How much added weight difference is it if I'm perfectly weighted with my shorty in freshwater at 6lb. How much weight should I add for saltwater to compensate?
Bouyancy weight freshwater vs saltwater
Started by
Hexkraut
, Aug 08 2006 10:49 AM
7 replies to this topic
#1
Hexkraut
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Posted 08 August 2006 - 10:49 AM
#2
Capn Jack
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Posted 08 August 2006 - 11:21 AM
A rule of thumb that I use is adding 1 pound for each 40 pounds of your total weight (you plus all of your kit).How much added weight difference is it if I'm perfectly weighted with my shorty in freshwater at 6lb. How much weight should I add for saltwater to compensate?
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#3
ScubaDadMiami
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Posted 08 August 2006 - 04:00 PM
There is no need to guess for a quesiton like this. Here's how you do it. Sorry, math is involved.
You get all of your gear, and you climb on the scale. See how much you weigh. At this weight, if you are "perfectly weighted" as you say (and I have no reason to doubt you
), this means that you can figure out exactly how much fresh water you displace. All we need to do is to displace that much water in salt water to be "perfectly weighted" there.
Let's say that with all gear and your six pound weight, you weigh 187.2 pounds. Since we all remember (you do remember, don't you? ) that fresh water weighs 62.4 pounds per cubic foot, we can determine how many cubic feet you displace in the water by dividing your total weight by the amount of weight displaced by a cubic foot of fresh water: 187.2 / 62.4 = 3 cubic feet of fresh water displaced.
Now, we need to figure out how to make you displace the same amount in salt water. Salt water weighs 64 pounds per cubic foot. If you were properly weighted, you would displace 3 cubic feet of salt water (just like you do in fresh water because your size has not changed): 3 * 64 = 192 pounds.
What is the difference?: 192 - 187.2 = 4.8 pounds. So, let's call it five pounds.
BTW, the density changes slightly depending on temperature and salinity. So, please, no nitpicking about the fractions.
You get all of your gear, and you climb on the scale. See how much you weigh. At this weight, if you are "perfectly weighted" as you say (and I have no reason to doubt you
), this means that you can figure out exactly how much fresh water you displace. All we need to do is to displace that much water in salt water to be "perfectly weighted" there.Let's say that with all gear and your six pound weight, you weigh 187.2 pounds. Since we all remember (you do remember, don't you?
) that fresh water weighs 62.4 pounds per cubic foot, we can determine how many cubic feet you displace in the water by dividing your total weight by the amount of weight displaced by a cubic foot of fresh water: 187.2 / 62.4 = 3 cubic feet of fresh water displaced.Now, we need to figure out how to make you displace the same amount in salt water. Salt water weighs 64 pounds per cubic foot. If you were properly weighted, you would displace 3 cubic feet of salt water (just like you do in fresh water because your size has not changed): 3 * 64 = 192 pounds.
What is the difference?: 192 - 187.2 = 4.8 pounds. So, let's call it five pounds.
BTW, the density changes slightly depending on temperature and salinity. So, please, no nitpicking about the fractions.
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#4
Terri
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Posted 08 August 2006 - 04:08 PM
There is no need to guess for a quesiton like this. Here's how you do it. Sorry, math is involved.
Oh no....not math!!!
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#5
Dive_Girl
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Posted 08 August 2006 - 04:15 PM
Or a diver weighing 187.2lbs with all gear and your six pound weight, using Capn Jack's Rule of Thumb, would come up with the same rounded answer (5lbs):A rule of thumb that I use is adding 1 pound for each 40 pounds of your total weight(you plus all of your kit).
187.2 / 40lbs = 4.68
I readily use rules of thumb, especially when weighting new divers to start with and tweak further when in the water and as the dives progress.
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#6
Walter
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Posted 08 August 2006 - 04:21 PM
Or you can simply take that total weight and multiply by .024 or add 1 lb for every 40 lbs. All of them work.
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#7
JackBSwift
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Posted 08 August 2006 - 04:36 PM
what happens if one train is leaving Boston at 9 am with a speed of 75 miles and hour while another leaves San Diego...... oh wait.. wrong science problem, sorry
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#8
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Posted 08 August 2006 - 04:46 PM
what happens if one train is leaving Boston at 9 am with a speed of 75 miles and hour while another leaves San Diego...... oh wait.. wrong science problem, sorry
That's quite all right, the answer is Thursday at 6 PM in the corner bar.
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