View Full Version : Stuart's box - Stage 2
Lizardland
02-06-08, 12:56
Could be an interesting thread! Post a pic of yourself kitted up and talk through your set up. So long as the comments remained constructive it could serve to make current or future setups safer/simpler/cheaper.
I'll start the ball rolling then with the reasons as to why I set my kit up the way I do. I don't have many pictures of my kit set-up so apologies that these aren't very clear:
From the back:
http://www.lizardland.co.uk/francemay2004/uw-03.jpg
And the front:
http://www.lizardland.co.uk/francemay2004/uw-06.jpg
I like nice, simple kit that has an element of redundancy to it and this is how I tend to do most of my diving, my rebreather only really comes out for deeper stuff or training dives. Twinset because I'm not happy with the margins a single and pony gives, I think it's very hard to rig a pony as cleanly as a twinset. Single wing because my suit is my backup buoyancy. Manifold so I don't need to switch regs and anyone who needs air who grabs the reg in my gob automatically gets the long hosed reg. Regs are just TX40's which are fairly cheap and very simple, not oxygen rated but they've been fine for everything I've put through them.
Single piece harness, nothing to break on it, once it's set up then no reason to adjust it again so no need for any buckles or clips or straps. One d-ring on the left waist strap, one on each shoulder strap and another at the back on the crotch strap. Wing, just a simple Dive Rite wing, no bungees that will empty it if it gets a leak. Aluminium backplate, I found I was too heavy with steel. I use backplate/wing because I find it a lot more comfy than a stab jacket, and with a twinset it gets the weight off my back and makes reaching the valves easier.
Regs, right hand reg has the long hose and wing inflator. I breathe the long hose and donate from my mouth, the reasons have been done to death so I won't repeat them. Long hose is looped across my chest and round my neck, easy to deply, nothing to get caught on and easy to replace. It's on the right because that gives the most length of hose available. Wing is on the right because I don't want to jump off a boat with my wing off, if I can breathe then the wing will work. Back-up reg is on the left and on a bungee round my neck so it's always there, I can even reach it without using my hands. Suit hose is on the left too as is the SPG. My SPG is clipped off on the left waist d-ring, I don't need it right under my nose and I'm not bothered if my buddy can't see it there :) The tighter you loop a HP hose the more likely it is to burst so I keep the hose as straight as possible. Basically, all my main hoses are on the right, all the less critical stuff is on the left, makes thinking which valve to shut down easier.
I usually have the battery pack for my light on the right waist, it keeps it out the way and unlikely to get damaged, it also takes off a bit of lead. I've no weight belt to dump, it's all sandwiched between the twinset and the wing. I clip my reel to the d-ring on the back of my crotch strap, it sits out the way, underneath the cylinders. Everything else gets shoved in pockets on my drysuit.
If I'm diving a single then I still use a backplate & wing but with a smaller wing. I still use the long hose.
It probably sounds a bit familiar to a few people on here, I wish it was all my own idea but it isn't. I started off diving pretty soon with a backplate and wing, moved on to breathing the long hose and just picked up little bits now and again. After a few years it became a DIR-type setup by default which I'm fine with because the logic makes sense to me.
Cheers,
Stuart
you want to get yourself a pony, Stuart ;)
Lizardland
02-06-08, 14:58
I've got one, out of test since 1996, still with the same air in it too :D
What size & W.P. of tank are you using on the twins Stuart ?
JB.
Lizardland
02-06-08, 15:57
Twin 12/232's. I was using 7/300's for a while but they're a bit limited though they are really nice to wear. Otherwise I'm not a fan of 300bar cylinders, I found they had usually cooled back to about 260-270bar so you aren't really gaining much except for a load of extra weight.
Twin 12/232's. I was using 7/300's for a while but they're a bit limited though they are really nice to wear. Otherwise I'm not a fan of 300bar cylinders, I found they had usually cooled back to about 260-270bar so you aren't really gaining much except for a load of extra weight.
How do you find that for weight / manouverability ?
I guess you can take a bit of lead off , but it must still be a fairly hefty setup ?
Cheers JB.
Lizardland
02-06-08, 17:02
With the 12's I'd guess they don't really weigh much more than a pony and heavier weightbelt, a couple of kg maybe? All the weight is on the harness too rather than hanging round your waist which makes moving/standing a bit easier as well. I'd bet it's probably lighter than a 300bar 12 and a pony.
Yogi Diver
02-06-08, 17:18
Twin 12/232's. I was using 7/300's for a while but they're a bit limited though they are really nice to wear. Otherwise I'm not a fan of 300bar cylinders, I found they had usually cooled back to about 260-270bar so you aren't really gaining much except for a load of extra weight.
Did you find you needed the extra air then?
Twin 7/300s = 4200 litres
Twin 12/232s = 5568 lires
Twin 10/232s would appear to be a better compromise?
Lizardland
02-06-08, 18:24
Twin 7's are 4200 if they are filled to 300, I've found that you don't get that in them, usually it cools back to 260 or 270 if you're lucky unless the guy in the shop takes his time ,which most don't.
Twin 10's are too short for me, I can't get into them when they are on a boat bench, I can't sit in them while waiting to go in and they kill my back underwater after about 20min. They're a bit tight for doing two dives on as well.
12's are perfect for me, I can get two reasonable dives out of them or one dive with a bit of deco and still have a decent bailout for stops and sharing. The length is spot on, really easy to get in and out of and they sit on my hips underwater, the weight isn't that bad on the surface, like I said not much more than a single, pony and heavy belt.
The set I'm wearing in the photos is a twinset I sold a couple of years ago, they were twin 20's :D
The set I'm wearing in the photos is a twinset I sold a couple of years ago, they were twin 20's :D
Errmmmmm .....mental !! :D:D
I take it when you get them filled they don't view it as one tank !
Probably another good reason for avoiding twin 10s.
As you say , you can probably get 2 dives out of 1 fill with twin 12s , but if you only got 1 from twin 10s then effectively doubles your air costs.
Thats why I like my 15 , makes me feel like I'm geting something for nothing :D:D
Also isn't there a reliability issue with using 300bar , puts more stress on the first stage.
Or is that just a myth.
I can feel myself being drawn down the path of darkness......must avoid looking at manifolds.....stay away from wings......:)
Thanks for the info.
JB.
As Stuart states, twin 12s offer a great set up. :D
My pony hasn't been used for about a year now: what was meant to be an occasional configuration for "special" dives has become my standard now (twin 12s). My diving buddies here in Norway seem to like to go a bit deeper than my uni chums did in Scotland and I like to have plenty of air on my back in case we verge into deco (which seems to happen quite regularly). :eek:
Also, my trim is much better with twin 12s rather than 12+3 pony. In saying that though, I still think that ponies are of use & will keep mine. :rolleyes:
Although, when my back made a rather alarming "pop" noise yesterday while lugging my kit after a dive, I did think that a single cylinder might be a better option. No harm done though as I can almost stand upright now... may even get a dive in on Wed night! :o
Well I guess I'll just have to get a shot of somebodies then !
I find my kit heavy enough as it is .
I always imagined having an extra 15Kg on your back would just about finish me off.
If your boat diving ( 2 dives ) does that mean you have to take 2 twinsets on ?
And my final stupid question for the moment.
What about the 50bar rule ?
Does that become the 25bar rule , or are you way beyond that anyway - proper gas planning and all that :O)
Cheers JB.
Interesting points JB, My thoughts exactly on the two twinsets, as If I was going to go down that road I would like to go for twin 300bar/7s, however for two dives I would need two twin sets, rather expensive, or I would have to go for twin 12's and just one set. If I use just a bit too much, then that restricts my second dive, so do I have two twin sets of 12s too, sh!t that gets expensive. So for the time being I am sticking to single and pony.
No the 50bar rule is not reduced to 25bar, this is when gas planning comes in and the rule of thirds, rather than a 50bar rule!!
Lizardland
03-06-08, 09:20
Yeah, there's an extra 15kg on your back but if you were using a pony then you can drop about 5kg from that. I dropped a lot of lead from my weight belt too, I don't use any lead in freshwater and a couple of kg in the sea, on a single, pony and stab jacket (I think they really add buoyancy because of the bulk) I had a fat shot belt. I'd reckon the lot is maybe 3kg more than the pony set up when you take lead into account. The thing you do have to watch is that because the weight is sitting high up on your back is twisting with it on when moving around on the surface as it can strain the muscles in your back. Generally though it's fine once it's on.
You can do two reasonable dives quite happily on twin 12's without needing another set. If I'm planning deco then I plan for the minimum gas I need to get me and anyone I'm diving with back to the surface or to a deco gas cylinder (1min on the bottom sorting a problem out, the ascent and any stops plus another min if there's a switch to a deco stage, all doubled for two divers). I don't use thirds, I've found in deco diving it can be a bit too liberal, it's a good starting point for planning but it's better to work out what you need. If it's no deco then usually half the set on the first dive then 30bar on the second. You can actually have a longer first dive than everyone else because you're essentially draining a 12 (but with the same amount in reserve) whereas anyone on a single is going to stop with a bit of air left in the cylinder. Obviously, if you know in advance what the dives are then you can adjust the margins to get the best combo.
If I use just a bit too much, then that restricts my second dive
If you had a single 12 then you don't have the choice of using too much. You treat the twinset exactly the same. When the limit comes you go up, otherwise there's no point in having the limit. The extra air that is in the twinset should be thought of as a pony, there in emergency but not there to extend a normal dive.
Cheers,
Stuart
Cheers guys.
Just before I launch into another contentious debate about the 50 bar rule can I ask how your twin cylinders are connected ?
Or are they connected ?
Cheers JB.
Lizardland
03-06-08, 10:13
They have a manifold. Both cylinders are available from either reg.
Cheers guys.
Just before I launch into another contentious debate about the 50 bar rule can I ask how your twin cylinders are connected ?
Or are they connected ?
Cheers JB.
You've just launched a contentious debate about manifolded and non manifolded :rolleyes:
The most popular seems to be manifolded i.e. connected. You're basically diving a big single that you save half of if you spring a leak by closing the manifold. Or isolate before you go into a confined space where you wouldn't be able to reach your valves.
Lizardland
03-06-08, 10:51
You've just launched a contentious debate about manifolded and non manifolded :rolleyes:
The most popular seems to be manifolded i.e. connected. You're basically diving a big single that you save half of if you spring a leak by closing the manifold. Or isolate before you go into a confined space where you wouldn't be able to reach your valves.
I prefer a manifolded twinset to independants. It does depend on being able to reach the valves and you never truly know you'll be able to until you have to. You can be confident but never certain.
If it's something obvious with a reg or a hose like a freeflow then you'd shut down the appropriate valve, swap to the other reg and still have access to both cylinders. If it's a problem with the manifold itself then shut off the isolator so you've got two independant cylinders now and breathe the leaking side til empty.
It is handy to isolate when going into a confined space but you have to remember to open it again or you get misleading readings on the SPG. A good habit to get into is checking your valves are open whenever you've been inside something, the left valve can get rolled shut if you scrape the ceiling (I've had it happen twice).
Then there is the whole upright/inverted debate... Obviously upright is correct :D
That's it settled then , inverted twin non-manifolded 10l 300bar for me it is..............!
I can see the benefit and the sense of your set-up Stuart.
I think for my postion it would constitute trading off a slight decrease in the risk of underwater injury for a 100% certainty of serious injury just trying to get the thing on my back :O)
Still on the plus side at least you know nobody is going to run away with it.
You'd actually be surprised how easy they are to get around with once they are on your back.
The average male shouldn't have too much trouble. Just be mindful of how you turn, bend etc!
Ok , I am going to give it a try , next time I'm out and somebody has a twinset.
Cheers JB.
What about the 50bar rule ?
out of interest, can you define the '50 bar rule'?
if we are having one contentious debate, we may as well make it two...:D
I prefer a manifolded twinset to independants. It does depend on being able to reach the valves and you never truly know you'll be able to until you have to. You can be confident but never certain....
...Then there is the whole upright/inverted debate... Obviously upright is correct :D
Ahhh Stuart, you were doing so well 'till then ;)
I'm trying hard to stay away from the contentious debate... but... I'm certain I can reach my valves when things are going wrong and I have a throatful of water (don't ask ok :o ), I am certain I can't roll a valve open/closed on the roof accidentally and... Inverted is clearly superior ;);)
BUT,
Joking aside, I'd say try both, discuss both with people who dive them, then go for the set up *you* feel is best. To a large extent it probably depends as much on what sort of diving you do as on which setup a committee would call "best"...
If you want to try a set of manifolded inverted 10's then drop me a pm and we'll try to sort something out. I dive tens because I'm quite short and 12's are too clumsy/heavy for me, too long to sit comfortably. I can get two decent dives out of them (miserly you see lol) and manifolded for all the usual reasons (but the manifold only just open). I'll try and dig out some pics and do a full description sometime :)
Edited to add, someone with a bigger brain than me pointed out that the gas laws aren't linear once you get up towards 300bar, ie even if your gauge is reading 300 bar you should calculate the quantity of gas at around 270 bar to get a useable figure...
Oh and on the second dive, assuming a normal shallower cautious profile dive I use a "reserve" figure of aiming to surface with 30 bar rather than 50 bar, BUT it's very dependent on the location/conditions/circumstances! I've been places I'd happilly arrive with less and places I'd want *lots* more available at the end of the dive... ya gotta think and make decisions, one size does not fit all ;)
Lizardland
03-06-08, 18:53
out of interest, can you define the '50 bar rule'?
if we are having one contentious debate, we may as well make it two...:D
Swim around until you reach 50bar then go up. Or some use it as hit the surface with 50bar.
I think that's probably fine when you're doing typical Scottish shore dives where you might have started off deep but towards the end you'll be in the shallows. And unlikely to be doing deco. For boat diving where you're more than likely going to be spending most of the dive at a constant depth I don't think it's particularly good, a lot can happen on the way up from depth.
Ahhh Stuart, you were doing so well 'till then ;)
I'm trying hard to stay away from the contentious debate... but... I'm certain I can reach my valves when things are going wrong and I have a throatful of water (don't ask ok :o ), I am certain I can't roll a valve open/closed on the roof accidentally and... Inverted is clearly superior ;);)
No accounting for taste :D
Joking aside, I'd say try both, discuss both with people who dive them, then go for the set up *you* feel is best. To a large extent it probably depends as much on what sort of diving you do as on which setup a committee would call "best"...
True. I'm probably biased but I think right way up is the way to go :p One thing to bear in mind is with a right way up manifold that not many people are able to reach it straight away. It needs a bit of work getting the bands in the right place, getting the straps adjusted and actually learning where the valves are -- the most common mistake I've seen people make is reaching to where they think the valves are rather than where they are. It isn't hard but a lot of people get discouraged because they think that's it, I can't do it.
My rebreather cylinders are inverted and I was quite surprised that they aren't as easy to reach as I was expecting.
I dive tens because I'm quite short and 12's are too clumsy/heavy for me, too long to sit comfortably.
I think that's possibly a problem with inverted 12's with most people. If I put normal 3's inverted where I can reach them then they stick a fair bit above my shoulders. I'd imagine inverted 12's would make me look like Rocketman.
Cheers,
Stuart
Ok , I am going to give it a try , next time I'm out and somebody has a twinset.
Cheers JB.
Don't try it - you'll just spend money - living in ignorance is cheaper (from the owner of a set of carver skis, a full suspension mountain bike, an automatic car and associated fuel, other bits of diving kit that, while better than before, I hadn't noticed I was missing them until it was too late!)
Edited to add, someone with a bigger brain than me pointed out that the gas laws aren't linear once you get up towards 300bar, ie even if your gauge is reading 300 bar you should calculate the quantity of gas at around 270 bar to get a useable figure...
As the owner of 2 12l cylinders, one 300 and one 232 bar I must assume that is correct. Although you have a bit more air in the 300 bar the extra you seem to get is out of proprotion with what you'd expect and the bl&&dy weight. Although it has had the odd beneificial use I wouldn't buy the 300 bar again.
However as someone who is naturally nosey (on obviously lazy) I would like to know why and haven't yet made any effort to do so. Anyone got a good link to why this is the case? If not, this may has piqued my interest and I may trawl the net to see what I can find.
Just remembered I forgot to mention... I wouldn't have twinned 300 bar cylinders unless they were free, and even then I'd think twice(exempt 7's)! A good mate got a set of twin ten 300's tried them at powmill in a drysuit with a few kilos off his belt... and landed on the bottom of the quarry with a thump, filled a wing *full* and still had to fin to get out :eek: so he took all his weights off and it did pretty much the same thing!
I've tried lifting them and they seemed waaaay heavier than twin 12's, obscenely heavy in fact, and as has been pointed out they don't give you *that* much extra gas.
Unless you're a professional weightlifter who has to tie anchors onto yourself to sink I'd avoid...;)
Lizardland
03-06-08, 21:18
I saw a guy on a boat a couple of years ago with a pair of 300bar 12's that he'd never used before, he couldn't even stand up under his own weight with them without someone else pulling him up. I last saw him dragging/scraping himself over the Thesis with his wing rock hard full :D
...I think that's possibly a problem with inverted 12's with most people. If I put normal 3's inverted where I can reach them then they stick a fair bit above my shoulders. I'd imagine inverted 12's would make me look like Rocketman.
Cheers,
Stuart
Actually I meant 12's are too long generally, I find a ten is just a nice length whichever way up I put it, 12's are too long and dumpy's are just weird :p
If you stand up and starting with your arms at your sides reach behind you as though you are reaching around a wing your hands will probably be naturally about "mid butt height" lol, that's where my cylinder valves sit, it means they are where my hands naturally fall so there's no stretching or twisting and I can grab the valve with a full hand grip without stretching.
There's a brief poor view of it in this clip (with a flag badly stowed on the back of the cyls for reasons we wont go into :rolleyes: )
xd41ilWvfHU&NR
The cylinders look shorter than they are because of the black boots on them (means I can sit the set conventional way up on a rib if I want), and trim is neutral, I can do all the nonsense pointless "helicopter turns" with it or go upright as in the vid.
Probably wouldn't suit a taller person mind.... :D
(edited because i forgot to add the url DOH!)
You won't need 2 set's of twin 12's (unless you breath like a dyson),on sunday i had 2 dives 1st one to 40M (average depth 23M) which lasted 44 mins and the second to 31M (average depth 19M) which was 42 mins and even after those 2 dives i had 80 bar left which x2 is really 160 bar of a 12L,so plenty for another dive :)
You won't need 2 set's of twin 12's (unless you breath like a dyson)
I do see a flaw in your reasoning here.....:rolleyes:
I do see a flaw in your reasoning here.....:rolleyes:
If it's that bad you need to buy a rebreather and then your air consumption is immaterial ;) nice little SCR if you dive above 40m, CCR if you like the deepie stuff :cool:
Many of them are lighter than twin 12's too!!
nice little SCR if you dive above 40m, CCR if you like the deepie stuff :cool:
If only we knew someone selling a SCR :rolleyes: :D
If it's that bad you need to buy a rebreather and then your air consumption is immaterial ;) nice little SCR if you dive above 40m, CCR if you like the deepie stuff :cool:
Many of them are lighter than twin 12's too!!
Go on Peter - GO FOR IT !!
It will solve all your problems and make your life complete...........!
Oh and you missed out Dishwasher BTW :O)
and make your life complete...........!
Yes, it was the completion of my life feature that had stopped me so far! :eek:
Lizardland
04-06-08, 08:49
Yes, it was the completion of my life feature that had stopped me so far!
My ex-girlfriend told me I could either buy a rebreather or put a kitchen in. I now have a microwave and the emphasis is on the "ex" :D
out of interest, can you define the '50 bar rule'?
if we are having one contentious debate, we may as well make it two...:D
Why not , you get the choppin' block ready I'll go find my head :O)
The 50bar rule , as defined by the hallowed institution that is ScotSac ( might just be a club rule though ) goes something like this.
When you get to 50bar - game over , head up.
As you can see it has the benefit of being simple , easy to understand and easy to remember. Oh and you'll probably find there is a red line on your SPG at the 50bar mark just to help you.
So , a usefull and conservative 'rule of thumb' or a dangerous generalisation which could lead the unwary into unsafe gas (lack of) planning.
Lets have a look at a typical 'Sport diver' dive profile.
Single 12l , about 20m depth , 25l/m SAC.
Allow 4 mins for ascent ( shore dive scenario ) plus a 3min saftey at 3m.
By my calculations they would have about 33bar at the start of the safety stop and about 28 when they surface.
That gives them a margin of about 4 minutes at 20m to sort out any problems assuming they stay calm , and a lot less if they don't.
Good enough ?
Same scenario , but your buddy gets an OOA.
You hit the 3m mark with 16bar now and surface with 6.
Hmm , don't think I want to repeat that calculation assuming both your air consumption doubles :eek:
Sure in the real world , you would probably head up at a 'less leasurely' pace but its fun to knock these figures around.
Second scenario.
Same guy but at their depth limit of 40m.
Allow 5 minutes for ascent , 3@3 for safety.
25bar left at 3m , 19bar at the surface.
That gives you less than 2 minutes of margin at 40m.
Good enough ?
So , a good rule of thumb ?
In my opinion no.
There are too many variables in any dive for a 'one size fits all' approach , even without getting into deco stops etc and anyone who dives at whatever level should take this into account.
Of course it swings both ways too.
On a certain dive with a certain diver who's annonimity I shall fiercely gaurd ( so don't worry Peter ) I ran my tank down to 20bar , but then we were only guddling about at 6 - 9m.
Lastly , I 'adjust' the 50bar rule down 40bar when I'm using a 15l tank as that equates to the same amount of air.
Similarly , I guess you twin 12l guys would argue 25bar.
Ok , I'm off to hide now , someone PM me when its all over.
JB :D:D
If your doing the sums you should be past the 50 bar rule!
And if your at 40m you should be WELL past using the 50 bar rule!! :eek:
Oh and PADI say come out with 50!
Yes, it was the completion of my life feature that had stopped me so far! :eek:
LOL :D :D
Quick , hide the Visa bill :)
If your doing the sums you should be past the 50 bar rule!
And if your at 40m you should be WELL past using the 50 bar rule!! :eek:
Oh and PADI say come out with 50!
Well , as I say , I tend not to use it anyway.
Comming out with 50 sounds like an even worse rule - that would involve thinking and stuff :eek:
Oh , and just for the record , I wouldn't contemplate going to 40m , square profile , with a single 12l.
stafforddiver
04-06-08, 11:12
I dive with a twin set 2 x 12's, manifolded and an OMS wing.
Its a great set up, I can do 2 reasonable dives or 3 training dives on it. Can do a deep dive down to 60 meters if need be.
On a shallow bimble I feel quite happy coming up with 30 bar.
You have to treat the kit with respect, never move it about except on your back as this means you are less likely to injur yourself. Its really well balanced though, always sit down while wearing it if you can.
On a RIB, take the set off in the water and clip it to the side of the boat, get into the rib and then 2 of you pull it out, its loads easier than a pony and a 15lire cylinder.
The downside is the cost of keeping it in 02 service each year.
Cheers,
gareth.
Lizardland
04-06-08, 11:30
I think that's an OK situation for a shore dive provided you are working your way back up and have an early limit, like I'll have hit 15m at 100bar or whatever that is going to put you in the shallows when you are approaching your limit. However... there is about 10bar that you can't breathe in the cylinder (a Jetstream will do the opposite, it will freeflow the last of your air when the pressure drops too low to close the valve), the reg needs that as a minimum to work so your reserve is down at 40bar now. Most gauges are most accurate in the middle of the range, at high and low pressure they might be another 10bar out so your 50bar reserve could be even less.
For a square profiled dive like from a boat then I don't think it is an adequate limit unless you're diving shallow. Over about 20-25m I plan a bit more carefully. For, say, a 35m wreck dive I'd be planning something like this:
20l/min SAC
1min on the bottom to sort out whatever problem occurs, 90l
3min ascent (I usually use 1/2 the depth to plan for it), 168l
3min stop at 6m (if no deco), 96l
Total, 354 litres.
That's the minimum I need to get up on (the DIR lot do an even slower ascent so even more wind needed). But if I have to share air then I need twice that so 708l. In a 12 that's ~60bar, add on 10-20bar for the reg and gauge error, ~80bar reserve. It's easy enough to estimate that at 35m I'd be using about 8bar a minute on a 12 so I could make a rough estimate underwater of how long I had.
Yeah , that sounds fairly sensible.
One point I would like to make though is this.
You are suggesting , I think , that your second stage will start to fall over when the tank pressure gets to about 10 bar , ie you can't actually breath the last 10 bar in your tank !
Now I know that the normal inter-stage pressure is 9bar or so and that the second stage will in theory stop operating properly as this pressure falls.
Having had the pleasure of sucking a tank dry ( Oooh ermm ) in the pool , I was mightily shocked at how suddenly things went from perfectly OK to no air at all.
Not more than 4 breaths I reckon , or about 1 bar at most.
Further investigation of the cylinder indeed confirmed that it was completely empty.
I accept that at depth things may be drastically different as your second stage is actually having to do some work , but I have no intention of finding out :O)
At 30m , yes , 3bar ambient so you wouldn't be able to get at least 3bar of your air out until you ascended.
Anybody wish to own up to having first hand experience of this ?
I was using ATX40 reg BTW.
Thanks for the info , JB :O)
stafforddiver
04-06-08, 13:15
For a square profiled dive like from a boat then I don't think it is an adequate limit unless you're diving shallow. Over about 20-25m I plan a bit more carefully. For, say, a 35m wreck dive I'd be planning something like this:
20l/min SAC
1min on the bottom to sort out whatever problem occurs, 90l
3min ascent (I usually use 1/2 the depth to plan for it), 168l
3min stop at 6m (if no deco), 96l
Total, 354 litres.
All sounds very sound and thought out.
I think I would add a stop for a minute at 15 meters and another 1 at 9 meters, just to padd it even further. On that sort of dive on a square profile, I'm usually carying a 7lite of something like 50%, would swap at 15 meters on to that as depending on buddy would do a few minutes deco.
Assuming you loose half or more you remaining air/ nitrox due to a serious kit failure and also double or trebble the SAC it beocmes quite interesting to work out an adequate reserve and then some contingency.
Gareth.
Yeah , that sounds fairly sensible.
One point I would like to make though is this.
You are suggesting , I think , that your second stage will start to fall over when the tank pressure gets to about 10 bar , ie you can't actually breath the last 10 bar in your tank !
Now I know that the normal inter-stage pressure is 9bar or so and that the second stage will in theory stop operating properly as this pressure falls.
Having had the pleasure of sucking a tank dry ( Oooh ermm ) in the pool , I was mightily shocked at how suddenly things went from perfectly OK to no air at all.
Not more than 4 breaths I reckon , or about 1 bar at most.
Further investigation of the cylinder indeed confirmed that it was completely empty.
I accept that at depth things may be drastically different as your second stage is actually having to do some work , but I have no intention of finding out :O)
At 30m , yes , 3bar ambient so you wouldn't be able to get at least 3bar of your air out until you ascended.
Anybody wish to own up to having first hand experience of this ?
I was using ATX40 reg BTW.
Thanks for the info , JB :O)
You normally get a pressure drop across any type of regulator. The should account for the difference between working and ambient.
Lizardland
04-06-08, 13:34
All sounds very sound and thought out.
I think I would add a stop for a minute at 15 meters and another 1 at 9 meters, just to padd it even further. On that sort of dive on a square profile, I'm usually carying a 7lite of something like 50%, would swap at 15 meters on to that as depending on buddy would do a few minutes deco.
That's fair enough, I was keeping it to a no-deco dive to keep it as a simple example. For stops I usually add in an extra minute to switch gas and an allowance for when the deco gas bottle fails.
Assuming you loose half or more you remaining air/ nitrox due to a serious kit failure and also double or trebble the SAC it beocmes quite interesting to work out an adequate reserve and then some contingency.
It certainly does become interesting. That's why anything deeper than 40m and a lot of dives 30m+ I'll do on CCR. On OC you either end up using shorter bottom times or carrying more/bigger cylinders. Less than 30m and it's just not worth diving CCR, even 30-40m I try to avoid it.
Cheers,
Stuart
You have to treat the kit with respect, never move it about except on your back as this means you are less likely to injur yourself. Its really well balanced though, always sit down while wearing it if you can.
I've got a little trolley to shift mine around on when not actually wearing it for diving. If I do have to lift it I make a conscious effort to lift correctly and for the minimum distance possible.
As to rock bottom, I've been playing about with some of the 'rules' for this you can find on t'interweb. Most of them work in cu.ft. but a common thead seems to be;
normal SAC x 1.5 (to allow for stress) x ambient press. x 2 (to allow for two divers on the 1 set. Allow a minute on the bottom for sorting things out then calculate the gas required to the first stop. Then calculate all the air required for all the stops and total the lot. Divide by your cylinder capacity and that will give you your rock bottom.
I'm sure someone will correct me if this is incorrect but when I worked it for a 20 minute 45 metre dive it ran out as 145 bar in twin twelves which I thought was surprisingly close to using a third in and having two thirds to get out.
Lizardland
04-06-08, 20:35
I've got a little trolley to shift mine around on when not actually wearing it for diving. If I do have to lift it I make a conscious effort to lift correctly and for the minimum distance possible.
Most twinsets are over the manual handling limits, most shops I've seen ignore that and I've wondered what happens when someone puts their back out humphing a set around.
normal SAC x 1.5 (to allow for stress)
Mine is usually 12-14, so 1.5 isn't far off what I use. Bloody hell, does that mean I'm DIR? :D
When I'm using the rebreather I overestimate how much OC gas I'll need by a lot, usually double for the bottom because something going wrong can drive your SAC up massively, like into the 50's.
Most twinsets are over the manual handling limits, most shops I've seen ignore that and I've wondered what happens when someone puts their back out humphing a set around.
My guess is the employer would be liable for failing to provide the equipment for the employee to shift the set. When I take mine in I prop it against a handy wall next to the charging panel and none of the bottle monkeys even attempt to move it (though they'll always lean it away from the wall to have a good look for the test stamps:rolleyes:)
Mine is usually 12-14, so 1.5 isn't far off what I use. Bloody hell, does that mean I'm DIR? :D
Dunno, I worked my SAC out from a dive on the Beagle last week and it was 14, I think that qualifies me as a Duh! diver or given my avatar, a Doh! diver.
The 50bar rule , as defined by the hallowed institution that is ScotSac ( might just be a club rule though ) goes something like this.
When you get to 50bar - game over , head up.
You were quite right to state that this is not a ScotSAC rule! :rolleyes:
Having a rule to start your ascent at 50 bar regardless of the type of dive sounds absolutely mental to me. :o Are you sure that your club advocates such a rule or is it just for the shallow bimbles that have been alluded to? :cool:
I'm not sure that PAID even does the 50 bar rule per se - I flicked through the open water manual and all I could find was the following paragraph on the theory [pg 69]
Managing Your Air
While you're underwater, get in the habit of checking your SPG frequently. Most SPGs have a marked caution zone - be sure to let your instructor know if your air gets low. Digital SPGs usually blink or otherwise alert your air is low. You instructor will have you signal you air supply level, either indicating that you're not near the caution zone, or using your fingers to show how much air you have in bar/psi.
and the following reference in the practicle dive (which I know you'll all love :rolleyes:) [pg 119]
Naturally, you wan to avoid an out-of-air situation by always keeping an ample reserve supply. You may need this air to retrieve something you drop after surfacing :D and make sure you don't completely drain your tank. As a rule of thumb, plan to surface with at least 20-30 bar/300 psi in your tank. Many divers reserve about 35 bar/500 psi; the smaller cylinder and the more complex the dive, the more reserve you want to keep. With proper planning you should be able to make a slow, comfortable ascent, a three minute safety stop at 5 metres/15 feet, and reach the surface without using your reserve. This is one of the marks of a good diver.
The open water qualifies you with PADI to dive to 18m. The ADVANCED course (yes, I know - the use of this word has been discussed before :rolleyes:) has about a page on air consumption calculations in the Deep Diving [pg 69] section, which qualifies you for 30m. Albeit this page is a bit more complete it could hardly be described as comprehensive and doesn't really set any specific guidelines other than the reserve mentioned above.
Any PADI instructors might like to chip in with what they are told to teach.
I certainly remember being told of the 50 bar rule, you should be coming out with 50 bar after the dive, but I think that was clearly just the instrcutors margin of safety, not PADI rules as such. On the open water course there was no indication of how this might be achieved other than trial and error and in the advanced course you specifically got the info to calculate this, although I don't think I was actuallly required to do so.
Although some will be throwing their hands up in horror, these rules do suffice at first. You are told not to push the boundaries with air and NDLs, etc, so it should be okay. As a beginner there is a lot to remember and as you quallfy further more info is imparted, although I would agree that the AOW course info is a bit short on specifics - oh well, nothing like throwing petrol onto the fire.....
If your doing the sums you should be past the 50 bar rule!
Oh and PADI say come out with 50!
i agree with reg, if your doing sums....!
comming out with 50 bar... another slant on the lesser understood rule.
or is it be at your safety stop with 50 bar??
or leave your safety stop with 50 bar??
Having a rule to start your ascent at 50 bar regardless of the type of dive sounds absolutely mental to me. :o
i quite agree charlie, although this is how its often understood by some.
Swim around until you reach 50bar then go up. Or some use it as hit the surface with 50bar.
kind of makes you wonder why having your SAC rate calculated isnt incorporated in to any basic open water training.
its not rocket science..
You may need this air to retrieve something you drop after surfacing :D and make sure you don't completely drain your tank.
brilliant Peter, you found the answer that had alluded others...
you keep 50 bar for a quick bounce dive..:D
glad i didnt go after the reel i dropped recently in 110m of water, i only had 90 bar left in my twin 12's.:rolleyes:
glad i didnt go after the reel i dropped recently in 110m of water, i only had 90 bar left in my twin 12's.:rolleyes:
wimp :D
Oh , and just for the record , I wouldn't contemplate going to 40m , square profile , with a single 12l.
No, I wouldn't do that either - well not again anyway :o
No, I wouldn't do that either - well not again anyway :o
wimp
Lizardland
05-06-08, 09:16
I agree, I don't get why checking your SAC isn't a basic skill either. If you teach someone to log their dives and record pressures as part of that then it would make sense to get them to do a quick calc.
I have a Sensus Pro dive recorder and one of the nice features about the dive log software it comes with is that it will calculate your SAC from the depth data it stores and the start/end pressures you enter.
glad i didnt go after the reel i dropped recently in 110m of water, i only had 90 bar left in my twin 12's.:rolleyes:
That's tonnes! I've done 90m with 100bar in a pair of 3's :D
If only we knew someone selling a SCR :rolleyes: :D
As it happens.... :p:D
Joining the other argu... err... discussion, I was taught by BSAC instructors to aim to arrive at the surface with at least 50 bar remaining *but* to be aware that the rule only applied to gentle shallow no stop type dives. We also calculated SAC as a matter of course.
Will have to check the current Ocean Diver pack but I have a feeling rule of thirds is taught from the off now?
That's tonnes! I've done 90m with 100bar in a pair of 3's :D
i like fresh air, none of that skanky 2nd hand air for me...:D:D
well, not yet anyway...:rolleyes:
Lizardland
05-06-08, 22:51
i like fresh air, none of that skanky 2nd hand air for me...:D:D
well, not yet anyway...:rolleyes:
If filling a twinset wasn't more expensive than filling a tank of diesel I would as well :D
If filling a twinset wasn't more expensive than filling a tank of diesel I would as well :D
that might be a reality soon... be carefull what you wish for..:eek:
What is your diesel not Free ????? :D :D
dive granny
17-06-08, 22:55
You'd actually be surprised how easy they are to get around with once they are on your back.
The average male shouldn't have too much trouble. Just be mindful of how you turn, bend etc!
Not for wee 5ft 1" D.G.s then:D
Not for wee 5ft 1" D.G.s then:D
No! :eek: :D