Best small tank choice for sidemount vs backmount doubles

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phoque

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Hi,

I bought a set of used OMS LP46 tanks on here this year to dive tiny doubles on recreational dives (mostly shore diving in the North Atlantic). The set has worked great so far and I am very pleased with the overall feel of the setup, as it is stable, well balanced, and provides me with ample gas supply for my needs. I usually bring a HP 100 or 120 with me to allow for transfilling ~1000 psi or so during the surface interval when needed, which then allows me to comfortably do 2 1hr+ dives at the sites that we frequent.
The one problem I have had is my error to place boots on the small tanks to stand up the setup, and this has led to surface corrosion of the tank bottoms (rusty orange water was flowing out of the drainage hole after every dive...). Since the necks were also showing signs of rust, I decided to remedy the situation by stripping and refinishing the tanks completely. I used a mild citrus-based stripper, a wire brush to clean out the rust, cleaned the surface with isopropyl alcohol and acetone, and applied 4 coats of ZRC cold galvanize to protect the steel (2 sprayed, 2 rolled). Now the tanks are ready and look great, have gone trough a new visual, and are ready to dive.
My dilemma is the following. I also want to learn sidemount and plan on using an equally small set of tanks for local recreational dives. I plan on purchasing a set of Faber LP50s, but I wonder if there is a set that would work best for sidemount vs backmount, or if they would be roughly equivalent. Since the LP46s are disbanded, I wonder if I should keep them for sidemount, and band the new LP50s together for backmount, or vice-versa.
For background, the LP46s are a little shorter (2 inches or so) and more negative (0 when empty vs +1.24 for the LP50s), and their diameter being identical, I can use the bands equally on either set.
In your opinion, is there any rationale for deciding which set to use for which style, or would you argue that they are pretty much equivalent. I am tall @ 6'2" for context if that may factor into the decision.

Thanks very much for any relevant input you may have. Much appreciated!
 

tbone1004

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if you're 6'2" the 50's will likely be better for doubles for you. I wish Faber would make HP versions of the 50's, but no such luck. The 50's will also have their buoyancy offset by the bands and crossbar so you probably won't need to adjust your weighting. If you're diving dry, that's what I'd do.
If diving wet, the 50's MAY be a bit nicer for you as they are less heavy on your hips. Doubles tend to make you a bit head heavy, and sidemount tends to make you a bit foot heavy so the 50's in sidemount will help counter that a little bit and may make it less of a difference when you go back and forth.
 

ajtoady

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I love my Faber LP 50's!! Pump them a bit you have 130 or so cu ft between the pair. Sidemount or twin back mount , they fill the bill. I dive solo a fair amount and they give me the redunancy I like. In back mount twins I use independent doubles and in side mount, again independent units. Bouyancy characteristics are also what I like. However, to each their own.
 

Marie13

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I’ve been diving a set of LP50s SM for a few weeks and they are lovely.
 

ajtoady

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I’ve been diving a set of LP50s SM for a few weeks and they are lovely.
Much nicer for sure!! I like the light weight and they trim nicely. Most of my dives are in the 1 hour range and usually 60-100' deep. So more than enough gas.
 
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phoque

phoque

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Thanks for your input.
As far as overfilling, I don't do it, usually only fill to ~2600 which would be ~ 87 cuft or so for the double 46s, but that's plenty sufficient for two dives with a small infusion during SI with the transfill whip and an HP120, so no need to overpump them to begin with.
@tbone1004 Thanks a lot for your thoughts. I only dive dry locally now, and I was leaning towards using the 50s for backmount doubles and the 46s for sidemount indeed. As far as small HP tanks, like you, I wish there was a good option, but I was actually considering not buying LP50s as a second set and going with Faber FX40s instead, for sidemount. Is this a bad idea? This would only provide 80 cuft @ 3440, and with their low internal volume, transfilling a little gas during SI for a second dive would certainly be less efficient than with the LP tanks, but based on my estimates and personal consumption, it would be doable as well, more limiting for sure, but would still provide sufficient gas for two good dives of 50-60 min each. They are also 5.5" in diameter, but much shorter and more negative than the other LP sets. Is this a bad idea for sidemount, or would it actually potentially be quite nice as a minimalistic setup? I realize these cylinders are generally only used for rebreathers, and I'm not even sure they are still being made, but Piranha has some older hydro ones at a nice price, so was considering.

Thanks!
 

tbone1004

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@phoque I don't think the FX40's would be worthwhile for sidemount. Too stubby for me. My tank attachment point for sidemount is VERY high compared to most, but it's about a 16" gap if I remember correctly. The FX40 is 17.7" long, with only 15" usable for attachment points since you can't mount to the bottom of the crown. The gap is between the valve knob and the bottom attachment point so there is probably 2-3 inches available there but the attachment point is still going to be at the very bottom of the tank. That will help drive the weight forward to the valve so it may work fine, but I do much prefer neutral cylinders for sidemount if at all possible.
 
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phoque

phoque

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@tbone1004 and @rjack321
Sorry for the delay. Thanks for your input. I suspected the FX40 would be too short for setting up in sidemount, but just wanted to confirm. I went ahead and purchased a set of new Faber LP50s. Will set them up as doubles when I have time to build a stand to affix to the bands in order to stand them up without boots. Same for my LP46s, will reband them as backmount doubles for now until I get to my sidemount class, which probably won't be until early spring next year. Then I will disband one set (probably the 46s) for sidemount.
Thanks for the advice. Much appreciated.
 
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