i'm 6 ft 215 and i dive a 3mil suit with 14 lbs. even with 10 lbs i don't sink and i'm talking about calmly sitting on the surface with no air in my bc i'd love to dump weight out of my bc but if i'm not sinking i don't see how i could ever get down to 4 lbs. I'm a very calm diver my heart rate actually drops a bit when i dive so i don't see this as a factor. Thoughts? or was 4lbs a typo? Is your wet suit old? mine is fairly new that could explain some of it.mjh:
Is this a weight problem? or am I close?
- Thread starter DougK
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Also about the same size, used a huge amount of weight in confined water (about 24# i think), dropped to about 14# so far in salt with 3mm and AL80 (use 8# in fresh in same config), still dropping a little each time, might try 12# next time who knows? My breathing is getting better, i am learning not to make any unneccesary movements and all that is helping. Of course if i get in better shape and lose the other 10-20# in my weight loss target (get down to 210-220#) and replace some of my fat with more muscle then i expect to lose more weightbelt lead as well again - but also some more as i become more proficient in the water.
kelsays
Guest
Alll the responses so far are good ones.
The biggest problem I have found with new divers that were trained properly about how to check the weighting, is that they are not yet consistantly emptying ALL the air form the BCD.
Even a little air can cause more of a bouyancy change as you ascend and descend than is necessary. Although you will probably always have a little air, the less air the better. Why not have another diver observe you as you descend and see if there is air remaining in the BC as you leave the surface. With a full tank, you should not have any air in the bcd when you break the surface on the descent unless you want to be overweighted for a particular reason. Then as the tank empties you might have to add a bit to compensate for the air you have used, but that will be minimal.
The biggest problem I have found with new divers that were trained properly about how to check the weighting, is that they are not yet consistantly emptying ALL the air form the BCD.
Even a little air can cause more of a bouyancy change as you ascend and descend than is necessary. Although you will probably always have a little air, the less air the better. Why not have another diver observe you as you descend and see if there is air remaining in the BC as you leave the surface. With a full tank, you should not have any air in the bcd when you break the surface on the descent unless you want to be overweighted for a particular reason. Then as the tank empties you might have to add a bit to compensate for the air you have used, but that will be minimal.
Doug, I'm trying to figure out something similar myself, and I haven't quite resolved the physics of the situation. I believe I have typically been diving too heavy and trimmed in a moderately foot-low posture. In an effort to improve my skills and reduce my air consumption (particularly to use the BC less to adjust buoyancy,) I have been working on breath control, moving weight around in my config (weight integrated back flotation BC with two non-ditchable pockets on the back) and experimenting with less weight.
Last weekend, I did some shallow diving <20 ft. in freshwater to help put weed netting in at a public swimming area. To try and get my horizontal trim and neutral buoyancy just right, I had moved from six to 8 lbs in the back pockets, leaving 14lbs total in the ditchable pockets. To work on the trim, I also moved the whole BC up on my body by shortening the distance from shoulder to bottom of BC...
...and Eureka, when I went in I was floating just at mouth level, swam easily down to 1ft. off the bottom, and pulled up in perfect trim and neutral buoyancy. Tried a couple of frog kicks...no silt stirred up! Tried back kicks...I actually went backwards instead of rotating head up like I experienced when I was foot heavy. This was cool, bring on DIR-F!
Fast forward to 1200 psi (this was an AL80, by the way, with a 7mm full wetsuit with hooded step-through vest which I find to be difficult to manage buoyancy-wise at that depth.) I've been pinning the fabric to the bottom, which of course has a tendency to force me up as I beat the pins into the bottom. I'm glad I'm not doing this on the space shuttle! Hmm, not trimming up as well as I was at the beginning... Exhale and check breathing rate. Seems okay, but on exhale the trim gets worse. Whoa, this tank is dragging my butt up in the column! If I don't do something I'm going to be a polaris missile, fins first! (In hindsight, it may have just "felt" this way as the bottom of the tank tried to float, I may have stil stayed relatively neutral overall, just been standing on my head. Mild struggle to get head up, surface, back to the drawing board on weighting and distribution.
My fundamental questions: If I'm basically neutral at the beginning of the dive with a full tank, how can I be weighted correctly when the buoyancy of the tank is going to swing by close to 6lbs from full to empty? Do you make up the full 6lbs just with breath control?
If I am trimmed correctly at the beginning of the dive and the tank becomes "stern buoyant" as it empties, what do I do to correct the trim? Shoot for an average of beginning and ending "ideals?"
Isn't the BC really there to "compensate" for out of balance weighting, which it can only logically do at depth when the exposure protection has lost buoyancy, or should you be looking for it at the surface at the start of the dive to overcome the overweighting needed to end neutral with a 1/3 full tank and an empty BC?
With exposure protection this compressible, do you just give up on achieving neutral at the end of the dive between say 15ft and the surface? I know that divers make the 7mm combination work at shallow depths -- how? I need to be confident in my ability to do shallow safety stops in this rig, and right now I wouldn't want to count on it. I was always fine in a 5mm suit, but floating feet down and relying too much on the BC to handle buoyancy.
I pretty carfully worked out the buoyancy of the components of my rigs in a pool and then in a quarry, and I think I had that "by the book," but something was not right.
Any comments or advice welcome, and sorry to be hijcking your thread Doug but it seemed related enough to be useful to you as well.
FWIW, I'm 6'1", 165 and low body fat (~14%.)
Last weekend, I did some shallow diving <20 ft. in freshwater to help put weed netting in at a public swimming area. To try and get my horizontal trim and neutral buoyancy just right, I had moved from six to 8 lbs in the back pockets, leaving 14lbs total in the ditchable pockets. To work on the trim, I also moved the whole BC up on my body by shortening the distance from shoulder to bottom of BC...
...and Eureka, when I went in I was floating just at mouth level, swam easily down to 1ft. off the bottom, and pulled up in perfect trim and neutral buoyancy. Tried a couple of frog kicks...no silt stirred up! Tried back kicks...I actually went backwards instead of rotating head up like I experienced when I was foot heavy. This was cool, bring on DIR-F!
Fast forward to 1200 psi (this was an AL80, by the way, with a 7mm full wetsuit with hooded step-through vest which I find to be difficult to manage buoyancy-wise at that depth.) I've been pinning the fabric to the bottom, which of course has a tendency to force me up as I beat the pins into the bottom. I'm glad I'm not doing this on the space shuttle! Hmm, not trimming up as well as I was at the beginning... Exhale and check breathing rate. Seems okay, but on exhale the trim gets worse. Whoa, this tank is dragging my butt up in the column! If I don't do something I'm going to be a polaris missile, fins first! (In hindsight, it may have just "felt" this way as the bottom of the tank tried to float, I may have stil stayed relatively neutral overall, just been standing on my head. Mild struggle to get head up, surface, back to the drawing board on weighting and distribution.
My fundamental questions: If I'm basically neutral at the beginning of the dive with a full tank, how can I be weighted correctly when the buoyancy of the tank is going to swing by close to 6lbs from full to empty? Do you make up the full 6lbs just with breath control?
If I am trimmed correctly at the beginning of the dive and the tank becomes "stern buoyant" as it empties, what do I do to correct the trim? Shoot for an average of beginning and ending "ideals?"
Isn't the BC really there to "compensate" for out of balance weighting, which it can only logically do at depth when the exposure protection has lost buoyancy, or should you be looking for it at the surface at the start of the dive to overcome the overweighting needed to end neutral with a 1/3 full tank and an empty BC?
With exposure protection this compressible, do you just give up on achieving neutral at the end of the dive between say 15ft and the surface? I know that divers make the 7mm combination work at shallow depths -- how? I need to be confident in my ability to do shallow safety stops in this rig, and right now I wouldn't want to count on it. I was always fine in a 5mm suit, but floating feet down and relying too much on the BC to handle buoyancy.
I pretty carfully worked out the buoyancy of the components of my rigs in a pool and then in a quarry, and I think I had that "by the book," but something was not right.
Any comments or advice welcome, and sorry to be hijcking your thread Doug but it seemed related enough to be useful to you as well.
FWIW, I'm 6'1", 165 and low body fat (~14%.)
Continuing along the same lines: doing a bouyancy check at the *end* of a dive is too late for that dive. Isn't it possible to do a bouyance check at the beginning of a dive (based on a descent initiated with an empty BC and full exhalation), and then just add some amount (6 pounds?) based on the amount of air in the tank?
I hate the feeling of having to fight to stay down at the end of a dive, when the tank is empty, especially with the 7mm wetsuits needed here.
I hate the feeling of having to fight to stay down at the end of a dive, when the tank is empty, especially with the 7mm wetsuits needed here.
radeye:
I hate the feeling, and even more recognize that to progress to diving SW wrecks around here (waiting for warm water vacations just means too little diving,) which will require lots of practice, deco training, etc., one of the most basic things I'll eventiually have to be able to do is execute decompression stops at 20 ft and 10 ft. Longish ones under much less friendly conditions than the side of a fresh water pond with practically speaking no more nitrogen in my tissues than if I was sitting on the shore.
Until that far off day, I still need to be able to do a safety stop without struggling to stay down.
kelsays:
Please explain...... You are saying as I use air and I have less air in my tank I may have to add air to my BC to copmpensate?!?!?!?
You are a mistaken. You should be a little overweighted at the start of a dive (4 or 5 pounds). The reality is as you use air from your tank you become more bouyent. You should have to take air out of your BC to compensate (although this is minimal and will probably not be noticed as depth changes require bouyency adjustments). The last thing you or anyone wants is to be posative at the end of a dive and you are discribing a situation where a person WILL be 4 or 5 pounds posative at the end of a dive. For a new diver this can be hazardous as it can result in an uncontrolled ascent!!!!
I would also claim that I do not completly empty my BC then I decend. The reason for this is I am 5 pounds heavy at the start. I just release enough air to become negative. This means I need to put less in at depth to establish neutral beuyency also if something happens I am only slightly negative.
Here is a link to a site that has tank ratings including bueyency full and empty. You will see that the tanks are more negative when full. http://www.catalinacylinders.com/scuba.html
radeye:
Exactly! do a bouyency check with a full tank then add the amount of weight that your tank will lose (remember the higher the capacity of the tank the greater change in its bouyency from full to empty). Once you do this you should be neutral at the end of the dive.
Here is a link to tank rateings including bueyency ratings full and empty. http://www.saudidiving.com/tanks.htm
crpntr133
lost, even with a compass
I could never figure out why they tell you to start out with enough weight to allow yourself to sink with a full tank. I did this when I first started and it drove me crazy. I would breath down the tank and if I got above 20 ft or so I would rise to the top. I checked with a empty tank and adjusted and now have no problems. The lungs do the work for me.
Sideband
Guest
kelsays:
Ya lost me. As the tank empties it will be getting lighter and therefore MORE buoyant, right?(may still be negative but will be less so) If he added air to his BCD as he used air from his tank then he would be making himself overly positive wouldn't he? I'd think he'd need to DUMP air from the BCD as the tank got lighter to remaian neutral at a constant depth.
Joe
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