Double LP 121's?

[Rings890]

Has anyone out there used these? I am going to be investing in some new cylinders and these looked nice as far as legth and weight characteristics. Mabey a bit long at 29.2" in length before valves. I am currently am using steel 100's and they are a bit short for my body length so I find myself tipping forward, when I adjust my backplate this is pretty much taken care of until I go to my other set of alu80's. If anyone has used these LP121's , did you find them top/bottom heavy when full or near empty? The cylinders are from XS Scuba so I think that means that they are Worthington steel.
My alternative is LP 108's or mid pressure 120's

 

[Tom Winters]

As long as your back can take the load, you'll be ok. Not much difference in weight between LP108's and LP121's. A single 121 righteously filled weighs in at 56 pounds for a single. Doubled with a manifold - maybe 115 pounds - has wrecked any number of diver backs - enough to put some out of diving too.
I never had any trim probs with my 125's or 108's, but I dive 'em singled - my twins are LP85's which might be THE most perfect doubles ever.

 

[DIR-Atlanta]

I am currently am using steel 100's and they are a bit short for my body length so I find myself tipping forward, when I adjust my backplate this is pretty much taken care of until I go to my other set of alu80's.

The best way to address the problem of tipping forward is by adjusting the position of your feet, not your backplate - move them forward or back as necessary to get the proper trim. Using fins that are negatively buoyant (like Jet fins) helps a lot, too. Most doubles (of any size) can be trimmed out easily in this way.

The problem with adjusting the backplate is that (as you discovered) when you go to a different set of doubles, they don't trim out the same. It's much easier to change the position of your feet during the dive than to readjust the backplate each time.

 

[StanS]

Since I assume we are talking about doubles would you not adjust the bands on the doubles to the correct height for each different set of doubles. Then when you switch your backplate each different set of doubles would ride correctly. I have several sets of doubles and I simply switch my backplates.

 

[DIR-Atlanta]

Since I assume we are talking about doubles would you not adjust the bands on the doubles to the correct height for each different set of doubles.

Bands on doubles are normally adjusted such that the top edge of the upper band is right below the "crown" of the tanks (i.e. right where the exterior wall of the tank starts to straighten out). This position is important, as it places the manifold, valves, and first stages at the correct location to facilitate valve drills. If you go messing with the position of the bands (or the position of the backplate relative to the bands), then you are going to wind up with valves and first stages in an inconsistent location from one set of doubles to the next. That makes if more difficult to develop good muscle memory for valve shutdowns.

As I stated in my previous message, the best generally applicable way to trim out a set of doubles is to adjust the position of your feet, by bending your knees and extending your lower legs beyond a 90 degree angle. This will help eliminate the heaviness at the head - and the more negative the fin, the easier this is to do.

 

[Rings890]

Thanks everyone,
I know where you are coming from Atlanta, my fundamentals instructor had said some of the same things, I am able to trim out my rig by moving my feet out; it however feels unnatural when I dive my steels vs. my aluminium’s. I just ordered a pair of LP108’s (figured the 121’s were way too long). The 108’s are only .5” longer than my alu 80’s so it should be ok.