Buoyancy weight

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Kaneda13

Contributor
Messages
118
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Location
Indianapolis
# of dives
100 - 199
Been working on getting my weight down as much as possible to help with my dive time before running out of air. My last 2 dives I've beaten my previous record for time down, the last one at 58 minutes (probably closer to 56 as we surfaced for a minute to better talk about what we want to explore in the quarry). Anyway, in fresh water with a full 3mm wetsuit, an AL80, and my normal gear, I was carrying 2 x 3lbs in my side pockets, and 2 x 2lbs in my trim pockets. I felt good the whole dive, using only 3 or 4 bumps on my inflator to keep me off the bottom. They problem came up at 900PSI left in my tank. On both dives I'm becoming positive at 900PSI left in the tank. My normal plan is to be on the surface at 700PSI, so I'm loosing a few minutes of time, and even after dumping all my air, once I hit 900 I'm going up, ready or not. Should I move up to 4 x 3lbs, or would it be ok to swap out one of the 2lbs for a 3lbs, or will that make me "lop sided" underwater?
 
so you are becoming positive at 900psi....and you are carrying 10lbs?

ide try adding 2 more lbs, so 4x 3lbs and give that a try.

also, dont worry about removing weight, as you dive, and get more comfortable in the water, youll find yourself naturally needing less and less.....use what you need to properly do the dive, and dont worry about it.
 
Being improperly weighted and making out of control ascents, is dangerous. You should add at least 3-4 lbs, and should be able to stop your ascent with zero air in the tank and zero air in the BC and at a depth of 0.5 feet.

If you think otherwise, you have been taking advice from the wrong people. This has nothing to do with air consumption and everything to do with safety.
 
On both dives I'm becoming positive at 900PSI left in the tank.
This corresponds to a bit less than 2 pounds of air left in your tank.
de try adding 2 more lbs
Good advice...you should now not be positive even if your tank is empty.
You should add at least 3-4 lbs,
Probably too much.

The caveat to the advice above is that you haven't said what kind of exposure suit you are wearing. A wetsuit will compress as you go deeper than 10-20 ft and you will lose buoyancy from that. Equally, it will expand during your ascent and you will regain its buoyancy. So being neutral at 900 psi without telling me your exposure suit and your depth means i cannot give you a void guess about extra weight needed....just that you DO need some extra weight.
 
as said above, an out of control ascent is very dangerous and must be avoided. add 4 lbs and try again. try to hold at 10 feet with 500 psi or less in your tank with no air in the bcd. i would even try it after working hard. many people when giving out weighting advise often forget that there are times when your breathing can be elevated. this can drastically change your buoyancy. a couple of lbs over weight is not going to cause any issues. better to be 2 lbs over than 2 lbs under right ? 10lbs over.....now thats a different story.
 
as said above, an out of control ascent is very dangerous and must be avoided. add 4 lbs and try again. try to hold at 10 feet with 500 psi or less in your tank with no air in the bcd. i would even try it after working hard. many people when giving out weighting advise often forget that there are times when your breathing can be elevated. this can drastically change your buoyancy. a couple of lbs over weight is not going to cause any issues. better to be 2 lbs over than 2 lbs under right ? 10lbs over.....now thats a different story.

I agree. I think everybody wants to maximise their time under water and help their sac rate (always a good goal), but safety is way more important. A couple of pounds are not going to make a huge impact on air consumption, and the type of exposure suit (not just the thickness, but also the type of cell) really plays into how much extra you will need. An open cell wetsuit will compress more and the buoyancy will also change much more.
 
Just checked the aqualung website, and they just lost it as a HydroFlex 3mm wetsuit, not sure the make up of the neoprene in it. This has all been very good information so far, am I very much appreciate all the info. I’ve been renting a belt with weights on it up until now, normally only has 2 of each weight. May have to ask for extra 3s.
 
I'm with @tursiops, 500 psi in an AL80 weighs just over a pound. Add 2 pounds and then make sure you can hold your safety stop and make a slow, controlled ascent to the surface. Make sure you have the air out of your BC, I find the butt dump to be most reliable way to do this.
 
Others have answered the question about needing more weight. As for how to place that weight, I'd get two 1lb weights and add them to your integrated pockets to start. See how that feels. If your trim feels off, you can move them to your trim pockets (add 1lb to each side, so you'll have 3 lbs in each trim pocket). You can also adjust your tank position a bit to adjust trim. Moving the BCD up on the tank brings more of the weight towards your legs. Moving the BCD down on the tank moves the weight towards your head. Small adjustments are usually all that is needed - like 0.5" to 1" or so - and keep in mind that ideally you want to be able to reach your tank valve while also not banging the back of your head into your first stage.
 
Moving the BCD up on the tank brings more of the weight towards your legs. Moving the BCD down on the tank moves the weight towards your head.
This is actually true only when the tank is full. Below 1200 psi or so, the lower end of the tank becomes buoyant so the effect reverses.
 
https://www.shearwater.com/products/perdix-ai/

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