Negative buoyancy...

[cloudwalker_3]

As someone who's negatively buoyant, I'd like to hear about other people's experiences of being negatively buoyant or techniques for dealing with this.

Personally, I’m okay with some kind of buoyancy aid, (like a wetsuit for example!) and I’m very comfortable under the water but trying to tread water is a little difficult sometimes. Generally I’m most comfortable either in and under or out.

 

[fjohnson]

A wetsuit will help, but like I've said before, I saw a muscle builder/football player who wouldn't float even with a thin wetsuit and waterski vest on, although the vest was undersized.. still, I couldn't believe it. I agree, treading water is no fun. Maybe a tube float is an idea.. a place to hang on the surface. Maybe a wetsuit will do it too. A wetsuit does it for me.. 3 mil full suit, fresh water, no weights is perfect for about -25' (-7.5m) nuetral.

 

[cloudwalker_3]

I do feel sorry for the muscle builder but it's kinda nice to hear that I'm really not the only one. I though for a long time I was just rubbish at floating until a few years ago I found out that some people, (like him and me obviously) are negatively buoyant.

Thanks for the tip on wetsuit thickness and about the tube float.

Out of curiousity, assuming you've picked out your wetsuit, how do you work out, (if you need them...) what weights to wear? Is it a matter of trial and error or is there a formula? Or two, (one for fresh water and one for salt...)?

 

[smellsfishy]

I was taught to set my buoyancy so I'm buoyant at the surface and don't need to kick to stay afloat yet I'm neutral at 33 feet. This way at the surface I have nice relaxed breath ups, but on the way back up from depth I'm positive at 33 feet so would still be buoyant for safety reasons should I have a shallow water black out at depth of less than 33 feet.

I know spearfisherman who like to set their buoyancy so they're neutral near the bottom where they're fishing so perhaps only 15 - 20 feet depth.

Also, I know certain competitors who set their neutral buoyancy for 66 feet for an easier return trip.

Unfortunately there is no exact formula you just have to play with the weights depending on the suit you're wearing and the water you're in.

I wear 7 or 8 pounds with my 5mm freediving suit in freshwater. I would have to wear more than that in salt water.

Good luck !

 

[donmoore]

There is another factor to negatively buoyancy. I discovered this after bragging how low of fat I most have because of negatively buoyant. How much you fill your lungs has a lot to do with your buoyancy. It’s nothing, with some lung expansion exercises, stretching, and work on taking a bigger breath to get 1 or more extra liters than you could when you first started. A liter of air displaces 2.2 lbs of water!

Almost nobody has a lower body fat than Martin Stepanek, yet with 8-liter lungs I don’t think he will ever be negatively buoyant on a full breath at the surface. The other important thing to catch from this insight is how dangerous SWB is. Almost all people exhale when they black out. Regardless of what you are wearing in neoprene and weight, if you only have 4-liters lungs, just think what your buoyancy is would be if you suddenly added 8.8 lbs of lead to yourself. Actually it’s probably more like adding 12 lbs of lead weight, because the lead is going to displace some water where the air you lost is total weight. It’s like some pushing you down with their hand using 8.8 lbs of force. 4-liter lungs are probably the bottom of lung capacity range for most divers, so for most its even worst.

So if you find you’re negatively buoyant at the surface, I recommend you get a hold of a spirometer of if you can’t go to your doctor and tell him you think you have Asthma and would like a lung capacity test. Then learn lung expansion techniques and how to take the biggest breath you can.
don

 

[smellsfishy]

Interesting points Don.

I'm curious though, I've heard that many people when blacking out under water will have a laryngospasm that prevents loss of air. I wonder if anybody can speak to the percentages of people who lose their air vs people who retain it ?

 

[naiad]

I think most people lose their air when they black out. The laryngospasm then prevents water from getting in. From what I have seen in pool training, when I have been the buddy to someone who has blacked out, or have done so myself, usually they let go of at least some air. This is often the first sign that something is wrong.

 

[smellsfishy]

Sort of like a 1 way valve, makes sense. I wonder how much air they lose. Do they drop to residual capacity ? How much buoyancy is lost ?

 

[naiad]

I think it is a passive exhale. The amount of buoyancy lost depends on how much air they had to begin with.

 

[Aquagenic]

I too am negatively buoyant at the surface, but it is easily fixed with a 3mil.

Actually, to be completely honest, I used to always be negatively buoyant, now I'm positive with full lungs (even sans suit). I must have increased my lung capacity. The problem comes when I am trying to breathe up. On the exhale I sink when not wearing the full suit.

Solution: I like to carry a boogie board with me when I'm not wearing the full suit. I breathe up hanging onto it and grab it when I re-surface. Besides that, I always rigorously follow the buddy system to maintain safety.

~JMP

P.S. Btw, I'm itching for some deep diving again Don, but due to my land legs, it may have to be lake diving.

 

[naiad]

I am the opposite. Without a suit, I can only be negatively buoyant at the surface if I do a forced exhale. With a suit, there's nothing I can do except use lots of weight.

If you want something to hold onto while breathing up, a noodle might be good.

 

[cloudwalker_3]

Noodle? Do you have a link for one of these?

 

[naiad]

Here... (At the bottom of the page)
http://www.gb-sports.co.uk/swimmingfloats.html

 

[Aquagenic]

Yes, a noodle would be perfect, but I'm not sure I could get past the unprofessionalism of using a noodle. A boogie board just seems much more official, if not as efficient. But I may be the only one restricted by this view. Till later...

~JMP