How much air in your BC?

[SparticleBrane]

I suppose I will answer "How much air in your BC?" since I never actually did, earlier...

It depends on the gear setup and my weighting.
With full double 130s my wing (DSS Torus 49lbs model) tends to have a good deal of air in it. With a single Al80 and my 30lbs Halcyon Eclipse...not too much.


Of course, as the dive progresses, air is slowly let out to compensate for the tanks getting lighter.

 

[elan]

I'm actually fairly sure that I can dump faster from my rear dump than from my inflator hose, and in fact, tech divers are often taught that, in the face of a runaway inflator, the rear dump should be used for that reason.

I see more reason in this, as one of the members of our Ontario diving forums has pointed out that this will give one an opportunity to use the fins for slowing down while finning head down, dumping the air with the rear dump valve. I cannot see how this can be done with the hose.

 

[LeadTurn_SD]

I'm actually fairly sure that I can dump faster from my rear dump than from my inflator hose, and in fact, tech divers are often taught that, in the face of a runaway inflator, the rear dump should be used for that reason.

Hi TSandM.

That's interesting, and not what I would have expected.... my concern with doing it that way is that you'd be tying-up your left hand (to pull rear dump) leaving only the right to disconnect the inflator hose, which is causing the problem and wont stop until you disconnect it. I'll try it that way, but I'm not sure I have the dexterity to disconnect the hose one-handed (but maybe it is easier than I think).

The way I'd practiced this was left hand grab inflator and depress and hold exhaust button, while right hand disconnects the inflator hose. It is quite fast that way. Flare and exhale as needed

But I've never had a real runaway inflator (thank goodness), so maybe the way I had practiced is not as effective....

Best wishes.

 

[Coldwater_Canuck]

All good points. There is a simple way. Do a buoyancy check. When you have that right, add 4 lbs if you're diving an aluminum 80 (probably less with a steel tank-depending on the make and model- but you'll have to play with it). You should be neutral at the safety stop with an empty BC.

Do you not want to be slightly negative at the safety stop, so that you can control your ascent in the last 15 feet? If you were neutral at 15 feet, then when you hit 10-14 feet wouldn't you just lose control and shoot up.

 

[LeadTurn_SD]

Do you not want to be slightly negative at the safety stop, so that you can control your ascent in the last 15 feet? If you were neutral at 15 feet, then when you hit 10-14 feet wouldn't you just lose control and shoot up.

I try for as close to neutral as possible.... in fact, at the end of the dive I may actually be very slightly positive once I hit about 10-15 feet (I hold a deeper safety stop, closer to 20 feet than 15). I have the advantage of using a 3mm suit, but still, you can add or subtract several pounds of buoyancy with lung volume alone, so being slightly positive in the final few feet can be controlled by breathing technique. You don't want to be so light that you struggle to sty down, but most wetsuits are a bit less buoyant at the end of the dive (after having been at depth) than in the beginning (the neoprene does not "rebound" to full thickness immediately).

In general you want to carry the minimum weight needed to allow a comfortable safety stop. If you weight yourself to still be more than just a hair negative at the safety stop, you are dragging around too much weight.

Really, you just need to experiment to get the weighting right. All the "Rules of Thumb" will just get you in the ballpark. Then you need to test and fiddle a bit.

Best wishes.

 

[rongoodman]

That's interesting, and not what I would have expected.... my concern with doing it that way is that you'd be tying-up your left hand (to pull rear dump) leaving only the right to disconnect the inflator hose, which is causing the problem and wont stop until you disconnect it. I'll try it that way, but I'm not sure I have the dexterity to disconnect the hose one-handed (but maybe it is easier than I think).

You'll be using your right hand to shut off the right post, which is feeding the inflator hose. You can then disconnect it at your leisure.

 

[TSandM]

Just to pass along something I learned the hard way -- if you have shot an SMB to tell the boat where you are, and want it to stand up and be seen, you need to be negative enough to be able to pull down on it with a pound or two or force. If you are positive at your stop, you are not only trying to swim YOU down, you're trying to swim down hard enough to keep the bag standing up, too. It is not fun.

 

[dumpsterDiver]

Just to pass along something I learned the hard way -- if you have shot an SMB to tell the boat where you are, and want it to stand up and be seen, you need to be negative enough to be able to pull down on it with a pound or two or force. If you are positive at your stop, you are not only trying to swim YOU down, you're trying to swim down hard enough to keep the bag standing up, too. It is not fun.

Yes and being 2-3 lbs negative at the end of the dive might keep you from accidentally rising up and getting hit by a boat.

A gallon of water is about 8 lbs. Being "over weighted" by 3 lbs equates to carrying an excess of 3 lbs of bouyant air which has a displacement of about 48 ounces, Carrying less than a "big gulp" worth of extra air in the BC on a dive is not going to present a lot of additional drag or negative consequences.

 

[dumpsterDiver]

As for how to dump air in an emergency: I would lay on my back, spread eagle to make a lot of drag, and pull the dreaded pull dump on my inflator. while keeping a gentle tension on the pull dump, I can simultaneously work on unhooking the LP inflator with both hands.

I think it is very tough to unfasten the LP inflator with one hand, when the other is occupied pulling on a rear dump? Unless of course you have an AIR2 inflator which is actually large enough to manupulate with one hand.

 

[LeadTurn_SD]

You'll be using your right hand to shut off the right post, which is feeding the inflator hose. You can then disconnect it at your leisure.

I was thinking singles... thanks, didn't even think about doubles, but that makes sence.

So, for singles, since I only have one post, and shutting that off might not be a good option , I may stick with the way I've practiced (I'm too much of a klutz to disconnect with one hand I'm afraid).

Best Wishes.