View Full Version : Deco Question
OK, so here's a new poll on diving etiquette.
You're diving a wreck in the 40m range. Viz is around 4-5m and the wreck is large. It's the first time you've dived it and so you're not really sure of your bearings. But it's an excellent dive with loads to see. After about 25mins you've worked your way back to the vicinity of the shot line, and you see from your computer that you have accumulated 4 mins of deco, and you have 120 bar of air left.
You're the dive leader, so you signal to your buddy to ascend the shot line, but he shows you his contents gauge and he too has 120 bar. He signals to you with a wave if his hand that he would like to use some more of his air for a further bimble around the deck.
You can see his point, but you're also slightly concerned that you might not be able to find your way back to the shot, and you're not super keen to ascend an SMB line all the way up from 44m. You would prefer to use the shot now, as you know where it is. You're also mindful of the deco clocking up.
What do you do?
A) Insist upon ascending the shot line now.
B) Consent to your buddy's request for a few more minutes.
c) Other.
quote "and you have 120 bar of air left. " I presume they are both on scuba with the same size of cylinders. Taking that they have 12L cylinders thats 12x(120-50)=840 litres of free air. (50 bar reserve) Take the RMV as 25L/Min on the surface and average the ascent at 10m/Min say 4min @ 20m or 3 Bar thats 75L/min for 4 mins = 300Litres. And 4 min at 3 meters 4x(1.3x25)= 130 litres and 1 min at 20m Pyle stop (3x25) =75 litres That leaves 840-(300+130+75) = 335 litres of free air. and at 44 meters you use (5.4bar x 25 L/min) =135 litres / Min, with deco increasing.....
Theres the calcs what would u do?
quote "and you have 120 bar of air left. " I presume they are both on scuba with the same size of cylinders. Taking that they have 12L cylinders thats 12x(120-50)=840 litres of free air. (50 bar reserve) Take the RMV as 25L/Min on the surface and average the ascent at 10m/Min say 4min @ 20m or 3 Bar thats 75L/min for 4 mins = 300Litres. And 4 min at 3 meters 4x(1.3x25)= 130 litres and 1 min at 20m Pyle stop (3x25) =75 litres That leaves 840-(300+130+75) = 335 litres of free air. and at 44 meters you use (5.4bar x 25 L/min) =135 litres / Min, with deco increasing.....
Theres the calcs what would u do?
Kinda removes scope for debate, doesn't it;)
I think on this analysis we'd all be like a rat up a drain pipe ...
but i wonder what people think instinctively without examining the math (for me there is a "trick" in the question ... or rather, a trap that it's easy to fall into in a deep dive .... i.e. thinking you have more time than you actually do.
hold the purge button on his octopus until he has 80 bar left and then ask him the question again :)
alexmaclennan
20-09-06, 23:29
If you have a regular buddy and either he or you wants to call the dive. Thats what you do. If you're not with your regular buddy then definitely call the dive.
alex
Lizardland
20-09-06, 23:31
you're also slightly concerned that you might not be able to find your way back to the shot, and you're not super keen to ascend an SMB line all the way up from 44m. You would prefer to use the shot now, as you know where it is. You're also mindful of the deco clocking up.
It sounds like you've already answered your own question. If you have concerns then go up.
If it was me and everything was going fine then I'd be inclined to go for a further root around. But then I dive a rebreather and I've got four hours of gas on my back. I've also got a pee valve so I'm sorted for long times in the water :)
It depends on a lot of things for me really. Some skippers like you to agree a run time and stick to it. I dived with a skipper out of Weymouth who refused to let a diver back on his boat the next day because he deliberately exceeded his planned time. If it was a buddy I knew then I'd be a lot happier in doing a bit more time, if it is someone I don't then I'd tend to stick to the plan. Some skippers too prefer everyone to either come up the shot or for everyone to bag off rather than a mix of both. If we'd agreed to come up the shot then I'd do it, especially if I wasn't sure if I'd find my way back to it again.
Without looking at tables, I'm guessing that after 25min at 44m then it isn't really going to take that much longer there to start racking up a fairly hefty deco, especially if you aren't using a richer deco gas.
I'm quite happy to send a bag up from that depth. I've done it from deeper. If I have to send a bag up from somewhere deep then I use a reel loaded with sisal or hemp twine. You send your bag up, when it hits the surface then you tie the line off on to a bit of wreck and cut off the reel. You ascend what is now a fixed line (so you don't need to reel in on the way up) and when you get to the top then you unclip your bag from the line. The bit of line you leave behind rots away within a couple of weeks. I lived in the US for a bit and that is how a lot of wreck divers use DSMB's there. I'd only really use it when I had to, generally if I couldn't find the shot on a deeper wreck because if you have a lot of deco then it keeps you in the vicinity of the shotline. You can drift a long way with a lot of stops, this keeps you in the same place. Usually you need about 1/3 more line than your max depth e.g. for a 50m dive you'd need 65-70m of line.
If it was just a short hang, say 10min, then I'd bag it as normal as you aren't going to drift that far. Also if it was critical that I got back to the shot then I have in the past laid a guide line from the shot to wherever I was going.
Cheers,
Stuart
Give him the "I have a problem signal" and then "the up signal". He then has to go with you.
He has a duty of care to stay with you.....;)
neither diver should have been down there in the first place without a dive plan.
plan your dive, dive your plan.
neither diver should have been down there in the first place without a dive plan.
plan your dive, dive your plan.
So right Stewart, As u and I know we always have a diveplan and stick to it...
So right Stewart, As u and I know we always have a diveplan and stick to it...
i dont do anything more than a verbal quick calculation if im less than 30 meters & shore diving.
anything below 30 meters or a clyde dive from a boat goes something like this calculation for a non deco dive. based on the B200 at furnace, based on the diver with the smallest cylinder & highest breathe rate.
12 litre cylinder x 210 bar = 2520 cubic litres of air.
2520 divided by 6 atmospheric pressures = 420 litres of air.
420 litres of air divided by 20 litre per minute estimated breathe rate = 21 minutes of air.
21 minutes of air divided by 3 (rule of thirds) = 7 minutes of bottom time air with 14 minutes of travel air/spare air.
7 minutes of bottom time @ 45 meters = 1 minute decompression at 3 meters.
its the silly things that bite you on the @ss when you least expect it.
deviation from a plan will get you nailed one day.
i speak from experience.
bubblemaker
22-09-06, 16:27
There is no decision to be made, you get your @ss up the shot line, and if they refuse, take their reg out, and punch them square on the grid!!! Or put a buddy line on them.. whatever.
If they refused to ascend, then i wouldn't be diving with them again. Mostly because they are dangerous, possibly because they are dead!
There is no decision to be made, you get your @ss up the shot line, and if they refuse, take their reg out, and punch them square on the grid!!! Or put a buddy line on them.. whatever.
If they refused to ascend, then i wouldn't be diving with them again. Mostly because they are dangerous, possibly because they are dead!
Back to this world, you like me would signal up and if they didn't come then you would leave them.... I'm not putting myself in danger for an Idiot..
On air 40m RN no deco limit is 12min, 10min for a fat old bas like me. Computer showing 4min of deco, I'd bin that computer and get a brain. After 25min at 40m you should be showing 25min of deco if not 30min. So you've got about 120 bar and if your buddy doesn't want to leave when you signal up, give him a wave, you were diving solo anyway.
Experienced this one a few times, one in particular at Scapa when my buddy decided to go deeper than planned, to cut a long story short, despite pain in my ear, I grabbed him then forcefully took him to the shot line. I must say I was not amused and diplomacy left me after we were back safely on the charter boat.
academyofdiving
02-02-07, 12:11
It goes back to the basic training rule of PLAN THE DIVE....DIVE THE PLAN and there should be no deviation from the original plan unless it is to abort the dive for whatever reason.
OK, so here's a new poll on diving etiquette.
You're diving a wreck in the 40m range. Viz is around 4-5m and the wreck is large. It's the first time you've dived it and so you're not really sure of your bearings. But it's an excellent dive with loads to see. After about 25mins you've worked your way back to the vicinity of the shot line, and you see from your computer that you have accumulated 4 mins of deco, and you have 120 bar of air left.
You're the dive leader, so you signal to your buddy to ascend the shot line, but he shows you his contents gauge and he too has 120 bar. He signals to you with a wave if his hand that he would like to use some more of his air for a further bimble around the deck.
You can see his point, but you're also slightly concerned that you might not be able to find your way back to the shot, and you're not super keen to ascend an SMB line all the way up from 44m. You would prefer to use the shot now, as you know where it is. You're also mindful of the deco clocking up.
What do you do?
A) Insist upon ascending the shot line now.
B) Consent to your buddy's request for a few more minutes.
c) Other.
Ive quickly ran 25mins at 40m on the Suunto Dive Manager and it gave me 30 mins of Deco.....
I'd be going up.......
gogs
Ive quickly ran 25mins at 40m on the Suunto Dive Manager and it gave me 30 mins of Deco.....
I'd be going up.......
gogs
what would you do on that dive if your suunto packed in?
"what would you do on that dive if your suunto packed in?"
The deco profile you planned and scribbled on your slate "just in case" of computer failure of course... and if I hadn't, or I wasn't certain it was appropriate I'd chuck in a couple of deeper stops then hang at 6m until my gas was (nearly) gone before ascending...
But that's the back up plan for when *everything* has gone wrong :eek:
Getting back to the original question, if I want to go up and a buddy doesn't, I'll tell them once more and then leave them. I'm not their keeper and I wont kill myself for an idiot. :mad:
I was brought up to dive on the rule that *anyone* can call *any* dive at any time. They don't need to give an excuse, "I wasn't happy", is a more than good enough reason.
We are, after all, supposed to be diving for the fun of it aren't we...?
Smudge
(anyway, I don't use Suunto's, hate the things! :p :D )
what would you do on that dive if your suunto packed in?
As what Smudge said....
a dive that deep would have been planned, the plan written down on a slate. Any 'worst case senario' would have been on it too. It the sh*t hit the fan, I would do what Smudge said, fire up a DSMB so the surface know Im about and hang on it at 6m until im down to 50bar or there abouts...
gogs
Being new to this forum, dont want to upset anyone, but this is a bit of a no-brainer.
I dont dive to that sort of depth, so taking similar circumstances to a depth I do dive to, then it is fairly simple, being either buddy!!! If one of the pair wants to ascend you ascend, end of!
Magic Mark
07-07-07, 12:07
I can not see the problem, you are the dive leader you have made a plan
Dive the plan and lead the dive... that is how it works.:confused:
Dive Tramp
07-07-07, 13:11
Jeez, Gord, was this a completely hypothetical scenario or did you never dive with him again?:eek:
This was about a buddy i've dived a lot with. I think sometimes people can become too comfortable as buddy pairs and neglectful of good discipline. This can also be a factor if you are married to the buddy in question... :rolleyes:
To be honest, my wife and I prefer not to dive together for these reasons ...
We have different styles of diving - I'm a compulsive planner and control freak whereas she prefers to bimble along and see what happens. But let's just not go there ...
This can also be a factor if you are married to the buddy in question... :rolleyes:
That is a good point - I come from a family where everyone dives and my buddies have virtually always been related to me. (When my father died I was in charge by default, hence doing the divemaster course). If your buddy does something stupid you tend to be more inclined to stick with them even if you jeopardise your own safety.
That is a good point - I come from a family where everyone dives and my buddies have virtually always been related to me. (When my father died I was in charge by default, hence doing the divemaster course). If your buddy does something stupid you tend to be more inclined to stick with them even if you jeopardise your own safety.
Are you saying that your dad died in a diving incident and that you were there? That sounds terrible. Sorry to pry and obviously only respond if you want to.
Dive Tramp
09-07-07, 23:19
This was about a buddy i've dived a lot with. I think sometimes people can become too comfortable as buddy pairs and neglectful of good discipline. This can also be a factor if you are married to the buddy in question... :rolleyes:
To be honest, my wife and I prefer not to dive together for these reasons ...
We have different styles of diving - I'm a compulsive planner and control freak whereas she prefers to bimble along and see what happens. But let's just not go there ...
I guess I'll be somewhere in the middle there, Planning AND Bimbling, but ,and in contrast to Shmeeg's post (and I hope I read that you took the DM course after your Pa's non-diving related demise, Shmeeg:o ) whether I'm leading or not, we go up "on the plan" if not before, otherwise,... I've been diving alone, again!:(
No - he died of a heart attack not at all diving related but he was always the one that organised the dives, got the boat and gear ready, found the site etc, then someone (me) had to take over and did the divemaster course to increase my skill level. My younger brothers and sister had pretty much only just done ther OW courses at that point.
Just for the record - I now dive with my husband Gedan (I'm sure you've figured that our already). Although he is less experienced that me he is far more anal about safetly (which I'm not saying is a bad thing), hence all the questions he posts about pony bottles and setups etc. If he had his way he'd have spare bottle on every D-ring.:D
I really enjoy diving with my other half - if one of us isn't happy or is cold or anything else, then we don't worry about telling each other - unlike with other buddies when you sometimes don't want to wreck the dive.
He's also probably the only diver who would put up with me shoving a video camera in his face on a regular basis!
dive granny
11-07-07, 23:05
Being complacent about your regular buddy is a subject that came up on our malta holiday. I was once accused of 'spoiling peoples dives' by a person I have never even dived with though my Buddy was cool about being my buddy, but I still have hang ups about it, and sometimes decline dives because of it.:(
Being complacent about your regular buddy is a subject that came up on our malta holiday. I was once accused of 'spoiling peoples dives' by a person I have never even dived with though my Buddy was cool about being my buddy, but I still have hang ups about it, and sometimes decline dives because of it.:(
If you don't mind me asking what happened?
I'd be wondering what the hell I was doing having a deco dive - and why Chris was doing one and not gettting out the bloody water fast!
Slightly longer I normally only dive with Chris or others I know well on hols - my dad and my daughter. I rarely dive with anyone else and part of that is cause we all do the safety checks beofre going in regardless of pressure to rush it and we know what is planned, very simply, and we all would get out the water for each other than force a dive for a bit more bottom time.
I know alot of you guys dive singly, but if you are a buddy pair and your buddy ain't happy the dives over and you should go gracefully rather than moaning about wasting maybe 5 quid on gas.
On the selfish side of this another reason not to dive with an unknown entity is that you don't have to abort your dive early because someone you don't know can't really dive well.
On the selfish side of this another reason not to dive with an unknown entity is that you don't have to abort your dive early because someone you don't know can't really dive well.
only ever come across this scenario on holiday.
simple solution, i ask people in the group what air they have until i find one similar to the air guzzling buddy. team them up & wave good buy.
Rob Andrews
13-07-07, 01:32
Interesting thread, you've missed out some detail (i think deliberatelly) but if you assume as others have your on a single 12 you should have been gone ages ago! (you shouldn't even be there IMVHO).
Lets change the scenario just slightly, your at 44m with 4 mins deco showing and your back at the shot with 120 bar. You signal ascend to your buddy and before he has time to respond his low pressure inflate hose ruptures! His 120 bar is gone in less then 30 seconds! His sac rate has gone from a calm 14lpm to over 40lpm and you have to put him on your octopus. Still think your gonna make the surface?
Lets do the maths.
You have 120bar*12l=1440l
1min on bottom to donate occy and sort out your stuff
60lpm (if your fairly calm)*5.4atm=324l
4 minutes to get to 6m if you really go for it at an av depth of 24m
60lpm*4mins*3.4atm=816l
5mins of deco at 6m
40lpm*5mins*1.6atm=320l
324+816+320=1460l
All that was allowing for everything running perfectly in a very stressfull situation and you both calming down almost back to normally while doing deco, and you didn't quite make it!! Now I know were not going to sit and drown on deco trying to get those 5 minutes in but its food for thought.
What if you'd have stayed and run down to that 50bar reserve? Curtains!
As people have said, plan the dive, dive the plan, your reserve gas is just that, a reserve, don't use it to extend the dive as your safety margin has just gone.
I really enjoy diving with my other half
Well, him and your super helpful instructor / dive guide :D
Yogi Diver
06-01-08, 16:53
First time I've ever heard of the hemp trick. Sounds like a great idea. Will keep it in mind when (If) I get back in the water.
Yogi Diver
06-01-08, 17:03
[QUOTE=Smudge;5312]"what would you do on that dive if your suunto packed in?"
As someone who never takes his slate on a dive because my eyesight would make it a waste of time anyway, I have always taken the view that if my computer fails, I abort the dive, ascend at 10 metres/min maximum. (Much slower than my smallest bubbles!) and take as many and as long a safety stops as my remaining air allows unless I am 100% certain that a standard 3 mins at 5 metres will suffice.
That's pretty much exactly what I said! :D;)
"The hemp trick"? :confused:
Yogi Diver
06-01-08, 18:07
Sorry Smudge, I'm new to this forum and was trawling through some old posts and responded to a post by Lizardland who suggested using disposable twine in a reel to send up a DSMB and tie it on to the wreck, then cut the DSMB free on the surface which seems agood idea if you can't find the shot and don't want to drift with your DSMB.
I read your post later. It's good to know someone agrees with me. Makes a change.:-)
Np :D I'd forgotten about the twine thing myself, heard a variant where your dsmb is as normal and you tie it to the wreck or whatever with a twine waster which will break more easily than your dsmb line (most important that last bit ;) )
That way you don't have to change your reel, just carry a couple of short bits of string/twine.
Mind you... never tried either so I can't say they work well or not!
Yogi Diver
06-01-08, 19:07
Another good possibility but, if the line snags or your waster does not snap, you have lost a reel. Mine cost me £80 so I'd rather it came to the surface with me.:o
I can see the possibilities though if sending a DSMB up from 50 Meters. Empty the reel, assuming very little excess on it, and tie the twine to the end and the wreck. Break the twine from the surface and you keep your 50 meters of good line. Only really viable from maximum depth though?
Lizardland
06-01-08, 21:24
Another good possibility but, if the line snags or your waster does not snap, you have lost a reel. Mine cost me £80 so I'd rather it came to the surface with me.:o
I've had exactly that situation, stupidly let go of the reel when the lock wasn't fully on and it disappeared. Fine, I thought, wait til it hits the bottom then just pull it up and roll the spare line into a ball but it got snagged in the wreck (the Akka). Someone found it a couple of days later in a hold.
I'd be happy that I had found the line in the first place,no way I'd leave it now
Lizardland
06-01-08, 23:33
I'd be happy that I had found the line in the first place,no way I'd leave it now
Finding the shotline for me is about 30% happiness and 70% surprise :D
on a lot of boats over here, they drop the anchor, and you have to navigate your way back to the boat! Certainly interesting with a nice current, especially when the boat has a 4 minute swing from SW to SE.
but we're way off topic now.
dive granny
09-01-08, 00:00
I saw in B & Q today mason's twine on a rewindable roller 60 m of twine. It cost £8 with the twine. Would that be any good. I took a pic with my phone but dion't know how to put it on here
Lizardland
09-01-08, 00:23
I saw in B & Q today mason's twine on a rewindable roller 60 m of twine. It cost £8 with the twine. Would that be any good. I took a pic with my phone but dion't know how to put it on here
Not if you're using it as a waster. I'd looked at them before (they do them in pink or yellow, very fetching :D ), if it's the ones I'm thinking of then it's a synthetic material. If you use hemp twine as a waster then it rots away within a few weeks in seawater, if you use synthetic then it stays there forever. If you do use hemp twine then you need to wrap it VERY tight on to your reel otherwise it absorbs water and will just break when you come to use it. It's also best only to take it when you are definitely going to be coming up on a bag rather than the shot as after a few good soakings then the line does get weaker. A lot of Americans use sisal but you need a big reel as it's much fatter than hemp but a lot more resilient. Google "jersey reel", there's a good description here: http://www.shipwreckexpo.com/shipwreckdivingequipment.htm (near the bottom "Jersey Up Line").
If you want a good emergency reel then get a spool of braided nylon from a chandlers for about £4. Nothing to jam or break, I keep one in my drysuit pocket on most dives. It's handy if your main reel jams or for short roots about in wrecks.
Cheers,
Stuart
"what would you do on that dive if your suunto packed in?"
The deco profile you planned and scribbled on your slate "just in case" of computer failure of course... and if I hadn't, or I wasn't certain it was appropriate I'd chuck in a couple of deeper stops then hang at 6m until my gas was (nearly) gone before ascending...
But that's the back up plan for when *everything* has gone wrong :eek:
Getting back to the original question, if I want to go up and a buddy doesn't, I'll tell them once more and then leave them. I'm not their keeper and I wont kill myself for an idiot. :mad:
I was brought up to dive on the rule that *anyone* can call *any* dive at any time. They don't need to give an excuse, "I wasn't happy", is a more than good enough reason.
We are, after all, supposed to be diving for the fun of it aren't we...?
Smudge
(anyway, I don't use Suunto's, hate the things! :p :D )
Computers should be left in the car at all times Smudge. Sorry, revenge for tieing myself to the boat the other day.:D
Computers should be left in the car at all times Smudge. Sorry, revenge for tieing myself to the boat the other day.:D
lol, yes well...excuses... erm, ok, it was clearly much safer that way as there was absolutely no risk that it was going to fail while I was relying on it during the dives... ;)
or.... I was just doing it to prove that we can still dive without a computer... or even without depth/time if your buddies depth/time monitor that you borrow fails on you :eek:
Still, I managed two nice dives *despite* everything going wrong that could :rolleyes: ( I did mention the unexpected leak from the spg that I sorted while I was down there...?)
Didn't half feel an idiot when I realised it was still in the car though! :o
this is a really interesting thread, and I've just read through it... To answer the question, if I had found the shot line, I wouldn't be leaving it. I might allow an extra minute of deco to add on if they were insisting on having a look about, but what's the point? I've been caught out before (not in a serious way, just a boring one!) by the amount of deco that adds up during slow ascents. I've been lucky to have always had pretty solid buddies though and this isn't a situation I've ended up in yet.
As far as complacency underwater, I go through swings depending on my buddy\ dive site. I use twin 7s and rarely dive below 30m these days unless it's on a specific trip to a wreck or something, so I dont worry about air and don't really calculate it before a dive. I also dive with people I know well and who I don't need to watch like a hawk all the time (which is handy when I'm photographing!).