Weights adjustment when switching to an HP Steel Tank

[dhuskins]

What you weigh and what other gear you have on has little impact on the formula you are asking about. Assuming you are neutrally buoyant with a given set of gear using an AL80, then simply switching to a steel 100 changes your buoyancy by the amount of difference in tanks. Specifically, the difference in buoyancy weight when the tanks are emptied to the amount at the end of your dive.

One thing to keep in mind is weight distribution. A typical HP100 is a couple inches shorter than an AL80. It's not enough to worry about. When you take the weight off, remember to remove it proportionally to how you have it distributed. If two thirds of your weight is in your belt and one third is in your BC trim pockets, then start by taking one pound out of each trim pocket and two pounds out of each waist pocket (or four pounds off the belt).

Shorter steel tanks may require you to hop back into the pool to figure out how to redistribute your weight, but the formula for figuring out how much weight to remove is still the same.

 

[ScubaSteve]

When I switch from AL80 from my HP120's (steel of course) I lose 6 lbs and have a comfortable dive. As has been mentioned, that is a good place to start.

 

[ligersandtions]

Going from an Al80 to and HP100, you should be able to drop about 6 pounds. However, at 38 pounds, it does sound like you are probably overweighted. Your best bet would be to do a proper weight check with the new tank and make sure you need all that weight.

There are multiple way to do a weight check but I prefer to do it at the end of a dive, with less than 500psi in my tank (purge down if you don't breathe down that far during the dive), no air in my wing, and a comfortable amount in my suit to keep me from feeling the squeeze or getting cold. I do this at 10 feet (some prefer to do it at the surface, but I figure 10 feet is my shallowest stop and I can dump air from my drysuit if I need to be neutral shallower and I actually am down near empty on my tank).

Please make sure you need all the weight you are diving with. There's no reason to go with the weight you had on your belt during your certification class if it's significantly more than you need (it's very common to come out of OW grossly overweighted).

 

[ligersandtions]

When I switch from AL80 from my HP120's (steel of course) I add 6 lbs and have a comfortable dive. As has been mentioned, that is a good place to start.

Are you sure? Maybe you meant you remove 6 pounds going from Al80 to HP120....

 

[ScubaSteve]

Are you sure? Maybe you meant you remove 6 pounds going from Al80 to HP120....

Oops...sorry YES....I was thinking I was writing going from steel to AL but wrote reverse.

 

[ligersandtions]

Oops...sorry YES....I was thinking I was writing going from steel to AL but wrote reverse.

Just wanted to make sure! Don't want to confuse any new divers

 

[Jupiter31]

Depends on exactly which AL80 tank you're talking about, but the "lead" difference will be closer to 5lbs. For instance a Catalina 80 is +2.8lbs buoyant empty, so that's a net difference of 5.3lbs vs the HP100 you cite above.

Assuming your weighting is correct with the AL80, all you need to do is subtract the "empty buoyancy" of the AL80 from the "empty buoyancy" of the Steel to tell you how much you can drop (-2.5lbs minus 2.8lbs = -5.3lbs)

Very good explanation and I agree 100%

I switched from AL to Steel a few years ago and would never go back - but weighting/trim/boyancy is not an exact science - at least not for me - so plan on doing some experimentation.

It also gets a little trickier the more rubber you have on (and I'm not touching on dry suits - its a science on to itself) - so plan on doing some adding and subtracting, realizing weighting will be different for a 3mm vs a 7mm.

Steel is worth it - would never go back!

 

[diver 85]

Oops...sorry YES....I was thinking I was writing going from steel to AL but wrote reverse.

now you've done it---screwed up half the dive world's thinking...........lol

 

[ScubaSteve]

now you've done it---screwed up half the dive world's thinking...........lol

I've become that which I hate.....ooooohhhhh the self loathing

 

[Capt.JimDavis]

Thank God, I don't wear a belt... I dive with a Zeagle Ranger BC. So the weights are integrated.
No more that evil belt...