Buoyancy I’m confused

[Eric Sedletzky]

Did you use a AL80?

Ha ha ha, lol!!!
Uh No,
A steel 120
The only thing aluminum 80’s are good for around here are OW classes and target practice.

 

[AfterDark]

Ha ha ha, lol!!!
Uh No,
A steel 120
The only thing aluminum 80’s are good for around here are OW classes and target practice.

I hear ya, that's the OP issue IMO an AL80 target. They just don't contribute enough to negative buoyancy to make them useful in a cold water configuration.

 

[Diver below 83]

Dive buddy always has me a couple lbs too heavy. But it’s been helpful as a starting point

 

[Eric Sedletzky]

An al 80 adds 3-5 lbs positive buoyancy over comparable steel tanks, plus we have no idea how the OP is weighting himself, e.i. elevator diving or minimal weighting with no air in bc at 15’ at end of dive.
Plus adding as much as he claims for salt seems a bit excessive to me.
Maybe the brand new 5 mil needs to be taken down good and deep a few times and break that sucker in.
Brand new suits can be kinda fluffy when new and that’s not a good example of how they will be after several dozen real dives to depth.

 

[mmerriman]

So I went to do some pool work in my new suit and I was shocked at the amount of weight it required. It’s a mako spearfishing 5mm suit, my backplate weights 9 lbs and I’ve always heard 2 lbs per mm. So I expected to put 1 lb on the belt. But I needed 12lbs! That’s in fresh water! I don’t understand. Is open cell worse?

what kind of crazy math is that? yes the thickness of your exposure protection factors in, but your body weight does even more so - plus what are you using for a tank?

 

[AfterDark]

what kind of crazy math is that? yes the thickness of your exposure protection factors in, but your body weight does even more so - plus what are you using for a tank?

He posted an AL80

 

[mmerriman]

He posted an AL80

yeah saw that after and your reply.

 

[dalpe933]

I'm not showing off. MM is MxM which is the same as M². However, Mathematics is one of my degrees.


Are you serious? 9# of steel = 9# of feathers = 9# of lead. In the water the feathers would probably have some positive buoyancy due to trapped air. Density has NOTHING to do with it when it comes to steel and lead.

Cheers - M²

well that is also not entirely accurate, since the biggest relationship with buoyancy is water displacement, density has a lot to do with buoyancy. that is why you do weight check at the end of your dive. throughout your dive your volume doesn't change but your mass does from the loss gas in your cylinder. so a change in density.
I'm not saying their is a big difference in buoyancy between 10# of lead and 10# of steel but their is one. 10# of feathers on the other hand huge difference!
Archimedes' principle

 

[MargaritaMike]

well that is also not entirely accurate, since the biggest relationship with buoyancy is water displacement, density has a lot to do with buoyancy. that is why you do weight check at the end of your dive. throughout your dive your volume doesn't change but your mass does from the loss gas in your cylinder. so a change in density.
I'm not saying their is a big difference in buoyancy between 10# of lead and 10# of steel but their is one. 10# of feathers on the other hand huge difference!
Archimedes' principle

You are totally correct. Archimedes' principle is the statement that the buoyant force on an object is equal to the weight of the fluid displaced by the object. Since the medium is water, the weight of the water is dependent on the volume of the water displaced. The difference in buoyancy will be a function of the volume displaced. The formula: Volume = mass / density. Since mass and weight are equivalent at the equator (and pretty damn close almost anywhere on the surface of the earth), and they both are 9#, the volume displaced will be a function of density. The greater the density the lower the volume. Anyone can plainly see that 9# of SS with a density of 8.03 g/cm³ displaces .0180 ft³ of water and 9# of lead with a density of 11.34 g/cm³ displaces .0127 ft³ of water, a difference of 0.0053 ft³. With the density of water is 62.4 lbs/ft³, it is readily apparent that a 9# back plate in water is 0.33072# or 5.29152 ounces more buoyant than 9# of lead, which is sort of what @Jcp2. Where he went wrong is by stating they weighed different amounts. What he might have said is they exhibit different buoyancy characteristics. I was not wrong in stating 9# of steel = 9# of lead. Where I went wrong was when I failed to measure the volume of steel required to weigh 9# verses the volume of lead to weigh 9#. This will determine the amount of the medium displaced, which will determine the buoyancy.

Everyone knows that lead must be heavier than steel. I've never seen a lead ship floating, but I have seen a steel ship floating.

Cheers - M²

 

[Bob DBF]

I'm not showing off. MM is MxM which is the same as M².

Well I was taught in grade school that MM = 2000, that would mean that M² = 1,000,000, I'd say that’s quite a difference. Mathematicians.


Bob