Page 2 of 2 FirstFirst 12
Results 11 to 18 of 18

Thread: Hello fellow tank breathers!

  1. #11
    Quote Originally Posted by FoxHound View Post
    Great info on SAC and the calcs dude! Spot on and something that every diver needs to know.

    The part that I have put in bold i want to stress even more......a camera does more then just increase your gas consumption. Cameras are a huge distraction and in all honesty should not be in the hands of a new diver. It leads you to forget to check things like your spg. I've been in the water with some divers that when they have a camera in their hands they forget all other skills.

    In contrast, if you look at the sport of skydiving, you cannot wear a camera helmet until you have 200 jumps minimum. And you are not even holding those cameras, they are mounted to a helmet........the reason being, even if you don't think they are....they are a HUGE distraction.

    So lets go back to diving.....camera are a HUGE distraction.....and I mean HUGE.


    ETA: btw, calculations using tank volume in liters, and pressure in BAR........much easier, less math
    Yeah, original message was long enough. Didn't want to throw in camera is a distraction as well. But since you brought it up... a little story.

    On a dive in Aruba. We are heading for a wreck which a lot of glass bottom boats bring tourists to. During the briefing we are told to be careful about going to the surface. We don't want anyone getting hit by a boat. The dive boats drop us off around 5 minute swim from the wreck. We descend and start heading for the wreck. The viz is 10 feet so everyone is following the guide. I don't see anyone besides me with a compass. So they are all reliant on the guide (this is another issue I won't get into). It is a group of 22 divers (yeah I avoid these now). With large groups I like to hang out at the back to avoid being kicked/hit/smacked/etc. Around 3 minutes in and everyone has stopped swimming. Everyone is kneeing on the sand and looking around confused. It takes me a few minutes but I realize the guide is gone. Not a problem. While I wait for him I decide whether to head for the wreck on my own and hope the guide finds us or head back to the boat and call no joy. Going to the surface to execute a 'lost buddy' procedure is not an option because of the glass bottom boats.

    Before I can decide the guide comes back with a diver in tow. The diver has a DSLR camera with strobes and arms. We continue to the wreck and a good dive is had by all (well I had a good time).

    When we get back on the boat I ask the guide what happened. Apparently, the diver with the camera was too busy fiddling with his camera. On the way to the wreck we went from 35 feet to 20 feet going over a reef. As he went shallow the air in his BCD expanded which made him buoyant. As he floated upward the air expanded more. In a matter of seconds he was ascending for the surface at an alarming rate. The guide chased after him and dragged him back down. With the low viz it was easy to lose the guide and everyone just stopped when they lost him. The guide took a few more seconds to get the camera guy neutral and bring him back to the group.

    Luckily, no one panicked and everything worked out okay. However, the guide could have been slow to react and the camera diver could have been hit by a boat. I could have decided to go to the wreck, the guide calls no joy and brings everyone else back to the dive boat and I'm lost at sea. Someone could have decided to surface and see if they could find the guide or they might have surfaced in order to find the dive boat. Either way, it might have resulted in a diver getting hit by a boat. All because someone had a camera and lacked the buoyancy control and situational aware which should accompany it.

    Don't even get me started with the amount of reef destruction I've seen from people with cameras in hand.
    This signature left intentionally blank

  2. #12
    TadPole
    Join Date
    12/29/2011
    Location
    DeRidder, Louisiana
    Posts
    10
    Of course thats not what I wanted to hear but I know you guys are right about the camera thing. I just have a hard time thinking..I only get to go on these trips a few times a year and would like to share what we've seen and have some photographic memories....I do however take my safety underwater very seriously and have found myself tying the camera off when currents are up or I dont feel like I am moving through the water comfortably....perhaps I will leave the camera on the boat for the deeper, stronger current dives and try taking photos on our shallow dives??? Or better yet, just pay the dive op for a videographer to come along.....

    Great responses guys! I do appreciate hearing from you!
    .....just happy to be here....

  3. #13
    Grouper
    Join Date
    02/09/2009
    Location
    Canada
    Posts
    689
    The camera can be fine....just pay attention to whats going on.

    If you find yourself not able to do all the multi-tasks....then leave the camera behind. I'll bring a camera on any carrib dive. I wont bring a camera on any of the deep, strong current, etc dives here in the north.....i have too much else to pay attention to.

  4. #14
    TadPole
    Join Date
    06/14/2011
    Location
    Manchester, UK
    Posts
    28
    Hi BeeRayMac

    There is nothing wrong with taking a camera, even when relatively inexperienced*. Just get yourself a simple point and shoot one (they will be cheaper anyway) and make sure it has a short lanyard so you can drop if you need to.

    Stick it in a BCD pocket and use some common sense when you take it out, if swimming close to something that you might damage or when there is a lot to deal with (current etc) then leave it in the pocket, if hovering over a sandy floor at 10m or doing a safety stop holding on to a shot line then take a couple of pictures.

    Have a word with your guide/instructor/buddy about the camera. Most will be more than willing to take a couple of pictures of you.

    As you dive more you SAC will come down, mine is probably 1/3 of what it was when I started. It is also not really worth comparing one person's SAC to another as it is not a "skill" that your can directly work on (indirectly you can effect it by remaining calm, good buoyancy etc).

    Most important thing either way, go diving and enjoy it :-)



    * inexperienced is not meant in anyway derogatory, I am just making an assessment based on what I have read. Assuming PADI OW or AOW

  5. #15
    Grouper bfmorgan's Avatar
    Join Date
    11/20/2010
    Location
    Michigan
    Posts
    630
    Very nice post....the DM experience shows!
    Quote Originally Posted by scubadiver888 View Post
    Hi BeeRayMac,

    Being underwater is not natural for us. Water is a lot denser than air. The way you move above water will burn a LOT of calories underwater. Burning calories means consuming air. So you need to learn how to move underwater in such a way as to not burn so many calories.

    First, switching to doubles will burn a LOT more calories. The task loading will also add stress to your dive. Turtling is great for the people watching you learn doubles. Everyone at my shop almost pee'd themselves laughing at me when I got stuck on my back. Took me a good 5 minutes in the pool to not get upside down. Bottom line, there are better ways to deal with poor air consumption.

    First, if you have too much weight you will sink. To prevent this you can either (a) add air to your BCD or (b) reduce the amount of weight you are wearing. If you go for option (a) then as you descend the water pressure will compress the air and you'll need to add more air. As you ascend the air will uncompress and you will need to dump air. So you'll be wasting air on your BCD rather than breathing it. Additionally, you burn calories keeping track of adding/dumping air. A lot of the time, if you are a little heavy you will unconsciously kick your feet. This will burn calories.

    So you want to work on your buoyancy. The fin pivot exercise was supposed to demonstrate how you can go up and down using your lungs. I like to get in the water with no extra weights. I put the regulator in my mouth and exhale. If I don't sink I go back to poolside/shore and get some weight (maybe 2 pounds or if I feel REALLY floaty 4 pounds). I try again. As soon as I have JUST enough weight to make me sink I add 5 or 6 pounds. The reason for the extra weight is for the air I'll breath. An AL80 has around 5 pounds of air. As you breath the air, you will become lighter. So if you are JUST heavy enough with a full tank, you will be 5 pounds too light with a near empty tank.

    If you are wearing a wetsuit, you will need to add air as you go down to compensate for the wetsuit compressing. Conversely, you will need to dump a little air as you come up. At first, because you are a little heavy, you will need to add air to your BCD to be neutral in the water.

    All this adding/dumping air takes practice. Starting off with JUST the right amount of weight helps a LOT.

    The next trick to better air consumption is trim. If you have too much weight near the bottom you will float head up. If you have too much weight near the top you will float head down. You want to float horizontal. You want to cut through the water like a fish. Tilt your head down and you will go head down. Tilt your head up and you will go head up. So you can control your trim using your head. If you put your hands together and out in front of you, you can move your arms up and down to affect your trim as well. Where you place your weight helps with this as well. Your lungs float and your tank sinks (at first). So you'll want to flip onto your back a little. If you put your weights evenly distributed it will help stop you from twisting to one side. If you don't, you'll spend time kicking your fins in order to stop yourself from twisting sideways. This will burn calories. Good trim helps reduce air consumption.

    For most people, it takes around two dozen dives to get all this stuff dialled in perfectly. If you just focus on buoyancy and trim for the next dozen dives, you will see your air consumption improve.

    If you are still burning through your air and you know you have good buoyancy control and trim, you might just need a bigger tank.

    You are diving to 30 METRES? Or did you mean 30 FEET? Every 33 feet (34 feet in salt water) or 10 metres is one atmosphere. The pressure change means adjusting buoyancy. If you are working on buoyancy and going from 0 to 33 feet it is hard. If you are going from 0 to 99 feet it is even harder. I'd stick to shallow reef dives and work on my buoyancy. Once you get the buoyancy control nailed, then start adding more task loading.

    Lastly, SAC Rate stands for Surface Air Consumption Rate. When you start diving they give you the simplified rule of "back on the boat/shore with 500 PSI." When you start diving more complex dives and deeper dives this isn't really sufficient. Some divers will figure out how many cubic feet of gas they consume per minute. The amount of air you consume is dependent on depth. I'll consume twice as much air at 33 feet as I would on the surface. So you go to 33 feet, look at how much air you have. Swim around normally but stay at 33 feet for 10 minutes. Look at how much air you have left.

    If you started with 3000 PSI on an AL80, you had 77.4 cubic feet of air. If after 10 minutes you have 2400 PSI left you used 600 PSI in 10 minutes. But we want cubic feet. If 3000 PSI = 77.4 cubic feet than 600 PSI = 15.5 cubic feet (600 / 3000 * 77.4). So you used 15.5 cubic feet of air in 10 minutes or 1.55 cubic feet of air for 1 minute. At 33 feet you are breathing TWICE the air as you would at the surface (33 feet = 2 atmospheres, 0 feet = 1 atmosphere, i.e. ATA). So your SURFACE air consumption rate would be 1.55 / 2 or 0.775 cubic feet per minute. If you know your SAC rate is 0.775 cu.ft. / min. then you can calculate exactly how much air you will need.

    For example, diving the Keystorm and going to the propeller it is 115 feet deep. This is 115 / 33 + 1 or ~4.5 ATA. If you use 0.775 cubic feet of air at 1 ATA then you will use ~3.5 cubic feet of air at 4.5 ATA. For safety, you probably want to keep 1/3 of your tank in reserve. So with an AL80 you should only use 77.4 / 3 * 2 or 51.6 cubic feet of air (2000 PSI). If you want to use only 51.6 cu.ft. of air then total dive time would be 51.6 / 3.5 or 14.75 minutes (14 minutes 45 seconds). The RDP says you should only stay on a 115 foot dive for 13 minutes. So the AL80 is enough air to do the dive safely. A SAC rate of 0.75 is a very good SAC rate.

    On the other hand, if you know your SAC rate is 1.0 then at 4.5 ATA you would be using 4.5 cu.ft. of air per minute. 51.6 / 4.5 would be ~11 minutes. So going to the NDL of 13 minutes means using part of your emergency reserve.

    For new divers, they typically have a SAC rate of 1.5. So diving the Keystorm would be 4.5 * 1.5 or 6.75 cu.ft. / min. Your total bottom time with this SAC rate should be 51.6 / 6.75 or ~7 minutes. I see a lot of new divers on dives like the Keystorm where they are dangerously low on air by the time they finish the dive. A little current and their SAC rate goes up to 2.0 (~5 minute dive time). but they stay down until the gauge reads 500 PSI. After a safety stop they surface with 50 PSI in the tank. If your first stage pressure is 149 PSI, you should never let it go below 150 PSI. They probably have water in their tank and don't even know it.

    Now this is a LOT for a new diver to learn. If you are good with math and physics it isn't a problem but if you are not this can be an added stress. So you need to find someone to help you with this or keep your dives shallow. This is why I recommend sticking with OW and 60 feet max for a while. Once you master the basics, start going deeper and learning about SAC rate.

  6. #16
    Grouper bfmorgan's Avatar
    Join Date
    11/20/2010
    Location
    Michigan
    Posts
    630
    Quote Originally Posted by BeeRayMac View Post
    Unfortunately I have never calculated my SCA rate but knowing this now I will see what it is on our next few dives. I know that I do get excited and try to see as much as possible while on bottom and have even tried do some photography....I dont know if that is a contributing factor or not. I am sure I will never match her simply because lung capacity (couldn't tell me that during our arguments..lol) but if I can come withing a few hundred pounds I am sure her dives, as well as mine, will be a bit more enjoyable.

    As for a larger tank....I would gladly use one but I dont know if the dive shops down there rent those...I will definitely inquire about it though. Thanks for the help!
    If your goal is to have more PSI than your wife on a dive, I have an even simpler solution. Get her a smaller tank, like a 63 cu. ft. She will be happy with the lighter weight and you will more closely match on psi.

  7. #17
    TadPole
    Join Date
    12/29/2011
    Location
    DeRidder, Louisiana
    Posts
    10
    I like to get in the water with no extra weights. I put the regulator in my mouth and exhale. If I don't sink I go back to poolside/shore and get some weight (maybe 2 pounds or if I feel REALLY floaty 4 pounds). I try again.
    Forgive me, but when you say no extra weight do you mean you only have the weight of your BC & tank when performing this?
    .....just happy to be here....

  8. #18
    Quote Originally Posted by BeeRayMac View Post
    Forgive me, but when you say no extra weight do you mean you only have the weight of your BC & tank when performing this?
    To start with, I start with only my essential gear and no lead weights at all. Now it could be that you know you'll need at least some lead weight. For example, me with skin and essential gear I might only need 2 pounds of weight. I'll start with none just to check. Me with 3mm wetsuit, BP/W and steel tanks I start with no lead weight and sink like a rock. On the other hand, me with BCD, 7mm wetsuit and AL80 I start with 12 pounds because I know I'm some where around 16 to 18 pounds.

    If you have no idea though, start with no lead weight and work your way up. Another option is binary search. Guess. Maybe you think you need 10 pounds. Put on 10 pounds, if you sink, try again with 5 pounds. If you float with 10 pounds, try again with 20 pounds. If you sink with 20 pounds, try 15 pounds. If you float with 15 pounds, try 17 or 18 pounds (I usually go with even numbers so I can spread the weight out evenly).
    This signature left intentionally blank

Page 2 of 2 FirstFirst 12

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Hello! Any fellow Buckeyes?
    By JJP161 in forum Welcome to our Scuba Forum! Introduce Yourself!
    Replies: 7
    Last Post: 12-03-2009, 20:21
  2. Hi fellow divers!
    By madrid in forum Welcome to our Scuba Forum! Introduce Yourself!
    Replies: 1
    Last Post: 01-17-2009, 22:43
  3. Hi fellow divers
    By stairman in forum Welcome to our Scuba Forum! Introduce Yourself!
    Replies: 1
    Last Post: 08-09-2008, 08:22
  4. Hello Fellow Divers
    By PCDivers in forum Welcome to our Scuba Forum! Introduce Yourself!
    Replies: 12
    Last Post: 11-20-2007, 09:38
  5. Hello Fellow Divers
    By thanrahan1 in forum Welcome to our Scuba Forum! Introduce Yourself!
    Replies: 2
    Last Post: 11-12-2007, 08:26

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •