Over vs underweighted

[ligersandtions]

I'm just a rec diver. I do not carry stages and have not dove doubles (although I would like to someday). Maybe swim was a poor choice of words but I do not "float" my way up, I try to stay as close to neutral as I can so that I'm in control of the ascent and only rise when I kick. At depth my wing is usually almost empty. Back in the day, and if I remember correctly they taught us to weight for depth not the surface. It seems that has been reversed in current times/teachings.

I hope you forgot what they told you rather than them teaching you wrong....but you should have been taught to weight yourself for your safety stop at the end of the dive (i.e. 15 feet with ~500psi in your tank....no air in your wing, just hovering neutrally).

 

[boulderjohn]

I hope you forgot what they told you rather than them teaching you wrong....but you should have been taught to weight yourself for your safety stop at the end of the dive (i.e. 15 feet with ~500psi in your tank....no air in your wing, just hovering neutrally).

There are those who would disagree. If you do that perfectly as you describe, then you will be positively buoyant for your final ascent after the safety stop, which should be the slowest and most controlled part of your ascent. Weighting for neutral on the surface with a near empty tank eliminates that problem.

 

[miketsp]

Why would you ever HAVE to be either one?

..snip..

Want an example? You should have been with us a trip to Cuba - Isla de La Juventud - a couple of years ago. Lead was in shortage (due to an embargo by some country that will remain nameless) and the weights were all a mixture, in varying proportions, of tin and lead. Also there weren't enough weights for all the divers so during your SI another diver would dismantle your belt to make up another. So there was no such thing as a standard weight and all the 14 dives during the week were done with different weight combinations.
I only got caught out once with a belt that was too light. The rest of the week I dived overweighted and that was the unanimous choice of everyone on the trip once they realized what was happening.

 

[LeadTurn_SD]

I hope you forgot what they told you rather than them teaching you wrong....but you should have been taught to weight yourself for your safety stop at the end of the dive (i.e. 15 feet with ~500psi in your tank....no air in your wing, just hovering neutrally).

Off topic: No "stinkin" safety stops or BC's "back in the day", so actually Twistedarts was not far off (assuming he was talking about mid-1970's when a lot of us did not use BC's, I used a silly "safety vest" ). You did have to be "spot on" with your weighting, because you swam up from depth without a BC to help.

In to the "present day" and back on topic: Being slightly "overweight" is certainly easier to manage than being slightly under, and is not usually a problem.

When I talking slightly, I'm talking just a few lbs above "perfectly weighted". I intentionally overweight myself by about 2-4 lbs because I shore dive, often with a fair amount of surge in the shallows, and a little extra weight helps.

Having said all that, I do tend to agree with String and Sparticlebrane in cases where there is going to be a "gross" error in weighting. If a new diver is 5 lbs too light, he/she will simply be stuck on the surface until the problem is fixed.

New divers tend to be overweighted by their instructors during class, with the understanding that as the diver gains experience they will begin removing the weight on their own... but maybe not... I've seen new divers wearing ridiculous amounts of weight, to the point that if they had a BC failure on the surface (forgot to turn on their air, did not connect the inflator, whatever) they could have difficulty staying on the surface.

 

[friscuba]

It does because its directly related to density which is directly related to the weight needed

Fresh water is 1.00kg/m3. Salt water ranges from 1.020 - 1.030kg/m3. So the difference between the red sea and the pacific (the lightest waters) is still only a fraction of 1% of the total mass in terms of weighting (even factoring different temperatures) - thats insignificant especially when your weights come in 1kg chunks.

The DEAD sea on the other hand does make a substantial difference where its 33% salt content is 10 times that of the ocean.

Care to revisit that? A cubic meter of fresh water weighs a heck of a lot more than a kilo. Gotta be per liter.

My weight is approx 104.5 Kilos. The human body is mostly water weight and thus takes up close to the same amount of space as water, in essence, I'm really close to taking up 104.5 liters of space in fresh water... depends on air spaces in my lungs and such.

Let's call the space I take up 100 kilos/liters even.

Maybe my math is wrong... but.... salt water, being .02 times denser than freshwater, would require an additional 2 kilos (100 X .02) of weight to keep a 100 liter object that was neutral in freshwater neutral in saltwater. In water being .03 times denser, you'd be looking at 3 kilos for that hundred liter object that was neutral in fresh water.

I'm thinking the poster who claimed the Red Sea requires some extra weight might be correct.

 

[Twistedarts]

Off topic: No "stinkin" safety stops or BC's "back in the day", so actually Twistedarts was not far off (assuming he was talking about mid-1970's when a lot of us did not use BC's, I used a silly "safety vest" ). You did have to be "spot on" with your weighting, because you swam up from depth without a BC to help.

yup it was 1977. took the nasds course in puerto rico. we have come a long way.....

 

[ligersandtions]

There are those who would disagree. If you do that perfectly as you describe, then you will be positively buoyant for your final ascent after the safety stop, which should be the slowest and most controlled part of your ascent. Weighting for neutral on the surface with a near empty tank eliminates that problem.

Okay, so you could be weighted for your safety stop at the end of your dive or you could be weighted for the surface at the end of the dive....either way, it is not weighting for being at depth. That's all I was getting at....you need to be weighted properly to be safe at the end of your dive, and that includes holding a safety stop because you don't want to blow it when you've come near or exceeded your NDL.

 

[Sas]

New divers tend to be overweighted by their instructors during class, with the understanding that as the diver gains experience they will begin removing the weight on their own... but maybe not... I've seen new divers wearing ridiculous amounts of weight, to the point that if they had a BC failure on the surface (forgot to turn on their air, did not connect the inflator, whatever) they could have difficulty staying on the surface.

Yes, this is a problem with overweighting. I was overweighted by about 8-10lb after OW class. I couldn't sink so I was given more and more weight, but really I would be kicking and holding my breath when trying to descend. I think I had great instructors for my OW with the exception of not teaching me about proper weight checks - I was told "when you get better you'll be able to remove weight" but no real instructions of how to go about doing this. Anyway, a fair while ago when I was pretty new I had my one of the vents on my BC lock open once just after jumping in the water and had a lot of difficulty staying on the surface as when I inflated it would just purge all the air out. I was about to ditch my weights as I was tiring out after a few minutes of kicking to stay on the surface but my buddy was able to fix my BC.

Even so I would much rather be a few pounds overweighted than underweighted. I did a shallow pier dive (3-4m) and forgot to add 2lb with my drysuit. Did 70mins BT approx and it was exhausting finning down the whole time (my pictures turned out horrible too ). I often dive a few lb overweight when I swap between a 12L hire tank and my own 10L as I didn't have the right weight sizes to reduce my weight with the bigger tank, and I don't find it a problem. However, I like to be correctly weighted so have bought new weights to allow me to easily swap

 

[LeadTurn_SD]

Yes, this is a problem with overweighting. I was overweighted by about 8-10lb after OW class. I couldn't sink so I was given more and more weight, but really I would be kicking and holding my breath when trying to descend. I think I had great instructors for my OW with the exception of not teaching me about proper weight checks - I was told "when you get better you'll be able to remove weight" but no real instructions of how to go about doing this. Anyway, a fair while ago when I was pretty new I had my one of the vents on my BC lock open once just after jumping in the water and had a lot of difficulty staying on the surface as when I inflated it would just purge all the air out. I was about to ditch my weights as I was tiring out after a few minutes of kicking to stay on the surface but my buddy was able to fix my BC.

Even so I would much rather be a few pounds overweighted than underweighted. I did a shallow pier dive (3-4m) and forgot to add 2lb with my drysuit. Did 70mins BT approx and it was exhausting finning down the whole time (my pictures turned out horrible too ). I often dive a few lb overweight when I swap between a 12L hire tank and my own 10L as I didn't have the right weight sizes to reduce my weight with the bigger tank, and I don't find it a problem. However, I like to be correctly weighted so have bought new weights to allow me to easily swap

Thanks for sharing Sas, especially the 1st paragraph. A lot of new divers will read the Basic Scuba Discussions forum. They'll see that an experience like the one you had is not uncommon and is important to anticipate (not being able to inflate the BC at the surface, and how to quickly react to solve the problem).

I think most of us agree that a few pounds "heavy" is a MUCH easier than a few pounds "light".... by mistake I grabbed the wrong weightbelt a few weeks ago, and when I arrived at the beach and realized I was going to be 4 lbs "light" I decided to give it a go anyway. I had kick down hard until I got past about 20 feet, then "think heavy thoughts" for the rest of the dive, especially near the end. I did a "swimming" safety stop in the shallows. Definitely not much fun to be underweighted.

Safe Diving.

 

[Phil G]

I had kick down hard until I got past about 20 feet, then "think heavy thoughts" for the rest of the dive, especially near the end. I did a "swimming" safety stop in the shallows. Definitely not much fun to be underweighted.

Safe Diving.

That, plus while swimming feet up, you wont get very far or more very fast.

Phil