Weighting for descent vs bottom

[Freewillow]

You guys are amazing and wrong at the same time.

You should carry weight in order to be neutral at the end of a dive - safety stop- with an almost empty tank with your lungs 2/3 full. What you guys seem to forget is that you should be negatively buoyant if you empty your lungs. 2/3 full lungs gives you a huge margin in order to avoid un uncontrolled ascent from 10 feet. Think about it

 

[Storker]

also dive steel tanks to the weight swing to positive is less with an empty tank.

Huh?

I was meaning the swing into the positive side of neutral. An Al 80 is way positive and steels are closer to neutral @ the same psi. The way steels float may help.

Still not with you. Care to elaborate?

 

[Killerflyingbugs]

When an AL 80 is empty its about 4 lbs + while a Steel 131 is about neutral empty a steel hp 120 are about 1 lb+ empty(500 ish psi) Steel tanks also have better trim, they float more horizontal (valve side still heavy, just less so), Al 80s the valve weight is more apparent and they like to sit more valve side down. I personally find it harder to trim with a AL 80 because of the way they float empty. I hope I am making sense.

 

[RainPilot]

Steel and Ali tanks will definitely trim differently but the buoyancy swing will be the same as it is only dependent on the weight of the gas you use up. I like steel tanks as it's a bit less weight for the rig dry which my knees and back thank me for but otherwise no difference when it comes to weighting process.

 

[archer1960]

When an AL 80 is empty its about 4 lbs + while a Steel 131 is about neutral empty a steel hp 120 are about 1 lb+ empty(500 ish psi) Steel tanks also have better trim, they float more horizontal (valve side still heavy, just less so), Al 80s the valve weight is more apparent and they like to sit more valve side down. I personally find it harder to trim with a AL 80 because of the way they float empty. I hope I am making sense.

So attach a 4 lb weight to your Al tank, and it will act like a steel one. The shop owner where I usually go is pretty good, but this (the real differences between AL and Steel) is something he just doesn't "get". When I went from an Al 80 to an HP 117, I just looked at the data sheets and found that the steel was 4 lb more negative than the Al when empty, so I dropped 4lb of lead and my weight was perfect. I did have to redistribute it to fix trim issues, but the total amount was just right.

 

[Killerflyingbugs]

I get it man, that's why I dive them.