Adjusting weights for sling bottle?

[4sak3n]

Ideal? Only you can decide that for yourself. You need to sit down and run through the calculations to make an estimate of how much gas you would need in an emergency. Be certain to be conservative i.e. use an elevated SAC rate in the calculation, a low ascent rate, build in time at the bottom to solve problems etc etc

I did so and while a 19 cft might be suitable for me, it was definitely not ideal. So I went with a 40 cft cylinder (the place I bought it from didn't have an 30s).

Also bear in mind that your pony won't always be full. You lose 50 psi in a purge when setting it up here, you accidentally hit the purge button when lifting it up there and pretty soon you'll be down to 80% or 75% capacity. Unless you top off your pony every time you dive with it (which is a pain in the posterior) you will want to make sure you have some built in padding. So if on a bailout you need 19 cft of gas, better to have a 30 cft cylinder just in case because it is likely your 19cft bailout cylinder won't have 19 cft.

To give you an example, I recently used my pony on about 4 dives in about 2 weeks. At the end of the two weeks Seabiscuit (my pony) had gone from 200 bar (~ 2900 psi) to 160 bar (~2320 psi). I did breathe off her for a few breathes at the beginning of dives to check as well.

Anyway, what I am getting at is do the calculations for yourself keeping in mind that you need to be conservative and don't assume ideal conditions (i.e. 100% full bailout bottle).

I've also been told that 19s are harder to sling than 30s or 40s because of their length. No idea how true it is but it is another thing to keep in mind.

P.S. For what it is worth, I don't consider a 19cft bailout to be "ideal" by a long shot for my diving.

 

[String]

If its a sling bottle and you may remove it on a dive for ANY reason then you cannot change your weight requirements just in case. Even if you dont plan on removing it the change in lead required is so small for a tank that size it properly isnt worth bothering about.

If its properly slung you shouldn't need to alter the weight positioning either. Balance should be ok anyway.

Edit:- I'd also class 19 cubic foot as too small for a sensible bailout but its better than nothing PROVIDED you know its limitations and stay within those regarding depth and time.

 

[Diveral]

I need to get one of those 40's. I dive with a Faber Steel 50 slung on the left side and have to remove 3-4 lbs from the same side front weightpocket or I dive with a noticeable list.

AL

 

[String]

Surprising given people dive with 2 x 7l or even 1 x 12l steels side mount without altering weight balance at all.

 

[Web Monkey]

Also wondering how much the bottle will change my bouyancy if I add a 19cf bottle.
Will I be more bouyant or less?
Can I ditch some of the weight or will I have to add more?

19 Cubic Feet of air weighs approximately 1.5 pounds (0.0807 * 19), so you'll absolutely need to add 1.5 pounds to compensate for the weight of the air you'll use when you breathe off the tank. If you're already neutral and don't do this, you won't be able to control your ascent.

Now that that's out of the way, you probably won't actually have to change much. I generally need to add a 1 pound trim weight on the opposite side to offset the weight of the tank and valve, so the 1Lb weight and the pound or so from the valve and regulator seems to be about right.

Terry

 

[4sak3n]

Never mind lil ol me ...

 

[Web Monkey]

Surprising given people dive with 2 x 7l or even 1 x 12l steels side mount without altering weight balance at all.

Depends on the BC. With my wing, I can just shift a little air to the "heavy" side. With my SCUBAPro Classic+, I need to match the weight pretty much exactly or I tilt (can't trap any gas anywhere in the bladder).

Terry

 

[battles2a5]

19 Cubic Feet of air weighs approximately 1.5 pounds (0.0807 * 19), so you'll absolutely need to add 1.5 pounds to compensate for the weight of the air you'll use when you breathe off the tank. If you're already neutral and don't do this, you won't be able to control your ascent.

Not really. Yes, there is 1.5 pounds of air in the 19. But an AL19 is about .1 pounds bouyant in salt water when emtpy. Add a reg and the whole system is negative when empty. So you do not need to add 1.5 pounds of balast to your rig for a small bottle like this. This doesn't really become a consideration until you start talking about larger stages (80's, etc.).

 

[Web Monkey]

Not really. Yes, there is 1.5 pounds of air in the 19. But an AL19 is about .1 pounds bouyant in salt water when emtpy. Add a reg and the whole system is negative when empty. So you do not need to add 1.5 pounds of balast to your rig for a small bottle like this. This doesn't really become a consideration until you start talking about larger stages (80's, etc.).

There is 1.5 pounds difference between full and empty. This needs to be compensated for with extra weight. The weight may come from weights or equipment, depending on what you're diving with.

You also need to add a trim weight if the pony makes you tilt and you're using a BC that won't allow trapping air on one side.

Terry

 

[battles2a5]

There is 1.5 pounds difference between full and empty. This needs to be compensated for with extra weight. The weight may come from weights or equipment, depending on what you're diving with.

You also need to add a trim weight if the pony makes you tilt and you're using a BC that won't allow trapping air on one side.

Terry

If your backmount rig is weighted correctly you absolutely DO NOT have to add weight for a pony system that is negative when empty. The diver will just be 1.5lb's more negative full than it will be in empty. Let's work the math out.

Assumptions:
AL19 Pony Full = -2.5lb (1.5 lbs gas, -1 for bottle and reg)
AL19 Pony Empty = -1lb (gas is gone, still -1 for bottle and reg)
Diver w/ Properly weighted rig a/ AL80 @ 500psi: -1lb (for the sake of argument)

So:
Diver w/ Full Pony (-1 + -2.5) = -3.5lbs
Same diver w/ Empty Pony (-1 + -1) = -2lbs

You don't need to add weight for the pony.