Buoyancy and wetsuit advice needed

[Cosmographer]

I posted this in the exposure suits section a few weeks ago, but seeing as how no one there was able to assist, I thought I'd give this forum a try since it's more frequently visited.

The problem: Too buoyant. In my new 5mm jacket/pants combo, I need more than 8kgs to avoid a runaway ascent near the end of the dive. 5-6kgs is enough for descending, but as my tank lightens towards the end of the dive, nothing seems to be able to keep me down - no chance of a safety stop whatsoever, even when finning full force straight downwards. 8kgs wasn't enough, so next time, I'll try 10?

Background: I normally use 3.5kgs (without a wetsuit or in a 3mm shorty) and maybe 4kgs (in a 3mm full suit). My new suit consists of a 5mm jacket and 5mm pants: not a farmer john style overall - these pants end just above the waist.

Potential issues: I'm thinking that the extra weights needed going from a 3mm to this new 5mm is unusual. Obviously, a more buoyant suit like a 5mm will need more weights, but that much more?! So I suspect that the problem might be one of two things:

1. Since this is a new wetsuit, it is exceptionally buoyant and will become more manageable as it gets broken in. But is there really THAT much of a difference in buoyancy between used and new suits?
2. Air is getting trapped inside somehow. This seems likely because throughout my dives, especially when I angle my head downwards, I can hear and feel lots of bubbles rushing down my suit towards my legs. I'm not sure where these bubbles come from. Maybe my reg? Also, the neck seal isn't particularly tight (there is actually a golf-ball sized opening where the collar sticks out from the back of my neck), and I can imagine air from the reg floating into it that opening. Would that make sense? Is this just the nature of 2 piece wetsuits?

Any advice would be much appreciated.

 

[Bigd2722]

1. yes
2. yes

 

[mala]

more neo =more lead.

you could go for a steel tank?

you dont have to have all the lead in one place -if it helps you can spread it around a bit.

 

[ScubaSteve1962]

Try this site. Have you ever properly weighted yourself??

Scuba Buoyancy Masterclass 1of9 - Buoyancy Control for Scuba Divers -Scuba Tech Philippines

 

[DivemasterDennis]

You will need to add weight due to the increased thickness of the wet suit as well as because it is new (assuming you others have 100 dives or so on them. My wife recently replaced an old (150+ dives, 4 years old) 3 mil with a new three mil and added a pond of weight. But you also report facts that suggest air is getting trapped. Now and then during a dive "vent" the air by pulling out the collar of the jacket and "flapping" it a little. Do something equivalent for the pants ( I'm not familiar with "pants" as wetsuit) Finally, do a proper weight check before each day's diving until you settle in on proper weight for this gear package. It will vary a bit at first.
DivemasterDennis

 

[NE_SSI_Diver]

I would suggest a new tank. If you are using an Aluminum 80 then it will become positively buoyant towards the end of the dive. You can try a steel tank, but there are many options you can research (there was an article on this subject not too long ago on Scubaboard).

Also, tanks which are negatively buoyant can reduce the amount of lead weight you need. This is not a huge issue in warm water diving, but can be helpful when diving in 7mm wetsuits and drysuits.

 

[TSandM]

10 kg does seem a little high for a 5 mil suit, even a new one. (I'm basing that on the fact that we typically put about 20 to 24 lbs on our OW students in 7 mil Farmer Johns -- although they are diving steel tanks, and the bigger people can need up to 30.) But generally the air-trapping problems with wetsuits are seen more at the beginning of the dive than at the end; by the end of the dive, the air bubbles have usually gotten displaced with water somewhere along the line.

One way to investigate this would be to take your wetsuit, tie a line to it (perhaps at the zipper pull) and put it in some kind of mesh bag. Move it around until you're sure the air is all out of it, and then see how much weight you have to add to the bag to get the wetsuit to sink. This will give you an idea of how much of the weight you are carrying is directly needed to offset the buoyancy of the suit. Numbers for tank buoyancy are readily available, and you will probably know whether your body is neutral or very buoyant. If you add everything up and it comes within a kg or so of what you're carrying, then you're probably correctly weighted.

Weighting is what it is. When I took GUE Fundamentals, the instructor was on a rant about how everybody out of OW dives overweighted. He said, "I've seen little women your size packing around TWENTY-EIGHT pounds of lead!" I told him, "Well, that's what I'm doing." He said, "We'll take some of that off you tomorrow." He tried, and he couldn't. (I'm not a stupid woman, and I had done my weight checks.) Sometimes the weight people need isn't what you would guess, but if they need the weight, they need it. Only a good, formal weight check can tell you for sure. And I CAN tell you from personal experience that problems holding a safety stop do NOT necessarily mean you are underweighted. Technique plays a BIG part there.

 

[divin'dog]

If you have a golf ball sized opening at the collar (which is big), I'm thinking that your suit might not be fitted as well as it should be.. and is large enough to collect your exhaust depending on your position (head down). Do you wear a hood? Could your exhaust also be going into your hood and then into your suit when inverted? I know my exhaust will sometimes get into my hood. I still have to squeeze the hood to get the bubbles out sometimes. Having a skin-in hood helps.

Check your buoyancy at the beginning. Squeeze out all the air. Find where pockets of air may exist. If your suit is too loose, you will have folds that trap the air (not good). If you squeezed out all the air from your suit at the beginning, but find air making its way into your suit in the middle of the dive, then, yeah obviously, I'd say your exhaust is making it's way into your suit from that golf ball sized opening. I wear a hood all the time even in warm water (albeit a 1mm microprene) but the exhaust easily finds its way into my hood and at times into my suit if I invert. Like you, I can feel the bubbles going from head to toe. It can wreak havoc on your buoyancy if you're not aware of it.

As for more weight... add weight after you are sure that's what you need. Don't worry about preconceived amounts of weight that other people dive with because it just might be what you need. This may take a few dives to get right esp with a new suit. Body types and suits and gear and diving experience are all different and affect buoyancy.

---------- Post added ----------

Weighting is what it is. When I took GUE Fundamentals, the instructor was on a rant about how everybody out of OW dives overweighted. He said, "I've seen little women your size packing around TWENTY-EIGHT pounds of lead!" I told him, "Well, that's what I'm doing." He said, "We'll take some of that off you tomorrow." He tried, and he couldn't. (I'm not a stupid woman, and I had done my weight checks.) Sometimes the weight people need isn't what you would guess, but if they need the weight, they need it. Only a good, formal weight check can tell you for sure. And I CAN tell you from personal experience that problems holding a safety stop do NOT necessarily mean you are underweighted. Technique plays a BIG part there.

Thank you TSandM, for saying that... So many divers base their final weight on preconceived weighting notions which is a good place to start but they may end up far away from that (with either more or less weight). If you go through the proper process and you need a certain amount... well, then, you need a certain amount!

 

[Cosmographer]

Thanks for all of the advice. I haven't had a chance to dive since I posted this question, but I'll put this info to good use, and hopefully, I'll get this sorted out by our next dive trip.

 

[stairman]

Some people are more buoant than others. Im a floater and take a ton of weight to sink. The added neo as stated means added weight and its very important to hold your SS with 500 PSI. The air getting trapped is contributing as well and you might have a semi semi dry wetsuit. When I changed wetsuits from 3 mill to 7, I was wearing double steel 95's, and was on my head my feet were so floaty from the added leg neo. Had to abort and lower my backplate/tanks to trim out. Ive seen some folks leave loose weights in a mesh bag on the line at 20 ft, to be added in case someone is under weighted at their safetystop. Good luck!