Wet Suit Compression/Expansion

[Scubakevdm]

When I was doing my checkout dives this July I ran into a slight problem. We dove down in to a rock mass with a bunch of lobsters and hung around there at about 35 feet for 15 or so minutes. When coming back up to about 20 feet, my compressed wetsuit expanded and I floated to the top with my BCD totally deflated and 33 pounds still attached.

To me, this could be very dangerous if I were diving at a deeper depth and I was on my way to my 15 ft safety stop. Are there any ways to prevent another accident like this from occurring?

Here's what jumps out at me. How do you know your BCD was completely deflated? Did someone, like your instructor examine it, because it's hard to see yourself. 99 times out of 100, new divers that tell me they need more weight because they popped up on their safety stop popped up because they were overweighted, not underweighted.
If students are overweighted, they are forced to carry around a larger than necessary bubble of air in their BCD in order to be neutral. The larger the bubble, the greater the effect that changes in depth have on buoyancy. If the bubble is large enough even a slight change of depth can cause a change in volume and a corresponding change in buoyancy that is beyond the capacity of the lungs to control. New divers are especially prone to losing control in a situation like this, because they simply don't have the experience to feel slight changes in buoyancy and nip them in the bud, as a technical diver with a 22 lb gas swing has to be able to do. By the time they realize they are out of control, it is way too late even for coarse changes like fully dumping their bcd to keep them off the top.
Here's what I see:

1. An overweight scenario as described above.

2. A student inverted, deflator in hand with their left arm extended towards the bottom and about a 17 lb bubble of air in their BCD bulging towards their butt.

3. A student head up with deflator in hand, held at chest level with a 7 or 8 lb bubble in their bcd behind their head.

4. A student head up, deflator in hand left arm extended, left shoulder the high point, but with a BCD design that traps about a 1 or 2 lb bubble right behind their neck that they have to roll around ad work out the shoulder dump.

I think that Charlie also brings a great point, and agree that it is very common for new divers to react upon realizing that they are out of control by taking a deep breath.

 

[jponline77]

33 pounds is pretty normal for a starting diver in a 7mm wetsuit with gloves and booties. I agree with TSandM, in my OW class a few people ended up going to the surface. You'll get a better feeling about your bouyancy as you get more experienced. I think it's better to be slightly overweighted when you are starting out rather than perfectly weighted.

It is possible that if you were perfectly neutral with a full tank at the surface at the start you would be positively bouyant at the end of the dive and therefore struggle to stay down.

I was diving with about 32 pounds of weight with a 7mm wetsuit and was perfectly neutral with an empty tank. So, 33 sounds like it's in the right ballpark.

 

[jon m]

I love it when folks who have NEVER had a dive in a 7mil farmer john try to tell you how YOU MUST be overweighted, don't you???

don't worry about how much weight you are carrying (for now) concentrate on your BC and knowing/seeing where air will be trapped(most likely the case) in it in ALL positions you might find yourself in (ALL POSITIONS!) then you will know how to get the bubble to the nearest exit port.. if that doesn't work you ACTUALLY MAY be underweighted! (imagine that, it is a possibility) as everyone , depending on body style/fat/etc will carry different weight...
remember-
there is a very big difference in the amount of weight needed with a farmer john and a single peice 7mil. i weigh 250lb and use a one peice with a vest (i need 24lb) my wife weighs140lb and wears a farmer john. she displaces MUCH less water than i do, and should need less weight. she needs 36lb to get down....

 

[Scubakevdm]

I love it when folks who have NEVER had a dive in a 7mil farmer john try to tell you how YOU MUST be overweighted, don't you???

don't worry about how much weight you are carrying (for now) concentrate on your BC and knowing/seeing where air will be trapped(most likely the case) in it in ALL positions you might find yourself in (ALL POSITIONS!) then you will know how to get the bubble to the nearest exit port.. if that doesn't work you ACTUALLY MAY be underweighted! (imagine that, it is a possibility) as everyone , depending on body style/fat/etc will carry different weight...
remember-
there is a very big difference in the amount of weight needed with a farmer john and a single peice 7mil. i weigh 250lb and use a one peice with a vest (i need 24lb) my wife weighs140lb and wears a farmer john. she displaces MUCH less water than i do, and should need less weight. she needs 36lb to get down....

Well, I have some news for you. Here's the rules... an object is buoyed up an an amount equal to the weight of the volume of the water that it displaces. The water doesn't care if it's you or if it's your wife. If your wife weighs less than the weight of the water she displaces, she will float. If she weighs more than the volume of water that she displaces, she will sink. There's nothing magical about a farmer john that changes this equation, and there is no absolutely no correlation to the weight that she should be diving with and the volume of water that you displace.

I an 250 lbs too. I wear a 7mil one piece in the early winter and late fall and a drysuit in between those periods. When I wear the 7mil, I wear the equivalent of a 16 lb weight belt.

So that you can feel good about my qualifications in this discussion, I was certified in a farmer john, but back then they were 1/4 inch, not 7mil. I made my first 367 dives that way. I earn my living teaching people how to dive and helping them to dive better, and it is my experience that of out of control ascents are caused 99% of the time by divers being over weighted. I thought this information might be useful to people who are dealing with this most common of issues. So as not to be misleading, technically you are right, I have never dove in a two piece, 7mm farmer john so I may not know what I'm talking about.

 

[jon m]

Well, I have some news for you. Here's the rules... an object is buoyed up an an amount equal to the weight of the volume of the water that it displaces. The water doesn't care if it's you or if it's your wife.


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whoaaaa!!!! first, what gave you the impression i was quoting you? i was talking about all "you wear 30lbs, you MUST be overweighted" folks. i actually thought your advice was spot on, and i echo it.
also, there is a BIG difference in the farmer john and single piece bouyancy. i understand how water displacement works, and that was my point. my wife at 140lb, much smaller than i , SHOULD need less weight, but she doesn't. all that neoprene, trapped air and more water displaced causes her to need more weight than i do.
when we dive warm water, she needs less than me beacause she displaces less water.

 

[SteveAD]

There are actually two factors that define bouyancy. The weight of the water an object displaces is the bouyant force, but it is countered by the objects mass as a downward force. It is not unheard of for a smaller woman to need more weight than a larger man in warm water because her lower density causes her to be more "floaty"

 

[Thalassamania]

When I was doing my checkout dives this July I ran into a slight problem. We dove down in to a rock mass with a bunch of lobsters and hung around there at about 35 feet for 15 or so minutes. When coming back up to about 20 feet, my compressed wetsuit expanded and I floated to the top with my BCD totally deflated and 33 pounds still attached.

To me, this could be very dangerous if I were diving at a deeper depth and I was on my way to my 15 ft safety stop. Are there any ways to prevent another accident like this from occurring?

A few thoughts if I may:

• 33 lbs of lead seems a tad on the heavy size, but is just at the extreme far end of the range, not out of the range. Several folks have suggested that you will use a little less weight as you gain experience, calm your breathing and learn to get every last one of those pesky air bubbles out of your suit and BC, but since you’re an experienced free diver, I’m not so sure those effects will be as pronounced as others expect.
• You were down for 15 (or so) minutes at 35 feet. Lets call it 20 minutes. It’s not inconceivable that you went through 50 or even 60 cubic feet of air, which could lighten you by four to five lbs. Because of your freediving you likely know how to shift that much buoyancy on your lungs.
• The increase in buoyancy had to come from some where, using up air was one source, there are really only three other possible sources:

1. Breathing higher in your cycle.
2. Trapping air in your wetsuit.
3. Trapping air in your BC

You need to look at each of those three individually.
​

Please be sure and let us know what you find.

 

[Scubakevdm]

whoaaaa!!!! first, what gave you the impression i was quoting you? i was talking about all "you wear 30lbs, you MUST be overweighted" folks. i actually thought your advice was spot on, and i echo it.
also, there is a BIG difference in the farmer john and single piece bouyancy. i understand how water displacement works, and that was my point. my wife at 140lb, much smaller than i , SHOULD need less weight, but she doesn't. all that neoprene, trapped air and more water displaced causes her to need more weight than i do.
when we dive warm water, she needs less than me beacause she displaces less water.

Sorry. My bad... I sometimes forget that I'm here to help. My apologies.
As far as the consideration of your wife's lead, as the guy below you is pointing out, and as I was trying to point out in my little tantrum, it is the tug of war between the volume of water displaced by your wife and everything attached to her, which pushes up and the weight of her and her stuff, which pulls down. So, though she displaces much less water than you, she also weighs much less than you.