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?

 

[Mike McG]

If you are underweighted it's actually quite difficult to descend at the start of the dive without exhaling and swimming down and you would certainly find out the end of the dive. As long as you can comfortably hold a safety stop at the end of your dive at 5m you are not underweight.

 

[boulderjohn]

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

It has been a while since I last taught an OW class. I was unaware that PADI had any such recommendation. When I taught, we just did weight checks. As several people have said, individual people have individual needs for weights, depending mostly on personal body composition.

In my own diving, I have found that I prefer not to be what many people would call perfectly weighted. I like a few extra pounds, but only a few, during an NDL dive.

 

[Wibble]

You MUST do your own weight check. It's for you, not a beauty contest with other divers.

I will submerge in 1.5m/4ft of water, get into flat trim and see how much gas I need to hover 15cm/6" of the bottom. With a full cylinder/tank, I MUST have added some air to the BCD/drysuit as there's 2kg of air in the compressed cylinder (assuming a single tank).

For the first dive I'll be very sensitive to weighting at the end of the dive to ensure there's enough weight to hold the safety/deco stop at 4.5m/15ft. May adjust the weighting accordingly.

I need for:

• Carribean OC sea diving: hot water (30C/85F), single cylinder ali80, rash vest, budgie smugglers: 2kg/4lbs weight
• Warm water OC sea diving (20C/70F), single cylinder steel 12 litre, drysuit, thin underclothes: 8kg/18lbs
• Cold FRESH water OC diving (7C/45F to to 12C/53F for 1h 15m), drysuit, thick undersuit + extra layer, sidemount with 2x steel 8.5 litre cylinders: about 8kg/18lbs
• Cold FRESH water CCR diving (7C/45F to 12C/53F for 2+ hours), drysuit, thick undersuit + extra layer, Revo rebreather (2 x 3 litre cylinders diluent+oxygen, 2 litre drysuit inflate, 2 x ali7 litre bailouts, drysuit heater battery): about 3kg/6.6lbs
• Cold sea water CCR diving (7C/45F to 12C/53F for 2+ hours), drysuit, thick undersuit + extra layer, Revo rebreather (2 x 3 litre cylinders diluent+oxygen, 2 litre drysuit inflate, 2 x ali80 bailouts, drysuit heater battery): about 4.5kg/10lbs
• UK south summer sea water CCR diving (15C/60F to 18C/65F for 2+ hours), drysuit, thick undersuit (no extra layers), Revo rebreather (2 x 3 litre cylinders diluent+oxygen, 2 litre drysuit inflate, 2 x ali7 bailouts, no heater battery): about 3kg/6.6lbs

But if diving somewhere new with any significant kit changes, will always do a weight check.

Kit that affects buoyancy during the dive, i.e. changes your weighting during the dive:

• Gas you are breathing. Rough weighting is 2kg/4.4lbs per full-size cylinder.
• Twinset/doubles which contain twice as much as a single and will be consumed during the dive (4kg/9lbs)
• Decompression/bailout stages where the gas will be consumed; must add weight to offset the gas volumes -- an empty ali80 gets very floaty!
• Heavy SMB reels (Kent Tooling - 1.5kg/4lbs) which will be detached from you in use
• Other cylinders that may be dropped off en-route or handed off to other divers
• Always consider an urgency scenario where you've had to use more gas than normal -- overstaying your dive time, helping other people, etc. -- empty tanks get very floaty!

Bottom line: always be aware of being too light at the end of the dive, this is extremely dangerous because you cannot hold your decompression/safety stop.

 

[clownfishsydney]

I remember going on a dive on a charter boat in the Poor Knights in New Zealand. On the way out to the dive sites, the divemaster came around and asked how much weight we needed. I told him about 8 kg (17.6 pounds, say 18). He insisted I need something like 24 pounds. I kept telling him what I needed, he kept telling me I needed 24 pounds.

Finally, I told him to go and look at the information in the form I had earlier filled out and then come back. He never came back. At the time I had over 3,100 dives under my belt. Just shows that divemasters and dive instructors do not necessarily know what weight you need.

 

[dmaziuk]

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.

FWIW I used ~4 kilos (10 lbs) back when I weighed 80 kg and used a jacket BCD. Now I'm more like 90 kg and use a shiny! metal backplate, but I still carry about 4 kg weight total with a 3/2 full suit or a shorty that used to be 2/1 -- all with Al80 tanks.

As others said, it really depends on your body composition: meat sinks, fat floats, bones sink, lungs float really well.

 

[tursiops]

Gas you are breathing. Rough weighting is 2kg/4.4lbs per full-size cylinder.

Air weighs about 1.3g/liter or 0.08 lbs/cuft.

• Your 2kg only accounts for about 1540 liter, but an 11 liter tank at 200 bars has about 2200 ljters. Are you using just 70% of your tank? A 12-liter tank suggests you are using just 64%.
• Your 4.4. lbs only accounts for about 55 cuft, but an AL80 tank holds about 77.4 cuft.. Are you using just 71% of your tank?