View Full Version : twin 12's, extra 15....options on cyl's??
NickBCotswold
21-09-2007, 08:30
hi guys
novice OD here with currently 15 dives (by this time next week should have approx 20 dives - then off to sharm in Nov for another 5-6!)
currently diving using a single 12lt....as a heavy breathing novice a 20m dive is lasting around 20-25 mins (usisng rule of thirds) - on holiday in croatia rented 15lt cyls and was getting 30-40min dives in.
My question is that whilst more experienced members of our club are getting two dives in off one cyl, i'm only getting one - and have to borrow another cyl or get refill before the afternoon dive......
I'm kinda independant and am looking at buying another cyl at the dive show.....
would I be better off buying another 12lt with a veiw to eventually coupling it up to make a twin set, or buy a single 15lt for a longer deeper first dive of the day?!
I dont know technically much about twin sets etc and how two cylinders couple together and not even sure you can make a twin set from two single 12lt cyls.....so any advise thankfully received!
Nick B
Ben Panter
21-09-2007, 08:46
Hi Nick,
Don't think that the rate you breathe at now will be the same forever. As you relax in the water and things become 'normal' you can look forward to getting 1.5x the time you manage at the moment from a tank!
There is no problem buying another 12 to make a twinset in the future. You may wish to buy a set of manifold valves - reckon on an extra £100 for that - but it's quite acceptable not to use one. Most divers go their entire lives without ever wanting or needing to 'twin up' - and there is a huge range of diving available to you before you need to take that option, despite the opinion of many t'internet divers.
Having said that, I'm not that keen on 15l tanks - they're a bit big and bulky, and the mass is moving further from your centre of gravity and hence makes you slightly less stable in the water. Diving in Croatia would be warm water, you were probably diving more frequently than you do at home so I'm not sure if you can make a direct comparison.
Unless you really need one I would move towards another 12 and work on doing a shed load of diving to get relaxed and lower your air consumption. I'm sure you'll get lots of opinions though!
Cheers,
Ben
Ben Panter
21-09-2007, 08:49
You might find this page useful too:
BSAC diving Wiki - Heavy Breathing (http://www.bsacforum.co.uk/wiki/index.php?title=Heavy_Breathing)
Ben
NickBCotswold
21-09-2007, 09:15
Hi Ben
many thanks and great link........
looking back through my log book can see a slow improvement on air consumption...... sure it will continue to improve as i gain more experience etc
thanks for the advice about buying another cyl........ think another 12lt is the way to go, then eventually that will give me the option of coupling them together if thats the way i want to go in the distant future!
Nick B
garethwoodruff
21-09-2007, 11:31
Hi Nick,
Just thought I would muddy the waters slightly....
Personally I would suggest buying a 15 litre cylinder, I have used one for diving for years and don't find them substantially heavier than a 12 litre.
If you have a 15 litre for a first dive of the day (tends to be the deeper dive) and a 12 litre for the second dive.
If your unsure about the weight of a 15 litre, I would suggest borrowing one from someone in the club to have a dive from.
As a relativley new diver, twin 12's are probably a year or 2 down the road, and you may not go down that route in the event anyway. Whilst my air consumption improved as I gained expereince, it was not a massive improvement, and i wished I had bought a 15l, in the end I sold a 12 litre to buy a 15 litre.
Cheers,
Gareth.
NickBCotswold
21-09-2007, 12:17
hmmmm........exactly what i was pondering in the first place!!!!!
any other opinions?!!
Nick B
NickBCotswold
21-09-2007, 12:56
also........to add some confoooosion to it........
if i'm buying a new 12lt OR 15lt cyl, should I look at the M26 thread for notrox for next years legislation??!!
confoodled.com!
lol
Nick Argue
21-09-2007, 13:48
My question is that whilst more experienced members of our club are getting two dives in off one cyl, i'm only getting one - and have to borrow another cyl or get refill before the afternoon dive......
Nick B
Yep, I remember that stage in my diving, you will get better with experience.
would I be better off buying another 12lt with a veiw to eventually coupling it up to make a twin set, or buy a single 15lt for a longer deeper first dive of the day?!
Nick B
My take on the cylinder size is to buy what you need for the diving you're doing now and ignore the twin issue. If you're an average sized bloke I'd get a 15 as it's really not much heavier than a 12.
I regularly lend my 15's to mates who've bought 12's and want a bit more air for a particular dive.
Nick
Ben Panter
21-09-2007, 14:43
No. It's by no means certain that it will even be used in the UK, and if it is then perhaps adapters will be allowed or possibly you could buy a new valve for the top for £25 or so. The cylinder body itself will not change.
Ben
Another vote for getting a 15L, when I dived singles it was always 15 first dive, 12 second.
Now I use my 15L to top off my twinset and for teaching (two dives for me on a 15 matches two instruction dives with trainees on a new 12 each time). Never really use my single 12's since I gave up pool training.
Paul Oliver
21-09-2007, 19:51
Single tank diving i have a 15L, much better than a 12L once you get to 30m stuff, like Pete i also use my 15L to top of my twinset for dive 2 when out on a days diving, so it will still get plenty of use.
Hi Nick
As you know from previous posts I'm in a similar stage of training as yourself. Ive just bought a 15L (great deal off ebay) and am looking forward to jumping in with it at Stoney in the next couple of weeks to see how it feels. On the advice of others Im planning to use it for air and get my 12L O2 cleaned for a nitrox mix for my second dive of the day.
On the advice of others Im planning to use it for air and get my 12L O2 cleaned for a nitrox mix for my second dive of the day.
When I single tank dived I did it the other way round, big tank was deeper therefore nitrox was good to eliminate/reduce deco, second dive tended to be so shallow it did not matter.
NB this is the opposite of what most nitrox courses recommend, however the rule to increase fraction of oxygen and/or reduce depth for the second dive is actually stating the important bit in a different way, which is reduce the ppN2 for the second dive. 32% @ 35m = ppN2 of 3.06, 21% @15m = ppN2 of 1.975 so if you do a typical south coast two dive day you are still fulfilling the requirements by doing so as above.
Another vote for getting a 15L, when I dived singles it was always 15 first dive, 12 second.
I'm going to throw in my lot with the 15L-brigade.
A 15 *is* a bit heavier - but not a lot. It is a bit bulkier - the CG is further from your back, so it tends to be a bit more prone to rolling during the dive. But overall, it's a good setup; you should have loads of gas available once you're over the initial "breathe like a Blackpool donkey" stage, and that means you now have a choice about how long you want to be in the water.
Vic.
I'm going to throw in my lot with the 15L-brigade.
...and I'm going with the single 12L faction :)
'Cos I'm a shortarse, I bought a dumpy 12L when I realised I'd been bitten by t'underwater bug. That gives the worst of both options - CG slightly further out than a standard 12, and heavier - but meant I didn't alternately crack the back of my head or my pelvis against the first stage or boot, respectively.
After about 150 dives, I finally got myself tuned and weighted correctly. Suddenly I went from a strained 25 minutes at 20m (in British water) on a 12 to a very comfortable 40 mins+ on the same cylinder. When I realised that carrying 2-4 kg extra weight just makes you fiddle and blow air off, diving became a lot easier. Unfortunately I peaked at Stoney one day last year on an alu 10L by managing to do 30 mins at 20m and still come out with more air than our resident fit undergraduates had on 12s. I shall never reach such heights (depths?) again.
Anyway: humour (oh, was that what it was?) aside... get your buoyancy right. You won't believe the feeling when you do. I still can't, sometimes!
Nigel Hewitt
21-09-2007, 23:14
Anyway: humour (oh, was that what it was?) aside... get your buoyancy right. You won't believe the feeling when you do. I still can't, sometimes!
eg: Dive for a week on a 3+3litre rebreather topping up from two 7Ls and take over 90bar home in each. 12 dives down to below 40meters, half an hour to an hour (except the one when I didn't quite zip the suit right up).
OK I did get the suit bottle topped up occasionally but that's only 2L.
Getting the weight right (just a fraction negative) makes all the odds to the gas you burn through just staying neutral in the water.
The gas used in excessive buoyancy adjustments, both in the BCD and big breathing, is wasted gas and comes off your dive time. I suspect this is the biggest factor in bad air consumption. We can tell people to relax but we taught them to control their buoyancy by breathing and if the weight is wrong, just a couple of kilos over, it is one total tinned worm experience so no wonder they're all wound up like a big spring.
Hi
Just to throw my two pence into the arena regarding your origional question.
When I first started to dive (more years ago than I care to mention), I like many started with a single 12 and a breathing rate that could match that of an unfit elephant.
Then as you are considering, went down the route of getting buying a 15L for 'deeper' dives, only then to buy a 3L pony rig as a bailout.
This set up did work very well for me and I dived with this set up for a few years. Only to replace my 15L with another 12L so I could put together an 'unmanifolded' twinset, and again this lasted me quite a few years until I eventually fitted a manifold.
Obviously over the years of practice and becoming more relaxed I can easily get 2 30m x 30min dives from my twin 12's and still have enough gas left to do some instructional work with trainees.
Personaly, I would suggest you have a good think about the type of diving you wish to be doing in 12-18months time (and be realistic). Then if possible beg / borrow / hire the equipment you are thinking of buying to see how you take to it, and make your decision from there.
Things to remember (sorry if I'm being patronising), don't run before you can walk (using a twin set / 15 + pony, incurs a greater task loading), in time your breathing rate will come down considerably, and 15L & 3L cylinders are very sellable, and if you purchase the right type of reg for your pony it can be used on the left hand post of a twin set.
Hope this helps :o
Andy
hi guys
novice OD here with currently 15 dives (by this time next week should have approx 20 dives - then off to sharm in Nov for another 5-6!)
currently diving using a single 12lt....as a heavy breathing novice a 20m dive is lasting around 20-25 mins (usisng rule of thirds) - on holiday in croatia rented 15lt cyls and was getting 30-40min dives in.
My question is that whilst more experienced members of our club are getting two dives in off one cyl, i'm only getting one - and have to borrow another cyl or get refill before the afternoon dive......
I'm kinda independant and am looking at buying another cyl at the dive show.....
would I be better off buying another 12lt with a veiw to eventually coupling it up to make a twin set, or buy a single 15lt for a longer deeper first dive of the day?!
I dont know technically much about twin sets etc and how two cylinders couple together and not even sure you can make a twin set from two single 12lt cyls.....so any advise thankfully received!
Nick B
Its mostly already been said but I'll put my thoughts down.
I've only been diving about 9 years, I used to worry that I used air - but if you don't use it - well you must be dead!!!!!
So I don't worry now.
I was advised to buy a 12l cylinder and instead got a 15l which I have never regretted and also use a 3l pony for either backup air or deco depending what I'm doing.
The full story is that I own 2 x 15l's and either dive on air on the 1st dive and nitrox on the second or nitrox on them both ie single cylinder plus pony.
I have been pondering for a couple of years whether to go to twins but it doesn't really lend itself to RIB diving - so as has been said look at what you intend doing with your diving - eg are you likely to be lowering your kit by rope at Seahouses harbour when the tide is out????? its far easier if you can split your kit!
Oh and yes more diving and practice slows down the breathing rate - a couple of weeks ago I had a 64min drift dive (so I was relaxing and not working) travelled a km came up with 120bar - for me I'd rather be happy knowing I've got loads in reserve - cos I use less air when I'm happy.
hope it helps
Steven
garethwoodruff
23-09-2007, 09:45
I have been pondering for a couple of years whether to go to twins but it doesn't really lend itself to RIB diving - so as has been said look at what you intend doing with your diving - eg are you likely to be lowering your kit by rope at Seahouses harbour when the tide is out????? its far easier if you can split your kit!
Oh and yes more diving and practice slows down the breathing rate - a couple of weeks ago I had a 64min drift dive (so I was relaxing and not working) travelled a km came up with 120bar - for me I'd rather be happy knowing I've got loads in reserve - cos I use less air when I'm happy.
hope it helps
Steven
If you think out twins and RIB diving, they are not that bad, certainly easier to handle than a main cylinder and pony.
What I do is hand up weight belt, take the twin set off and get someone to hold it or clip it on to the side of the boat (inflated). I then get in the boat, and help the person holding onto them pull them out, that way they become a 2 man lift, that works great.
On a twin set you only need one set for 2 dives and as we often go out for 2 dives, there is no need for a second cylinder and changing cylinders in the boat.
The club have pretty much accepted that now :o
If you think out twins and RIB diving, they are not that bad, certainly easier to handle than a main cylinder and pony.
What I do is hand up weight belt, take the twin set off and get someone to hold it or clip it on to the side of the boat (inflated). I then get in the boat, and help the person holding onto them pull them out, that way they become a 2 man lift, that works great.
On a twin set you only need one set for 2 dives and as we often go out for 2 dives, there is no need for a second cylinder and changing cylinders in the boat.
The club have pretty much accepted that now :o
I hear what you say, we often take 2 cylinders with 4 divers but not if there are 6 of us!
Now if we all go to twins do we say oh we can only take 4 now??
Then like I said we use different mixes for different dives - do you use your twins as independant twins with different mixes - or go for a stage? more weight in the boat.
Nevermind where you put them.
Its not that we haven't thought about it we have at great length.
cheers Steven
Ian@1904
23-09-2007, 15:23
I used 15 ltr cylinders for three years (200 dives) before changing to a twinset. I still use the 15ltr cylinders when taking trainee/novice divers for a dive or two. These days I can get two dives @ say 15 metres out of one cylinder.
I was discussing gas consumption with a regular buddy this weekend, she now has 70 dives and her gas consumption is starting to noticeably improve as her technique and relaxation have improved.
If you attach a pony then the kit can be cumbersome and unbalanced when being carried.
garethwoodruff
23-09-2007, 16:25
I hear what you say, we often take 2 cylinders with 4 divers but not if there are 6 of us!
Now if we all go to twins do we say oh we can only take 4 now??
Then like I said we use different mixes for different dives - do you use your twins as independant twins with different mixes - or go for a stage? more weight in the boat.
Nevermind where you put them.
Its not that we haven't thought about it we have at great length.
cheers Steven
Depends on your RIB and its layout, we've got a 5.9 meter, but no bottle rack, and with a bit of careful loading you could get 5 twinsets on them, maybe 6.
When you look at the amount of space a twinset takes up and then compare it with a 15 and a pony, not a huge amount of difference.
We don't tend to do dives that need stage cylinders off the club RIB, not much deeper than 30 meters.
Just one Nitrox mix in the twin set, (has to do for both dives) personally I use a manifolded set, not sure that makes a huge amoutn of difference. I do 90% of my dives on nitrox anyway these days, the extra few squid in the grand scheme of things is not an issue.
Paul Oliver
24-09-2007, 09:09
If you attach a pony then the kit can be cumbersome and unbalanced when being carried.
Stage rig the pony, thats what i do now and its much more comfortable, read Charles Hoods kit review of an Aqua elevations Pony Bag in Dive magazine this month, its converted him :)
I used 15 ltr cylinders for three years (200 dives) before changing to a twinset. I still use the 15ltr cylinders when taking trainee/novice divers for a dive or two. These days I can get two dives @ say 15 metres out of one cylinder.
I was discussing gas consumption with a regular buddy this weekend, she now has 70 dives and her gas consumption is starting to noticeably improve as her technique and relaxation have improved.
If you attach a pony then the kit can be cumbersome and unbalanced when being carried.
maybe while being "carried" but not underwater!!!
actually if in a bag yes - but does anyone use them now??? on a clamp not unbalanced at all
Steven
toptribefan
03-10-2007, 20:04
All of this is very interesting but brings us back to the old addage.......
The only correct answer is the one that works for you!
You will find your own answer, you may even tell us, until then I would borrow kit if you can until you find a setup you are happy with then buy it. Dont get hung up on buying something at the Dive show, LIDS will be along shortly!
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