Need help calculating new weight

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dlwalke

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Location
Atlanta
# of dives
100 - 199
Last year, I was diving rentals (AL80s) and weighed about 150. 10 lbs on my weight belt seemed about right. I recently purchased Pressed Steel E7100s. Their buoyancy is about 6 lbs less according to the chart that diveriteexpress has on their website. I have also gained about 12 lbs (long winter). I forgot the formula that relates body weight to belt weight. I am assuming that the 12 lbs is fat, not muscle (probably lost a couple of lbs of that also). So what's a good guess as to what I should be wearing now. Maybe 6 lbs??

Got a dive trip scheduled this weekend and don't want to be fussing with weight adjustments of the side of the boat.

Thanks,
Dave
 
The whole body weight to belt weight calc that at least one agency uses is not in any way accurate, its enough to plant you on the bottom of the pool and more than you should need for actual diving - at least i always see people shedding weight after using that formula thus far :wink:

As for weight to use, same wetsuit and other equipment? When was the last time you went diving, how much experience do you have? IF same, and a bit of experience i think 6# might be a good start, you can always trim from there if needed. IF you havent been diving in a while and might be anxious you might hold more air in your lungs and so 8# might be better and once you get your comfort back drop the weight a bit. I am not sure where you read it on DRE but according to their specs empty would be -1 vs +4.4# for the 100 and 80 tanks, its only a little difference, but 4# is the max i would take off if i were diving most weekends, try taking off only 2#, see how your weighting is and drop 2# more if you can easily hold the stop and have air left in your BC when you surface (ie check without air and if you sink substantially when you surface you need a bit less, if you barely drop you are pretty close).
 
I've heard about 10% to start. Looking at what you were you would need 11lb with AL80 - 6 for tank, rings in about 5lb. So I would setup for 6-8 so you are evenly distributed and not rolling to one side or the other. Even if you setup at 8 you should be overweight but it wont be bad and should be easy to handle the first dive and see if you think you need to drop any. 2-4 pounds heavy isn't bad. I see a lot of divers who lean towards 5-10lb heavy. I perfer to be just a bout 2 pounds heavy incase I have to drop down fast for any reason.
 
When students ask me this, I say pretty much the same thing every time.
Take some time to go to the pool, shallow beach site and play with your weights until you find a comfortable weight, that you can descend, and ascend with no problems or anything like that.
Remember the basic buoyancy check that you forst learnt! Now's the time to use it!

D...
 
Using rule of thumbs based upon total body weight would be taking a big step backwards since you already know what works with a very similar setup.

Even if all 12 added pounds really were fat, the buoyancy difference is still only about 1 pound (human fat density is around sp of 0.92).

If the tank buoyancy difference is -5.4 pounds, then your best guess on overall difference is -4.4 pounds, which would imply about 6 pounds of lead if nothing else has changed.

As Simbrooks suggested, 8 pounds of lead would probably be a better place to start. It's a lot better to start off a 2 or 3 pounds overweight than to be underweighted. A couple extra pounds of weight just means you have a bit more air in your BC that increases drag and increases buoyancy change with depth a bit more. Being underweighted can cause you to lose control at your safety stop.
 
Charlie99:
Using rule of thumbs based upon total body weight would be taking a big step backwards since you already know what works with a very similar setup.

Even if all 12 added pounds really were fat, the buoyancy difference is still only about 1 pound (human fat density is around sp of 0.92).

If the tank buoyancy difference is -5.4 pounds, then your best guess on overall difference is -4.4 pounds, which would imply about 6 pounds of lead if nothing else has changed.

As Simbrooks suggested, 8 pounds of lead would probably be a better place to start. It's a lot better to start off a 2 or 3 pounds overweight than to be underweighted. A couple extra pounds of weight just means you have a bit more air in your BC that increases drag and increases buoyancy change with depth a bit more. Being underweighted can cause you to lose control at your safety stop.
Thanks. Yeah, I didn't mean total body weight..I meant what would an additional 12 lbs of body weight imply vis-a-vis weighting. So I'll try the 8, vent (if I need to) to about 500 psi at the end of my safety stop, and re-evaluate.
 
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