Captain Calamity(Offline)

Firstly, hello everyone. Time to stop lurking and make my first post.

Earlier this year I moved to a wing/BP as my six year old BCD was beginning to get tired. I also changed my regs to a long hose system at the same time.

Most of my diving is to less than 30m, but occasionally I will go deeper, and as I have gained experience over the last few years I realise that some of my early exploits (46m on a single breathing air) were just plain dumb. As my future plans don't include deep (>40m) or deco diving, I thought I could increase my safety margin ad dive skills by swapping to twins, doing a fundies course with my regular buddy, and doing a recreational trimix course (this seems would be the simplest way to get a trimix qualification for recreational depths without doing a whole load of other courses first which I would likely not ever use - I still wish to make min/no deco dives, just less narked ones).

Anyway, enough background, here is my dilemma:

When I look at minimum gas requirement I only really need twin 12s beyond 25-30m - and I don't go that deep often. One option would therefore be to hire twin 12s on those occasions when I really need them, but then what do I do for the shallower dives?

If I dive a single then I have to reconfigure my regs each time I swap over, and if I only dive a hired twinset a handful of times each season my valve drills will get rusty (AFAIK even getting an H valve won't let me practice shutdowns a la twinset).

If I dive twin 7s then these would be about right for the majority of my dives, would allow me to keep practicing shutdowns, I would have a fully redundant system at all depths, and my kit would always configured the same.

I thought that I had talked/reasoned myself into buying twin 7s, but I am aware that twin 12s are the far more common UK choice. Am I missing something here, or do the twin 7s be a better choice for me? Finally, would a 10L stage cylinder be a reasonable way to increase my gas reserve on those deeper dives without needing to hire twin 12s?

CC

Ahmed Adly, Marlin Inn DC(Offline)

I have this same problem actually but reversed.
I have a set of twin 12ss (alu 80s) and dive with them ALL the time.

What seem to be best for me is that I will make a set specially for single steel 15 liter tanks that I will buy. And will keep the other twin 12s.

twin 12s are good for about any situation and can have stages added when needed.

I bet I have been no help to your question, but this is my plan.

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RichieG (Online)

I would advise against hiring a twinset as it takes a number of dives to become familiar with them.

I dive a single 12/15 when diving from a rib and twin 12's on larger dive platforms.

If you can afford it its far better having multiple sets of regs.

neilh (Online)

Welcome

Picking up your last point first, if you took a 10L stage with a single 12 then realistically you're only 2L off twin 12s anyway - with the hassle of a stage instead

Granted the twin 12s are going to give you more than enough to cover min gas for most of your shallower dives, but is that a problem? With you and your buddies SAC would twin 12s give you enough gas for a typical day's diving? What about twin 12s with a top up from a 15L in between dives?

Personally I've moved from a single tank to twin 12s. I get the extra resilience of a manifolded set, plus they're nice to dive and have more than enough gas for what I do. Depending on the dives I'll either decant from a 15L into them in between dives to cover the second dive, or I'll take a stage (mainly because I'm trying to get used to diving with a stage).

I am setting up some regs for a single tank, but that's more for holiday dives where hiring twins might not be an option.

Diving Dave(Offline)

You can get two (maybe more) 'shallow' dives out of twin twelves. I would imagine most people do more than one dive at anyone time so if you're lugging two single tanks along anyway why not bolt them together and give yourself a bit of redundancy?
As has been said, it's worth having some consistency kit-wise - otherwise you're talking about doing potentially your most challenging dives in your least familiar rig.

Just my thoughts...

And howdy - welcome to the board

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Dave

Gav(Offline)

If it helps, what I've just done to cater for the diving that my club does whilst at the same time trying for as uniform a configuration as possible, to help in preparation for Fundies, is to have twin 12s and have a single 15L with the single tank version of my twin wing with its own set of regs.

That way I simply change the backplate over depending on whether I'm doing a wreck dive or a reef. It also helps as the club tend to do a wreck in the 25-35m range in the morning and a drift in the afternoon and mid-week, so it also means I have enough gas for the whole day.

Not the cheapest option at the start, but I think that over the long term it will save money on fills and help me to get used to diving the same system.

HTH

Gav

Captain Calamity(Offline)

Thanks for the replies so far, and for the warm welcome.

I dive out of Portland, and haven't ever had more than one dive per boat ride, so the two dives per fill issue is something I hadn't really considered, but equally doesn't really apply to me. I didn't mention earlier that I do an awful lot of shorediving with a friend who doesn't dive much deeper then 15m - and there's no way I am taking a 12L twinset for that. In reality, I doubt that I will be doing more than three or four dives/year in the UK > 30m.

Given that I already own my own wing, regs, and would buy my own wing that suited both 7s and 12s, would there really be a huge difference between swapping twin 7s for twin 12s? I would make sure I buy the same manifold that the hire shop use for my own personal 7s, so the only actual difference would be the weight and size of the cylinders.

After looking at the responses to my first post it seems to boil down to which set of equipment would be right for me the majority of the time - given my established pattern of diving I still tend towards the 7s, as almost every time 12s would be overkill (I cannot image lugging them into Chesil Cove for example!).

If (and here I have to trust you all) the difference between twin 7s and 12s is enough to be dangerous when using the 12s just occasionally, then perhaps there is some merit in using the 7s for everything and taking a stage bottle on the odd deeper dive that I do, even if it is more hassle for a similar amount of gas?

I am not sure that I can justify the expense of keeping twin 12s that I use just three or four times a year, on top of a single tank setup, whereas always diving the 7s would keep my valve drills sharp and should mean that I always have a redundant air supply.

CC

Clare Gledhill(Offline)

Hi. I tell most people not to buy 7s. And that comes from someone who had two sets of 7s, did DIR F in them - and got rid of them both to dive 12s.

However - if Chesil Cove were my local site and I was regularly diving in that range - and diving Chesil Beach at that - I'd stick with 7s. 12s on the Cove are too much hassle to be honest.

I'm not too keen on the "take a stage for deeper dives" approach though I must admit. Twin 7s give you reasonable gas reserves up to the mid 20s. Beyond that 12s are a better bet. It's a shame that we can't use the same kit for all our diving - I think that every time I look at 15s or 18s in my shed. We just have to tailor our kit to the diving we do the most.

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Michael-Fisch(Offline)

I have multiple sets of D7s, D10s, D12s and D18s.

The D7s are used for all weenie dives, shallow, short, no deco etc, and are used often in all the local mudpuddles I dive in.

The D10s are used for deco dives where the ability to move heavy doubles is limited.

The D12s are used for everything shallower than 80M, I can pump them high enough for a 20 minute bottom time at 75M. Carrying them is OK, but many other things are more fun than trying to climb over 30" steps with D12s.

The D18s are only used when the dive requires them, in the water they're great, but I stay in the water longer because I'm dreading having to climb out wearing D18s. Out of the water they are a bear, and I hate them until I get back underwater with them.


In other words, get the D7s, and enjoy them! If others are diving single tanks, you will be disadvantaged diving D12s. Eventually your diving might change to where you need D12s, at that point hopefully enough time has gone by that the expense of having 2 sets of doubles is not a concern.

Michael

Captain Calamity(Offline)

OK, so my plan for now is to go with the D7s which I know will be the right choice for my diving at the mo. Given that my diving has slowly progressed over the last few years, I guess that one day i'll need the D12s too, so will just have to bite that bullet when the time comes.

CC.