Buoyancy Check Methods

[fisheater]

I've been saying exactly this for years until I'm blue in the face seemingly to a deaf crowd.
I would add, the check needs to be done after a full length dive at depth because wetsuits cool off and also compress further with more time at depth. Just going straight into the shallows from shore with a warm plump wetsuit with a near empty tank doesn't approximate the real thing.

I listened. I did that. I have excellent weighting as a result. I've passed that advice along.

 

[TSandM]

Of course, you are always somewhat overweighted starting the dive.

I just want to address this, because this misuse of a term is common and I think contributes to a good deal of confusion.

At the beginning of a dive, a properly weighted diver will be NEGATIVE with an empty BC (and dry suit, if one is used). This is because the diver is carrying gas he intends to exhaust into the water during the process of the dive, and that gas has weight. At the beginning of the dive, the diver will be negative by the weight of the gas in his tank, and this amount is obviously more for bigger tanks. This is normal, and is not being overweighted. This gas weight, and exposure protection compression (if one is using neoprene), are the reasons one needs a buoyancy compensator. That's why you start out with a bunch of air in your BC, and by the end of the dive, most or all of it should be gone.

People argue about how to weight themselves -- some say, if you are wearing thick neoprene, it's okay to be neutral at the beginning of the dive with full tanks, because the neoprene won't fully rebound on ascent, and the difference will allow the diver to hold a safety stop. Some people weight themselves neutral with 500 psi in the tank, and at safety stop depth; I don't like that, because I want to be able to control my ascent all the way to the surface, and I've had the experience of being delayed at depth and having to swim my shallow stop because I couldn't hold it hovering. I weight myself neutral in water shallow enough to stand up in, and with about 300 psi in the tank. I may carry a pound or two extra that way, but I won't be unable to stay down when I want to.

 

[Kharon]

... There's no substitute for a real weighting check, conducted in the shallows, by holding a neutral hover at safety stop depth with no air in your BCD (superfluous weight removed incrementally until the hover is achieved).

Wow! Never heard this before. It sounds so much better than the way I was taught (SDI same as PADI). Why isn't it taught this way? Anyway, thanks for the information. I will be re-doing my weight checks and revising my weighting spreadsheet (I layer) using this method.

 

[Eric Sedletzky]

I just want to address this, because this misuse of a term is common and I think contributes to a good deal of confusion.

At the beginning of a dive, a properly weighted diver will be NEGATIVE with an empty BC (and dry suit, if one is used). This is because the diver is carrying gas he intends to exhaust into the water during the process of the dive, and that gas has weight. At the beginning of the dive, the diver will be negative by the weight of the gas in his tank, and this amount is obviously more for bigger tanks. This is normal, and is not being overweighted. This gas weight, and exposure protection compression (if one is using neoprene), are the reasons one needs a buoyancy compensator. That's why you start out with a bunch of air in your BC, and by the end of the dive, most or all of it should be gone.

This is true with a dry suit. Shells don't compress and neither do undergarments so the weight of the air that you consume is the only variable in the equation.
Plus diving dry I'm sure nobody want's to be shrink wrapped at 15 feet with an empty wing so a little extra weight might be appreciated to hold the diver down so they could have a little gas in their suit.

People argue about how to weight themselves -- some say, if you are wearing thick neoprene, it's okay to be neutral at the beginning of the dive with full tanks, because the neoprene won't fully rebound on ascent, and the difference will allow the diver to hold a safety stop. Some people weight themselves neutral with 500 psi in the tank, and at safety stop depth; I don't like that, because I want to be able to control my ascent all the way to the surface, and I've had the experience of being delayed at depth and having to swim my shallow stop because I couldn't hold it hovering. I weight myself neutral in water shallow enough to stand up in, and with about 300 psi in the tank. I may carry a pound or two extra that way, but I won't be unable to stay down when I want to.

With neoprene we don't have the option to add air to the suit.
I am the wetsuit king. I am a wetsuit connoisseur and oficionado. I'll bet I have a wider variety of wetsuits than anybody else on this board.
I have spent countless hours of experimentation with weighting and the different characteristics of different wetsuit materials.
I can tell you that when I achieve the perfect weighting of holding the 15' stop with and empty wing and 500 psi with any of the suits I have, the dive always starts with me slightly positive at the beginning of the dive to where I don't need any air in my wing to stay afloat, and that's up to my steel 120.
From 15' to the surface is a big difference in pressure, it is the most critical balancing point between expansion and compression of air. This is why I was taught that the less air you have (preferably none) in your BC at this depth will mean you will have the easiest time holding that stop. This is why with wetsuits, ALL variables need to be considered including how cold, pressure, and time will affect the buoyancy characteristics of wetsuits, unlike shell drysuits in which do not have those variables.

Once I did a dive in a cheap bargain wetsuit that I got on a sale rack. I was positive at the beginning of a dive, dove to depth, used up my air, and was more negative at the surface at the end of the dive than when I started. The wetsuit was so bad that it never fully recovered, or at least not in the time frame of the dive. I ended up cutting the suit apart and making booties out of it.

 

[knotical]

Another vote for:
Do it at the surface, at the end of a dive, with a nearly empty cylinder
You want just enough weight to be able to descend again if needed. And on future dives you’ll be able to slowly ascend after safety stops, which is important because that’s when the greatest proportional pressure changes occur.

Besides, it’s often logistically easier to do the check at the surface because you can pass weights to or from someone on the boat/dock.

 

[Steve_C]

I agree with the 300 psi, end of dive, shallow water. I will add that I do the check without any "disposable equipment." Between the pony I sling and the reel there are a couple more pounds. But there are scenarios where the pony is used or passed off and the reel is used to shoot an SMB. So they should not be part of my weight check. I add a pound to account for the empty pony going buoyant.

 

[Progen]

... There's no substitute for a real weighting check, conducted in the shallows, by holding a neutral hover at safety stop depth with no air in your BCD (superfluous weight removed incrementally until the hover is achieved).

Wow! Never heard this before. It sounds so much better than the way I was taught (SDI same as PADI). Why isn't it taught this way? Anyway, thanks for the information. I will be re-doing my weight checks and revising my weighting spreadsheet (I layer) using this method.

That was what I was taught in the Peak Performance Buoyancy Pt. 1 when I did my Advanced Open Water course. Sure helped me tonnes as I found that I needed 2kg less than I thought.