No Steel! Huh? What?? Why???

[viceroy]

I was just looking at a local technical diving site and while going through a list of requirements to dive with this particular outfit, I noticed something strange.

For the travel cylinders, they state that they must be AL 4-12 litre cylinders.

My question is why?

 

[Charlie99]

Lots of people focus on steel vs. aluminum when what they are really concerned about is buoyancy characteristics.

 

[viceroy]

I agree, but why would they restrict the travel/deco tanks to aluminium when they also state that the primary twins should be steel?

 

[Charlie99]

I don't use travel tanks, but my guess is that they don't want you to be carrying excessively negatively buoyant tanks as travel tanks. Since they are ditchable, you can't take them into account in your weighting. Since they are negatively buoyant, you need extra air in the wing to compensate for their negative buoyancy.

Since you aren't going to ditch the primary twins, you can use their negative buoyancy to reduce the amount of lead you carry.

 

[Scared Silly]

As said, it is all about buoyancy. In general, when full Al cylinders are a couple of pounds negative. Clipping off a couple pounds is not enough to greatly affective your buoyancy. Whereas most steels are more than that and can affect your buoyancy and your wing capacity needs.

 

[viceroy]

Okay...that makes sense.

Thanks

 

[TSandM]

Al80's also ride better as slung cylinders, especially once they are not entirely full, because they tend to float butt-high.