Under weighted New Diver

[gnat]

Hello Scuba board. I have a question regarding whether I'm being underweighted for dives. During my OW dives in the ocean I used 4Kg in weights. According to PADI, this is less than the recommended weighting for someone of my size and gear config (71kg male, 3mm full wetsuit, jacket bcd, 80l tank), which is around 5% of my body weight + 2 kg, which is 5.5kg. I did fun dives with 5kg since I weigh 80kg now.

I had no issues with weighting during training and fun dives dives since but I wonder if there are risks to being underweighted and if I should increase it?

 

[TMHeimer]

Do the weight check. Also, don't let anyone tell you you are overweighted if the weight check says you are not. People vary a lot due to body make-up. One diver may need like 40 pounds and another of similar weight/size and equipment like 30 pounds. Some say that you will be able to drop a few pounds once you are experienced and have really good buoyancy, breathing, finning, etc. I could never understand that-- would not the weight check say the same thing whether you have 4 dives or a thousand?

 

[inquis]

would not the weight check say the same thing whether you have 4 dives or a thousand?

Not necessarily, and a couple possibilities come to mind. The most likely is that newer divers often breath from the top (or middle) of their breathing range, and the greater residual volume needs more lead in order to be neutral. A related effect is breathing more rapidly and not taking the time for a nice exhalation. Later on, they breath more normally with less residual volume, so less lead is required.

Another possibility is they may unconsciously fin a bit; if they're not in horizontal trim (very common), they will need more lead in order to "not ascend". The distinction that "not changing depth" may not be the same thing as "neutrally buoyant" is missed. I know it sounds crazy, but I've had someone swear to me they were "holding still" when they were definitely not. For illustration, I had them first get neutral/still (in their opinion) and then had them cross their ankles. They immediately descended. As such a diver improves their trim or quiets their feet (or hands to a lesser degree), they need less lead.

 

[PatW]

Hello Scuba board. I have a question regarding whether I'm being underweighted for dives. During my OW dives in the ocean I used 4Kg in weights. According to PADI, this is less than the recommended weighting for someone of my size and gear config (71kg male, 3mm full wetsuit, jacket bcd, 80l tank), which is around 5% of my body weight + 2 kg, which is 5.5kg. I did fun dives with 5kg since I weigh 80kg now.

I had no issues with weighting during training and fun dives dives since but I wonder if there are risks to being underweighted and if I should increase it?

Yeah, if you can hold your safety stop with a nearly empty tank and all the air out of your BCD, you are fine.

Being slightly underweighted is not too bad. You can invert and gently kick down to hold the safety stop. Or you can just hang onto the mooring line.

 

[TMHeimer]

Not necessarily, and a couple possibilities come to mind. The most likely is that newer divers often breath from the top (or middle) of their breathing range, and the greater residual volume needs more lead in order to be neutral. A related effect is breathing more rapidly and not taking the time for a nice exhalation. Later on, they breath more normally with less residual volume, so less lead is required.

Another possibility is they may unconsciously fin a bit; if they're not in horizontal trim (very common), they will need more lead in order to "not ascend". The distinction that "not changing depth" may not be the same thing as "neutrally buoyant" is missed. I know it sounds crazy, but I've had someone swear to me they were "holding still" when they were definitely not. For illustration, I had them first get neutral/still (in their opinion) and then had them cross their ankles. They immediately descended. As such a diver improves their trim or quiets their feet (or hands to a lesser degree), they need less lead.

Yeah, I see what you're saying and have had these aspects mentioned to me before. But I do question how many of these "defects" are present when a new diver does a weight check. Such as-- are they actually breathing differently (from the top of their breathing range) than they normally breathe when not diving?
Maybe, but it seems a stretch. As well, they're probably not finning at all during the weight check--probably in shallow water just too deep to stand in. When I started out, I don't recall needing more weight than after 20-100 dives, but that was 20 years ago, so maybe?

 

[dmaziuk]

Being slightly underweighted is not too bad. You can invert and gently kick down to hold the safety stop.

I've done that once and have been carrying two extra pounds since.

 

[fred32176]

It sounds like you are properly weighted and your brain interprets being neutrally buoyant as being floaty or underweighted. On land stuff that doesn't fall when dropped floats in air. Your brain associate not going down when still with being floaty or underweighed.

 

[tursiops]

On an aluminum tank, that difference can be as much as 4-5 pounds of buoyancy.

It has nothing to do with the tank being made of aluminum; the only thing that matters is how much air you've used from your tanks...aluminum or steel. Air weighs about 0.08 pounds per cubic foot, or 1.3 grs per liter. So if you've used 70 cuft or 2000 liters of air during your dive, you've lost about 5.6 pounds or 2.6 kg of gas. If you were perfectly neutral at the beginning of the dive, you will be buoyant at the end of the dive.

Being slightly underweighted is not too bad. You can invert and gently kick down to hold the safety stop. Or you can just hang onto the mooring line.

This is a BAD idea. You can pop up to the surface much more quickly than is safe, and you do not always have a mooring line to hang onto.

 

[coldwaterglutton]

It has nothing to do with the tank being made of aluminum; the only thing that matters is how much air you've used from your tanks...aluminum or steel. Air weighs about 0.08 pounds per cubic foot, or 1.3 grs per liter. So if you've used 70 cuft or 2000 liters of air during your dive, you've lost about 5.6 pounds or 2.6 kg of gas. If you were perfectly neutral at the beginning of the dive, you will be buoyant at the end of the dive.

This is a BAD idea. You can pop up to the surface much more quickly than is safe, and you do not always have a mooring line to hang onto.

I never said it was because it was an aluminum tank, I said it had to do with the air in the tank being consumed. And gave the example that on an aluminum (80) that's a 4-5 pound buoyancy difference. I thought I was pretty clear about that but if it wasn't clear to the OP then that was the point.

Here's what I said:

There is a need to account for the change in your tank's buoyancy during the dive. As air is consumed, the tank becomes more buoyant. On an aluminum tank, that difference can be as much as 4-5 pounds of buoyancy.​