I have a reference sheet in my logbook.
Here's how to create one:
Weigh yourself. Write it down.
In a pool, determine how much weight you need to sink you in your bathing suit, fins and mask with about a half-breath in your lungs. Put another way, how much weight can you just barely float with if you have a full breath? Don't kick! Write that down as your "base" weight requirement. (This is typically between zero and eight pounds, depending on your specific density).
Now take your BC, make sure it is fully deflated and has the stuff you carry on every dive attached (knife, backup light, etc). If you only dive AL 80's, go ahead and attach the tank and regulator too. Drain the tank to 500 psi. (if you dive more than one kind of tank don't attach it at this time - we'll get to that later). Weigh the BC & attachments. Write it down.
See how much weight you need to sink the BC - usually about 2 pounds (3 or 4 with AL 80@500 psi attached). Write that down. If you use more than one BC (I use a different BC in tropical waters than at home, and a BP/W for doubles) do the same for each.
For each wetsuit you use, record its dry weight, then put it in the pool and stack weights on it until it just barely sinks. If you have a farmer John, or a vest or hood, do this for each separate piece of neoprene. (Make sure there's no trapped air) Record the weight required for each suit piece.
For a drysuit, you'll have to put that on, dump it to the underwear loft you want to use diving, and see how much weight you need to sink it. Record both the weight of the suit and underwear, and how much weight you need to sink it for each underwear configuration you use.
Accessories: Record the weight of each accessory. For accesories that float, record the weight required to sink each. For those that sink, you'll need to construct a buoyancy scale to see how negative they are. I use a four foot long aluminum tent pole suspended in the middle, hung from the diving board. On one end I hang the accessory (under water) I'm measuring, on the other a mesh bag (under water) into which I put weights until balanced. Record negative buoyancy as negative numbers.
Tanks: Make tank measurements at 500 psi or less, with regulator attached. Weigh each tank with regulator attached and record that. For aluminum tanks, see how much weight you need to just sink it - typically 1 or 2 pounds, depending on your regulator. For steel tanks use the same balance system you used for negatively buoyant accessories and record each tank's negative buoyancy.
Once this is done, you now can create your buoyancy chart, with the weight and buoyancy of you and each piece of gear you dive with.
To see how much weight you need for any particular combination of gear, just add everything up algebraically and there you have your perfect fresh water weighting, every time. For salt water, just add up the total weight of you and all your gear, multiply by 2.5% and add that to the fresh water weighting to get your perfect salt water weighting. Every time. No guesswork.
I know this sounds like a lot of work, but it's really more fun than work, and you only have to do it once for each piece of gear you use, and once for each new piece of gear you add to your total diving gear collection.
And believe me, it sure is nice to be able to hit the water perfectly weighted every time, no guesswork, no uncomfortable safety stops, no overweighting either...
Rick
