Why Aluminum ?

[joel smith]

What no one has said here is that those USD steel 72 tanks came in a variety of exterior finishes. They sold some with a yellow or black Tuff-Koate exterior without a galvanizing dip under it. That led to some horrendous corrosion problems under that coating that was hard to detect. It also led to steel tanks falling out of favor, and contributed to the turn to aluminum tanks, which they stated had no corrosion problems. I saw this with some of these steel double 72 tanks that we had in the US Air Force.

Some of the newer divers are saying how great the steel 100 cubic foot tanks are, with the added 10 pounds of negative weight; I would rather dive the 72s with nearly neutral buoyancy. I have seen student become completely dependent upon their BCs for "lift" in pool sessions where they had no exposure suit on. It can lead to BC dependence, and not learning the skills of buoyancy control from the beginning.

By the way, I have just decommissioned most of my aluminum tanks, which are around 35 years old now. They will be used for display only, as they were made with the special permit and can be subject to sustained-load cracking. I am keeping my AL UDS-1 tanks, and am getting those hydroed right now; they have never been subjected to sustained loads.

SeaRat

Not sure about the 10 pound of negative weight , At the end of a dive I am neutral with 2 lbs. of weight using steel 100 and my dive time is almost double. Using al 80 Ineed 8 lbs and feel very bouant. I guess its all in what you like , but as a new diver I was
amased at the way the steel tank worked and felt to me.

Sorry I didnt word this right I meant it feels like I wanted to float to the surface after diving with the al 80. I do still use an 80 on occasion short hour long night dive. But for now I just like the steel 100, maybe after 100 dives Ill feel different , and sorry for getting off the subject.

 

[elan]

Feeling buoyant and being buyant is not the same. If you put the weight difference of 7 lb (this is as i rmember how worthington is less buoyant than catalina) to the tank straps and not to the belt you will have the same feeling. The feeling depends upon where you place your weight

 

[spectrum]

A lot of the steel cylinders from "the day" were not hot dipped galvanized and would require external surface maintenance. Most of what we see today is either hot dipped or has another durable finish such as the Faber process and we consider them bullet proof. I got a stash of them last year and they all need attention before I recommission any of them.

Based on the variety of finished back then I can see where a "corrosion resistant" aluminum cylinder could have some bling. Also in the day shoppers were not going to the internet to compare empty buoyancy specs and all of the nits that we dig into. The diver would learn as they configure for the cylinder or by word of mouth.

Pete

 

[spectrum]

Feeling buoyant and being buyant is not the same. If you put the weight difference of 7 lb (this is as i rmember how worthington is less buoyant than catalina) to the tank straps and not to the belt you will have the same feeling. The feeling depends upon where you place your weight

It depends on what you call the same. Yes you can have correct buoyancy. However you end up heavy on your feet as detailed here.

Pete

 

[elan]

Well put those 7 lb on the tank neck and you will not have heavy feet issue 7lb is quite enough to play with in terms of trim.

 

[elan]

Pete great article, i think you also need to add diver height consideration vs. Short/long cylinder and mention that it makes a difference when one needs to reach the valve to be able to open it in emergencies and can affect the trim if its short. My personal favourite for single tank is Faber lp85.