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Thread: Hello fellow tank breathers!

  1. #1
    TadPole
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    12/29/2011
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    Hello fellow tank breathers!

    New here and just wanted to take a second to introduce myself. I am relatively new to diving, certified in Feb. 2011, and am absolutely loving it. I done my PADI certification in Cozumel and have since returned 3 times with the 4th planned for January.

    I must admit that the whole realm of diving can be a bit overwhelming at times and quite often I find myself saying "I'm ready to do that"....I only have about 24 dives under my belt and I have found myself asking this question..."I wonder if I can dive with doubles?"

    Let me say this first, unfortunately I tend to be a bit of an air hog and never get the full amount of allowable bottom time in. Also, because my wife is my dive buddy she is often forced to surface at 1000-1500 psi because I am down to 500. I know I need to work at controlling my breathing but I cant help but ask the following questions. I would appreciate any feedback offered.

    A) Should I consider diving with doubles to allow me to get the most of my bottom time?

    B) I am not worried with technical diving at the moment. Most of my dives are between 15 - 30 meters and are boat dives with my wife. How would doubles positively or negatively affect me on these dives?

  2. #2
    Megalodon
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    First off, welcome to the forum. Lot of great folks here and you can feel free to ask away as you will get some good answers.

    All of us with few exceptions are air hogs when we first start diving. Task loading, new experiences and all that only add to it. Rather than getting doubles, which are a huge task loading all by themselves, work on lowering your SAC, relax, work on your trim, dial in your weight, etc and it will come.

    Going to doubles is not an easything, it's not just two tanks instead of one. there is additional weight, balance issues, valve issues (valve drills are a bit of a pain to learn and as a new diver, I don't recommned the additional task load.) Turtleing is not fun either. If you feel you need more air, I would go with a larger tank: maybe a 100 steel that could help with the air issue and keep you in the single tank mode.

    I once saved a man in Wichita just to watch him dive...(inventor)

  3. #3
    TadPole
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    Thanks for that....you will have to forgive me but, what is SAC? I often find myself over using my breathing to control my bouyancy which I think is a weight selection issue. Hopefully I can get it right on my January trip and see if that will give me a bit more air. Again, appreciate the advice!
    .....just happy to be here....

  4. #4
    Grouper bfmorgan's Avatar
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    Greetings, welcome to the forum. I will second Navy's recommendations. I dive with 100 cu. ft. tanks because I am an air hog. I am getting better (certified in May 2011),but still have a ways to go. My son (24 years old) is my frequent dive buddy. I will be at 400-500 psi, and he will have 1,500-2000 psi. Your air consumption will improve over time, and there are some steps that you can take to improve it (see Navy's suggestions). If Navy's suggestion don't fix the problem, go to a bigger tank. People are not all the same, so some of us will have larger lung spaces than others. It is quite likely that you will never get your air consumption down to your wife's level. I know several very experienced divers who have high air consumption levels....in this case, the solution is a larger tank. I track my SAC from dive to dive. It is better on easy relaxed drives, and gets worse in cold water. Many new divers find it difficult to relax and take it slow, it feels like we are racing to the finish line. In those cases my SAC is really bad. Do you know your SAC? That will give us an idea if you are truly an air hog. Women will almost always have a lower SAC rate, so you may never match your wife's SAC.

  5. #5
    TadPole
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    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!
    .....just happy to be here....

  6. #6
    Grouper
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    I can't provide any better advice than what Navy and BF have already, but I just wanted to welcome you aboard. Deridder huh? I grew up in Leesville. Do you do any local diving and if so, where?

  7. #7
    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.
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  8. #8
    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!
    Oh, any additional task loading will affect your air consumption. Putting a camera in your hands will definitely add to your air consumption.

    Also, at some point you will be limited by the NDL and not air consumption. For example, I often end dives with 1200 to 1800 PSI in the tank because I have reached my NDL. At that point, how close you are to your wife doesn't matter. So focus on improving your air consumption relative to the last dive. NEVER compare your air consumption to someone else. It really doesn't matter because everyone is different.

    The larger tanks tend to be steel tanks. A steel tank will be ~6 pounds less buoyant. So you need to remove ~6 pounds from your weight belt if you switch from an AL80 to say a steel HP100. The dive shop renting you the tank will be able to give you exact differences.
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  9. #9
    Shark Zeagle Eagle's Avatar
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    Great thread guys. Lots of good info. I gave up trying to out-breathe my wife. I take a lot of video and am scooting all over the place to get the "right" shot. So, I dive a 100 when I can get it and my wife gets a 65.

    My wife manufactures air under the water. She denies it; but, I know she does. I mean those things can't be for just looking at.
    --Zeagle Eagle

  10. #10
    Grouper
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    Quote Originally Posted by scubadiver888 View Post
    Oh, any additional task loading will affect your air consumption. Putting a camera in your hands will definitely add to your air consumption.

    Also, at some point you will be limited by the NDL and not air consumption. For example, I often end dives with 1200 to 1800 PSI in the tank because I have reached my NDL. At that point, how close you are to your wife doesn't matter. So focus on improving your air consumption relative to the last dive. NEVER compare your air consumption to someone else. It really doesn't matter because everyone is different.

    The larger tanks tend to be steel tanks. A steel tank will be ~6 pounds less buoyant. So you need to remove ~6 pounds from your weight belt if you switch from an AL80 to say a steel HP100. The dive shop renting you the tank will be able to give you exact differences.

    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

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