Twin cylinders??

[george_austin]

I would recommend the new diver trains himself on dive planning and diving using an LP steel 72. Stop moving any and all body parts that require an excessive amount of oxygen replenishment while diving. Streamline your rig instead of adding more bulk. Get rid of anything that floats and requires lead to sink it. Smaller tank, smaller BCD, thinner wetsuit. Plan your dives where a minimum amount of swimming is required - there ain't nothing a half mile from the boat that's not right under it as well. Usually.

My dive partners and I (4 of us), after probably close to 20,000 dives combined and in all conditions, are of the general consensus that the perfect tank for just about any dive you want to do is a single HP80 (steel) - the "Blue Steel" Faber "short dog" - Tank capacity is only part of the equation as the new diver needs to factor in tank displacement, buoyancy characteristics and handling convenience topside. All of this adds to confidence and being relaxed before he even suits up.

 

[2airishuman]

I would try to address the cause of the high SAC before going as extreme as twins.

High SAC often has multiple causes, some of which can be fixed over time, and some of which cannot.

I think it is important to recognize that many people who are unhappy with their SAC are big people diving in a group made up mainly of somewhat smaller people. I am told that my "ideal" bodyweight is around 220 pounds; I carry around 15 pounds of, er, extra. There is no way I am ever going to have a SAC that is the same as a reasonably skilled diver who is of more average build. The OP hasn't provided us any info regarding his body shape, but I would imagine that above average size is contributing to his SAC.

A downside of switching between singles and twins is that the reg configuration differs. On twins, you'll have a first stage on each cylinder valve and one of your second stages connected to each first stage. If you cannot get a twinset, you'll have to either reconfigure your regs, keep a separate set for singles, or use a H-valve or Y-valve (if you can actually find one).

If you're going to dive twins properly, you'll need a set of regs for your twinset (2 1sts, 2 2nds, and one or two spgs depending on whether your twins are mainfolded or not), PLUS, realistically, another set of regs for when you are diving singles.

If you're going to dive a stage, you will need a regulator for that, but can leave your single-tank reg set up the way it is.

H valves and Y valves pose their own problems and only work well with specific configurations, which are beyond the scope of this thread. They are not IME a reasonable substitute for a separate reg for singles.

I'm not sure your diving conditions but if your dive boat doesn't offer steel tanks, just look at local dive shops and rent them separately from the dive boat. Most of the dive boats I like would only do AL80s or LP steels, but more than a few of the dive shops had steel HP tanks for rent

Depends where you go and what you are willing to tolerate logistically. If you're in some tropical paradise and don't have a car, you're limited to what the operator will give you. Even with a car it's a hassle. Some tropical paradises don't really have HP steels available for rent, at all, period.

Yes. I'm sure having an ali80 stage would be fantastic for someone with less than 50 dives. I really can't understand why most people wait until they are doing mixed gas dives with lots of deco before using the biggest stage possible.

I don't think a stage is beyond the skill of a diver who is skilled enough to be fully comfortable switching regs, as long as they have a BC that will work with one. Mentorship would be a good thing, if available. Some instructors might be willing to cover it in the context of some other class, e.g. AOW.

I've never seen someone taking their twindies apart to swap in a full bottle. Ever. And I've dived all over the UK and on lots of boats.

Depends on whether you're using a twinset or independent doubles, and what you're trying to achieve. I've done it.

 

[Akimbo]

Diving doubles isn't rocket science, especially with IDs (Independent Doubles) and no-decompression diving. An independent air supply and packing 50%+ more gas than you need is never a bad idea as long as you can pack the weight and don't mind the extra expense. Warm water dive boats that supply tanks rarely offer anything other than single aluminum 80s so that is very likely what you have to work with.

 

[Akimbo]

@kemahdiver

Thinking a bit more about this, you might be able to meet your objectives with three single 80s on a typical 2-dive boat trip. Let's say you suck your primary ID down to 500-700 PSI and the backup down to 1400-1600 on the first dive. You could probably just swap the primary for another full bottle, saving money on Nitrox purchases and possible tank rentals. Just a thought since you don't mind packing the weight.

 

[Basking Ridge Diver]

You could probably just swap the primary for another full bottle, saving money on Nitrox purchases and possible tank rentals. Just a thought since you don't mind packing the weight.

It works and I have used this method - but most dive boats on vacation will not allow you to dive double tanks due to the risk of you going into deco. Unless you get on a tech boat - and the OP is still new - this may not be an option most of the time.

The boats I use in NJ allow this option and it is a great way for me to save a few bucks rather than renting 4 tanks. I have a low SAC/RMV and it works for me. The OP's mileage may vary...

 

[Slow]

High SAC often has multiple causes, some of which can be fixed over time, and some of which cannot.

I think it is important to recognize that many people who are unhappy with their SAC are big people diving in a group made up mainly of somewhat smaller people. I am told that my "ideal" bodyweight is around 220 pounds; I carry around 15 pounds of, er, extra. There is no way I am ever going to have a SAC that is the same as a reasonably skilled diver who is of more average build. The OP hasn't provided us any info regarding his body shape, but I would imagine that above average size is contributing to his SAC.

Everyone likes to tell us newer divers that we just need to work on this, that, or the other thing. My RMV runs 0.55 to about 0.65. My dive buddy on the last trip had a RMV of about 0.25. I'm 6' 200 lbs. I'm not diving over weighted. I'm much fitter than average. Based on some video I've seen and everything I've been told, I'm very calm in the water. There's only one or two things I can do to be a bit more streamlined...but even when we're sitting still my dive buddy's RMV is half of mine...and I'm sitting there being as zen as a monk and breathing as slowly as I can without triggering that CO2 build up gaspy breath-reaction.

And I still get told I need to work on my diving and if I just would dive more I would do so much better. Um...yeah...no. I'm not buying it. A little better maybe, but I'm never gonna have an RMV of 0.25. After a few months of doing a lot of research, both on diving directly and on physiology, I think the most important thing I can do here is get over it. Just like I can't ride my bike like Chris Froome, I can't have an RMV of 0.25. So, either be OK with the dive times I have or get a bigger tank...my plan on the next trip is HP100s.

Doubles seems a bit more complex than I want to try...but if someone else wants to deal with that complexity, that's their business, more power to them.

 

[kemahdiver]

The OP hasn't provided us any info regarding his body shape, but I would imagine that above average size is contributing to his SAC.

For whatever it is worth, I am 6'4 and 260 and seem to be getting softer every week . Don't know what my shape is but i am about a 40 in the waist and 52 around the chest...an upside down pear??

 

[kemahdiver]

Thanks to all that took the time to respond. I appreciate all the great responses and advice. I've learned that I want/need to learn more about all the options mentioned but for now it all seems a bit more than I am ready for. For now, I think I'll get a regular BC, do a lot more diving, look for operators that provide larger tank options, and continue critiquing and improving my efficiency.

 

[KevinNM]

Everyone likes to tell us newer divers that we just need to work on this, that, or the other thing. My RMV runs 0.55 to about 0.65. My dive buddy on the last trip had a RMV of about 0.25. I'm 6' 200 lbs. I'm not diving over weighted. I'm much fitter than average. Based on some video I've seen and everything I've been told, I'm very calm in the water. There's only one or two things I can do to be a bit more streamlined...but even when we're sitting still my dive buddy's RMV is half of mine...and I'm sitting there being as zen as a monk and breathing as slowly as I can without triggering that CO2 build up gaspy breath-reaction.

Is your dive buddy a much smaller female? Because yeah, you are never going to get there if that the case. 0.6 isn't bad.

 

[KenGordon]

On SB low air consumption is treated as if a proxy for penis size. Posters boast of whole dive air consumption I can't match sitting on a couch watching TV.

Do not base expectations of normal air consumption in what SB posters say.

Trying to reduce breathing is bad idea as it is how you expel CO2 and expelling CO2 is most of the point of breathing. At depth you have much more O2 than you need. High CO2 leads to all sorts of bad things and is no fun at all.

Getting relaxed and breathing properly are important, but as the odd poster above has pointed out there is only so far it goes. A similarly relaxed small person will use less gas. Small women will generally use less gas still. The last time I did a lot of OC dives in a warm place we had a diver with 14 dives who never got out of the water with less than 100 bar. She was young, fit and moderately relaxed.