Air integrated computers and drysuit diving

[DA Aquamaster]

The was made previously but has perhaps been missed - adding air to the dry suit is no different than adding air to a BC - if you need 3 pounds of buoyancy after a descent, you'll add the same amount of gas to get 3 pounds of bouyancy whether it is a dry suit or a BC.

Now, if it cuts into the safe minutes remaining, it will do it with a BC as well as a dry suit.

The issue also is that it bases time remaining on current use, so if the time remianing drops, it will give those minutes back the next time it recalculates current use.

The other thingwith a wisdom is that it calculates air time reamining and NDL remaining and displays whatever is less. So air time remaining really only shows at shallower depths, where gas consumption is already comparatively low. So the loss of a few minutes of air time remaining displayed is of no consequence. At depth where you are NDL limited, it is a total non issue.

I have about 500 dives on various wisdoms with a dry suit and it was never a problem. Once you get over the gee whiz factor it is not even a number you really look at - NDL remaining is a lot more useful. Gas planning during the dive is much better done with the pressure reading - are you where you need to be during the dive given te psi used and your current position along the dive plan?

At best the air time remaining number is something a fairly new diver can look at to get a ballpark indication of how a change in depth changes the air time remaining, and once you get a feel for that, you don't even need that particular piece of information.

 

[Pegger]

The amount of air required to make you neutral at depth is greater in a drysuit than lets say , a 3mm shorty, right?
I just wasn't sure as to whether managing that extra volume of air, drysuit or BCD, during a dive profile like a wreck would eat into your "safe dive mins." substantially or not.

Regards,
Steve

 

[nuisancepilot0]

I absolutely agree. But if you really want a real air-integrated bottom time based on actual useage you have another option to use a seperate bottle for inflation. I tap into a 13' pony (air not argon) with a y and isolation valves. I use my primary for bouyancy control but switch to the pony for safety stops on the last dive for the day. This ensures I use the pony on occasion to keep the air rotating and the first and second stages moving. I would caution you that you should keep the 12 hr min between dives (if you switch to your pony) between days due to the air used at your safety stop not being calculated for N2. I also stay for an additionall 3 minutes @ 20' for my last dive because of this. Using the new Wisdom 2 the stops are typically 20' (not 15') which was a suprise for my first dive with it.

One other option (what I used to do with single 72's) was to inflate manually during my exhale @ depth. You already "used" the air, so why not put it to good use? Not so much of an option with a suit though.

Pegger,

I'm not sure, but I think you may have a mistaken concept how your air intergrated computer works.

Your "safe dive time" given to you by your computer is a dynamic function that is constantly recalculated based upon the sampling rate of your PDC.

This calcualtion incorporates all of the breathing gas lost from the tank, both the gas you breathe and that gas used to inflate your dry suit.

The amount of gas required to inflate your dry suit is, for the most part, quite insignificant.

I've never thought about doing any calculations on the amount of gas required to manage a dry suit during a dive, but I dare say that it would be less than 2 cubic feet.

I think your concerns are unwarranted.

the K

 

[masterof0]

The amount of air required to make you neutral at depth is greater in a drysuit than lets say , a 3mm shorty, right?
I just wasn't sure as to whether managing that extra volume of air, drysuit or BCD, during a dive profile like a wreck would eat into your "safe dive mins." substantially or not.

Regards,
Steve

I disagree. The amount of air required to make you neutral is the same regardless of whether you are wearing a drysuit or shorty. The amount of air you should have in your bcd (or drysuit) should equal the amount of lead you have offsetting the weight of the air in your tanks. So at the start of the dive if you have 6lbs of air in your tank, you should be overweighted by six pound. To become neutral you are going to transfer six pounds of compressed air to your BC or drysuit which will expand. As you continue to use up air from your tank, you will become more positively buoyant which will offset the lead on your belt. To maintain neutral buoyancy, you will release some of the six pounds of air from your BC or drysuit which will offset the buoyancy you have gained from the air you have used from your tanks.

 

[ianr33]

Your forgetting about suit compression. A pair of swimming trunks will not lose buoyancy with depth. A thick wetsuit or a drysuit with thick undergarments will compress at depth requiring more air to be added.

Try dropping to 100 feet in a drysuit without adding air. You wouldnt like it!

 

[masterof0]

Dont disagree. But in the grand scheme of things, the amount of air required to remain neutral should have a minimal impact on your dive time. The amount of air required to offset 6lbs of lead is not going to be enough to swing your dive time by even 5 minutes.

Your forgetting about suit compression. A pair of swimming trunks will not lose buoyancy with depth. A thick wetsuit or a drysuit with thick undergarments will compress at depth requiring more air to be added.

Try dropping to 100 feet in a drysuit without adding air. You wouldnt like it!

 

[TSandM]

This baffles me . . . The "safe dive time remaining" display is simply advisory. If you put a bunch of gas in your drysuit and it drops temporarily, it's no biggie. If you are using up your gas because you're inflating and deflating your drysuit, you're running out of breathing gas, and you limit your dive accordingly. What kind of computer you use is not going to change the amount of gas you use for buoyancy, and your decision about your dive time is based on the gas you have and your decompression limits, not some flaky number your computer flashes at you.

 

[ianr33]

in the grand scheme of things, the amount of air required to remain neutral should have a minimal impact on your dive time.

Agree.

. The amount of air required to make you neutral is the same regardless of whether you are wearing a drysuit or shorty.

Disagree.

 

[masterof0]

ianr33...I agree with what you are saying. In theory, which is the point I am trying to make, is that the amount of air in your BC should be enough to offset the amount of lead you have on your belt. In practical application, depending on what suit you will be wearing you will get differing amounts of compression which will require different amounts of air, but the amount is not significant enough to argue for the sake of this thread.

 

[jlovold]

The best way to cope with your problems would be to get rid of your air-integrated computer, and get a regular pressure-gauge and a computer, or rather a bottomtimer, as you seem to be suffering from too much information and too little/wrong thinking...

The above is not meant as harsh as it may sound, but relying too much on electronics will not improve your diving-skills.

Also, if adjusting the buoyancy really messes up your air-consumption, you should think about maybe ditching 10-12 kgs of lead, as you must be grossly overweighted!