Weight band for AL tank...good or bad?

[Icarusflies]

Hello All;

I d like to have your opinion about this. Many people are talking about the advantages of steel over AL tanks and for what I have seen, besides resistance, the main advantage is buoyancy. Couldn't we have the best of both world getting an AL tank and attaching a tank pocket to it. Like this we will basically have a cheaper tank with the buoyancy characteristics of a more expensive steel tank. What is your opinion about this???

 

[spectrum]

Strapping a 4-5 pound weight to an AL-80 is essentailly the same as just adding it to your weighting except that it will raise your center of gravity. A camband is most useful for positioning weight to correct your trim. Otherwise you might just as well have the weight down low on a belt or integrated pouch.

The beauty of a steel cylinder, especially HP is that you get to drop some ballast weight because the cylinder will remain less buoyant through the dive cycle and it weighs less out of the water.

This explains it:
http://home.gwi.net/~spectrum/scuba_al80.html

Any cylinder will have it buoyancy shift as you breathe it down and any cylinder can be correctly weighted for.

Pete

 

[The Kraken]

Many people use weight pouches on tanks to improve trim.

Some people, because of their particular physical characteristics, simply cannot get horizontal in the water with all their weight on a belt or in intergrated pouches.

For example, if at a safety stop with the tank at 500 psi you require 8 pounds to be neutral, you could put 6 pounds in trim weights on the tank, keep 2 pounds in easily ditchable weight, and still be able to ditch some weight to become positively buoyant if the situation required.

Diving with a good buddy could actually allow you to put all of your weight in trim pouches on your tank. Should you be required to dump weight, your buddy could do it very easily.

the K

 

[ClayJar]

I add weight to a cam band around the shoulder of an AL80, which trims me out (I have no BC trim pockets) and makes the tank effectively neutrally buoyant. What diving steel tanks will do better than that, however, is decreasing your total dry weight.

An AL80 weighs about 31.4 pounds empty at which point it's about 4.4 pounds buoyant. A Worthington X7 Steel 80 (HP) weighs only 28 pounds empty at which point it's a full three pounds negative. So, diving the AL80, you'll have 36 pounds of tank and tank weights to be neutral with an empty tank, while diving the X7-80, you'll have only 28 pounds with the tank *and* that includes three pounds that you would've needed on your weight belt.

So, the difference in buoyancy can be easily corrected by adding weight (giving the best of both worlds), but moving from an AL80 to an X7-80, you get rid of 11 pounds of dry weight (showing that there is still a reason steels can be "better").

 

[joe rock]

This explains it:
http://home.gwi.net/~spectrum/scuba_al80.html

Pete

Pete, very nice explanation. As a relatively new diver (1 year) who dives almost exclusively cold water, the difference when I bought my steel 100 HP was like an epiphany The combination of weight I shed between experience and using the 100 made a remarkable difference in so many ways!

JR

 

[Icarusflies]

Thank you for the feed back.

 

[FredT]

A 1/8" thick disk of lead inside the boot works quite well on the buoyancy issue, but the tank corrosion if not removed after each dive day can kill the tank in a couple years.

Alternatley a "tail weight" attached to the bottom hole in your backplate will do the same thing and not risk the tank.

 

[ClayJar]

A 1/8" thick disk of lead inside the boot works quite well on the buoyancy issue, but the tank corrosion if not removed after each dive day can kill the tank in a couple years.

I've seen a "weight-integrated boot" in the dive shop (complete with T-handle release). It's got a price tag on it, but they use it to hold micro-fiber towels, as nobody in their right mind would buy the thing.

(Putting weight on the bottom of an AL80 is rather pointless. It puts the weight at about the same lever-point as it would be in weight pockets or a weight belt, removing all the benefit of shoulder weight, and it puts the weight up high at tank level behind your back, making you axially less stable. Looking at the physics from an equilibrium standpoint, it's the worst of both worlds.)

As far as the corrosion goes, separating it with a nice plastic disc and giving it a fresh water rinse after the dive should work, eh? (Assuming you want to remove ditchable weight to such an illogical location.)

 

[dumpsterDiver]

When diving with a lot of wetsuit and an aluminum tank, I sometimes put a lead shot ankle weight around the tank valve. It flopps around a tiny bit, but I quickly got used to it. It is a very comfortable way to add a little weight to the upper torso which helped my trim when I was wearing a 3mm vest, 7mm farmer john and 7 mm jacket and a double hood. This configuration puts a lot of bouyancy on the chest and much less on the legs.

Steel tanks remain expensive and prone to corrosion and for that reason the standard 80 aluminum is still practical for certian diving. I have 4 steels and 6-8 aluminum tanks.

 

[ClayJar]

(Tangentially to the topic, I might add that by having the extra weight on a cam band, on the *extremely* unlikely event that I have my cam band fail, I can swap it out and keep diving, with only a slight penalty to my trim. )