How will my weight loss affect weights needed?

[EFX]

I agree that trial and error is sufficient. I included the calculations to provide a scientific basis for what most responders were saying by experience. I wanted to show that buoyancy changes are affected not just by a change in dry weight, as most responders here seemed to be suggesting, but also by a change in volume (only one poster mentioned volume by name). Your example brings up an important point about buoyancy that is not mentioned very often: body volume. The fact that she weighs a lot less than you implies she should use less lead weight (that's the W in the equation). If she's bigger around (no offense meant) than she makes up for the loss in buoyancy by water weight displaced (the VD in the equation) and has to use more lead weight to compensate. Hence, the small difference in lead weight used between you and her. Taller, thinner people will be tend to be less buoyant than shorter, bigger people.

 

[Bob DBF]

Dive with your usual weight. and drop some after the first dive if you feel that is appropriate. A pound or two will make no difference in the grand scheme of things, provided you were correctly weighted before.

Congrats and have fun.



Bob

 

[cocoajoe]

It overestimated my weight by 4 pounds.

Me too

---------- Post added August 18th, 2014 at 03:10 PM ----------

The trick is losing fat without losing muscle

 

[SWAMPY459]

No way this is correct.

If you have a thick wetsuit, and you use most all your air, you will be unable to stop from floating up from5 or 10 feet. What if there is a boat coming? Do you want to be pinned to the surface? Also this advice is ridiculous because you will be completely unable to hold down an smb. You need some weight to hold the smb vertical...

I'll say it again, maybe you will hear it this time. At the end of the dive, with all the air out of your wetsuit at 15-20 feet let all the air out of your bc and with a nearly empty tank, if properly weighted you should be NEUTRAL and that means you have a balanced rig..... If you sink, and have to fin up you are overweighted. If you can't stay down, you are underweighted.

 

[Bob DBF]

I'll say it again, maybe you will hear it this time. At the end of the dive, with all the air out of your wetsuit at 15-20 feet let all the air out of your bc and with a nearly empty tank, if properly weighted you should be NEUTRAL and that means you have a balanced rig..... If you sink, and have to fin up you are overweighted. If you can't stay down, you are underweighted.

And once I find out what NEUTRAL is, I add proper additional weight in case I need to empty my tank while holding 10' or be able to descend quickly to avoid surface traffic, both of which could save my life. This is not a classroom exercise.



Bob
--------------------------
I may be old but I'm not dead yet.

 

[colecaz]

I agree with swampy and bob

 

[mrdre]

I'll say it again, maybe you will hear it this time. At the end of the dive, with all the air out of your wetsuit at 15-20 feet let all the air out of your bc and with a nearly empty tank, if properly weighted you should be NEUTRAL and that means you have a balanced rig..... If you sink, and have to fin up you are overweighted. If you can't stay down, you are underweighted.

Well.. that's what the textbook says and that's what they teach to the students, just like "always breathe deep" and "never hold your breath". In reality if you are wearing a very thick wetsuit and you are neutral at 15 feet then you will be extremely positive at 5 feet. If you ended up at 5 feet (it happens) - you will have very hard time descending to 15 again. More likely you will pop-up on the surface helpless. Sometimes you would prefer to descend to 5 feet and swim like that instead of on the surface, sometimes you have to swim through kelp few feet underwater. In case there are boats not being able to descend actually might cost diver's life.

If you carry a pony bottle you may need to be overweight to compensate for it's positive buoyancy while it's empty. It's in case you had to use it at some point.

The rule "neutral at the end of the dive at 15 feet" doesn't apply to every dive. If you are in warm waters, wearing skinsuit, then yes, but in some cases it's necessary to be a little overweight.

 

[TMHeimer]

My weight tends to vary within a range 0f 20-25 pounds. Doing a weight check solves all. I have not changed my weighting, as it always seems good. As pointed out, a pound or 2 less weight probably won't matter much. Maybe I'm just too lazy.