Venus,
The measurement is 11" from the top knot/boltsnap to the knot/bottom of the SS clamp band around the bottle. Then the length of the loop of nylon cord hangs 2" below the band, so the total boltsnap-to-boltsnap measurements on my bottles is 13".
You can 'customize' your rig measurements, but you don't really want to - you may not be the diver using it. The gas you carry may be used by anyone on your team (you may need to hand off your bottle for some reason). So, the bottles should all be rigged the same way, so that any diver can use any bottle.
There is enough room on a Luxfer 19 to rig the sling harness, but if you use a 40" hose on your stage/deco regulator the hose (when banded to the bottle) will extend beyond the bottom of a Luxfer 19 bottle.
And the size of the bottle you need is not determined by how tall you are, nor your build (fat, skinny, whatever). You need to do the math.
Essentially, you need to identify what sort of dives you're doing, to what depths, and identify the situation where you think you'd need the bottle. (For example, "...OOA at 100 fsw, tangled up in fishnet".) Then you estimate your recovery time that you'd need to spend on the bailout bottle. (For example, "1 minute to figure out what the hell is going on. 3 minutes to cut my way out of the silly net. 1 minute to find the upline (or whatever). At an ascent rate of 30 feet per minute from 100', 3 minutes to my 10' safety stop. 3 minutes at 10' for a safety stop. 1 minute for a slow ascent to the surface from 10'. Total minutes on bail-out = 12 minutes.
Now you know how long you'll be on the bottle. Next you need to calculate how much gas you'll be sucking down while you're dealing with your issues at 100'. It doesn't really matter what your respiratory minute volume (RMV) is when you're cooing over cute fish, because when you're tangled in a net you will be considerably more anxious - hence you'll be breathing harder. Some folks use an estimate of double their normal gas consumption, or say ~1.3 cubic feet per minute. It's tough to tell, because most people get seriously escalated when they realize they're in deep crap, and their heartrate increases and their respiratory rate skyrockets. Many divers conclude its better to have a bit too much gas than a bit not enough...
So, with an estimated respiratory rate (RMV) of 1.3 cfpm, and a duration of 12 minutes, you'd be looking at a need for 15.6 cubic feet of gas (round up to 16). In which case a 19 would work, but a 13 or LP 14 would not.
Obviously, all these values are made up - your values may vary significantly. But the point is, you don't pick a tank because you are such and such a height or weight. You select the tank based on its volume relative to the volume of gas you've calculated to fit your need in what would constitute an emergency situation for you - e.g. based on the dives you're doing.
Best,
Doc
