Doing multiple bouyancy checks

[swimmer_spe]

I have 3 different immersion suits, 4 if you could my swim suit, that I will be using at a pool to dial in my weights.

The pool is fresh water.

I know that I should have about 500 psi in the tank, however, I see 2 problems doing that:
1) 4-6 dives in a pool. I will be going in and out of the pool and I am certain that I will have drained down my tanks to below a point that I could breath from. I want some safety so that the lifeguard does not have to come in and rescue my sorry @$$.

2) It is ridiculously cold out. It is hovering around -10 C to -20 C. I do not have a place that is heated that I could put the tanks so that I could relieve that much pressure. I am certain that cracking the valve at this temperature would eventually cause a freeze up of the valve.

So, How do I do this? I want to go in with my dry suit (Change the layers a few times) and my wetsuits and get some good numbers for my weights.

I plan to be diving in fresh water this summer anyways.

Oh, and, what is the basic math for figuring out what I need for fresh and for salt water?

 

[ajduplessis]

Add 4 pounds when diving salt.

Start with a drysuit. Dive the tank down the 500 and surface. Use a friend to help you with loose wieghts poolside with pen and paper. You should be able to get your weight dailed in within minutes. Get out and change exposure, redo buoyancy test and document. A buoyancy check is done on the surface. It should take little time and good luck with the cold.

 

[Rich Keller]

The dry suit will have to be tested in the water with each different configuration. The wet suit only needs to be tested in the water once. You could then put each type of wet suit into a net bag and add weights to see how much each suit needs to sink then just do the math from your original wet suit test.

 

[tbone1004]

buy a cheap luggage scale, take the tank with whateve rpressure is in it, deflate the bc completely and stick it in the pool and figure out how much it weighs. Air is about .08lbs/cf so you can calculate how much of that weight is air, subtract total gas volume from the weight so it would be as if you had absolutely 0 air in the tank.

After this, lay the scuba gear on the side of the pool so the regulator is hanging into the water. Wearing full exposure protection, MFS, hood, gloves etc, hop in the pool. Have a full stack of weight belts, 2x 1lb, 2x 2lb, 2x 3lb, 2x 4lb in weight weights, not bags, and a weight belt. Hop in the pool and hang onto the side, tuck your knees so it is like you are sitting and you will stay sucked to the wall. Stack the weight on the belt, so just through one slot on the belt in 2lb incremements until you can sink and breathe comfortably. It is important to make sure your wetsuits are flooded for this to make sure all of the air is out of them. Do this for each suit including your drysuit. Drysuit may take a bit of adjustment after that, but that is the most accurate way to do your weight checks for wetsuits. Take total weigh to sink you in your exposure suits, and subtract from weight of the rig less air.

 

[NAM001]

I did just what tbone above has said. its surprising how much different the scale tells you from the huron table. For my rig I ahve an H valve and of course 2 regs. I do it on a steel plate to insure it will sink. then i comp for the plate and ignore the wing. It was mentioned to bag the suit and throw in lead till it sunk. Sounds good to me. I wore each of the suits but it was summer. The dry suit was the biggy. I use a tls 350 and with 300g undies i needed 38# to get me down. With the 100g undies it tok 19# to get me down. When i was all done i just made a conversion table. suit a to suit b is add 3# ect. I also did the weight thing with nothing on to see what i contributed. I was 3 positive. each year i just check me and then correct all weighting by that amount. So out of that my dry suit was say 19 light and 3 of that was me, 16 was the 100g undies. When i fininshed i found that all i had to do to go to salt water was change to a different suit as opposed to adding lead. I did the tank measurement with a full tank so i had a definate number for that and then did the calc for empty tank (8# per 100 cuft).. when it was all over i had info that said ds with 300g 38 light, ds with 100g 19 light fj wet suit 19 ilght, 3/2 shorty 9 light. full tank with regs and h valve -15. you know what your plate weighs so you can pick and choose parts to get what ever buoyancy you want. As far as the tanks goes I did the same measurement for all the tanks. I measured the (plate and harness) seperately from the tank with a 10 # weight attached to it. the scale said 17 so I knew the plate was 7. The wings I count as neutral, however knowing the other numbers i know what wing to use.

 

[TSandM]

Figure out the tank factor for your tank. 13 cubic feet of air is approximately one pound. If the tank is full, you weight yourself neutral at the surface, and add 1 pound for each 13 cubic feet of gas you are willing to use (so, for an Al80, about five pounds). So you don't have to do the weight checks with an empty tank!

 

[swimmer_spe]

Figure out the tank factor for your tank. 13 cubic feet of air is approximately one pound. If the tank is full, you weight yourself neutral at the surface, and add 1 pound for each 13 cubic feet of gas you are willing to use (so, for an Al80, about five pounds). So you don't have to do the weight checks with an empty tank!

I am diving with a steel 120.

 

[tbone1004]

which one? not all 120's are actually 120cf which is why you have to do appropriate math. The most accurate way is to do it like I said above, or actually slightly more accurate is to get a mesh gear bag and take all of your neoprene exposure protection and put lead on it until it sinks, doesn't help with the drysuit though.