dry suit buoyancy

[dsteding]

Does anyone know generally how much lift and drop in feet can be achieved using just lung inhale and exhale (not using any DS or BC)? I'm sure that it depends on the depth you're at. Let's assume you're at 30-40 feet deep.

With an Al80 and a balanced rig I can essentially control my buoyancy throughout the dive with my lungs-provided I am relatively shallow so suit compression is not a huge issue. If one assumes a ~3 pound swing in suit buoyancy with depth ( 3 mm full suit) and ~6 pounds of gas, I THINK I could compensate for about 7-9 pounds of lift. The BC on such tropical dives becomes a convenience underwater, I don't have to breathe with really full or empty lungs.

I am probably on the high end of things, I'd bet the average to be comfortable is something along what Thal says, maybe 4-5 pounds.

 

[Dive Bear]

thats a good point too.

the more weight you add (double tanks, stages, heavy video cameras, whatever) the more problematic 'equilibrium' becomes.

what works for one drysuit diver in an 80 may not work for another with a couple steels...

Point taken! In my rant, I did not make an exception for my twin set brethren with their steel double tanks, steel back plates, steel stage bottles, steel reinforced spines and steely eyed gaze.

Don't forget that I also dive an MCCR. I understand that if your life support equipment makes you 20lbs negative, you will need to add air to your BC. However, I would ask that you throw me one small bone. If your gear is that heavy, I hope you are not adding a weight belt with 20 odd pounds of lead. What would be the purpose? Trim weights perhaps, but not a full weightbelt.

If I may refer to the original context of this thread, Scubascobey is in a PADI OW class, and she is having difficulty with trim and buoyancy. I quote “I'd end up rolling so my tank would be towards the bottom”. Granted I'm not there and I did not see what was going on, but I will hazard a guess that if Scubascobey took 2 to 4 pounds of lead off, she would need less air in her suit, which would result in less air to move around her suit and screw with her trim. In a nutshell, If you have a big bubble moving around your DS looking for a way out, you have too much air in your suit. If I understand her situation, she is also not allowed to use her BC. This means that she must reduce the amount of air in her suit, or learn to play a little game I call “balance the bubble”.

My wife is 5 feet tall and less than 90lbs. She used 22lbs of lead in her OW class and had a frightful time with buoyancy control. I've got her down to 16lbs of lead and I'm convinced she could take off at least 1 or 2 more pounds. She has much better control of her trim and buoyancy now than she did with all the extra lead.

On my first drysuit OW dive, I used 36lbs of lead. It was a fun dive, but I had a royal pain with my buoyancy. Now I'm down to 28lbs OC and 26 with my rebreather(Sports KISS with steel case). I'm 5'11” and I weigh 200 pounds in my sock feet. I use a very thick Andy's undergarment in addition to REI long handle underwear. On my next CCR dive, I'm going to try for 25lbs of lead and I don't think it will be a problem.

 

[Gdog]

Ok....I am an SSI AOW diver. We were instructed to never use the BCD for bouyancy, only for floatation at the surface. Bouyancy at depth is controlled by the DS. In a runaway situation, vent the neck seal. I have become comfortable with this, as it leaves me managing only one gas bag for bouyancy. However........I hate the feet up balloon feeling, and enjoy the head down posture while examining all of Gods creation down below. Any SSI divers out there instructed the same? At any rate, I am considering the BCD next dive, to see just how things go. I can understand how a newer diver could be confused in a panic situation with 2 bouyancy devices to worry about venting....but im very pleased that this thread was started, as it certainly brings to light what I have been wondering about....

 

[limeyx]

Point taken! In my rant, I did not make an exception for my twin set brethren with their steel double tanks, steel back plates, steel stage bottles, steel reinforced spines and steely eyed gaze.

Don't forget that I also dive an MCCR. I understand that if your life support equipment makes you 20lbs negative, you will need to add air to your BC. However, I would ask that you throw me one small bone. If your gear is that heavy, I hope you are not adding a weight belt with 20 odd pounds of lead. What would be the purpose? Trim weights perhaps, but not a full weightbelt.

Full weight of gear in doubles/stages etc. has little relevance to what weight belt you need honestly.

All weighting is done with just backgas (doubles) no stages, scooters, cameras etc.
So then you are really down to the differences in buoyancy between your back-gas tanks when they are empty.

So if I believe the manuf. specs, my double HP 100s are about -2 empty.
With those, I wear a SS plate and 8 pounds of lead. I would actually (possibly) add 2 if I was diving with AL80 stages, but not take any off.

if I dive with 130s, they are more negative to start, but pretty close to -2 empty, so I still wear an 8 pound belt.

So it's quite possible to have (not that I am trained for it) doubles 130's, camera, scooter, AL80, 2xAl40s and still have an SSBP and 8 pound weight belt.

Then add the 400G thunsulate instead of 200 and yet more weight.

 

[RPanick]

SSI suggests people start with just the dry suit, and not use the BC, at least a couple of years ago when I took the class. When you get comfortable with the suit, then switch to using the BC for bouyancy. The argument was to reduce the task loading, which makes sense to someone who has been diving for a while in a wet suit.

However, new divers in a dry suit will likely be way over weight, happens wet or dry. But in a dry suit being 10 or more pounds over will create a huge bubble in the suit. So in other words some serious weight trimming needs to happen before doing anything.

I would question putting a female diver that is 5'4" and 116 pounds in a 119 or 130 cf tank. My god, the 130 probably weighs half as much as the diver. Get a steel 80 to start with, life will be much simpler. I'm guessing that the boys around all use them and so that's what you are using. Your air consumption should be better than most of the people you dive with, you can get away in most cases with a smaller air supply. I think you will find trim is also much easier. I also agree with most of the other posts, it sounds like you have way to much weight.

When I was learning to use mine, I would take some clip on weights (or some that you can take off easy). I would then run my tank down to 1500 PSI, and sit at 15 feet, get comfortable and see how much of that weight I could get off comfortably. If I could get rid of all of it, I could go back on shore and get rid of another 4, then repeat. Before someone gives me a hard time, 1500 PSI gives you some time to play with things and adjust your trim and tweak. By the time you are done you will be down to 500-1000 PSI.

 

[TSandM]

What's wrong with 5'4" and 120 and a steel 130? I dove 130's in LA (and I match the parameters) and I loved them. They trimmed out beautifully and had a ton of gas, and I could easily walk in them (much easier than my doubles!). The only thing I needed help with was picking them up to put them on the seawall.

Admittedly, at home, I generally dive an LP95 when I dive singles. But my first dive in LA, I used an HP100, and Mo2 and HBDiveGirl ran me down to minimums before we got out of the water -- First time that EVER happened! The 130 was handy, and very manageable.

 

[mikerault]

With my dual 80 aluminums, a 6 pound plate, my salvo light and the bilaminate Next Gen suit over fleeces I use 16 pounds. I am 240, 5' 10". I control on my wing. With the duals I use a 50 pound lift wing. With a single using an aluminum 2 pound plate using a SS STA (about 2 pounds) a 35 pound lift wing and 14 pounds.

I keep hearing weights of 20+ pounds is it that you are using BCDs verses BP/W? I look back over my records and if I used a jacket style BCD I needed an extra 4-6 pounds of lead (even comparing to the aluminum with the STA).

Glad I have my BP/W!

Mike

 

[Tigerman]

With my dual 80 aluminums, a 6 pound plate, my salvo light and the bilaminate Next Gen suit over fleeces I use 16 pounds. I am 240, 5' 10". I control on my wing. With the duals I use a 50 pound lift wing. With a single using an aluminum 2 pound plate using a SS STA (about 2 pounds) a 35 pound lift wing and 14 pounds.

I keep hearing weights of 20+ pounds is it that you are using BCDs verses BP/W? I look back over my records and if I used a jacket style BCD I needed an extra 4-6 pounds of lead (even comparing to the aluminum with the STA).

Glad I have my BP/W!

Mike

Im actually shooting for 18 lbs with CD4 crushed neo next dive.. That might however be dropping a little too much a little too fast. I KNOW im going to drop some weight tho, im beginning to feel overweighted..
"About time"

 

[scubascobey]

Hey everyone.

Thanks to all of you for your input. I worked hard on this today, spending a lot of extra time on weight checks before and after my first dive. For this dive, I dropped from 27.5 down to 23.5. After this dive Thanks to all of you for your input. I worked hard on this today, spending a lot of extra time on weight checks before and after my first dive (with only 500 in tank). For this dive, I dropped from 27.5 down to 23.5. After this dive, I did another round of weight checks and decided to remove another 1.5 (from tank). I dove with 22 lbs on the 2nd dive (which was my Buoyancy Dive) and I totally mastered it! It was a HUGE difference going down in weight - a significant drop at that. I was able to find neutral all the way to 100 feet on my first dive (my Deep Dive) and held it all the way to ascent and easily handled the safety stop.

Thanks to everyone for your input which honestly gave me the balls to insist that my instructor take more time helping me find the right weight. Plus also the confidence to dive with less weight.

This is a great site. I love it.

 

[Cave Diver]

Glad to hear of your improvement. Overweighting is one issue that seems to plague a lot of divers.

I guess I'm lucky... I never need weights.