Best small sidemount tanks, roughly ’AL63/80 + redundancy’, non-cave fill

[MichaelMc]

What available small sidemount tanks do people like? Roughly ’AL63/80 + redundancy’ for 40’ - 80'. Most discussions seem to be of larger tanks, LP85+, which is more than I want to walk to the water every dive. Two of X, Y, and Z is always a good answer, but which would you get 4 of if you also had big tanks.

Survey has: tank, diameter, empty buoyancy, and neutral land weight. I left a broader than maybe suited tank range, but may be missing tanks. The small HP tanks seem too small.

In this sidemount diving, not pony, forum:
* LP50 stand out as sweet,
* Steel 72 are common, are a lot of gas, and some say pushed steel’s limits,
* AL40 get a serviceable nod.

AL40s are favored in non-side discussions of big ponys, with barely a mention of LP50s. But LP50s get play as CCR bailouts, if cave filled. Realizing that pony tanks spend their dives full, while side mount tanks go toward their reserves, and have different trim expectations.

Even when an AL30 may be more appropriate due to gas planning or something even smaller, we just grab the 40 because of how easily they carry. Same with why we use AL80's for stages even though LP72's are better in terms of size:weight:capacity on land, the al80's handle better in the water so we use them. Same reason no one uses al63's or 50's. You go straight to an al40, and if that isn't big enough, straight to an al80 *unless you were lucky enough to be able to grab a bunch of the AL72's when they were available that are even nicer*

Size: The redundancy sort of pushes to the 80 or 100 total gas range, depending on if a single 63 would have worked.

Heavy/Light: I understand there are separate views on best, based on heavy, HP, tanks or light tanks. And that can dictate rig differences with rear rails or light tank repositioning. I carry a lot of lead, but am happy not using my tanks as ballast.

Fills: I’m not in cave country, yet a top shop rented me an LP85 at 2950 PSI, saying ‘its fine’ when I raised an eyebrow. I’d rather avoiding full cave fills. I’m not sure the available small tank options are broad enough for the difference to matter in the selection.

Thanks,
Michael


Me: I dive Monterey single BP/W with a 20/10 wetsuit, normally AL63 when others have AL80, often next to a fill station. 120+ dives. Seated top of shoulder 25”, 5’9, 140 lb., 30” waist.

My Plan: I want to move to side for redundancy, fun, travel. I’m starting side mounting a pony off my plate with loop bungee. My plan is two LP50s. Then migrate to a sidemount rig. Then get two LP85s. LP50/85 mix and match seems to cover many dive lengths, with maybe ultimately LP50s as accelerated deco. I want to try side enough that I don’t plan on stopping at the pony state. 100’ is deep enough for me without Helium and a rebreather, and 60-80’ is fun enough. I help teach advanced single backmount students in the 30-40' range, under NAUI/AAUS.


Some prior threads: 2017: Best Tanks?, 2016: Tank choices, or just screwing around!!, 2016: Sidemount Tanks Options, 2012: What are Your Favorite Side Mount Tanks?, 2010: "Best" Tanks for Sidemount, and Why?,


Some specs for reference, or correction.

             Vol       Diam Len. Full / Empty Wt.    N.Wt.
AL S30  M.I. 30.0/4.3  5.25 19.5 -1.5 /  0.4  12.25  12.65
AL S40  M.I. 40.0/5.7  5.25 24.6 -0.7 /  3.0  15.30  18.30 *
AL S50  M.I. 48.4/6.9  6.9  19.0 -2.5 /  0.8  21.3   22.1
AL S63  M.I. 63.0/9.0  7.25 21.9 -2.4 /  2.5  26.9   29.4

Scuba Cylinders | Metal Impact w/o valve? (Metal Impact / Worthington)

LP27  Faber   27/ 4   5.46 14.43 -3.0 / -1.1  11.7   10.6
LP45  Faber   45/ 7   5.51 23.0  -2.7 /  0.6  17.6   18.2
LP50  Faber   50/ 7.8 5.51 25.2  -2.4 /  1.2  18.9   20.1 *
 M71  Faber   71/ 9   6.84 20.47 -4.4 /  0.9  28.7   29.6
FX71  Faber   71/ 9   6.73 21.26 -7.0 / -1.4  24.7   23.3

Blue Steel Scuba - Cylinder Specs salt w/o valve. M71: 3300 PSI, FX71 3442 PSI

 S72  various  71/    6.9  25.1  -5.4 /  0    26     26   *

Tank buoyancy numbers w/ valve

AL72  luxfer 69.6/    6.9  26    -1.6 /  3.6   28.4   32.0

Scuba Cylinder Specification Chart from Huron Scuba, Ann Arbor Michigan w/ valve

LP85  Faber   85/13  7.01  26.0  -3.8 /  2.3   31.2   33.5

 

[runsongas]

i would just go for the 85s or some lp72s.

you can clip on either in the water or it is a short walk from the stairs at the breakwater.

while lp45s/50s are nice tanks, you end up having to keep more of them around to swap between dives or have to get refills during your SI which gets annoying. and if you aren't getting free fills from breakwater scuba, those start to add up.

 

[MichaelMc]

Thanks!

If I'm assisting, I'd want to limit my encumbrance while supervising my singles backmount students. We usually need refills between dives, yet I usually use only 35-40 cu.ft. It's likely I can do two dives on two LP50s, certainly with three, and we have all those AL63/80s. So the worst two dive cost would be three fills not four.

If I'm diving recreationally, I'd favor Nitrox and be a little deeper, giving some benefit while disguising the two tank premium of small sidemount fills, as it is often per cu.ft. with a per tank minimum. It could add up, but against a two hour drive down there, it seems maybe ok. If I'm not near a shop, I could rent an LP85 or AL40, dive it with one LP50, then dive the two full LP50s.

Do most people diving sidemount plan on two dives per fill? For shore or boat?

 

[runsongas]

i do 2 dives off a pair usually with lp72s or larger unless if planned otherwise in advance. run times about 60 to 70 minutes or so.

 

[Scuba_Aaron]

I love diving a couple of steel LP50's with a wetsuit, nice, lightweight, compact and fun to dive.

 

[Caveeagle]

Fills: I’m not in cave country, yet a top shop rented me an LP85 at 2950 PSI, saying ‘its fine’ when I raised an eyebrow. I’d rather avoiding full cave fills.

Lol... 2950 is not a cave fill.

If you LDS is happy to give you a 2950 fill on a LP85, ...you should be happy, and be nice to them. I would feel safer with that tank at 3k psi, than ANY AL80 at the same fill.

 

[Scuba_Aaron]

I have my own compressor and I fill my steel LP's to 3000 PSI routinely.

 

[MichaelMc]

Lol... 2950 is not a cave fill.

I'd like to step away from the full on cave fills. I didn't know 2950 did not even make the cave level at all . I'm alway nice when I go there, they are good.

All I've read suggests the LP50 would be a good choice, I just did not know if I was missing something in the other options. The others seem a bit bigger, 72 or AL72, or maybe more otherwise useful, AL40. But LP50 seem to hit the sweet spot.

 

[Caveeagle]

I have started using LP72. (Rated 2250 psi) for recreational side mount when diving ow or cavern with my kids. I like the size and they are easy to handle. And I have 3 sets, because they work great for kids to use as single tank as well. Multi-use etc.

They do get floaty in the tails when low but that is manageable. I need 4# of lead when diving wet, 5m in freshwater in these tanks. I have experamented with putting the lead on a belt, the sm-Bc, and on the cam bands. So far on the cam band trims out best and makes it easiest for me to keep my rig unchanged for when I use HP100s on dives where I need more gas.

I have never used LP 50s, but they seem to be very popular. Of course with a respectable cave fill, a pair of LP50s is a lot of gas. But even at 2450-2950, you have 100+ cf of has and should be set well for most of dives. Especially if you trim out well and gain improved sac rate.

Fwiw, I will be buying the next set of 50s I find at a decent price.

 

[jerrwhy01]

If you're not in cave in cave country then in all honestly LP85's make little sense as you might get difficulty in getting them filled past 26/2700 PSI; I'd lean towards HP 100's in that case.

LP50's are awesome. If they're cave filled you get pretty darn close to an AL80 in terms of cubic feet, they trim out well, and a pair weighs about as much as an AL80 and BP/W. They are easy to manhandle which makes them great for recreational work. Even if you don't get them cave filled then 100 CF of gas is nothing to sneeze at.