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Scuba Forum / Scuba Equipment / August 2004Quick "formula" for buoyancy?
I am new to diving and I was wondering if there is a quick formula to roughly calculate the amount of weight that is needed for neutral buoyancy in fresh water? I know that I will need to experiment to fine tune it, but I am just looking to for a good starting place. I will be using 1 steel tank with a 7mm wetsuit. Thanks in advance, Kevin > I am new to diving and I was wondering if there is a quick formula to > roughly calculate the amount of weight that is needed for neutral [quoted text clipped - 3 lines] > looking to for a good starting place. I will be using 1 steel tank > with a 7mm wetsuit. 10kg. Finetune by adding or substracting until you feel comfortable. /marcin > > I am new to diving and I was wondering if there is a quick formula to > > roughly calculate the amount of weight that is needed for neutral [quoted text clipped - 5 lines] > > 10kg. Finetune by adding or substracting until you feel comfortable. That seems to be a lot of weight for fresh water and a steel tank, which is negatively buoyant. I usually start with 5% of my body weight and fine tune from there. I currently weigh 190 lbs. (86kg) With an aluminum 80 in salt water I use 8 lbs (>4kg) with no neoprene. That will stay the same throughout the dive, leaving me neutrally buoyant at 15 fsw (5m) with 500 psi (50 bar?) for my safety stop. Freshwater with a steel tank, I would wear no lead with no neoprene.. If you are wearing a 7 mm, it will compress at depth and therefore lose buoyancy, which it will later regain as you surface. YMMV  SignatureBut then again, what do I know? Lou Vallone LouVallone@aol.com http://members.aol.com/LouVallone Get in a swimming pool and add and subtract weight until you are neutral. If you have a full tank, add six more pounds after you are neutral. Do you know how much weight you need in salt water? If so, take the weight of the system (diver, tank, suit, lead, reg, knife, EVERYTHING), multiply by .0256, and subtract that much. SignatureChuck Tribolet triblet@garlic.com http://www.almaden.ibm.com/cs/people/triblet Silicon Valley: STILL the best day job in the world. > I am new to diving and I was wondering if there is a quick formula to > roughly calculate the amount of weight that is needed for neutral [quoted text clipped - 7 lines] > > Kevin I believe he said steel tank, not aluminum. You need MORE weight in salt water, not less. > Get in a swimming pool and add and subtract weight until you are neutral. > If you have a full tank, add six more pounds after you are neutral. [quoted text clipped - 14 lines] >> >> Kevin > You need MORE weight in salt water, not less. [snicker] There's one on every boat... There is no formula. There is only proper weighting. Signature"We're going to rush the hijackers." -Jeremy Glick, aboard United Airlines flight 93, September 11, 2001 Normal saltwater is .0256 more dense than fresh water. THAT formula works like gangbusters to check out gear in freshwater (a swimming pool, for example), and then go to saltwater and be right on. (The Red Sea is a bit denser than "normal" saltwater). I agree that formulas like "10% of body weight + five pounds" are bullshit. That would have had me underweighted by about six pounds in my old wetsuit (three 7mm layers), by about two pounds in my drysuit today, and overweighted a buddy of mine who dives a single 7mm layer by about 5 pounds. The only formula is to get in the water and get it right. SignatureChuck Tribolet triblet@garlic.com http://www.almaden.ibm.com/cs/people/triblet Silicon Valley: STILL the best day job in the world. > ? You need MORE weight in salt water, not less. > [quoted text clipped - 3 lines] > > There is no formula. There is only proper weighting. >Normal saltwater is .0256 more dense than fresh water. THAT formula works like >gangbusters to check out gear in freshwater (a swimming pool, for example), and >then go to saltwater and be right on. (The Red Sea is a bit denser than "normal" >saltwater). The problem is you get guys who insist that you add that 2.6% to the ballast only and not the entire weight of the diver and rig. Okay, so if the tank is neutral when empty, there's no reason I need to wear it when I step on the scale geared up, right? :) --- Rich http://richlockyer.tripod.com/ What I said had nothing to do with steel tank or AL tank. And I said SUBTRACT weight from what you need in salt water. That means MORE weight in salt water. SignatureChuck Tribolet triblet@garlic.com http://www.almaden.ibm.com/cs/people/triblet Silicon Valley: STILL the best day job in the world. > I believe he said steel tank, not aluminum. > [quoted text clipped - 18 lines] > >> > >> Kevin > I am new to diving and I was wondering if there is a quick formula to > roughly calculate the amount of weight that is needed for neutral [quoted text clipped - 3 lines] > looking to for a good starting place. I will be using 1 steel tank > with a 7mm wetsuit. There are formulas that will get you started but you need to get in a pool. Most of the time I look like I would float but in freshwater barely stay awash when holding my breath. I've had some really small people who needed far more weight than I did and some huge people who used little. As most people gain experience their weight needs drop and as your wetsuit ages it will loose buoyancy. Kit up with all YOUR standard open-water gear and get in a swimming pool, preferably with cylinder(s) that are only a little above reserve pressure (50 BAR / 750psi). Start with a relatively low amount of lead (say 5Kg/11Lb) and than add 1Kg/2Lb) at a time, until you can stay under the water with a normally full lung of air (I don't mean a huge busta-lung intake) and BCD/wing empty. A mate on the pool-side handing you one 1Kg/2Lb weight at a time is a bonus. That will then be the basis of your fresh-water weighting. Because salt-water is denser than fresh water, giving MORE buoyancy, you will need to add a little extra lead to stay down when sea diving. Normally, for an average diver about 2Kg is sufficient. If however you do the above with full cylinder(s), you will need to ADD extra weight, otherwise, as the cylinders are used up during the dive and become lighter, you will become too buoyant and not be able to stay down. One way to calculate this amount is to weigh your cylinder when empty an then again full (a good set of bathroom scales works Ok for this). The difference in weight is how much you will need to add if you do this test with a full cylinder. This difference between empty and full weight is the same, irrespective of whether the cylinder(s) are in water or not. TonyH. > I am new to diving and I was wondering if there is a quick formula to > roughly calculate the amount of weight that is needed for neutral [quoted text clipped - 7 lines] > > Kevin |
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