Weight Calculations

[fnfalman]

From speaking with novice divers locally, I get the impression that many divers get basic OW certified without really knowing how to do a proper weight check. Either that...or they simply forget how to do one over time.

Weight check was mentioned in my class but we never saw it in practice.

A lot of it has to do with proper descension techniques and instructors seem to be too quick with the students to give them help. I kept piling on weight until I carried 28-lbs of freakin' lead. Why? Because I kept kicking automatically and couldn't sink. Nobody ever mentioned that to me until much, much later after the course was over and a kind soul on a dive boat told me when he saw me make a descension.

 

[Indian Valley Scuba]

So unfortunate to hear that, but so true with instructors who don't understand the simple physics of Archimedes Principal and how it applies to everything we do in and under the water

 

[Bubbletrubble]

Weight check was mentioned in my class but we never saw it in practice.

Wow. I'm sorry to hear that. It was one of the things that my PADI instructor emphasized during basic OW class. New gear? Do a weight check. We worked together in buddy teams to do a proper weight check on our own in the pool. He told us to add approx. 2.5% of our total weight in lead when moving from the pool to the ocean. For most people, that was about 6-7 lbs.

FWIW, we also ended up doing weight checks at the end of each of our OW class dives.

 

[Frosty]

I couldn't work out why instructors tended to overload their students with lead untill recently when I was watching people doing their OW course. It looked to me that even overweight they were having trouble with the boyancy control.

 

[Indian Valley Scuba]

I am sorry, but proper weighting should be taught from lesson #1

Any instructor that fails to do is doing their client, and future fellow diver, a terrible disservice

Oh wait, there is a solution: Sell them a Peak Performance Buoyancy class after initial certification, and teach them how to take off all those extra pounds the instructor put on them in the first case!

 

[Arkman]

I appreciate all the responses. There are some good techniques for weight calculations.

I think maybe I wasn't clear. I understand that there all those techniques to get the weight close before the actual check but I'm wondering if there is a scientific way to figure out the actual weight needed. I realize its not practical but it was just something I thought of.

So if you put just me in a bucket of water would I sink or float. Well I know that if I have a full breath of air I can mostly float. When I breath out I sink. I know that, because I've done it several times. I guess what I don't understand is how to convert that into a number. Lets just say that I'm 5 pounds negative (with no air), just for argument sake, since I have no idea what I am.

Me = -5lbs
Suit (5mm) = +15lbs (according to what was posted above)
Tank (empty) = +4.4lbs
Regs = -3lbs(I have no idea)
Fins = -1lbs(no clue, i just know they are negative)
BCD(empty) = +5lbs(no idea)

In this scenario at the end of my dive I am 15.4lbs positive. This makes sense because I where about 16lbs in that set up. With a proper weight check that seems to be the right answer.

If one was so inclined they could figure out the weight needed to sink each equipment. With that being said the only variable is me. So how do I figure that out?

I don't mean to make this an argument about proper weighting and how to determine that. Everyone should do a proper weight check, at least I think. I'm mostly just curious if there is a way to figure out the characteristics of ones body. Like fnfalman man said. A person with more fat is so much different than a person who is all muscle.

Does this make sense?

 

[Brendon]

.

Is there a scientific calculation that could be used?

Take a master diver course... Archimedes principle. (mass/volume/density formula)

Given the known bouyancy of most gear, you can be as exact as you like...

 

[fnfalman]

If one was so inclined they could figure out the weight needed to sink each equipment. With that being said the only variable is me. So how do I figure that out?

That's the tough part. How much water do you personally displace? I'm sure there's a way to calculate fat/muscle density and your body's overall dimension.

 

[Sonic04GT]

Let's see...I weigh 270#, so that's 27 plus 4 equals 31 pounds

Reality check: In a 4 mil full suit in saltwater with an aluminum 80,
i wear a s/s backplate ( 6 pounds ) and zero additional weight for perfect buoyancy

I think the formula, while handy, may not apply in all cases

I concur. That would call for 20 lbs. I wear about 8 with a 3mm full.

With a steel 100 in salt water I use zero weight with a 3mm full. Could maybe get by with a 2lbs max.

 

[muddiver]

Let's see...I weigh 270#, so that's 27 plus 4 equals 31 pounds

Reality check: In a 4 mil full suit in saltwater with an aluminum 80,
i wear a s/s backplate ( 6 pounds ) and zero additional weight for perfect buoyancy

I think the formula, while handy, may not apply in all cases

You cheated and added a non-standard back plate. Standard basic openwater scuba gear does not include a back plate, doubles, a long hose, etc.......

Go dive a cave, show off.