Newbie questions about buoyancy and trim with drysuit

[Daryl Morse]

This is my first post. I finished my OW last weekend. I really enjoyed both the classroom and practical aspects of the course and I look forward to more learning and more diving, including doing the AOW dives as soon as I can.

Since I live in Vancouver, BC, where the water is cold, I did part of my last CW and all of my OW dives in a drysuit. I used an O'Neill 7000X (neoprene) drysuit and a Mares Syncro (low-end jacket-style) BCD. I was wearing 35 lbs of weight. I wore a t-shirt, long-sleeve fleece shirt and long-johns and socks under the drysuit.

During the CW dive, we practiced inflating and deflating the drysuit to get a feel for its buoyancy. We also practiced going head-down to migrate the air to the feet and then finning to get back upright and migrate the air back to the upper body. We did this enough to get a feel for how little air it took to cause an uncontrolled foot-up ascent. Although the depth of the pool obviously was less than we would experience during the OW dives, I felt like I had a reasonable enough understanding of how the drysuit behaved to not be concerned about it during the OW dives.

All of the OW dives were from the shore. The first three dives were to 40 feet and the fourth was to 60 feet. Once I got past the first few feet, I had no problem descending. I think I would have been able to descend with even less weight. I also had no problem establishing neutral buoyancy at the bottom using my BCD. (I put only a small amount of air in the drysuit to keep it warm.) However, when I was hovering cross-legged, I ended up tilted back 45 degrees, even if I started upright or tilted forward. I found it disconcerting. I would rather be in a 45 degree forward tilt. Is this due to trim? What can/should I do about it?

The instructor advised me to keep the dump valve on the drysuit open. I found it leaked when I descended so I closed it. Is dump valve leakage normal? What is the proper way to use the dump valve?

Two of the four dives finished with direct ascent (CESA and AAS). For the other two dives, we spent time looking around on the bottom after we finished demonstrating the skills. We ascended gradually by following the bottom. Except when I approached the surface when ascending, I was easily able to maintain neutral buoyancy by dumping air from the BCD and drysuit.

On the first of these these dives, part way to the surface at around 15-20 feet, I found it increasingly difficult to prevent becoming positively buoyant even with the BCD empty. I tried to fin back down to a level where I would be neutrally buoyant. When I did this, I could tell I had air trapped in the drysuit, because it went to my feet. I wasn't able to fin back down enough to become neutral. I was able to get back head-up, but I could not dump the air from my drysuit, even in a left shoulder up attitude. I ended up in an uncontrolled ascent.

On the second dive (to 60 feet), again I had no problem dumping air from the BCD and drysuit to maintain neutral buoyancy until we reached 15 feet from the surface, at which point I ended up in another uncontrolled head-up ascent to the surface. My BCD was empty. I had only a small amount of air left in the drysuit but I was not able to dump it, in spite of going left shoulder up and holding down the dump valve.

I'm disconcerted by this problem, because I know 15 feet is the proper depth for a safety stop. I want to solve this problem before I dive any deeper. My instructor thought I should increase my total weight to 40 lbs by using ankle weights. I'm concerned about that approach because it seems to correct the symptom, not the cause. Just a guess, but I doubt the BCD even has 40 lbs of lift. Even if it did, I would rather figure out why I can't dump the air out of the drysuit. I am wondering if the BCD is too tight. I cinched it up because I like the tank to be stable on my back. Maybe I should try it a bit looser.

Finally, is it normal to dump a litre of water out of a BCD after dive?

Thanks in advance for your advice.

 

[H2Andy]

i don't dive dry, so can't help there.

as for the amount of water in a BCD, yes, you can get quite a lot of water there
particularly if you are inflating and deflating it a lot. 1 liter is about a quarter of a gallon, so that is a bit on the high side, but, yes, particularly for a new diver working the power inflator, you could get that much in there.

 

[Helmet]

Hello Daryl,

It sounds like you have a fairly strong grasp of how drysuits work and buoyancy in general. Several thoughts come to mind. First of all, I highly doubt that you need more weight given that you were actually underwater. Did you do a buoyancy check? What is your body weight and type? Generally, the less weight that you have the easier it is to control buoyancy because you have a smaller bubble of air in the system. Another thought is that you should never try to fin down against positive buoyancy. You will never succeed in anything but losing control. Your fins may even come off due to the bubble in your feet. One suggestion would be to limit the undergarments as much as possible. They can trap air. Air in a drysuit takes time to vent out. You may think that you have it all out or that it isn't coming out when in fact it just needs more time. Patience is a virtue. In the meantime, however, you may still be rising and so breathing out and flaring out may slow your ascent. Ideally you want to develop good anticipation and vent air BEFORE you start to rise. You will, with experience, develop a sense of what a suit should feel like and what it feels like when the bubble is too big inside. Adding more weight is not the answer. This is a lazy approach that does not solve the issue but in fact will exacerbate the issue in the long run. The key is to do a buoyancy check with a near empty tank to find out your true weighting needs.. not just guessing and adding more. You are right to be concerned about the lift capacity of your bcd.This is especially a concern when wearing anything neoprene which will compress and lose buoyancy at depth.. even shallow depth.

Another thought that comes to mind is why were you hovering cross legged? Since when does anyone dive cross legged?
I know everyone teaches that but it makes little sense other than being fun in any other configuration besides a dry suit. We dive horizontal in the trim position. WE should hover in this position. It is the position of most comfort. It is the position that holds the tank in the most stable position and the air in the suit and bcd as well. Sit up and all the air rises and your entire buoyancy changes. You need to consider balance, stability and buoyancy as integrated and controlled by your body position as much as your equipment and movement in the water. Also, when trying to hover sitting up.. your tank tends to pull you backwards. This is a position of poor control. Try not to put yourself in positions where you give up control and maneoverability. Belly down, arms out front, legs slightly bent or bent 45 degrees and knees up.. not dropped. This is a position of control and should be considered "home" position. You an deviate fromn this but ideally you will then return to it again.

I personally feel that you were right to leave the valve closed.. but I wouldnt' say all the way closed. I teach people to close it about one full turn. That way air doesn't escape easily but you can also open it easily when it is time to start up. Pushing the button to vent is difficult. It isn't always convenient to reach across your body when wearing thick neoprene. Also, this makes it challenging to watch your gauges and buddy while ascending. You should only have to lift your arm to vent.

As for dumping water out of a BCD.. that is common when you are trying to control an ascent that is starting to get out of control but no it isn't common when ascending normally.

Overall I think that you have made a successful start at diving in a dry suit. Many people have similar difficulties that you have had so don't fret too much. Practice is important but only if it is "good" practice so find an instructor that you trust and work with them to refine your skills. Dive with instructors as much as possible outside of classes so that you can get feedback on your diving in general. Evaluate the feedback you are getting and don't be afraid to continue to ask challenging questions of your instructors. Above all, don't simply add more weight and expect things to fix themselves!

Feel free to PM me if you have any further questions or need clarification on anything I've suggested. Keep us all in the loop as to your progress!

Helmet

This is my first post. I finished my OW last weekend. I really enjoyed both the classroom and practical aspects of the course and I look forward to more learning and more diving, including doing the AOW dives as soon as I can.

Since I live in Vancouver, BC, where the water is cold, I did part of my last CW and all of my OW dives in a drysuit. I used an O'Neill 7000X (neoprene) drysuit and a Mares Syncro (low-end jacket-style) BCD. I was wearing 35 lbs of weight. I wore a t-shirt, long-sleeve fleece shirt and long-johns and socks under the drysuit.

During the CW dive, we practiced inflating and deflating the drysuit to get a feel for its buoyancy. We also practiced going head-down to migrate the air to the feet and then finning to get back upright and migrate the air back to the upper body. We did this enough to get a feel for how little air it took to cause an uncontrolled foot-up ascent. Although the depth of the pool obviously was less than we would experience during the OW dives, I felt like I had a reasonable enough understanding of how the drysuit behaved to not be concerned about it during the OW dives.

All of the OW dives were from the shore. The first three dives were to 40 feet and the fourth was to 60 feet. Once I got past the first few feet, I had no problem descending. I think I would have been able to descend with even less weight. I also had no problem establishing neutral buoyancy at the bottom using my BCD. (I put only a small amount of air in the drysuit to keep it warm.) However, when I was hovering cross-legged, I ended up tilted back 45 degrees, even if I started upright or tilted forward. I found it disconcerting. I would rather be in a 45 degree forward tilt. Is this due to trim? What can/should I do about it?

The instructor advised me to keep the dump valve on the drysuit open. I found it leaked when I descended so I closed it. Is dump valve leakage normal? What is the proper way to use the dump valve?

Two of the four dives finished with direct ascent (CESA and AAS). For the other two dives, we spent time looking around on the bottom after we finished demonstrating the skills. We ascended gradually by following the bottom. Except when I approached the surface when ascending, I was easily able to maintain neutral buoyancy by dumping air from the BCD and drysuit.

On the first of these these dives, part way to the surface at around 15-20 feet, I found it increasingly difficult to prevent becoming positively buoyant even with the BCD empty. I tried to fin back down to a level where I would be neutrally buoyant. When I did this, I could tell I had air trapped in the drysuit, because it went to my feet. I wasn't able to fin back down enough to become neutral. I was able to get back head-up, but I could not dump the air from my drysuit, even in a left shoulder up attitude. I ended up in an uncontrolled ascent.

On the second dive (to 60 feet), again I had no problem dumping air from the BCD and drysuit to maintain neutral buoyancy until we reached 15 feet from the surface, at which point I ended up in another uncontrolled head-up ascent to the surface. My BCD was empty. I had only a small amount of air left in the drysuit but I was not able to dump it, in spite of going left shoulder up and holding down the dump valve.

I'm disconcerted by this problem, because I know 15 feet is the proper depth for a safety stop. I want to solve this problem before I dive any deeper. My instructor thought I should increase my total weight to 40 lbs by using ankle weights. I'm concerned about that approach because it seems to correct the symptom, not the cause. Just a guess, but I doubt the BCD even has 40 lbs of lift. Even if it did, I would rather figure out why I can't dump the air out of the drysuit. I am wondering if the BCD is too tight. I cinched it up because I like the tank to be stable on my back. Maybe I should try it a bit looser.

Finally, is it normal to dump a litre of water out of a BCD after dive?

Thanks in advance for your advice.

 

[SDAnderson]

The roll tendency from a sitting position will be to fall backwards, due to the heavy mass on your back - it's called "turtleing." Hovering cross legged is an exercise designed to help you learn to control bouyancy (not trim) and isn't something that you will ever do underwater, don't spend a lot of time worrying about it. Better to practice this skill prone, which is how you'll be swimming.

I keep my dump valve open from the time I leave the surface until I return - it's an automatic over-pressure relief valve. If you're getting water infiltration through the valve, the valve should be serviced.

The bottom line is that there is a balancing act between enough air in the dry suit and enough weight to stay down. You'll have to play with this interaction to see what works best for you. My guess is that you need to slow down your ascent to allow the air to work its way out of the drysuit, this is a fairly common problem. If that doesn't work you may need to add more weight. If you find yourself getting cold on the safety stop, you need more gas in the suit.

Is is normal to dump a liter of water from the bladder? No. Is it unusual, especially for a new diver? No. It comes from what is sometimes called "push button" diving, where the diver is constantly making micro-adjustments to his bouyancy with the bladder instead of his lungs. Poorly serviced valves in the bladder can also contribute. This will become less of a problem as you gain experience and skill.

Welcome to the undersea world, you're doing just fine. Keep at it.

 

[Michael Schlink]

What he said, all the way.
A litre of water is too much, could there have been water in the BC at the start of the dive? Also keep in mind that water in the BCD reduces it's lift capacity somewhat.
Next dive on your DESCENT stop at 15' and adjust for neutral. Pay attention to how much air you add to the BCD. If your not adding much or any your going to be TOO positive at the end of the dive. Try to add as liitle air to your suit as possible, just enough to stay warm and keep from pinching. On your ascent try to have something to control your ascent with, something to hold onto, and then come up in ten foot "steps", stopping along the way, giving time to vent your suit and control your ascent speed. I also don't like ankle weights. Your on your way to getting it all figured out. Just keep making small adjustments to your gear and be VERY careful on those uncontrolled ascents-Good luck

 

[Mako Mark]

the tilt backwards comes from the position of the weights compared to your center of gravity.

If your weights are towards the back, you will end up tilting back.

If your weights are forward, you will tilt forward.

Move a couple of you weights to the front.

I laso find that trying to wear the weights a little higher makes balance easier. Put your weight belt around your waist rather than your hips.

 

[ScubaRik]

In my drysuit course I was taught that the BCD was not used for bouyancy control at all. The drysuit was solely used for this purpose. The BCD was used to be able to float on the surface only. When you wanted to descend then all of the air was released from BCD and then not used again until reaching the surface.


.

 

[Doc Intrepid]

What works for some divers does not work for others. While most of us have heard of this, in the opinion of many this is a flawed practice. The reason is simple:

Gas trapped inside a drysuit will always seek to migrate to the highest point in the drysuit.

As the diver's 'attitude' or trim changes in the water column, the gas inside the drysuit will begin migrating up and down your arms and legs. This has two consequences.

First it can make precise trim control problematic. If you are attempting to hold a specific trim in the water, the migration of relative bouyancy from one part of your body (suit) to another can require a nearly constant effort to counter the resulting effects.

Second, under certain conditions it can be unsafe. The movement inside the suit of a significant amount of gas can contribute to instability and uncontrolled ascents - for example, a 'feet first' ascent.

The gas inside the suit expands as the diver ascends. So long as the diver ascends in a slow and controlled manner, it is unlikely that the gas in the suit will expand faster than the valve can vent it.

But...if the diver does NOT ascend in a slow and controlled manner, the gas inside the suit can expand faster than the valve can vent it - resulting in an ascent that is difficult to stop, particularly as the diver ascends from 33' fsw to the surface. Depending on many circumstances, uncontrolled ascents can have severe negative consequences.

Generally speaking, tools should be used for specific purposes. The purpose of a drysuit is to provide thermal protection to the diver. The purpose of a bouyancy compensator is to compensate for varying bouyancy requirements of the diver.

While drysuits can be used to compensate for bouyancy, this is not what they were designed to do. BCs will generally vent gas more rapidly and reliably than drysuits - because BCs don't have arms and legs that are occasionally higher than the vent.

In general,...I suspect you will find that you'll be able to control your bouyancy and trim with greater precision, feel more stable and comfortable, and be safer under a wider variety of circumstances if you use your drysuit to stay warm and use your BC to control your underwater bouyancy.

FWIW. YMMV.

 

[SDAnderson]

In my drysuit course I was taught that the BCD was not used for bouyancy control at all. The drysuit was solely used for this purpose. The BCD was used to be able to float on the surface only. When you wanted to descend then all of the air was released from BCD and then not used again until reaching the surface..

Wherever you learned it, it was (and remains) a bad idea. Use your suit to stay warm, use your BC to control your bouyancy. Using a hammer to drive a screw might work but it's better if you use the right tool for the job.

 

[Boogie711]

In my drysuit course I was taught that the BCD was not used for bouyancy control at all. The drysuit was solely used for this purpose. The BCD was used to be able to float on the surface only. When you wanted to descend then all of the air was released from BCD and then not used again until reaching the surface.


.

Completely disregard that advice. I believe that's only because your agency believes you're too stupid to handle both a BC and a Drysuit while you're diving. A Bouyancy Compensator is for buoyancy, a drysuit is to keep you dry. Period.

Do a search on "Dynamic Instability."