PST E7-80 vs PST E7-120, how does length affect trim?

[StSomewhere]

Rather than buy AL80s, I was thinking of getting at least one PST E7-80 (since the E7-100s don't seem to be available). I know I can get 72 cf into one of these little tanks at 3000 psi (similar to an AL80), and I know two LDSs that can definitely do 3000 psi fills.

Now my questions, these things are downright short, we're talking 20 inches long. How will this affect trim with such a short tank on BCD a or possibly a transpak/transplate? Am I going to be top heavy? Also, it seems that if you doubled these up (which is not in the cards for the time being) they would really make you top heavy. Would I be better off with an E7-120 or two? They (E7-120) seem awfully long for someone who's 5'10".

I've only dived with AL80s and AL63s, and the one time with an LP 95 (that weighed a ton!) so I don't really have much of a point of reference.

 

[mempilot]

How will this affect trim with such a short tank on BCD a or possibly a transpak/transplate? Am I going to be top heavy?

I owned two of HP80's. I was top heavy with my backplate. I got rid of them. Some people love them, but they really jacked my trim down.

Also, it seems that if you doubled these up (which is not in the cards for the time being) they would really make you top heavy.

These tanks do not make good doubles. There is no room to adjust the bands up and down. You end up concentrating a lot of mass high up on your back. Most people that try this, end up selling them or breaking them down again.

Would I be better off with an E7-120 or two? They (E7-120) seem awfully long for someone who's 5'10".

The 100's make decent doubles since they are the same size as AL80's. They are kind of hard to find, but... As for the 120's, I've never dived with them, so I can't tell you anything about them.

BTW, I'm 5'8", and so the 80's would affect your center of lift even more than they did me.

 

[teknitroxdiver]

I would go with the 100 or 120s. I've handled the E7-80s and they are tiny. I didn't dive the tank, but dry-testing it showed that it would cause some problems while gearing up and while diving. The tank is very short, which means you may have some problems getting the base of the tank far enough down that you can set your gear down on the tank bottom while putting it on. Also you may find that putting the tank high enough to allow access to the valve would be difficult. The E7-100 is still 2 inches shorter than an AL80, and would provide a better length balance between compactness and practicality.

As for doubles, the E7-80 would not likely be suitable for doubling up, due to their shortness. Maybe someone with a little more double experience can help you on this issue.

Edit: Personally what I plan to get is either E7-120s or E8-130s. Then again I'm 6'1, so length isn't much of a problem.