Buoyancy at safety stop

[dadiver]

I am taking my OW certification dive in a week, and I have a buoyancy question. I understand that you’re supposed to start your dive with no air in your BC while holding a normal breath and you should float at eye level if properly weighted. After the dive is complete, when ascending to the safety stop, I don’t understand how one can achieve neutral buoyancy to make the safety stop with a nearly empty tank. How does this work?

 

[rdriver]

Dadiver,
I think the correct way of figuring buoyancy check it with an almost empty tank then you will be some negative at the start of your dive but just right at the end. so the first dive of the season would be kind of a guess for weight but at the end of that dive you should be able with some addition or subtraction of weight be just perfect for the next dive.....also make a note of what gear your have on i.e. wet suit and thickness, knives, light. etc . so you will always be able to know where you stand within a one or two lbs.
Rob

 

[JeffG]

dadiver once bubbled...
I am taking my OW certification dive in a week, and I have a buoyancy question. I understand that you’re supposed to start your dive with no air in your BC while holding a normal breath and you should float at eye level if properly weighted. After the dive is complete, when ascending to the safety stop, I don’t understand how one can achieve neutral buoyancy to make the safety stop with a nearly empty tank. How does this work?

You need to add the weight of the gas that you will consume to your belt before you start.

So with the procedure you listed above, and if you are doing the test with a full AL80 you would have to add 5 lbs (Air/Nitrox is ~1 lb for every 13 ft3)

 

[annie]

I don’t understand how one can achieve neutral buoyancy to make the safety stop with a nearly empty tank.

I'm not an expert on buoyancy checks and weighting calculations - this is just my own personal musings. If your buoyancy check is ok, if you can sink, your safety stop should be ok. If you are diving with a steel tank, it will still be negatively bouyant even when empty. The stop is at 5m, which is .5 ATM more pressure than at the surface, so air in your suit etc will be less bouyant at the stop. If you're breathing properly and haven't too much air in the BC you should be ok.

However ali tanks become positively bouyant when empty so they will float at the end of a dive which is why you need to add more weight if you're using one of those. I think it's about 6 lbs you have to add (as opposed to steel).

 

[MikeFerrara]

All tanks regardless of what they're made of will be lighter at the end of the dive by the amount of air you used. An 80 cu ft tank holds about 6 pounds of air no matter what the tank is made of.

Adjust your buoyance so you're neutral with a near empty tank. Or..get neutral with a full tank and add a few pounds.

 

[MikeS]

dadiver once bubbled...
I understand that you’re supposed to start your dive with no air in your BC while holding a normal breath and you should float at eye level if properly weighted.

Although that is the PADI way of checking buoyancy, it doesn’t work well for several reasons. The biggest reason with new divers is that they are unable to relax enough to breath normally and stop moving their hands and feet.

The following is the best way I’ve found for new divers to adjust weighting. It is time consuming; don’t be surprised if it takes 20 minutes, which is probably why it isn’t taught. I think that you’ll find it is well worth the effort. The goal is to be able to achieve neutral buoyancy at the end of the dive (little or no air in your tank), just below the surface (minimum compression of exposure protection).

Start with a full tank in the shallow end of the pool, this is the best place to work; if you have a problem simply stand up. It is also much easier to add or drop individual weights here, you can leave them lying on the bottom and still reach them. The air in a near empty tank will not last long enough and it’s hard to relax if you’re worried about running out of air. Let all of the air out of your BC and lay flat on the bottom, stop moving those arms and legs (duct tape may be needed at this point), relax and breath normally. Add or subtract individual weights until you naturally start to bob up and down off the bottom as you breath. At this point, you’re very close to neutral. Adjust the position of the weights and/or location of tank in the cam strap until your entire body starts to rise up and down as you breath; as apposed to fin pivots. You may need to further fine-tune the amount of weight since you’re reducing the weight of the air as you breath it. Once you have this down you need to add weight equal to the weight of the air left in your tank. To do this check the pressure and add a pound of weight for every 500 psi (i.e. 3000 psi / 500 psi = 6, add six pounds).

Remember that adding any new equipment especially wet suit parts changes your buoyancy and hence amount of weight you’ll need. Going to salt water also necessitates adding additional weight.

Hope this helps,
Mike

 

[Wyno]

Sounds like it might work

 

[jbd]

the concept behind the method you are using is as follows.

Your BC should be completely empty. You take a larger than normal breath and hold it. You must be relaxed and completely motionless. When the surface of the water is at or slightly above your eyes(I prefer eyebrow level) you will be neutrally bouyant. If you can't get your eyes at or slightly below the water surface you need to add weight. If you sink then you are over weighted.

From this relaxed, motionless, breath holding situation all you need to do is exhale and you will descend slowly.

As the dive proceeds you will be using air from the tank and it will be getting more bouyant than it was at the beginning of the dive. This bouyancy increase was compensated for at the beginning when you took the larger than normal breath and held it and added enough weight to make you float at eye level.

I hope this helps.

 

[Al Mialkovsky]

The way I've mananged to find myself neutral with a full tank, and add five pounds. It's been perfect so far.

 

[plsdiver4377]

MikeS once bubbled...


Although that is the PADI way of checking buoyancy, it doesn’t work well for several reasons. The biggest reason with new divers is that they are unable to relax enough to breath normally and stop moving their hands and feet.

The following is the best way I’ve found for new divers to adjust weighting. It is time consuming; don’t be surprised if it takes 20 minutes, which is probably why it isn’t taught. I think that you’ll find it is well worth the effort. The goal is to be able to achieve neutral buoyancy at the end of the dive (little or no air in your tank), just below the surface (minimum compression of exposure protection).

Start with a full tank in the shallow end of the pool, this is the best place to work; if you have a problem simply stand up. It is also much easier to add or drop individual weights here, you can leave them lying on the bottom and still reach them. The air in a near empty tank will not last long enough and it’s hard to relax if you’re worried about running out of air. Let all of the air out of your BC and lay flat on the bottom, stop moving those arms and legs (duct tape may be needed at this point), relax and breath normally. Add or subtract individual weights until you naturally start to bob up and down off the bottom as you breath. At this point, you’re very close to neutral. Adjust the position of the weights and/or location of tank in the cam strap until your entire body starts to rise up and down as you breath; as apposed to fin pivots. You may need to further fine-tune the amount of weight since you’re reducing the weight of the air as you breath it. Once you have this down you need to add weight equal to the weight of the air left in your tank. To do this check the pressure and add a pound of weight for every 500 psi (i.e. 3000 psi / 500 psi = 6, add six pounds).

Remember that adding any new equipment especially wet suit parts changes your buoyancy and hence amount of weight you’ll need. Going to salt water also necessitates adding additional weight.

Hope this helps,
Mike

I've done this myself and it works like a charm.