Balanced Rig

**neilh** · January 20th, 2006, 03:26 PM

I get the idea of a balanced rig (I think I do anyway!) and I've been trying to get comfortable with how much weight should be removable[1] and how much you can therefore stick elsewhere.

Thinking it through the weight is there so that with say 30 bar of gas you can hold a stop at 3M with no air in the wing or suit, yes? The weight is therefore (simplistically) the difference between the negative bouyancy of your kit and the positive bouyancy of you under those conditions.

It seems to me that the only variable over the course of a dive is therefore the weight of gas you have[2]. At the start you'll be negatively bouyant because you have more than 30 bar (hopefully!).

If that's the case then in the worst case are we talking around 2-3Kg for a 12L of air/nitrox? If so that seems to be a realistic amount to be able to swim up, so removing weight would be unnecessary...

Am I thinking along the right lines here?!

[1] I know there will be some suggestions that if the rig is balanced this should be none

[2] Just thinking of fundies-level stuff here, no stages to complicate matters

JimC · January 20th, 2006, 03:49 PM

You are thinking correctly. I weight my self for 0 bar @ 0 meters because I want to have absolute control of my accent in the absolute worst case situation. For a single tank, min deco type dive this should leave you something like 2-4kg negative at the start of a dive. Something you can swim up. Which means you don't need any disable weight if your in a balanced rig.

Things get a bit more complicated when you have to think about wetsuit compression. This changes things considerably because you could easily be 10kg negative at depth. Not so easy to swim up.

vid · January 20th, 2006, 06:42 PM

Quote: (Originally Posted by neilh)

Thinking it through the weight is there so that with say 30 bar of gas you can hold a stop at 3M with no air in the wing or suit, yes?

agree in principal

but as said already, you should think of a total failure with just about 0 bar in the cylinder and potentially holding a stop at 1M (literally below the surface) - given that you want to be able to control your ascent from your last stop all of the way to the surface

Quote: (Originally Posted by neilh)

The weight is therefore (simplistically) the difference between the negative bouyancy of your kit and the positive bouyancy of you under those conditions
it seems to me that the only variable over the course of a dive is therefore the weight of gas you have[2]. At the start you'll be negatively bouyant because you have more than 30 bar (hopefully!).
.

yep

Quote: (Originally Posted by neilh)

If that's the case then in the worst case are we talking around 2-3Kg for a 12L of air/nitrox? If so that seems to be a realistic amount to be able to swim up, so removing weight would be unnecessary...

Almost, but you need to factor in (1) the change in buoyancy of your kit (eg dry suit and undergarments) with depth and (2) salinity of water, which will affect the buoyancy overall

vid

lamont · January 21st, 2006, 12:39 AM

The way that I approached this after fundies was:

1. get good at getting all the air out of your wing
2. get good at getting all the air out of your drysuit
3. get good at floating neutral and trimmed without kicking

Then, take weight off successively (2lbs / 1kg at a time or so) until you hit the point where at 10 fsw (3msw) and 500 psi (whatever bar that is) and you doing all the shaking and dancing necessary to squeeze all the air out, you're still uncomfortably breathing out of the bottom of your lungs to try to hold the stop. Then add a little bit back so its comfortable. At this point you're comfortable in the normal case, and with 0 psi you should be able to hold the stop with lower tidal volume if you have to.

Chances are good that you're not as good as you could be at getting air out of your wing and drysuit, so you'll be a little overweighted and as you get better at it you'll be able to remove more weight.

**neilh** · January 21st, 2006, 01:01 AM

All good comments folks, thanks!

Quote: (Originally Posted by vid)

Almost, but you need to factor in (1) the change in buoyancy of your kit (eg dry suit and undergarments) with depth

Ok, but if it's a membrane suit and thinsulate type of undergarment wouldn't there be no real change in bouyancy?

Quote: (Originally Posted by vid)

(2) salinity of water, which will affect the buoyancy overall

Fair point - but presumably this would be constant and therefore you could just add/remove additional fixed weight for salt/fresh water?

Some playing around called for this weekend I think

jluttichau · January 21st, 2006, 03:25 PM

Quote: (Originally Posted by neilh)

If that's the case then in the worst case are we talking around 2-3Kg for a 12L of air/nitrox? If so that seems to be a realistic amount to be able to swim up, so removing weight would be unnecessary...

You don't wan't to be in a situation where you depend on the option of swimming up, you wan't a balanced rig which means that you'll be able to do all you (minimum)deco. So you'll have to be able to remove some weight.

Cheers
Jonas

January 20th, 2006, 03:26 PM	#1 (permalink)
neilh(Offline) Haemoglobin on the bus... Join Date: Nov 2005 Location: Barnsley, UK Posts: 1,900	Balanced Rig I get the idea of a balanced rig (I think I do anyway!) and I've been trying to get comfortable with how much weight should be removable[1] and how much you can therefore stick elsewhere. Thinking it through the weight is there so that with say 30 bar of gas you can hold a stop at 3M with no air in the wing or suit, yes? The weight is therefore (simplistically) the difference between the negative bouyancy of your kit and the positive bouyancy of you under those conditions. It seems to me that the only variable over the course of a dive is therefore the weight of gas you have[2]. At the start you'll be negatively bouyant because you have more than 30 bar (hopefully!). If that's the case then in the worst case are we talking around 2-3Kg for a 12L of air/nitrox? If so that seems to be a realistic amount to be able to swim up, so removing weight would be unnecessary... Am I thinking along the right lines here?! [1] I know there will be some suggestions that if the rig is balanced this should be none [2] Just thinking of fundies-level stuff here, no stages to complicate matters

January 20th, 2006, 03:49 PM	#2 (permalink)
JimC(Offline) New Member Join Date: Nov 2005 Location: Ottawa Posts: 18	You are thinking correctly. I weight my self for 0 bar @ 0 meters because I want to have absolute control of my accent in the absolute worst case situation. For a single tank, min deco type dive this should leave you something like 2-4kg negative at the start of a dive. Something you can swim up. Which means you don't need any disable weight if your in a balanced rig. Things get a bit more complicated when you have to think about wetsuit compression. This changes things considerably because you could easily be 10kg negative at depth. Not so easy to swim up.

January 20th, 2006, 06:42 PM	#3 (permalink)
vid(Offline) New Member Join Date: Nov 2005 Location: london/surrey border, UK Posts: 353	Quote: (Originally Posted by neilh) Thinking it through the weight is there so that with say 30 bar of gas you can hold a stop at 3M with no air in the wing or suit, yes? agree in principal but as said already, you should think of a total failure with just about 0 bar in the cylinder and potentially holding a stop at 1M (literally below the surface) - given that you want to be able to control your ascent from your last stop all of the way to the surface Quote: (Originally Posted by neilh) The weight is therefore (simplistically) the difference between the negative bouyancy of your kit and the positive bouyancy of you under those conditions it seems to me that the only variable over the course of a dive is therefore the weight of gas you have[2]. At the start you'll be negatively bouyant because you have more than 30 bar (hopefully!). . yep Quote: (Originally Posted by neilh) If that's the case then in the worst case are we talking around 2-3Kg for a 12L of air/nitrox? If so that seems to be a realistic amount to be able to swim up, so removing weight would be unnecessary... Almost, but you need to factor in (1) the change in buoyancy of your kit (eg dry suit and undergarments) with depth and (2) salinity of water, which will affect the buoyancy overall vid

January 21st, 2006, 12:39 AM	#4 (permalink)
lamont(Offline) APLP Join Date: Nov 2005 Location: Seattle, WA Posts: 181	The way that I approached this after fundies was: 1. get good at getting all the air out of your wing 2. get good at getting all the air out of your drysuit 3. get good at floating neutral and trimmed without kicking Then, take weight off successively (2lbs / 1kg at a time or so) until you hit the point where at 10 fsw (3msw) and 500 psi (whatever bar that is) and you doing all the shaking and dancing necessary to squeeze all the air out, you're still uncomfortably breathing out of the bottom of your lungs to try to hold the stop. Then add a little bit back so its comfortable. At this point you're comfortable in the normal case, and with 0 psi you should be able to hold the stop with lower tidal volume if you have to. Chances are good that you're not as good as you could be at getting air out of your wing and drysuit, so you'll be a little overweighted and as you get better at it you'll be able to remove more weight.

January 21st, 2006, 01:01 AM	#5 (permalink)
neilh(Offline) Haemoglobin on the bus... Join Date: Nov 2005 Location: Barnsley, UK Posts: 1,900	All good comments folks, thanks! Quote: (Originally Posted by vid) Almost, but you need to factor in (1) the change in buoyancy of your kit (eg dry suit and undergarments) with depth Ok, but if it's a membrane suit and thinsulate type of undergarment wouldn't there be no real change in bouyancy? Quote: (Originally Posted by vid) (2) salinity of water, which will affect the buoyancy overall Fair point - but presumably this would be constant and therefore you could just add/remove additional fixed weight for salt/fresh water? Some playing around called for this weekend I think

January 21st, 2006, 03:25 PM	#6 (permalink)
jluttichau(Offline) Custom User Title Join Date: Nov 2005 Location: Denmark Posts: 437	Quote: (Originally Posted by neilh) If that's the case then in the worst case are we talking around 2-3Kg for a 12L of air/nitrox? If so that seems to be a realistic amount to be able to swim up, so removing weight would be unnecessary... You don't wan't to be in a situation where you depend on the option of swimming up, you wan't a balanced rig which means that you'll be able to do all you (minimum)deco. So you'll have to be able to remove some weight. Cheers Jonas