switching from AL tank to Steel Tank

[Daniel Bonder]

Hello, I am a new diver and have recently switched to drysuit diving, and have a buoyancy / weighting question. I currently dive with 30# of weight, (10% of 220# body weight + 4# for salt water, + 4# for AL80 tank = 30# total weight) I have 5 dives with my gear at this weight and am now comfortable in my drysuit and would like to switch to an XS Steel 100cu ft tank. What weight adjustments should I make?

 

[redacted]

5 lb

 

[Rred]

Going from an Alu80 to a steel 100, typically you can lose maybe 6# of lead in salt water. What you really can do to pin that down, is look up the buoyancy of your empty Alu80 online. Then look up the buoyancy of your empty steel tank online. Tanks vary, depending on the maker, and some weights are "naked" while other include a pound or two for the valve, so check bare tank versus bare tank, empty buoyancy.
Odds are the Alu80 will be something like 3-4# positive buoyancy while the steel tank may be 3# negative buoyancy..making a difference of 6-7# of lead you can lose. Be conservative, figure a pound or two less than what you calculate, and take a couple of 1-2# weights for final adjustments before the dive. (Can be stashed in pockets or tied on, whatever.)

 

[Beau640]

In general, it's about 5#

Check out the tank you use here compared the the tank you are planning on getting:

http://www.indianvalleyscuba.com/se...ction/information/CYLINDER SPECIFICATIONS.pdf

It tends to be about a 5lb difference between them and you can actually take about 5lbs off your kit.

 

[pinshootr]

more like 10 its. as the steel does not get floaty at the end of the dive like Aluminums

 

[eelnoraa]

5-6lb is the right number. Of course, you want to do weight check to confirm.

 

[cool_hardware52]

Hello, I am a new diver and have recently switched to drysuit diving, and have a buoyancy / weighting question. I currently dive with 30# of weight, (10% of 220# body weight + 4# for salt water, + 4# for AL80 tank = 30# total weight) I have 5 dives with my gear at this weight and am now comfortable in my drysuit and would like to switch to an XS Steel 100cu ft tank. What weight adjustments should I make?

10% of your body weight is a "rule of thumb" used by shops or instructors. It could be right, but often results in over weighted divers.

My definition of minimum ballast is the grand total of things that don't float required to allow me to conduct a shallow deco (safety stop) with near empty tanks. More ballast than that and I'm working too hard.

Now the question about steel vs aluminum tanks. There are two considerations. The first is the difference in empty buoyancy. The typical al 80 will be + 4 lbs empty and -2 lbs full. (some slight differences depending on maker, Catalina vs Luxfer, but it's ~.4 lbs and I will ignore it for now)

The typical hp 100 qill be -2 lb empty and -10 lbs full.

From a pure ballast perspective the HP steel will provide 6 more lbs of ballast than the al 80, +4 vs -2. In other words switching from a al 80 to steel hp 100 is the same as adding 6 lbs to your belt.

The second consideration is the impact of having 100 cu ft of gas vs 77 cuft of gas. That's about 2 lbs more. (100 cu ft of air is about 7.8 lbs)

That's unlikely to exceed the lift capacity of what ever you are currently using for a BC, but verifying you can still float your rig with a full tank if you have to ditch it is always a good idea.

Tobin

 

[archer1960]

Going from an Alu80 to a steel 100, typically you can lose maybe 6# of lead in salt water. What you really can do to pin that down, is look up the buoyancy of your empty Alu80 online. Then look up the buoyancy of your empty steel tank online. Tanks vary, depending on the maker, and some weights are "naked" while other include a pound or two for the valve, so check bare tank versus bare tank, empty buoyancy.
Odds are the Alu80 will be something like 3-4# positive buoyancy while the steel tank may be 3# negative buoyancy..making a difference of 6-7# of lead you can lose. Be conservative, figure a pound or two less than what you calculate, and take a couple of 1-2# weights for final adjustments before the dive. (Can be stashed in pockets or tied on, whatever.)

This is exactly the method I used when I went to a HP117, and it was perfect without any other adjustments. Though it took me 2 dives to get the 117 down to 500 psi so I could actually check my end-of-dive buoyancy.