question on importance of weight for choosing bcd

[acoda1]

quick question from newly certified open water diver. i am 5'5" 164lbs and waist size 33 have been looking at used and new bcds and see a lot in small size . checked manufactures size chart and see that I am good in shoulder length waist size and height but I am 9lbs heavier in weight for size. how important is the weight in choosing bcd as I did a recent dive in Cozumel and felt I was underweighted at 12lbs in med zeagle as at one point during a shallow dive 24feet the current grabbed me and I almost had an uncontrolled ascent . as I am some what bouyent I think I would rather be slighty overweighted and add air to bcd to obtain neutral bouyncy. so I was wondering if small size fits me would the weight differential help compensate with weighting or should I stay with a medium bcd and just tweek the weights to be slightly overweighted until I get more dives under my belt.

Please excuse spelling lol
Thanks for any and all help
Greg

 

[TSandM]

Greg, it seems as though there are several concepts all mixed up in your post.

First off, diver weight affects BC fit, because whatever the waist band is on the BC (cummerbund or strap and clip) it has to fit around you, and tighten down enough to keep the BC stable. If you are short and round, and buy a BC that is suitable for your height, the cummerbund may not make it around you, or may not have enough overlap to fasten securely. If you buy for your weight, you may have problems cinching the BC down around you. This is one of the reasons that actually going to a dive shop and trying stuff on is very useful; or you could buy a backplate setup where the harness can be adjusted to your size, no matter what it is.

As far as weighting during the dive goes, yes, heavier people require a bit more lead, for two reasons. One is that they are BIGGER, so it takes more neoprene to cover them. The other is that fat floats. But having a loss of buoyancy during a dive may or may not mean that you are underweighted, and adding weight and then air to the BC is NOT a good strategy for buoyancy stability. The reason is that, the more air you have to carry in the BC, the bigger the changes are when you go up or down -- large gas volumes expand the same percentage as small ones, but the absolute VOLUME of increase is bigger, and so is the related lift. The best strategy is to determine what your correct weighting is, by doing a formal weight check, and then using that amount.

Newer divers often have buoyancy "oopses", usually related to breathing changes, lack of a horizontal diving posture, and limited situational awareness (don't notice giong up until you're way off target depth). If the problems only show up at the end of the dive, when the tank is very low, they can be related to underweighting. But most of the time, they're not.

 

[dfx]

If the problems only show up at the end of the dive, when the tank is very low, they can be related to underweighting. But most of the time, they're not.

Another explanation to buoyancy troubles at the end of a dive (when going shallower!) is failure the vent the BCD properly.

 

[acoda1]

ok I will clarify . I had just looked at spg and had 1200 lbs was drift diving at Columbia shallows. from what you are telling me I believe it was that the current caught me off guard and I did not react quick enough to dump any air in bcd. also if I assume correctly weight guides for bcd are just that guides there are no hard and fast rules so if a small fits it should be good to go as long as the cummerbund has sufficient overlap.

yes no maybe

 

[lindenbruce]

Which BCD are you looking at? Most are sized by common sizing like small, medium, large, extra large etc. If a BCD is right in all dimensions except your weight, go up one size. As long as you can adjust the BCD enough to fit your body type. B.

 

[Bob DBF]

Number one, have you done a weight check at 15' @ 500# to see what you actually need? If you don't know what is perfect for optimum conditions, there is no basis for weighting for conditions.

I add 2# immediately in case I want to be at less than 15', or am at less than 500# and still need to be underwater.

If I am working in surge, I will add more weight, say another 2-4#, but diving in shallow surgey water is tricky and can put you on the surface regardless of your precautions. At that point, keep your airway open, and grab the bottom if acceptable. It's advanced diving, don't do it if you are not ready.

As I told my daughter, when she was little, "the ocean is not out to get you, it just dosen't care".




Bob
---------------------
I may be old, but I'm dead yet.

 

[dive_turkey]

If you're having trouble in between the sizes, you may also look at a more modular BC, like the Zeagle Ranger. It will get pricey, but you can always throw a set of Medium shoulder straps onto a Large Ranger, or vice versa. Also, the cummerbunds are adjustable by several inches. I can either wear a large adjusted all the way in, or a medium adjust almost all the way out. I also find myself in between sizes fairly often.

 

[Subcooled]

When you jump into water (without diving kit) then you float, right?
Most people do.

You need to add some lead to your kit so that you can sink.
The amount of lead required goes down as you relax and learn to exhale (difficult to sink will full lungs).

The BCD is meant to keep the air tank, regulators, and lead floating (when you remove them on the surface).
The BDD does not need more lift in lbs than the weight of your kit in water is.

Some people people are denser than others (muscle, not fat), and need less weight. Others are lighter and need more lead to become neutral/sinking. Hence, fat people need some more lift in the bcd (not because of the requirements of the dive but because of the requirement to keep the kit floating once it has been taken off).

________
Why don't you get a backplate and wing and a single tank adapter? That set fits both you and your kids and your neighbour with an easy adjustment. Besides, it feels more comfortable. Corsets are so 19th century...

 

[DivemasterDennis]

I think this discussion [points out the value of TRYING on equipment before purchase. Not only are the size variables discussed in this thread all important, but in addition, different manufaturers and models will vary A LOT in size, and the OP may be a small in one model and a medium in another. Having a BC that is too large is not a good thing. And of course, one that is too small is completely useless. Consider spending a few more dollars and buy something you can try on while wearing whatever exposure suit you will most often be wearing while using the bcd. The extra dollars you pay for a BCD you know is the proper size is worth every penny.
DivemasterDennis