Fast descents vs correct weighting

[lizardland]

I have noticed that an Al 80 with 20/35 is just slightly negative when full. As I am too cheap to blow it off, I can only wonder just how floaty that would be when nearly done. Never mind Al 80's with 10/50 or some such mix.

They float arse up. Stick them on a leash and send them up the shot. Or stick a bag on them and send them up, with a bit of luck the skipper will think it's some spidge and lift it. I don't plan on carrying empty cylinders with me. The buoyancy change on one cylinder is easy enough to account for, two or three is a different story.

 

[Dave Sutton]

Stu, have you ever had one actually float as opposed to just wanting to lift the butt of the bottle, with a regulator and rigging attached? In fresh water they still sink slightly. Have not tested in salt. The reason is that I am wondering if US DOT spec bottles are slightly heavier than European spec ones.

Dave

 

[Clare]

Some DOT spec bottles are heavier. A lot aren't though.

In salt an empty Ali 80 with reg (mk25 or equiv) attached will rise up a line IF you give it a good shove to get it going. In fresh it may well hang around once it loses momentum.

Not arguing that the bottle is not marginally positive when empty. Leaving 15 to 20 bar in them is of course better for the gear.

However, without dick swinging I have genuinely have lost count of how many empty bottles I have lugged at one time (i do recall having at least three leashes each with three empties plus a couple of floaty scooters and feeling like the guy selling balloons at the fair) and not once have I found it to be an issue if the bottles are stored on leashes.

Mind you, I weight myself for empty cylinders and no stages. If I did weight checks with full gas load then of course everything empty would bring issues.

Edit. To clarify, I weight check by descending to 6 meters with extremely low levels of gas (20-30 bar) then get neutral and remove swueeze from suit. Then ascend to 3 meters fumping to get neutral again and check how much gas in wing. This translates to lead on a litre per kilo basis. This is, to me, more accurate than descending to check as you can't empty your suit as efficiently on ascent as you would descending.

 

[Bobjr]

Stu, have you ever had one actually float as opposed to just wanting to lift the butt of the bottle, with a regulator and rigging attached? In fresh water they still sink slightly. Have not tested in salt. The reason is that I am wondering if US DOT spec bottles are slightly heavier than European spec ones.

Dave

Oh yeah they float in seawater (US, Euro and Aussie spec 80s) when they're empty Even with DSTs and heavy brass gauges ...

 

[The Duck]

Stu, have you ever had one actually float as opposed to just wanting to lift the butt of the bottle, with a regulator and rigging attached? ...

Ali80 with <20bar in is definately positive in salt water (not from CCR experience I hasten to add but from use as a bottom stage on OC - have to hang onto the leash tightly on the bottle rotation or it will be off to the surface).

Also seen someone send one up the dSMB line (again in salt water) - they go up rather nicely.

 

[tufty]

if its all gone pants and your on a full oc bail out (ie the unit is stuffed and attempting to kill you) you can always partially or completely flood the unit to add weight if needed:shrug: