1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

New diver checking in

Discussion in 'New to Scuba Diving' started by AdsDiving833, Aug 9, 2017.

  1. JohnL

    JohnL Well-Known Member

    Joined:
    Sep 22, 2015
    Messages:
    1,192
    Likes Received:
    526
    And yesterday, one of the less experienced group on our boat came back with 300 psi that is not much at all!
     
  2. JasonP

    JasonP Active Member

    Joined:
    May 10, 2012
    Messages:
    129
    Likes Received:
    27
    Yeah, that's very little. I bet they hadn't been down that long either. Depending on the dive and kit config, I'm happy to come back with less than 50 bar. If the last bit of the dive is in 5m off the beach, I really don't need that much. Or if I've got twin 12s, then 50 bar is actually a lot of gas. If I'm coming out of an overhead environment, I like to have more than a third left.
     
  3. snowman

    snowman Active Member

    Joined:
    Nov 13, 2010
    Messages:
    752
    Likes Received:
    158
    After one particularly strenuous swim against a current in the Maldives, one Russian on my dive boat showed me his SPG - It showed 0 bar!

    Obviously he was there to show it to me, so I guess it was a little off, but it certainly put my 30 bar in a more positive light! :D

    Having recently started diving on a twinset, I can't help thinking coming out of most dives with 1680 litres of gas (as BSAC suggest I should plan to) seems a bit profligate (Especially if it's Nitrox!).

    Like JasonP, I'm happy to run it down to 30 bar on many recreational dives, but as he says, you need to make a judgement call on when that's safe.

    M
     
  4. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    5,491
    Likes Received:
    1,227
    1680 / 12 = 140 bar left?
     
  5. snowman

    snowman Active Member

    Joined:
    Nov 13, 2010
    Messages:
    752
    Likes Received:
    158
    You dive twin 6s?

    Or is my maths askew somehow?

    M
     
  6. Leeb2018

    Leeb2018 Member

    Joined:
    Mar 6, 2018
    Messages:
    80
    Likes Received:
    23
    on twin 12s it would be

    1680 / 24 = 70 bar

    1680 liters is a massive reserve for a single cylinder to recreational limits
     
  7. JasonP

    JasonP Active Member

    Joined:
    May 10, 2012
    Messages:
    129
    Likes Received:
    27
    If it's the first dive of the day, when I'm probably doing deco, then I usually come out with way more than 70 bar on twin 12s.

    If it's a second dive, no deco, and it's something shallow that I don't really need a twinset for, then 70 bar is more than I think I need.
     
  8. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    5,491
    Likes Received:
    1,227
    BTW what's the logic/thinking behind needing 1680 litres?

    Normally it's something like two stressed divers chugging away from 30 metres doing all their stops. Completely takes the piss out of a PONY (~700 litres).
     
  9. splinter

    splinter Active Member

    Joined:
    Nov 28, 2010
    Messages:
    311
    Likes Received:
    129
    Rule of thirds.

    Like Lee said, with twin 12s, 1680/24=70 bar.

    Sent from my SM-G900F using Tapatalk
     
    Vanny likes this.
  10. Tel

    Tel Super Moderator
    Staff Member

    Joined:
    Jun 26, 2014
    Messages:
    1,846
    Likes Received:
    652
    :)


    You forget the pony is the SECOND redundant source, the primary being the reserve in the main which if thirds on a 12 is
    924, so total reserve would be 1624 :p

    Of course now i'm expecting a reply that says a pony is just a single reserve and with twins you can access all of that, well
    that would be IF you managed the shutdown and IF this didn't take that long at depth when still burning gas at 30m.

    If all went well you might even manage to save 100lts odd more than the pony :p
     
  11. Vanny

    Vanny Active Member

    Joined:
    Apr 18, 2016
    Messages:
    553
    Likes Received:
    180
    The rule of thirds isn’t unique to BSAC. It’s a common way for many agencies and industries using breathing apparatus to stipulate gas management. I would expect (I have no experience) that this could become even more conservative in overhead environments.

    The reserve the BSAC twin set course is recommending is assuming your actually Diving the equipment your training on to its potential. I.e a twin set for extended range Diving, when your 1600 litres maybe needed for ascent from greater depths or involve deco. For you and/or buddy.

    You could argue that if your Diving in a more recreational range then you’ve chosen inappropriate equipment.

    Equally if you are in a recreational, shallow no stop environment and choose to dip below a third reserve , encounter an equipment failure , isolate , you could end up effectively on a single cylinder with less than 50 bar.

    Those rules are not rules but there very good guidelines for a reason, usually someone else fooked it up first.
     
  12. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    5,491
    Likes Received:
    1,227
    Of course thirds are frequently not enough. Deep; overheads; diving with a gas hog, etc. Or sometimes thirds is too much; shallow; etc.

    Maybe it'll be better to work out what the minimum gas is and work with that.

    And 1680 is just 1/3 of 210 bar on a 12 litre 232 bar twinset. Lots of variables.
     
  13. snowman

    snowman Active Member

    Joined:
    Nov 13, 2010
    Messages:
    752
    Likes Received:
    158
    Indeed, to all the above.

    Whilst I agree that shallowish recreational diving may not be the perfect scenario in which to use twinsets, not everyone has the indulgence of buying multiple sets of gear and there are plenty of scenarios where it makes no sense to dive across a number of dives with totally different kit (not least the logistics of moving them!)

    The rule of thirds (whoever the body recommending it is) is hammered home from an early stage in my experience.

    To my knowledge (sure someone will find an example) no training officially says "Use your judgement to decide what's practical and safe" later on, except UPWARDS (which is totally right in some cases, of course).

    M
     
  14. JohnL

    JohnL Well-Known Member

    Joined:
    Sep 22, 2015
    Messages:
    1,192
    Likes Received:
    526
    In my BSAC training, dive planning was made on a SAC of 25, with the proviso that this could be adjusted on personal history, but to remain conservative. Rule of thirds was hammered home without exception.
     
  15. JasonP

    JasonP Active Member

    Joined:
    May 10, 2012
    Messages:
    129
    Likes Received:
    27
    Rules of thirds in an overhead environment is obvious. Third in, third out, third in reserve to get your buddy out. It's application to open water diving is somewhat less obvious to me.

    Technical agencies teach taking twice your deco gas plus 15 bar to have enough to get you and your buddy out.

    Sent from my LG-H990 using Tapatalk
     
  16. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    5,491
    Likes Received:
    1,227
    Does seem to be an over-simplification of something that varies with depth and circumstances with additional conservatism added to everything.
     
  17. Tel

    Tel Super Moderator
    Staff Member

    Joined:
    Jun 26, 2014
    Messages:
    1,846
    Likes Received:
    652
    Trouble is that it's an entirely necessary over-simplification.

    New divers, even those with a lot training in gas planning still run short, make mistakes or just get into bad habits.
    The diving standard of most experience with least experienced whether that's via a buddy or a professional guide etc.
    also needs the senior to instil good dive planning, when often they do not..

    So do we stick our head in the sand and say that all divers should plan the detail of dives knowing that this doesn't work
    or come up with a simple easy to remember system that has a far greater chance of both being remembered and used.

    Sure in time and with more experience such rules can actually be a negative, but in the early days when deco isn't even
    on the radar, it's way better to come back alive with extra gas using this system than the alternative.
     
    StuartM likes this.
  18. Wibble

    Wibble Fish don't talk
    UKD Supporter

    Joined:
    Apr 7, 2014
    Messages:
    5,491
    Likes Received:
    1,227
    The problem with oversimplification is it eshews thinking and is overly cautious. This means dives are unduly truncated, the reasoning is lost and no responsibility is taken.

    Of course I'm wrong which is the point of rigid rules.
     
    Nutter1979 likes this.
  19. Big Joe

    Big Joe Active Member

    Joined:
    Jan 9, 2010
    Messages:
    918
    Likes Received:
    187
    Fat old recreational diver of several years experience, with no ambition to go tech. Quite happy to do 30 ish metres on single 15 in UK. Stretch to 40 metres on a short dive in warm clear water with a 12. Usually find that I am along for the ride as a "Safety diver " - doesn't bother me as I know in advance what the situation is. As long as all divers leave the water with 30 bar plus I am happy. I have the feeling that the majority of people who dive don't have a clue what they are doing and rely on the club/dive shop/ independant trainer to look after them. Against that are the Teckie/rebreather divers who have there own point of view. At the end of the day - it doesn't matter - we all enjoy getting our heads under water. As long as the new people understand the risks, manage the risks and are wiling to accept the consequenses, we are all divers.
     
    Wibble likes this.

Share This Page

  • About Us

    Our UKDivers community has been around for many years and prides itself on offering unbiased, helpful discussion among people of all disciplines and abilities. We are working every day to make sure our community is one of the best and friendliest around.
  • Support us!

    The management works very hard to make sure the community continues to run reliably. Care to support us? All donations go to the running costs of the forum: hosting charges, software maintenance, etc. We'd really appreciate it!

    Choose option:  

    UKD Username: