Negatively buoyant without weights

[bigred]

I finished the pool portion of my OW class this past weekend, and I ran into an unusual issue with my weighting that I can't quite figure out.

We did the standard PADI "sink to eye level" exercise. On Saturday, 10 lbs of weight brought me to forehead level, which the instructor said was close enough. On Sunday I sank without wearing any weights at all.

I'm 6' tall and weigh 200lbs. I had the same BCD both days, and I'm pretty sure I was using the same tank. The only think I can think of is that my wetsuit was a size too large and air was getting trapped on Saturday. Either way, I'm uneasy about diving without being able to ditch weights and get buoyant in an emergency.

Any idea what's going on?

Thanks,
- Sean

 

[GlazierB]

I have several friends who are like you... One friend in particular would loose one of his weight pockets almost on every other dive. Never knew about it till it was handed back to him or a class of Search & Rescure students were called out on a class to find something.

After using 40lbs with singles I would LOVE to be like you, don't complain... The shore dives feel much better without 100lbs of gear!

 

[cummings66]

You didn't say what you had on for exposure protection. I bet you had only a swimsuit and under those conditions I think what you experienced was normal. I too can sink in a pool with just a BC and tank on. However, put a 3mm wetsuit on and I'll need 6 lbs, put a 7mm on and it goes to 16 lbs. A drysuit brings me to 24 lbs.

It all varies according to scuba tank, i.e. al vs steel. If you had al the first time and then steel the second you would experience a big difference in a pool and would sink like a rock compared to the first time in an al 80 for example.

Not that it's worth much, but in my current config which is a BP/W and steel tank, I carry 6 lbs of lead on a belt when I have my drysuit on.

In short, don't worry about it, by the time you add exposure protection you'll have lead on. Just what did you wear?

 

[TheRedHead]

If you put air in your BC it will make you bouyant whether or not you are negatively bouyant (which is doubtful). As you consume air in your cylinder, it will become more positively buoyant. Getting positively bouyant in an emergency is generally a bad idea.

 

[Zeeman]

It's a good thing. Enjoy it. You don't have to carry extra weight

Z

 

[Jim Baldwin]

I finished the pool portion of my OW class this past weekend, and I ran into an unusual issue with my weighting that I can't quite figure out.

We did the standard PADI "sink to eye level" exercise. On Saturday, 10 lbs of weight brought me to forehead level, which the instructor said was close enough. On Sunday I sank without wearing any weights at all.

I'm 6' tall and weigh 200lbs. I had the same BCD both days, and I'm pretty sure I was using the same tank. The only think I can think of is that my wetsuit was a size too large and air was getting trapped on Saturday. Either way, I'm uneasy about diving without being able to ditch weights and get buoyant in an emergency.

Any idea what's going on?

Thanks,
- Sean

The more comfortable and relaxed you become in the water the less weight you will use.

I'm 6' 175 lbs. and with a 3mm wetsuit I dive with no weights. If you can sink by slowly exhaling without any weights then you should be able to swim to the surface with a minimum amount of effort. Just remember that if you're diving with an Al 80 the tank will be 4 to 5 lbs. positive at the end of a dive so you may want to add 4 pounds of weights so you can hold a good safety stop at 15 feet.

 

[redacted]

Many, maybe most, divers in good condition are negatively bouyant in FW. Ditching weights at depth is a pretty bad plan. Just a couple steps above drowning. As long as you can swim your rig up in case of a BC failure, you are OK. If you must have ditchable weight, just add a bit more neoprene to offset it. A 3mm or 5mm shortie should add 5 to 10 lb of bouyancy which should be more than enough to make you bouyant and not too warm. Front zip would allow you to open it up if it is too much.

 

[rawls]

Have you discussed this problem with your instructor. If not then I would suggest you do. You need not worry if you have to ditch weights and still stay on the bottom. Your BC is a piece of equipment designd to keep you neutrally buoyant in the water and positively buoyant at the surface. During your ascent you maintain neutral buoyancy all the way to the surface. Only neutral buoyancy and no more. You should be dumping air as you ascend, not adding it. As long as you maintain neutral buoyancy you will be able to get to the surface weights or no weights. Hopefully you will never get to a point where you have to ditch weights anyway. You will do this only if you know you will die if you don't get to the surface...

 

[divingjd]

It's unlikely to cause the entire 10 pounds of difference, but is it possible that there was still water in the BC on Sunday? Did you do the buoyancy checks at the same time in the class both days (at the beginning, at the end, whatever). If you don't drain all the water out of the BC, it can have a significant effect on your buoyancy. If you did the buoyancy check at the beginning of the class on Saturday, your BC would probably be empty. If you did it later in the class on Sunday, after doing some descents and ascents and adjusting your buoyancy, you could have a fair amount of water in the BC. It would take over a gallon to account for 10 pounds, which seems unlikely. It's hard to explain the difference from one day to the next. A wetsuit that is too large is unlikely to trap air - the water usually flows through pretty easily. I would guess that it is a combination of factors, maybe some water in your BC, a different tank, and maybe being more relaxed on Sunday.

 

[vondo]

If you don't drain all the water out of the BC, it can have a significant effect on your buoyancy.

No, water is neutrally bouyant in water. What matters is just how much *air* is in the BC.