Neutral Buoyancy

[Garrobo]

I don't know how many times I've heard divers on the boat before jumping in brag about how little weight they need to stay down for a safety stop and then see them struggling to stay submerged at 15 or twenty feet at the end of the dive. I did the buoyancy test a few years ago and then added a few pound to make sure I'd be able to do a stop without fighting it. This worked out at 16 pounds for me at 180 pounds body weight and a 3mm full suit. With a shorty it could be a little less less but I don't mind the extra weight. My biggest problem used to be that after hogging the whole tank that it was like having a balloon on my back. These days I'll have anywhere from 1000 to 1500 left in my tank, depending on the depth and length of the dive so now I don't have this problem.

 

[molina67]

I'll keep playing with it. The 14 lbs once I stopped my descent and became neutral at about 50' was fine and I was able to ascend by fining and stopped and swam around for another few minutes at 10'. I just didn't understand the whole empty your BC and you should be neutral. Again thanks.

 

[eelnoraa]

The ultimte goal is to determine the minimum amount of weight such that you can to hold a 15 feet stop with a near empty tank. There are a few methods to archieve that. The key words here are "minimum", so you BC should be empty when you do this check.

 

[MauiScubaSteve]

1st Question: I read in the adventures in Diving manual (Peak Performance) that to start out for my weight 180 lbs and a 5mm wet suit at 10% my body weight (18lbs). My last dive I was using 14lbs and was sinking like a rock. I have used 12lbs and was able to stay neutrally buoyant without air in my BC. This leads to my second question... How do you descend feet first if you are neutrally buoyant without air in the BC without adding weight? This is the reason I went with the 14lbs. To stop myself from sinking I have to add air to my BC is this the right way?

I own and dive two 5 mm wet suits. My summer / shallow shore dive suit is an Aquaflex and my newer deep / boat dive suit is a Pinnacle Merino-Elastiprene; there is significant difference between them with regards to weight needed.

When properly weighted, descending feet first still may require a good exhalation with very still lower extremities. I prefer to "glide" down like a plane, or pull myself head first down the line.

 

[molina67]

Next time I go out I'll check with a full tank and then with it nearly empty. I guess I was thinking that being negatively buoyant was the same as over weighted. Thanks for clearing that up...

 

[fnfalman]

If you weigh yourself correctly then a) at beginning of dive with no air in BC and a lungful of air you should float at eye level, and b) at the end of dive at around 500-psi you can hold a safety stop with no air in BC - which is a lot different than being "neutrally buoyant" at such depth. If you're neutrally buoyant at safety stop then you're underweighted.

 

[MauiScubaSteve]

I think there is at least one more "school of thought" on proper weighting.

Neutral at the surface with an empty tank, or minimum weight needed to dive in 5-10' deep water until tank will not give any more air. Then if you are ever one of the two people involved in a rock bottom-ish alternate assent you can have a more controlled ascent from 20' to the surface when there is less than 300 psi in both tanks. Better yet would be both divers thinking from that school.