Floaters and sinkers

[glbirch]

Basic physics.
If your body weighs more than the water it displaces...you sink. If it ways less...you float.Does bone density have anything to do with it? If it affects your weight or displacement then yes it plays a factor.

Accurate, if not particularily useful. The question is how much of a factor is it in your buoyancy, especially in comparsion to body fat and muscle mass. Time to go crunch some numbers... (Math.... hulk hate math...)

 

[Hank49]

wait a few days........


jbm

You're sick, dude. haha

 

[mddolson]

On another thread, someone posted:

"My experience is that NO ONE (at least those who are not really obese . . . ) is inherently bouyant."

I thought that was very interesting. In the years that I've done swimming, snorkeling, and now diving, I've always heard that some people tend to be "floaters" and others "sinkers."

What's your take?

"NO ONE is inherently bouyant."
I have to disagree, I recently had a male student age 70 who floated like a cork. He required 12 lbs of lead in the swimming pool, with no wet suit to be neutral. He was not obese, infact he was very slim. His bone density was quite low, likely due to osteoperosis. His doctor ok'd him for physical activity, but he was cautioned to be carefull about falling. He was on calcium replacement prescription.

Mike D

One should never make all encompassing rules, there's always exceptions.

 

[O2BBubbleFree]

Basic physics.
If your body weighs more than the water it displaces...you sink. If it ways less...you float. Does bone density have anything to do with it? If it affects your weight or displacement then yes it plays a factor.

As I understand it, weight on land does not directly equate to displacement. It's a question of density. If an object is less dense than the water, it will float, if it's more dense, it won't (Archimedes law of buoyancy). Density is defined as weight or mass per volume. Typically muscle is more dense than fat, so it's generally surmised that lean people sink and fat people float. However, in addition to the above case of low-density bone, there are plenty of people on this board who display buoyancy characteristics in contrast to that supposition. I am one of those people who have extra body fat and sink like a mafia informant.

 

[voop]

Hmm.....up until recently, I used to be a "floater" -- despite years of diving etc. I then lost about 30 kg of body-mass (through diet), and I now must make a conscious effort to "float" at the surface. Now, with a 15l steel tank, I need no weight to get down in my neoprene drysuit -- I am quite negative in that configuration. Before, I would use 6-8 kg or so. (Incidentially, loosing weight also meant a substantial improvement in air-consumption for me...)

 

[IndigoBlue]

My experience.....

I'm not fat and never have been, so you can rule out that factor. (5'5", 120-25 pounds for years.)

I'm very comfortable in the water, and have been all my life, so rule out the nervous/stressed factor.

I float. I can lie on my back in fresh water indefinitely, breathing in and out, and I don't sink. When snorkeling, I can hover over an object as long as I like (no finning), without sinking.

I've often wondered why I seem to be so buoyant; I've been that way since I was a little kid. I have a medium frame, as far as bone size; mabye I do have light bones. I'd be interested in any studies along those lines.

I'd say that so far, most (with some very strong dissenters) agree that some people are more inherently buoyant. And, I'd add, it's not just fat folks.

True, true.

I first noticed "floaters" during the pool underwater swimming exercise for basic scuba training. These are the students onto whom you need to put a weight belt, with about 3 to 4 lbs of weight on it, so that they can stay underwater with a full breath of air and perform the underwater swim in their swimsuit. In warm sea water, they would float even after totally exhaling all their air even with no exposure suit of any kind. The average differential between fresh water and sea water is about 6 lbs for most divers. And that is why they are called "floaters."

I first noticed "sinkers" during swimming classes. These are the really lean people who cannot float to save their souls. They need to be moving forward through the water to keep them at the surface, the classic negative-buoyancy trim concept.

Everybody is different.

When you compound the above issues, such as by adding buoyant neoprene, or on the other hand by adding steel scuba tanks, the floating or sinking gets worse, if they are not properly matched with gear.

That is why it is necessary to consider the natural trim considerations of your student and the particular environment before you gear any person up. And when you are dealing with neoprene, then the buoyancy factors will change with depth as well. That is why I do not like wetsuits thicker than 3mms for scuba.

The classical offsetting combinations are:

1) wetsuit plus aluminum tank
2) drysuit plus steel tank
3) aluminum backplate plus steel twin tanks
4) steel backplate plus aluminum twin tanks

"Modern" divers vary from these classic conventions for various reasons, such as colder water, which requires more insulation, and therefore more negative weighting. A steel backplate with twin steel tanks is fairly common now, for a diver wearing thick insulation under a drysuit in cold water around 45F.

The most frightening configuration that I often see is a floater, with a thick wetsuit in cold waters, and a steel tank, with lots of lead weighting. This type of person would be much safer in a drysuit instead of a thick wetsuit, especially if the cove he/she is diving is deeper than 60 ft.

Natural buoyancy is worth considering when choosing gear. It is one of the last things divers learn, and often goes omitted from consideration.

 

[O2BBubbleFree]

I first noticed "sinkers" during swimming classes. These are the really lean people who cannot float to save their souls.

With exceptions. Like me for instance.

Everybody is different.

And the issue seems to be more than fat/lean.

 

[Qis]

Another sinker checking in. Dunno what my bf% is, I've never had it measured properly, and the scales that zap me can give me values that fluctuate quite a bit(apparently depending on if i've had a drink of water). a single test in the red sea confirms that i sink in the red sea with a full breath(the very tip of my head might have possibly broken the surface).
Can sinkers freedive safely without wetsuits or armbands?