If going from Steel tanks to Al, how much weight do I need to add?

[Ze_Abron]

Going diving in Monterey soon, the last time we dove LP steel tanks, I had 28 pounds of weight and the wife had 12.

This time we are renting from a different LDS, and we will be furnished with AL80's. How much extra weight will we need?

Thx!

 

[noreastDIVER84]

28 pounds?? with a steel?? was that with a drysuit. I think that is a bit much. I needed 34 pounds with a drysuit and an AL80. I only needed 14 with a 3 mil full suit and an AL80.

I am not sure of my weights now since I now have lp 112's and a new BC. I will determine that tomorrow afternoon in the pool.

 

[Ze_Abron]

Not a drysuit, but lots of very thick neoprene! A 7mm dry suit on top of a 3mm core warmer, with boots and gloves to match. Maybe it is a bit much...

With a 3mm I only need 8 to 10 pounds. My wife needs nothing.

 

[redacted]

Lot of variance in steel tanks. An Al80 is 4 to 4.4 lb of + buoyancy when empty. Find the buoyancy of your empty steel tank in this list and add the difference between it and the Al80 in lead.

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan

 

[noreastDIVER84]

Not a drysuit, but lots of very thick neoprene! A 7mm dry suit on top of a 3mm core warmer, with boots and gloves to match. Maybe it is a bit much...

With a 3mm I only need 8 to 10 pounds. My wife needs nothing.

Ok well the layers of neoprene would do it, I would venture to guess between 4 and 6 pound more than you were wearing.

 

[Bubbletrubble]

Listen to awap. He knows what he's talking about. There are lots of different steel tanks out there -- various sizes with various buoyancy characteristics.

And remember...there's no substitute for doing a proper weight check. Good luck.

 

[noreastDIVER84]

I second bubbletrouble on that, there is no substitute for a weight check. That is why I am getting into the pool at my LDS tomorrow.

 

[adm3745]

What awap said is exactly what you have to do

 

[wmspdi]

If doing a buoyancy check with a FULL aluminum tank just add six pounds AFTER you find your neutral weight (for the air in your tank that you will consume). You'll be about one pound negative, with 500 psi left in your tank, at the end of the dive. If you do something stupid, like breath your tank all the way down, and have to share air with your buddy, you will be neutral for your safety stop. Remember your weight will be different in salt water vs fresh water.

 

[redacted]

One problem with a buoyancy check at the beginning of a dive is, if you wear a bunch of neoprene or other gas trapping kit, it will often trap air and appear to be more buoyant than it really is. That could leave you a bit overweighted which is much better than being underweighted. So if you have do the check at the beginning of the dive, repeat it at the end when you will get more accurate results and then adjust for remaining gas in your tank. That should be about 1 lb per 13 to 14 Cu Ft. And then record it for future use. Then adjusting for a different tank is easy just knowing the tank specs.