View Full Version : Twinset debate!
Can of worms. Check. Can opener. Check.
Here's a question I've been wanting ask for a while. Why should somebody not go straight to a twinset once they have finished their OW or AOW training? I don't know what ,or if it, is written as to when you can expect to more on to twins but there seems to be a belief it just isn't done, that diving with a twinset needs more experiance and training. Which fair enough to use them to their full potential then yes you do need training.
But through my simplistic way of looking at things. What difference do they make to the diving of a relative beginner if they are manifolded? They are then essentially a single tank with two posts.
Pro's and cons to a beginner:
Pro's
Future proof.
No large outlay required later.
Less weight needed on belt/harness.
Once at a sufficient level to use them fully you have instant redundancy
Con's
Initial outlay is larger.
Heavier to handle.
More for a beginner to possibly set up wrong. But that's why we have buddy checks.
http://blog.b92.net/arhiva/files/images/can%20of%20worms.jpg
Let the thread begin....
I get a few funny looks humping a 15 litre on shore dives as it is, never mind a twin set, (not that I am bothered). I nearly always surface with loadsa air in reserve.
I have the new buddy explorer that has a small auto air bottle as a backup; if I didn’t have the buddy setup a twin set would have been a good option offering me some extra redundancy as I dive solo.
So I think a twin set would be a goodun for solo nuts, if double redundancy is on offer.
Lizardland
01-09-07, 17:07
Why shouldn't it be done? The Danish club I dived with had a rule that twinsets were required for any dive over 30m regardless of experience (pony bottles were never used for any diving). I know someone who was taught to dive in a twinset and wing right from the start.
At the stage most people buy a pony I bought twin 300bar/7's, it is a perfect mid range set, it's reasonably light and a lot more comfy than a single + pony because it sits flat on your back and doesn't move. Weight I think is something like 20kg and I don't need any lead with the set, a single 12 is ~13kg plus I need probably another 10kg to sink me.
I'd much rather see new(ish) divers who are looking to progress deeper or start going into deco use small twinsets than being fooled into thinking a pony bottle is a realistic emergency option. I'm a great believer in the old saying that if you think you need a pony then you need a twinset, if you don't think you need it then don't take it.
The biggest downside of twinset diving in a club environment is that they are a pain to fit into RIBs. The cost isn't much more expensive than a pony, the safety benefits are better. A lot of what we do and teach to others is bogged down in traditional views, you don't do it because you don't do it kind of thing. You dive with a single and pony, that's what you do. There is a great deal of misunderstanding, twinsets aren't just for megadeep or long dives, solo dives, etc. As Scott sums up, it's a single cylinder with two outlets.
Cheers,
Stuart
no reason at all why recently qualified divers shouldn't go to twins.
I personally use 15l & pony, but know a cpl of people who after 30 dives went DIR and have used twin 12's ever since...
Providing they can do their shut downs and drills sufficiently, have good buoyancy control and are smart with their profiles, run times etc then theres no problem.
However, the other side of the coin is several people go out to buy twins cause they belive it'll make them a better diver - all the gear and no idea can be dangerous in any sport.
I don't need any lead with the set, a single 12 is ~13kg plus I need probably another 10kg to sink me.
Stuart
Hi Stuart
With no weights to drop option on your setup I was wondering what's the score in an emergency uncontrolled accent.
I always thought that dumping the weights was the last bail out option if all other options fail. Thinking along the lines of bag rupture wi all that inherent weight. Supose it a toss up for the bends!
Humping a 15l on shore dives.....the mind boggles :D I don't see a problem for inexperienced divers using twinsets. I don't have twinsets these days but I like the balance they give me underwater.
There was a thread earlier this year ove on YD on the same subject, however the guy was a new diver and had done all his training on twin 12's and a wing. If the diving you do warrants twin 12's, use twin 12's and as has been previously mentioned so long as you can shut them down by way of either the manifold or a slob knob if a fault develops why not use them. There are plenty of "teckie" instructors that do twin set famil courses.
so long as you can shut them down by way of either the manifold or a slob knob if a fault develops why not use them.
This was the meaning of my post. A beginner can use twins but doesn't need to be bogged down with shutdowns. You're not taught to shut down a single. When they have progressed then shutdowns can be taught.
Lizardland
01-09-07, 20:02
Hi Stuart
With no weights to drop option on your setup I was wondering what's the score in an emergency uncontrolled accent.
I always thought that dumping the weights was the last bail out option if all other options fail. Thinking along the lines of bag rupture wi all that inherent weight. Supose it a toss up for the bends!
I wouldn't want to dump my weight in a drysuit from any real depth (I've seen it happen a couple of times from 30(ish)m, it wasn't good). I tend not to dive with any weight that can be dumped or come loose, with 7/300's I don't need any, with twin 12's I need a few pounds but I have a v-weight moulded to fit between the twinset and backplate. With my rebreather I have a couple of pounds on a belt because I'm too lazy to mould a new weight.
I wouldn't dive with a set that I couldn't float with just my drysuit inflated. With the 300bar 7's and 232bar 12's even with stages it is still possible. Unless you're using something far overweighted like twin 12/300bar then it shouldn't be a problem. If I'm diving in a wetsuit then I carry a small liftbag that I can partially inflate for a bit of buoyancy if I needed it.
Cheers,
Stuart
Peter and I were chatting about this recently! We use 12l plus pony and we have two 12l each, therefore going for two dives is pretty straightforward. We have a 300bar and a 232 so we can extend one of dives time if we want by using the 300bar. If we were to go for twin 10s or twin 12's without going to 300bars it would be less air than we currently have available to us. I am not convinced by twinsets, I can see the comfort issue under the water, but ontop of the water it looks awkward on a boat in rough conditions and tiring walking around somwhere like St Abbs harbour.
With a pony I have redundancy to get me to the surface without having to fiddle with valves or manifolds.
Anyway, just my thoughts, I am going to open another can worms on another thread tonight ;)
I'm a great believer in the old saying that if you think you need a pony then you need a twinset, if you don't think you need it then don't take it.
Cheers,
Stuart
The whole point of having a pony, IMHO, is that you don't ever want to need it, its there for an emergency!!
I think the debate over the pro's and cons of twinsets over singles and pony has been done
http://www.rebreatherworld.com/images/smilies/beatdeadhorse5.gif
This was the meaning of my post. A beginner can use twins but doesn't need to be bogged down with shutdowns. You're not taught to shut down a single. When they have progressed then shutdowns can be taught.
Ok, why would you want to shut a single down?
The point (which im sure you know) of being able to shut a manifolded twinset down is to try and save gas should a reg freeflow or a valve or hose fail therefore saving as much gas as possible, other wise you might as well dive one big single. If you cant shut down either dive independent 12's or dive with the manifold shut and use them as indies.
However if a beginner learns on manifolded twins, surely part of that learning curve will include shutdown drills.
Ok, why would you want to shut a single down?
The point (which im sure you know) of being able to shut a manifolded twinset down is to try and save gas should a reg freeflow or a valve or hose fail therefore saving as much gas as possible, other wise you might as well dive one big single. If you cant shut down either dive independent 12's or dive with the manifold shut and use them as indies.
However if a beginner learns on manifolded twins, surely part of that learning curve will include shutdown drills.
I'm thinking if a beginner was given a twinset. Why bog them down with shutdown procedures when there is so much else (and more important in the setting) they need to remember and learn.
Once they have reached a level where they are comfortable diving then shutdowns can be introduced.
You would never shut down a single. The point being that to give someone a twinset and not tell them (yet) about shutting down then they effectively have a large single on their back. For a beginner, keep it simple.
Scuba-Doh!
02-09-07, 00:13
AOW diver here, recently moved to indie twin 10s. I'm still looking to buy my own twinset (tanks are currently borrowed) and will go with a manifold when I do. I tried the pony & 12L through borrowing someones pony while they were on hol and although I appreciated the redundancy I didn't much like the outlay compared with a twinset.
I wouldn't want to dump my weight in a drysuit from any real depth (I've seen it happen a couple of times from 30(ish)m, it wasn't good). I tend not to dive with any weight that can be dumped or come loose, with 7/300's I don't need any, with twin 12's I need a few pounds but I have a v-weight moulded to fit between the twinset and backplate.
Stuart
Hi Stuart,
The weight dumping option has always sounded to me just a comfort blanket option to calm the minds of the inexperienced.
Most divers eventually cotton on to the fact that the Polaris ride to hell option of dumping weights at depth might not be preferable to drowning. In fact after the shock the old wives tale say drowning is not a bad way to go.
Enough depressing talk. Your idea of moulded weight added to the set sounds dam good. I squeeze twelve kg into my BCD integral pouches. They are only designed to take eight kg. My pouches are looking tired after only 6 months and I think I am straining the retainer clips. In fact I already had one accidental pouch detachment. Fortunately it was on the surface but it was rough seas and for a while I was swimming sideways, hell of an exit. Gona experiment with your idea.
Go on then, help me, why is a twin 7 got better safety beneifts than a 12l plus pony? :confused:
I can see that the twims are more streamlined than a main and pony, but as I'd need to buy a wing I am not rushing for that option yet. Billy mentioned stability and , as I've never tried twins I can't say how much more stable they are, but I don't really find my current set up much of a problem (although that is exactly the same way I felt about a front only suspension system on a mountain bike until some b******d let me try his full suspension set and ended up costing me about £1000!).
On the diving I regualrly do the people with twinsets simply seem to use the same set up for 2 dives, while we change cyclinders. As they are not carrying radically more or less air/gas than we are over 2 dives the only benefit they get in this regard is not changing. (7*300*2=4200, 10*230*2=4600, 10*300*2=6000, 12*300*2=7200, 12*230+12*300=6360[+3*230])
Most of the time in the UK I can't see me wanted to stay down twice as long or having the ability to without running into deco, which I don't really fancy nor am trained to do. I haven't yet seen any overwhelming evidence of beneifts that I would reap from a twin set yet posted here - I'll see if the safety response helps.
Admittedly I said all this about Nitrox 2 years ago, but definately saw the benefit of added time on last weeks Sound of Mull wreck trips over those on air!
Most divers eventually cotton on to the fact that the Polaris ride to hell option of dumping weights at depth might not be preferable to drowning. In fact after the shock the old wives tale say drowning is not a bad way to go.
Read the Last Dive by Bernie Chowdhury - lots of people there saying, very macho, that they'd rather drown at the bottom that surace missing decos. Screw that, Bernie lived, I'd rather go the surface and risk it all to maybe survive than guarantee drowning.
Obviously, I am planning to never have to make the decision!
I'd rather go the surface and risk it all to maybe survive than guarantee drowning.
Obviously, I am planning to never have to make the decision!
I don’t think for one moment that the human instinct to breath could be overcome even by near certainty of a big bend.
All, I think would zoom for air even at 40 meters +
I think the debate over the pro's and cons of twinsets over singles and pony has been done
http://www.rebreatherworld.com/images/smilies/beatdeadhorse5.gif
Ever heard of Pandora's Box?
Lizardland
02-09-07, 12:54
The whole point of having a pony, IMHO, is that you don't ever want to need it, its there for an emergency!!
Which is the question I asked, do you need the pony or don't you need it?
Go on then, help me, why is a twin 7 got better safety beneifts than a 12l plus pony? :confused:
For a number of reasons, you have a hell of a lot more air available in an emergency for a start. On, say, a 40m dive after 15min on twin7/300's then you'd have about 2500l of air left. If you're out of air then you're still going to have 1800-2000l of air left, three times what a pony is going to give you. Even on indies, you've got 1250l left.
For emergency planning then it's realistic to assume you are going to be breathing like Gary Glitter in a scout hall, so 1min on the bottom to sort everything out, 4min ascent and a 4min stop is going to come to 550litres(ish). Allowing for cooling and the reg's IP you are only going to have 600l in a pony. Enough to get you to the surface but if you spend any more than a 1min on the bottom then you aren't going to make it. You could blow off the safety stops to be sure you make it (you're not going to be ascending rapidly when you've got no air left are you?:rolleyes:) but it's just a vicious circle of bad choices due to unrealistic planning. That's also assuming you're doing it on nitrox, you aren't dealing with currents, putting up a SMB, etc; if you're on air and you're at the limit of your NDL then deco is going to rack up faster if you're taking time to sort something out on the bottom and those are stops that you don't have the luxury of being able to forget about.
Read the Last Dive by Bernie Chowdhury - lots of people there saying, very macho, that they'd rather drown at the bottom that surace missing decos. Screw that, Bernie lived, I'd rather go the surface and risk it all to maybe survive than guarantee drowning.
Obviously, I am planning to never have to make the decision!
In the real world we'd all take the choice of surface. However, don't underestimate a rapid ascent and missed deco. I've seen it happen, the guy died in agony whilst choking on the froth that was his lungs, it's a particlularly unpleasant way to go.
Cheers,
Stuart
If you're out of air then you're still going to have 1800-2000l of air left, three times what a pony is going to give you. Even on indies, you've got 1250l left.
To have 1800 left on twin 7s you'd need 128bar, it'd be 90 with 10s and 75 on 12s. I assume you'd lose some of this if you need to shut down.
To come up from 40m you'd need ([40-5/18]say 2 minutes at an average of [(40-5)/2+5] 22.5m, giving 3.25 bar at, in my case, 20sl/m, giving 130l ; plus 3 minutes at 5m = 90l ; all in all 210l or a third of the content of the pony. Even allowing twice the rate of ascent (or twice the breathig rate or some mixture in between) and a minute at the bottom that would total 450l.
At a 100 bar on your twin 7s at the end of a dive you would have at most 1400, which is alot more, if you don't lose it all while turning off the manifold.
Anyway, I think this sounds like horses for courses. If you are going deep on twins and applying the rule of thirds rigourously then I can see why you would want twins - and of course it does no harm to have extra gas. But it's not all free, it costs more, needs more discipline and requires you to act quickly. But given that I'm not planning 40m+ or deco diving I think a pony as a bail out sounds fine.
In the real world we'd all take the choice of surface. However, don't underestimate a rapid ascent and missed deco. I've seen it happen, the guy died in agony whilst choking on the froth that was his lungs, it's a particlularly unpleasant way to go.
Haven't seen it, and no wish to, but have read about it. That was why I wasn't aiming to find out.