I am 6'2/ weight 255-260lbs. I am going to be diving double 120;s soon. I have the oms bp/w set up now. And i want to get the same set up for doubles. Can anyone suggest what lift i would need with this kind of weight. I will be diving dry, if that helps also.
Just cuz I need the practice...
Wing capacity is *NOT* primarily a function of the cylinders you are using.
Gas volume plays a part, but Exposure suit buoyancy is a key element.
The "right" wing for 2 x 120's in warm water with a thin undergarment won't be the "right" choice for cold water with a more buoyant set of undies.
The assumptions I use for sizing a doubles wing:
The diver may need to breathe his back gas down to zero.
The diver may need to inflate his dry suit during a long shallow stop.
If the diver needs the option of using all of his backgas he needs to start the dive negative by at least the weight of his gas. 2 x 120 * .08 = 19.2 Lets call it 20 lbs for air or nitrox.
If the diver wants to be able to add a bit of gas to their suit at their shallow stop they need to add 2-3 lbs to the weight of the gas.
20 + 3 = 23.
Our example diver is now starting the dive negative by 23 lbs, and will need to have use 23 lbs of the capacity of his wing to remain at the surface.
Our diver needs in reserve enough capacity to deal with a total failure of his drysuit. While it's unlikely that a diver could loose 100% of the buoyancy, they cannot loose more than that.
Lets say our diver has tested their suit and knows that with minimum gas in it 24 lbs of ballast is required to get neutral.
20 lbs of gas + 3 lbs of "extra" suit inflation + 24 lbs of suit buoyancy = 47 lbs.
Our example diver needs a wing a bit bigger than 47 lbs.
Our diver also needs to be able to float their rig at the surface with full cylinders.
If 100% of the required ballast is on the rig, i.e. back plate, harness, regulators, empty cylinders, tank bands, v weights etc. then the rig will also be a maximum of 47lbs. negative.
The actual required ballast with empty cylinders in this example is 27 lbs, suit buoyancy + extra inflation. If the rig represents 27 lbs of ballast with empty tanks when you add back in the 20 lbs of gas the rig is now 47 lbs negative.
It should be pretty clear that the buoyancy of the divers suit is a key element in determining the required wing capacity, and in determining total weighting.
To test you suit:
Put on your thickest undies and suit.
Find some neck deep water and jump in holding a bag filled with too much lead.
Vent the suit while neck deep.
Remove lead from the bag until you just sink when you pick up your feet.
Weight the bag of lead.
If you do this test in fresh water you need to add 1 lbs of lead for every 40 lbs of diver. For you that's about 6-7 lbs.
Tobin
