when the CDG were having a meet there and none of us had any BCD's. But if you can get back to land then walk out. It's safer than trying to wind your way up a reel and hang on to a lift bag. If you're worried about destroying the vis the you can hand walk out.

Kirkandtiger · March 21st, 2007, 03:16 AM

Quote: (Originally Posted by lizardland)

and none of us had any BCD's.

That's pretty old school. Over here in the States, most tech divers now wear a BCD. - Kirk

GLOC · March 21st, 2007, 09:31 AM

Quote: (Originally Posted by Kirkandtiger)

That's pretty old school. Over here in the States, most tech divers now wear a BCD. - Kirk

The CDG is a cave diving group and many of them don't wear BCDs. When you see the restrictions these guys go through, you will understand why. Think of caving with quite a lot of wet bits which need scuba gear to traverse

You don't get nice large clear Floridian or Mexican caves in the UK unfortunately.

MonkSeal · March 21st, 2007, 09:54 AM

Oh, don't we use balanced rig?

GLOC · March 21st, 2007, 11:00 AM

Quote: (Originally Posted by MonkSeal)

Oh, don't we use balanced rig?

I think the OP was refering to diving with a wetsuit as when you dive with a drysuit this provides your redundant bouyancy.

Andy C · March 21st, 2007, 11:30 AM

Quote: (Originally Posted by GLOC)

I think the OP was refering to diving with a wetsuit as when you dive with a drysuit this provides your redundant bouyancy.

Isn't the point of a balanced rig the fact that you can swim it up even if you've lost your wing, therefore not actually requiring redundant bouyancy?

Andy

GLOC · March 21st, 2007, 11:49 AM

Quote: (Originally Posted by Andy C)

Isn't the point of a balanced rig the fact that you can swim it up even if you've lost your wing, therefore not actually requiring redundant bouyancy?

Andy

But if you are in a wetsuit and your wing fails at the start of a dive you WILL sink not matter how balanced your rig is and will require quite a bit of ditching kit to take place to maintain bouyancy - hence the comment about using a redundant bouyancy system if you are diving a wetsuit.

However, I am sure there are at least a couple of threads here talking about balanced rigs...

Michael-Fisch · March 21st, 2007, 11:49 AM

Quote: (Originally Posted by Andy C)

Isn't the point of a balanced rig the fact that you can swim it up even if you've lost your wing, therefore not actually requiring redundant bouyancy?

Andy

Andy, a set of D20s at 250 Bar has 12.5Kg of gas in it (assuming Nitrox). You can balance a rig for a certain point of your gas consumption, but you cannot have a balanced rig for the whole dive. If you are carrying stages the weight change will also increase. For monster dives you end up using a bigger wing due to your current wing being too small to compensate the weight shift of all the gas you are carrying.

Michael

March 20th, 2007, 11:36 PM	#1 (permalink)
TobyFish(Offline) Fine Upstanding Member Join Date: May 2006 Location: Telford, UK Posts: 795	Alternate lift device All, Well, my car just blew up, so my DIR kit and training are gonna have to wait a bit longer. But I'm still interested in all aspects of procedures and techniques. I've been thinking about redundant buoyancy. I understand why DIR doesn't advocate dual bladder wings. And I understand how the drysuit is the first-line redundant buoyancy in the event of a wing-failure. But people talk about carrying a lift-bag as a redundant lift-device. I assume this is even more important on a wetsuit dive. So I'm curious how you use the lift-bag as buoyancy in the event of all other buoyancy failing. Do you hold on to it and fill it enough to establish neutral buoyancy then "fly" it to the surface, dumping air from it to stay neutral? Or do you send it to the surface and winch yourself up to it using your reel? Or what? Every day's a school day Toby __________________ Rude-boy Volvo "Gangsta Rollin' in me nine-six-oh"

March 21st, 2007, 01:31 AM	#2 (permalink)
David Martin(Offline) Instructor candidate Join Date: Jan 2006 Location: London, E11 Posts: 419	Caveat - I don't know what the official line is, nor have I ever needed to do it for real... I would go for the second option (but replace "reel" with "spool", since that's what we carry). Deploying the DSMB/lift-bag and holding the line is a variation from a standard skill (deploying the DSMB); trying to ride a part-inflated DSMB/liftbag is a very different and rather more complicated skill. Trying to hold onto a moderately buoyant DSMB/lift bag and dump from it would be extremely difficult. Controlling a lift bag when attached to something other than you ascending/descending is relatively involved, but has the advantage that you can chose your height relative to it, to be near the dump valve. (Hence why when using a lift bag, to retrieve something (eg the shot) the usual option is to fill it until bag+load is just positive, ensure everything is out the way and then let go.) If the lift bag is pulling you up, the dump would probably be a significantly above from you. Using a DSMB is even worse, as the dump is at the bottom, with the gas at the top - a recipe for gas to be undumpable. If you couldn't control the bag, you'd be left with the options of letting go and sinking, or holding on and ascending uncontrolled to the surface. Consider deploying the DSMB/lift-bag. Assuming that the bag is fully, or semi-closed, it will stay inflated on the surface, provided that you inflated the bag sufficiently (ie you+bag were neutral before you launched it) the bag on the surface will have more than enough buoyancy - but importantly, not too much. By varying how hard you pull on the line, you can offset the correct amount of lost buoyancy. Obviously you need sufficient line to go from your current depth, rather than the depth at which you'd normally deploy. If using a balanced rig, the amount that you're negative with any kit failure should be a relatively small amount and you should be able to reel the spool in without any major issues. Also, it's a rare failure that will completely remove the lift capacity of your wing/drysuit, by altering your trim (to put any hole slightly downwards) you should be able to retain a significant amount of the original lift. This is one of the reasons in favour of non-bungeed wings. David Last edited by David Martin; March 21st, 2007 at 01:38 AM.

March 21st, 2007, 02:38 AM	#3 (permalink)
lizardland(Offline) LCS Join Date: Nov 2005 Location: Evidently Chickentown Posts: 593	Assuming you are diving from a boat. There is a simpler option if you are shore-based (for example cave diving), swim along the bottom back to land. A very disgruntled Stoney Cove employee wasn't overly impressed by that answer when the CDG were having a meet there and none of us had any BCD's. But if you can get back to land then walk out. It's safer than trying to wind your way up a reel and hang on to a lift bag. If you're worried about destroying the vis the you can hand walk out. __________________ Can you imagine drifting along in the sea with your mouth open and a load of f***ing plankton going in? You'd like it, would you? www.westons-cider.co.uk The Lot isn't the only place to dive: http://www.lulu.com/content/613554

March 21st, 2007, 09:31 AM	#5 (permalink)
GLOC (Online) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,963	Quote: (Originally Posted by Kirkandtiger) That's pretty old school. Over here in the States, most tech divers now wear a BCD. - Kirk The CDG is a cave diving group and many of them don't wear BCDs. When you see the restrictions these guys go through, you will understand why. Think of caving with quite a lot of wet bits which need scuba gear to traverse You don't get nice large clear Floridian or Mexican caves in the UK unfortunately. __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

March 21st, 2007, 11:00 AM	#7 (permalink)
GLOC (Online) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,963	Quote: (Originally Posted by MonkSeal) Oh, don't we use balanced rig? I think the OP was refering to diving with a wetsuit as when you dive with a drysuit this provides your redundant bouyancy. __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

March 21st, 2007, 03:16 AM	#4 (permalink)
Kirkandtiger(Offline) New Member Join Date: Mar 2006 Location: Minneapolis Posts: 7	Quote: (Originally Posted by lizardland) and none of us had any BCD's. That's pretty old school. Over here in the States, most tech divers now wear a BCD. - Kirk

March 21st, 2007, 09:54 AM	#6 (permalink)
MonkSeal (Online) Old Member Join Date: Feb 2006 Location: Zagreb, Croatia Posts: 475	Oh, don't we use balanced rig?

March 21st, 2007, 11:30 AM	#8 (permalink)
Andy C(Offline) New Member Join Date: Nov 2005 Location: Harby, Leicestershire, working in Leeds Posts: 142	Quote: (Originally Posted by GLOC) I think the OP was refering to diving with a wetsuit as when you dive with a drysuit this provides your redundant bouyancy. Isn't the point of a balanced rig the fact that you can swim it up even if you've lost your wing, therefore not actually requiring redundant bouyancy? Andy __________________ "When the Government fears the people, there is liberty. When the people fear the Government, there is tyranny" - Thomas Jefferson

March 21st, 2007, 11:49 AM	#9 (permalink)
GLOC (Online) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,963	Quote: (Originally Posted by Andy C) Isn't the point of a balanced rig the fact that you can swim it up even if you've lost your wing, therefore not actually requiring redundant bouyancy? Andy But if you are in a wetsuit and your wing fails at the start of a dive you WILL sink not matter how balanced your rig is and will require quite a bit of ditching kit to take place to maintain bouyancy - hence the comment about using a redundant bouyancy system if you are diving a wetsuit. However, I am sure there are at least a couple of threads here talking about balanced rigs... __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

March 21st, 2007, 11:49 AM	#10 (permalink)
Michael-Fisch (Online) New Member Join Date: Jul 2006 Location: Germany Posts: 264	Quote: (Originally Posted by Andy C) Isn't the point of a balanced rig the fact that you can swim it up even if you've lost your wing, therefore not actually requiring redundant bouyancy? Andy Andy, a set of D20s at 250 Bar has 12.5Kg of gas in it (assuming Nitrox). You can balance a rig for a certain point of your gas consumption, but you cannot have a balanced rig for the whole dive. If you are carrying stages the weight change will also increase. For monster dives you end up using a bigger wing due to your current wing being too small to compensate the weight shift of all the gas you are carrying. Michael