Am I addled, or just confused?
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Charles2
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No, it does not count. A pint of water on the inside occupies the same volume as it would on the outside and it weighs the same on the inside as it would on the outside; therefore, it's impact on your buoyancy is nothing.
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not at all. Water inside of a rigid or flexible container as long as the densities are the same will have no effect on negative buoyancy like adding lead. The difference being adding salt water to a vessel immersed in fresh water.
You can think of it more as removing the positive buoyancy of the air because it is offsetting the volume of air that it can contain, but not like adding lead. I.e. you put 1l of water inside of a wing, and you have effectively removed 1kg of lift capacity of that wing, but not added 1kg of negative ballast to the rig
You can think of it more as removing the positive buoyancy of the air because it is offsetting the volume of air that it can contain, but not like adding lead. I.e. you put 1l of water inside of a wing, and you have effectively removed 1kg of lift capacity of that wing, but not added 1kg of negative ballast to the rig
That's what I thought, but @ the end of my last FW dive (wearing a double fleece undergarment, AL BP, hood and double 85s) I removed my 4 one-lb. weight belt (under water) then let the weights drop on the ramp one by one to do a buoyancy check and found I didn't need any weight at all. Tanks were @ around 300 psi. and had gas in the suit.
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remember that in a drysuit everything is about how squeezed that suit was. Trying to get exact weight checks in drysuits is basically impossible and certainly can't be estimated because everyone likes their suit with a different amount of air.
What does that weight check have to do with your suit flooding? If your suit flooded, your undergarments are holding less air because the air space inside of the fabric has been replaced by water, so they will be less positively buoyant, but they aren't more negatively buoyant because they are wet. It is a bit of mental gymnastics, but you being less positive doesn't mean it is more negative when we are talking about something being displaced by water.
Think about it this way. Does your personal buoyancy change by 4lbs if you drink a half gallon of water before you dive? Do you all of a sudden get a pound less negative when you take a leak in the water? Your buoyancy doesn't change based on intake our outlet of fluid in your body because it is basically the same density as the fluid you are surrounded by.
What does that weight check have to do with your suit flooding? If your suit flooded, your undergarments are holding less air because the air space inside of the fabric has been replaced by water, so they will be less positively buoyant, but they aren't more negatively buoyant because they are wet. It is a bit of mental gymnastics, but you being less positive doesn't mean it is more negative when we are talking about something being displaced by water.
Think about it this way. Does your personal buoyancy change by 4lbs if you drink a half gallon of water before you dive? Do you all of a sudden get a pound less negative when you take a leak in the water? Your buoyancy doesn't change based on intake our outlet of fluid in your body because it is basically the same density as the fluid you are surrounded by.
This must be the answer, although the undergarments were only partially wet and the suit was not flooded.
My understanding is that you should do that same "weight-check" but with the least amount of air possible in the suit. So if the water is 72* and you are at 15' and you need no air at all in your suit and the squeeze is fine, you can base your weight off that. If like you said you had more air in your suit, for whatever reason (buoyancy or warmth) then that is what you should base your weight off of. Am I off on this as this is how I did/do my weight check in my drysuit.
PS - This also takes into account a 500psi tank.
PS - This also takes into account a 500psi tank.
If water replaces air in your drysuit, then you will be less buoyant. But water replacing lead will make you more buoyant.
Keep in mind that the change in your buoyancy is determined by two things: the mass (or weight) of the stuff and how much volume it displaces. If the volume stays the same, greater mass will make you less buoyant. If the volume changes, less volume displaced will make you less buoyant.
Water replacing an equal volume of air in your drysuit: the water is heavier than the air it replaced, you become less buoyant.
Water replacing an equal weight of lead: the water is much less dense than lead, so one pound of water takes up a much greater volume than one pound of lead. Greater volume makes you more buoyant. (Incidentally, this is why we use lead instead of water or even other metals... lead is denser than other common metals and therefore provides the greatest decrease, i.e. smallest volume, in buoyancy for a given weight of ballast.)
Keep in mind that the change in your buoyancy is determined by two things: the mass (or weight) of the stuff and how much volume it displaces. If the volume stays the same, greater mass will make you less buoyant. If the volume changes, less volume displaced will make you less buoyant.
Water replacing an equal volume of air in your drysuit: the water is heavier than the air it replaced, you become less buoyant.
Water replacing an equal weight of lead: the water is much less dense than lead, so one pound of water takes up a much greater volume than one pound of lead. Greater volume makes you more buoyant. (Incidentally, this is why we use lead instead of water or even other metals... lead is denser than other common metals and therefore provides the greatest decrease, i.e. smallest volume, in buoyancy for a given weight of ballast.)
I did forget that I started using the 4 lbs diving in the winter with lots of air in the suit. I also forgot that this buoyancy check thing had happened before when the surface temp became much warmer and I didn't need so much air in the suit. I also forgot that I added the weight when the surface temp was cold. Sooo....I must be addled, but not confused.
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