Question on buoyancy and weights

[Danny Heng]

Hi again. My second posting here. First was in the intro section. (Actually I did try posting on another thread but I must have clicked on the wrong button and it did not appear )

As stated in the intro... I have only 9 dives to date since my PADI OW certification last March. As I am diving off the islands near Semporna, Sabah, the water is relatively warm and I dive in a 3mm shorty. All my dives, I use 6 kilos of weight. No problems descending or ascending... only minimal problems achieving neutral bouyancy.

The issue that has been mulling around in my mind is this, when I am down at the reef, I find that I have to really exhale or inhale deeply in order to move down or up around obstacles. Because of that, I think that is the reason I am always the first diver to get low on air. Longest dive for me to date is about 47 minutes. Am I diving with too much weights? Should I try reducing it by a kilo or two?

I plan to dive Sipadan on the 24th. Should I try reducing the weights then?

Thanks

Danny

 

[tracydr]

Do you know how to do a weight check with a tank towards the end of a dive or with a tank that's low on air?
Kind of sounds like you might be overweighted but hard to say until you do a weight check. This will be explained in your Open Water book.
By working so hard breathing to modify your depth, you're essentially skip breathing, which is not really safe and considered a big no-no by most agencies.
working on breathing slowly and evenly should help you to get better with you're air. If you're a bigger person and have any anxiety you won't be as good with air. Also, poor conditioning will cause you to use more air.

 

[Cave Diver]

I find that I have to really exhale or inhale deeply in order to move down or up around obstacles. Because of that, I think that is the reason I am always the first diver to get low on air. Longest dive for me to date is about 47 minutes. Am I diving with too much weights? Should I try reducing it by a kilo or two?

I plan to dive Sipadan on the 24th. Should I try reducing the weights then?

Thanks

Danny

If you have the opportunity, when your tank is low,around 500 psi, and you are doing your safety stop, try taking emptying your bc completely of air and removing a pound or two of weight at a time. When you reach the point that you are struggling to stay down at 15' you've pretty much got your weighting correct.

 

[SnorkelLA]

Do you know how to do a buoyancy check? You should have learned it in class. Just doing a buoyancy check should tell you everything you need to know.

With all gear and weights on, with a half inflated BCD, let all the air out of your BCD, then hold a NORMAL breath. Not a "big-bad-wolf" breath. If you float at give or take an inch or two from eye level in either direction you should be fine. And just to check and see if you're not underweighted, after the check, let all your breath out, you should slowly descend.

Also, if you find yourself overweighted underwater for some reason, your BCD is there for a reason...


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[mala]

do a weight check at the end of a dive-if you can dump air at 5m then you are overweight.
it does sound like you are a bit heavy.

the more you dive the less air you will use-dont worry.

 

[ScubaSteve1962]

Try this site, and do a weight check, as you get your buoyancy you air consumption will go down.
Scuba Buoyancy Masterclass 1of9 - Buoyancy Control for Scuba Divers -Scuba Tech Philippines

 

[Danny Heng]

Do you know how to do a weight check with a tank towards the end of a dive or with a tank that's low on air?
Kind of sounds like you might be overweighted but hard to say until you do a weight check. This will be explained in your Open Water book.
By working so hard breathing to modify your depth, you're essentially skip breathing, which is not really safe and considered a big no-no by most agencies.
working on breathing slowly and evenly should help you to get better with you're air. If you're a bigger person and have any anxiety you won't be as good with air. Also, poor conditioning will cause you to use more air.

Hi again. Sorry if I was not clearer. Yes I know how to do a weight check. My instructor did it with me on my first day and 6 kilos was what it was then. Maybe I am over thinking this weight issue.

I take deep breaths or exhale more to ascend or descend but they are not fast breaths. I consciously try to breath slow. What is skip breathing? I do not understand or have not come across that term. I do know that I am not to hold my breath so I never do.

As for weight/size, I am 6ft2in (tall for an asian i guess) and yes I am overweight but I am very comfortable in the water. No anxiety felt when diving... I think. I have been swimming and used to participate in waterpolo and competitive swimming during my schooling day waaaaaaay back.

SnorkelLA... so THAT's what the BCD is for... gosh!!!!
Jokes aside... yes perhaps I should learn to use it more than I do. I find it fiddly and tend to minimise inflating my BCD.

Thanks for all the help here.

 

[TSandM]

Although everyone who has written that you need to do a proper weight check is absolutely right, let's look at some likely numbers to see if it's probable that your weighting is correct.

I'm assuming you are diving in some kind of jacket BC. Those are typically 1 to 3 lbs (.5 to 1.5 kg) positive, so you need to carry let's say 1 kg of weight to sink the BC.

Let's also assume you are diving an Al80 tank (I think that's a 12l, if I remember right). They are 2 kg positive when they are empty, and you have to carry enough lead to keep the tank underwater at the end of your dive, so that's 3kg of weight altogether, with the 1 you're carrying for the BC.

You are diving a 3mm shorty wetsuit. Wetsuits are the big unknown in this exercise, because how buoyant they are depends on the material of which they are made, their size, and their age. I'm 5'4" tall and weigh 120 lbs, and my 3 mil full wetsuit is 4lb (2kg) positive. I'll make the assumption that it's unlikely that your shorty is more positive than that, and you'd have to be a significantly bigger person for it to be equal to my full wetsuit.

So that all adds up to 5 kg at maximum for your gear. Most humans are roughly neutral, unless they are very obese (and there is a fudge factor in my numbers, because a kg is a little MORE than 2 lbs). So I'd say it's unlikely you need more than 5 kg, and it's not unlikely that you might need a kg less.

But being within 1 kg of correct weight won't have a huge effect on your buoyancy. The people who have real problems due to overweighting are generally heavier than that (I took nine pounds off a lady I dove with a couple of weeks ago!).

And going back to your original post, how much you have to change your breathing to change your buoyancy really has nothing at all to do with whether you are correctly weighted, assuming you are neutral when you inhale or exhale. If you have enough air in your BC to be neutral, then when you inhale deeply, your buoyancy will change by the amount you have expanded your chest. If you are a small person, this amount will be less than what a bigger person can accomplish -- and no matter who you are, it always takes time to see the change occur. It's not instantaneous!

Overuse of the breath for buoyancy control can definitely contribute to faster gas usage. THIS article by a British instructor, I found very interesting; I think it's quite likely that a lot of people dive with their BC set so they're a bit negative, and make up for that with keeping their lungs full, so that they can arrest any tendency to float up quickly by exhaling. Breathing outside of a regular, comfortable volume and rhythm WILL make you use gas faster than necessary.

But I also think 47 minutes on an Al80 for a brand new diver is nothing to be ashamed of! You can find any number of threads here about tips for improving gas consumption -- good buoyancy, correct trim, efficient propulsion, minimizing extraneous motion, and slowing down are all methods for doing that. But I'd start off with being reasonably pleased with you bottom time as is, I think, especially for your level of experience.

 

[Cave Diver]

I take deep breaths or exhale more to ascend or descend but they are not fast breaths. I consciously try to breath slow.

Sounds like you're using the correct technique, maybe it just needs a bit more refining.

What is skip breathing? I do not understand or have not come across that term. I do know that I am not to hold my breath so I never do.

Skip breathing is holding your breath between inhale/exhale in an effort to conserve air. Some people don't even realize they do it.

You might try to calculate your SAC rate which will give you a baseline for your air consumption. It's not unusual for newer divers to have higher consumption even if they think they're comfortable. Other things that you might consider is unnecessary movement of your hands/arms and streamlining of your gear. All of those can contribute as well.

 

[windapp]

It sounds like you are expecting your body to move a lot faster when you inhale or exhale than it will. You can't use your breathing to rise or fall on a dime. You need to anticipated obstacles, and start your breath change early. This is normal and good. If you quickly moved with changes in lung volume, you would crash the reef with every breath you take, and you wouldn't be able to take slow deep breaths while staying relatively level.