Dry suit versus BC buoyancy question

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LowDrag
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Dry suit versus BC buoyancy question

Post by LowDrag »

Since getting my White's I have read a lot of different threads about dry suits and controlling buoyancy. I see a lot of divers saying they only use their BC for buoyancy control and put just enough gas in their dry suit to stop the squeeze and then there is the "use only your dry suit" for buoyancy control crowd. My wife and I were taught to use our dry suits for buoyancy control and leave our BC's for buoyancy at the surface only. So, I am kind of confused here. Does it really make a difference which way we control buoyancy or is there a good argument for either method?


Inquiring minds want to know... :rofl:
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CaptnJack
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Re: Dry suit versus BC buoyancy question

Post by CaptnJack »

In a single tank its not a big deal. There's only about 8lbs worth of gas in a hp100, that's roughly 2L of gas volume you need to add to your suit and gradually subtract. Even if it all in your suit and it all migrated to your feet that's not neceassarily an uncontrollable shift.

Strap on big doubles and some stages and you will NOT be in control using your suit only. It just doesn't work since the required bubble is huge, big enough to pop your feet out of their booties and blow off you fins too. So yeah at this point you better be using the wing/BC for most of your buoyancy control because it keeps the buoyancy bubble in control and reasonably centered over your center of gravity.
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Joshua Smith
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Re: Dry suit versus BC buoyancy question

Post by Joshua Smith »

LowDrag wrote:Since getting my White's I have read a lot of different threads about dry suits and controlling buoyancy. I see a lot of divers saying they only use their BC for buoyancy control and put just enough gas in their dry suit to stop the squeeze and then there is the "use only your dry suit" for buoyancy control crowd. My wife and I were taught to use our dry suits for buoyancy control and leave our BC's for buoyancy at the surface only. So, I am kind of confused here. Does it really make a difference which way we control buoyancy or is there a good argument for either method?


Inquiring minds want to know... :rofl:

I have used both methods with fine results. I say it's completely up to individual preference.

FWIW, I found the "just add enough gas to the drysuit to take off the squeeze, and then use your wing" worked best for me on open circuit (single tank AND doubles), whereas on my rebreather, any gas in my wing underwater screws up my already questionable trim, so I just started using my suit instead. I think it's important to try lots of different approaches to find out what works best for you.
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LowDrag
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Re: Dry suit versus BC buoyancy question

Post by LowDrag »

Thanks guys...I kind of figured this would be the consensus of opinion. I am going to try buoyancy via my new wing this weekend I think. I report back.
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winte.r
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Re: Dry suit versus BC buoyancy question

Post by winte.r »

I just want to point out that suit material matters also, the OP has a shell but an uncompressed neoprene dry suit it is a bad idea to use the suit because there is less room for the bubble and if it gets to your feet it is much, much harder to get out.
I was dry suit certified by PADI and was told that they teach drysuit-only at the rec level to reduce task loading and then BCD-only for tech. My instructor said something along the lines of, "This is what I have to teach you, but you can ask any of the DM's or me how we manage it."
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rcontrera
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Re: Dry suit versus BC buoyancy question

Post by rcontrera »

Think about it for a minute ....

When in a wetsuit, a diver uses a BC to overcome the loss of buoyancy due to the compression of the suit material as he/she descends. That compression is due to the collapse of the gas bubbles in the material.

Now let's take the same diver and change to a dry suit. Instead of thousands of little tiny gas bubbles, we now have one large bubble. So, we still have a change in buoyancy at depth due to the compression of that bubble. HOWEVER, we also lose the insulation layer. If we use the valves in the suit to restore the insulation layer, the buoyancy magically restored itself too!

So, if using a shell style suit, insulation and buoyancy both track. Restore insulation and you are neutral. that kind of means you use your suit instead of a BC.

Now, let's put that same diver in a neoprene suit and we add in the additional buoyancy loss. Now, our diver has to use both the suit and the BC.

So ... I guess that means that everybody is right ... depending on what type of suit is used.
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winte.r
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Re: Dry suit versus BC buoyancy question

Post by winte.r »

That's kind of a misnomer, if you have achieved neutral buoyancy using only your dry suit it is true, but if you used your BCD to get neutral you're going to be adding to both as you descend, not just the suit, or you're going to make your bubble bigger.

No one mentioned it but I also think using the BCD is safer than the suit, you can dump faster and you can dump when inverted. Someone might say that proper bubble management makes this a null issue but that doesn't take into account other failures like a lost weight pocket or a stuck inflator.
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Re: Dry suit versus BC buoyancy question

Post by LowDrag »

winte.r wrote:I just want to point out that suit material matters also, the OP has a shell but an uncompressed neoprene dry suit it is a bad idea to use the suit because there is less room for the bubble and if it gets to your feet it is much, much harder to get out.
I was dry suit certified by PADI and was told that they teach drysuit-only at the rec level to reduce task loading and then BCD-only for tech. My instructor said something along the lines of, "This is what I have to teach you, but you can ask any of the DM's or me how we manage it."
We are diving dry but in a pair of White's suits (probably should have put that in my original post). She is diving the Fusion 1 and I am diving the Bullet. Still a dry suit but with a much more manageable bubble. I only say that based on what I have read here and on ScubaBoard and talking to other divers. Everyone I have talked to says they had to relearn buoyancy when they went to a shell type suit compared to a White's suit.
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Re: Dry suit versus BC buoyancy question

Post by kdupreez »

personal preference.

I prefer using both so i dont have an excessive bubble in the suit.. end inevitably ends up in my feet and makes life hard and feel head heavy / foot light.

bcd constains the air around center of balance (around tank) and I enjoy my dive a little more with just enough gas to remove the squeeze / stay warm in suit and the rest in bcd..

at the end of the dive, the wing is completely empty anyways, so the amount of gas in the suit always stays the same.

but, personal preference..
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Re: Dry suit versus BC buoyancy question

Post by KneeDeep »

LowDrag,
I've now have the same drysuit as you and use mostly my suit after descent.

But, when I had my USIA suit, I used just enough suit air to keep the squeeze off with a 200g undergarment. If I was to use my weezle with same suit, I needed to add more weight. All due to bubble management and trapping
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I have used both methods with fine results. I say it's completely up to individual preference.
+ to Joshua, preference and diving your gear.
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Re: Dry suit versus BC buoyancy question

Post by LCF »

I was originally taught to use my dry suit for buoyancy, but I had a lot of problems with control.

When I changed to allowing the suit to be squeezed and using the wing for most of my buoyancy, I wasn't nearly as warm, but I didn't end up on the surface feet-first any more.

As I gained facility with managing the suit, and with buoyancy control in general, I was able to shift more and more gas to the suit, which meant I was warmer and more mobile, and in general, more comfortable. Today, I'll run as much gas in the suit as I can keep stable -- as Richard points out, if the rig you are diving is sufficiently negative at the beginning of the dive, there is no reasonable way to offset that entirely with air in the suit. (And if the diving I am going to do may require a lot of odd positions in the water, as, for example, caves often do, I will NOT run the suit loose like that, because there is nothing more uncomfortable than getting a lot of air in your feet and not being able to drop them to get it out!)
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Re: Dry suit versus BC buoyancy question

Post by LowDrag »

Thanks everyone. I appreciate all of the answers. I figured it was going to be a personal like/dislike type of situation. I think I might try experimenting this weekend with just enough gas to keep the squeeze off and my BC for buoyancy. This way I can compare and see which way I like the best.
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Re: Dry suit versus BC buoyancy question

Post by Nwcid »

I will throw another one in here now. I use my BC for gross control and my suit for fine control. Usually as I descend I use the BC till I am almost neutral, then make minor adjustments with the suit. Sometimes if it is cold I will run a little more air in my suit. I know when I have too much air in my suit when my feet get a little light.

We have been warm water diving all week and I have had my first experience diving in shorts and a rash guard. We did a total of 20 dives this week. It took me at least 6 dives to not reach for my DS inflator when nearing neutral.
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LowDrag
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Re: Dry suit versus BC buoyancy question

Post by LowDrag »

Nwcid wrote:I will throw another one in here now. I use my BC for gross control and my suit for fine control. Usually as I descend I use the BC till I am almost neutral, then make minor adjustments with the suit. Sometimes if it is cold I will run a little more air in my suit. I know when I have too much air in my suit when my feet get a little light.

We have been warm water diving all week and I have had my first experience diving in shorts and a rash guard. We did a total of 20 dives this week. It took me at least 6 dives to not reach for my DS inflator when nearing neutral.
I look forward to having that problem someday... :partydance:
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Re: Dry suit versus BC buoyancy question

Post by H20doctor »

I wear a thick neoprene drysuit, atlan.. and I use my bc for trim.. I put just enough air into my suit to remove the squeeze.. argon in the suit, even warmer.. if you have done drysuit drills there's no issue with having a bubble in your drysuit, I often get a big air pocket in my boots, but I know how to rite myself and burp it out my arm vent.. as stated above it's all about personal preference
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Re: Dry suit versus BC buoyancy question

Post by Nwcid »

LowDrag wrote:
Nwcid wrote:I will throw another one in here now. I use my BC for gross control and my suit for fine control. Usually as I descend I use the BC till I am almost neutral, then make minor adjustments with the suit. Sometimes if it is cold I will run a little more air in my suit. I know when I have too much air in my suit when my feet get a little light.

We have been warm water diving all week and I have had my first experience diving in shorts and a rash guard. We did a total of 20 dives this week. It took me at least 6 dives to not reach for my DS inflator when nearing neutral.
I look forward to having that problem someday... :partydance:

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Re: Dry suit versus BC buoyancy question

Post by alm »

My experience:
Undergarment: Weezle Extreme in both cases
Tank: 119 cu ft single in both cases

1st Suit: 3 mm crushed neoprene, forearm dump
First Technique (about 100 dives): combo suit and bcd; very little air in the suit

2nd Suit: 2 mm crushed neoprene, shoulder dump
2nd Technique (a few dives now): suit only

Why did I start with the combo? Fear of the suit buoyancy getting away from me
due to the relatively slow forearm dump vs. quick bcd dump.

Why did I change? A hope that it would help keep the p-valve plumbing in my nether
regions from getting crushed due to dry suit squeeze. Unfortunately I still have
some squeeze from waist downward even when neutral with all buoyancy in the suit.
But I'm used to suit-only now, the bubble doesn't seem excessive, and I seem to be avoiding
any out of control ascent issues. However, my first
checkout dive with this setup in an overweighted state made me appreciate the comments
about the behavior of an overly big bubble; I felt like a balloon.
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Re: Dry suit versus BC buoyancy question

Post by LowDrag »

@alm:

The bubble issue is part of the reason why we went with White's suits. My wife and I did quite a bit of research and most people said they had to re-learn buoyancy because of the bubble in a bag suit. My buoyancy only got better when I went dry and my wife too. We took to our White's really well right out of the gate. I have put a good amount of air in my DS without any bubble management issue. So far, the only time I have had runaway ascent issues is when I mounted my tank too high on my wing and ALL my bubble headed for my feet. That was quite a struggle but I completed the dive and learned a valuable lesson.
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Re: Dry suit versus BC buoyancy question

Post by LCF »

alm, if you are experiencing squeeze in your lower body and legs, it's because they are below your torso. Physics is inexorable . . . air will always move to the highest point in the suit. It's very common, with the large amounts of weight we need to use in Puget Sound, for people to end up feet-low in the water. This is especially true if you are using a weight-integrated BC that doesn't have (or you aren't using) trim pockets.

If you try moving some weight around -- put some on the cambands, or wrap a 4 lb ankle weight around your tank neck -- you may find that the lower body squeeze goes away. You have to be careful about how much air you have in your feet then,though!
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Re: Dry suit versus BC buoyancy question

Post by LowDrag »

LCF wrote:alm, if you are experiencing squeeze in your lower body and legs, it's because they are below your torso. Physics is inexorable . . . air will always move to the highest point in the suit. It's very common, with the large amounts of weight we need to use in Puget Sound, for people to end up feet-low in the water. This is especially true if you are using a weight-integrated BC that doesn't have (or you aren't using) trim pockets.

If you try moving some weight around -- put some on the cambands, or wrap a 4 lb ankle weight around your tank neck -- you may find that the lower body squeeze goes away. You have to be careful about how much air you have in your feet then,though!
Amen to that!!! The floaty feet feeling sucks!!!
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Re: Dry suit versus BC buoyancy question

Post by LCF »

Ideal is to get your weight distributed so that you NEED a little air in your feet -- then your feet stay WAY warmer!
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Re: Dry suit versus BC buoyancy question

Post by alm »

lcf and lowdrag:

Thanks for the thoughts. I'm pretty happy with my current trim, my feet are nice and warm,
and my buddies underwater tell me I'm more or less horizontal, though I imagine it is "sideways comma" horizontal with
fins high, rather than "ruler horizontal". Given the choice of where the bubble sits
and the consequences, for now I'd rather
settle for having it where it is than get adventurous with moving it down any.

FYI anybody curious: this is a Bare 2mm crushed,
and after 3 or so dives buoyancy became completely automatic and almost effortless.
I see absolutely no evidence that a Weezle impairs dumping air with an upper-arm dump,
though it was an open question with the old forearm dump where the pause before
dumping started seemed much longer.

The one weird
"balloon" dive was overweighted in a swimming pool. When the necessary bubble is too big, my observation
is that your latex neck seal turns into a turgid doughnut when you go vertical.
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Re: Dry suit versus BC buoyancy question

Post by Nwbrewer »

alm wrote:
I see absolutely no evidence that a Weezle impairs dumping air with an upper-arm dump,
though it was an open question with the old forearm dump where the pause before
dumping started seemed much longer.
What brands were the dump valves? I'd be willing to bet that the one where it paused was an Apeks....
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Re: Dry suit versus BC buoyancy question

Post by spatman »

Nwbrewer wrote:
alm wrote:
I see absolutely no evidence that a Weezle impairs dumping air with an upper-arm dump,
though it was an open question with the old forearm dump where the pause before
dumping started seemed much longer.
What brands were the dump valves? I'd be willing to bet that the one where it paused was an Apeks....
When I dived a Weezle I definitely noticed a slower rate of exhaust from my SiTech shoulder valve. It required a little proactive venting in order to stay ahead of my buoyancy needs.

I switched to the Fourth Element Arctics and venting was noticeably more efficient.
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Re: Dry suit versus BC buoyancy question

Post by jerryehrlich »

spatman wrote:
Nwbrewer wrote:
alm wrote:
I see absolutely no evidence that a Weezle impairs dumping air with an upper-arm dump,
though it was an open question with the old forearm dump where the pause before
dumping started seemed much longer.
What brands were the dump valves? I'd be willing to bet that the one where it paused was an Apeks....
When I dived a Weezle I definitely noticed a slower rate of exhaust from my SiTech shoulder valve. It required a little proactive venting in order to stay ahead of my buoyancy needs.

I switched to the Fourth Element Arctics and venting was noticeably more efficient.
I believe the high loft nature of Weezle wear requires a little more ballast. This should solve your slow vent problem.

Jerry
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