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?

 

[inquis]

You need to check with close to empty tank to make sure you are correctly weighted at the lightest possible.

+1. An alternative is to check with full tanks but reduce your lead by the amount of gas you haven't yet breathed. If all is well on the check, add the lead back in and do the dive. (This does require that you have that much lead in the first place.) A full AL80 has about 5 lb/2.5 kg of usable air (full->500 psi/35 bar).

Certainly checking with a nearly empty tank is best (as trim will not be affected), but the above might be more feasible in some cases.

 

[LFMarm]

+1. An alternative is to check with full tanks but reduce your lead by the amount of gas you haven't yet breathed. If all is well on the check, add the lead back in and do the dive. (This does require that you have that much lead in the first place.) A full AL80 has about 5 lb/2.5 kg of usable air (full->500 psi/35 bar).

Certainly checking with a nearly empty tank is best (as trim will not be affected), but the above might be more feasible in some cases.

Great advice. If you do this, you can actually check your weight twice during the first dive: once at the begining by removing weight equal to your gas consumption and confirm at the end by draining the tank (safely!) during your safety stop.

5 lb/2.5 kg works for any nitrox mix between air and 40%. If you dive trimix, you will need to remove less weight but you know how to calculate this yourself

 

[bradlw]

wait a minute....wouldn't you need to ADD more lead for the weight of the air?

If you do a check and get just enough lead on board to be neutral with a full tank
then you're gonna be light at the end of the dive after sending 5# of air to the surface

 

[inquis]

wait a minute....wouldn't you need to ADD more lead for the weight of the air?

Yes. Subtract for the test, then add it back before the real dive.

 

[rotorguy]

You ask if there are risks to being underweighted. The risk is that at the end of your dive, with less air in your tank, you might have difficulty holding your position for your safety stop. Many instructors will consider 1KG extra weight for a new diver to be a reasonable precaution. As you get more dives in and get better at controlling buoyancy you can fine tune your weight to its optimum based on your gear configuration.

I was underweighted (for my experience level) for my first couple dives post OW cert and it was really unpleasant. I appreciate that the dive master was trying to help me get my weights dialed in but it was very frustrating to struggle with the safety stops. I basically had to hold a full exhale just to maintain, the slightest inhale damn near skyrocketed to the boat. I would have appreciated the extra kg. Buying my own equipment took a lot of the guesswork out of it and gave me consistency. I ended up at the weight they suggested but it was many dives later.