About to buy 2 tanks for Sidemount

Hi All,

I'm looking at venturing into sidemount diving and have yet to purchase any gear or join a course. But I figured I can get the tanks now because they are useful sidemount or not

In relation to this thread from another forum, the consensus seemed to be the "Steel 85", however, in my part of they world we tend to refer to them as in "Litre" capacity instead. Below are the tanks I can get but I just wanted to confirm if the 85 mentioned in the thread is the same 85 I got quoted from the supplier?

Thread where the "85" was mentioned.
Anyone have an opinion on the perfect side mount tank?

Below are what I'm quoted from the supplier, most likely I'll be going for the 10.5L 85cu/ft one.

All are Faber Steel tanks I got quoted.
85 cu/ft ( 10.5 Litre ) cylinder
100 cu/ft ( 12.2 Litre ) cylinder
125 cu/ft ( 15.0 Litre ) cylinder

Sorry if this sounds like a silly question, just wanted to confirm before I hand over my hard earned cash :depressed:

check around for used tanks. Used tanks are your friend. Problem with some of the fabers is they can get butt floaty which is bad. Lots of good sidemount divers posted in that thread. Personally I think the old steel 72's are the best tanks for it, but you have limited gas supply with only 72cf. They are also very very very cheap. Cheap is good. Read that thread you'll hear the same stuff here as there, and the predominant sidemount divers already posted in that thread. Responses will be the following
How tall are you? Height is an important factor when determining tank size
What are your weighting needs? aluminum 80's make great tanks for sidemount if you're diving thin wetsuits since you can get dialed in a lot closer since they float. Big steel tanks will make you too negative and you're fighting them the whole dive.
What are your gas requirements? do you need the insane amount of air required by 120cf tanks? Most likely not.

So, go out and find cheap steel tanks that are used, when you have a better idea of the above questions you can then go ahead and find the optimal cylinders for you. Tanks are generally the last things you should buy because they are obscenely expensive and you can't take them with you if you travel. So! you really should buy your exposure protection first, regs second *doubles set of regs in din configuration which can easily be configured for singles if need be, but you'll need em for sidemount and used with yoke bottles*, then bc.

Thanks saxplayer1004 for your response.

I'm still pretty average in terms of gas use, averaging in the range of 15L/min - 22L/min depending on how hard I have to work myself before I can go down. Relatively tall and skinny guy here, 186cm and weighing only 62kg.

Around 80% of my dives here are in drysuit, it's rarely warm enough in the water for a wetsuit for me, thus the choice for steel tanks.

At the moment I own all my own gear for a single tank dive including 2x 12.2L (100cu/ft) tanks, but that's shared between myself and my partner. She's a lot smaller than me and uses less gas, I was hoping to get 2x 10.5L (85cu/ft) tank for her to use in single tank dives and I can always take them if I go sidemount. From what I've read the 10.5L (85cu/ft) steel's seemed to offer the best balance between gas volume and convenience on dry land, thus my choice for them.

Will probably get the rest of the gear, reg / bc etc when I have decided to join a course.

ok, so here's why that's a bad idea.
She uses less gas, ergo she should have the BIGGEST tanks not the smallest. this is a very common thought, but it's wrong. Here's why. Say she's diving 75cf tanks and you're diving 99 cf tanks for easy math's sake. Her SAC is .75 of yours, so it works out. Here is the problem as you get into more advance diving. You will finish the dive each with 500psi left in your tank. Assuming 3000psi working pressure *again for easy math*, that is about 12.5cf for her, and 16.5 cf for you. We'll move to a cave because it's the easiest way of explaining it.
You dive thirds in tech diving *which sidemount diving is btw, you should not be using recreational diving techniques diving sidemount*. Third in, third out, third for reserve. You each dive to 2000psi on your way in and turn around, use 1000psi on the way out, and finish with 1000 psi at the end of the dive. Everything is hunky dory. That extra 1000psi is NOT for you, it's for your buddy. Now she used 25cf of gas on the way in, and 25 on the way out, leaving 25 for you. You used 33 on the way in, 33 on the way out and 33 for her. The problem is if you have a failure and need to use her air, you NEED 33 to get back out, but you only have 25. That's why she should be carrying the bigger tanks, because that way you have more air than you need and she still has plenty because she'll never hit thirds on her tanks.

The 100's and 85's are very similar tanks, and if you already have a pair that you like, then go ahead and buy another pair. I still recommend going used with whatever is in the area, but 100's are great tanks. They like the 85's here because they overfill the hell out of them to where they get 115cf of gas out of them, but to each their own. If you're 6'1" which is fairly tall, the 100's will actually work perfectly for you. Best way I've found to measure is to go from the bottom of your butt to your arm pit and that's about the optimal tank size for you. Depending on your inseam length, you'll get around 26-30 inches on average. That's the total tank length you really want. Conveniently that's the size of a LP85 and HP100 :-D Now here's the other catch with the 85's that may or may not be a turnoff. They're skinny. The tanks you have are 7.25 inches in diameter and the 85's are 7 inches in diameter. So any time you have to move cam bands around you're going to be adjusting them. Yes .25 inches makes a rather significant difference. So in reality, the 85's and 100's are almost identical tanks, and if you already have a pair, you're certainly not going to be disappointed in another pair of them. Now since you're buying new, the price difference between lp and hp makes a huge difference. In the used market it doesn't really matter, but new values tend to be significantly higher for the high pressure tanks, so if it saves you $200 then buy the 85's, but if the price difference is within $50 then I'd get the 100's

Thanks