From the Halcyon FAQ...
To further determine appropriate lift capacity, its important to understand a few other concepts about proper weighting.
Proper weighting requires that a diver be able to maintain a safety or deco stop at the end of a dive and with a nearly empty tank. This balance becomes critical during extended gas-sharing scenarios, when a buddy team might find their cylinder(s) nearly depleted (and extremely buoyant). A simple test can be carried out in a confined, shallow water dive site. Divers should be able to remain neutral at 10 ft (3 m) with only 500 psi (35 bar) in their tank; the wing should be empty or nearly empty. If you cant maintain neutral buoyancy, adjust weight accordingly. Avoid the common temptation to wear excessive weight. In an over-weighted situation, the divers need for buoyancy will increase by whatever amount they are over weighted.
Now that you are certain your weighting is correct, it is a simple matter to calculate your variable buoyancy needs. Your required lift has little to do with the amount of weight you are wearing, but instead is tied to your variable buoyancy. A divers variable buoyancy is determined by the weight of the gas in their tank plus the loss of buoyancy from their wetsuit (or neoprene dry suit) due to compression at depth. Divers wearing a trilaminate (shell-type) or crushed neoprene dry suit do not experience significant compression, making this calculation easier. The average ¼ inch (approx. 5 mm) Farmer John wetsuit loses about 9 lb. (4 kg) of buoyancy at 100 feet (30 m). Meanwhile, an 80 cf tank is approximately 3 lb. (1.3 kg) negative when full; that tank will be about 3 lb (1.3kg) positive when empty. So, when wearing an Al 80 tank and a ¼ inch (5 mm) Farmer John wetsuit, the variation in buoyancy from the start of the dive (at depth with a full tank) to the end of the dive (at 10 ft./3 m with 500 psi/35 bar) will be about 15 lb. (6.8 kg). Divers using such a configuration and weighted to be neutral at the end of the dive could need to add approximately 15 lb (6.8kg) of gas at depth in order to be neutral. Please note there are a range of factors that can affect required buoyancy. Divers should seek appropriate training to ensure they understand these variables.
Given that most divers would prefer to be more than just neutral at the surface, doubling their variable buoyancy requirement is one way to support additional surface floatation. In this case, one might select the Eclipse 30. There are a few other factors that can increase your lift requirements. One is a desire for your BC to float your gear without you in it. It is not necessarily a requirement, but it can be of benefitparticularly for divers that dive from inflatable boats or don their gear in the water. You will determine this lift requirement by adding together the lift needed to float the specific tank you use and how much weight is on the system.
As with any change in ones diving equipment, it is recommended that all divers make a few dives with their buddy in controlled conditions while establishing how these changes will affect in-water performance. Careful wing selection, together with proper training will help ensure adequate lift capacity while avoiding the excessive drag and instability caused by unnecessarily large or buoyant systems. Poorly chosen systems can be very detrimental to buoyancy and trim control while decreasing efficiency and increasing effort while diving.
To further determine appropriate lift capacity, its important to understand a few other concepts about proper weighting.
Proper weighting requires that a diver be able to maintain a safety or deco stop at the end of a dive and with a nearly empty tank. This balance becomes critical during extended gas-sharing scenarios, when a buddy team might find their cylinder(s) nearly depleted (and extremely buoyant). A simple test can be carried out in a confined, shallow water dive site. Divers should be able to remain neutral at 10 ft (3 m) with only 500 psi (35 bar) in their tank; the wing should be empty or nearly empty. If you cant maintain neutral buoyancy, adjust weight accordingly. Avoid the common temptation to wear excessive weight. In an over-weighted situation, the divers need for buoyancy will increase by whatever amount they are over weighted.
Now that you are certain your weighting is correct, it is a simple matter to calculate your variable buoyancy needs. Your required lift has little to do with the amount of weight you are wearing, but instead is tied to your variable buoyancy. A divers variable buoyancy is determined by the weight of the gas in their tank plus the loss of buoyancy from their wetsuit (or neoprene dry suit) due to compression at depth. Divers wearing a trilaminate (shell-type) or crushed neoprene dry suit do not experience significant compression, making this calculation easier. The average ¼ inch (approx. 5 mm) Farmer John wetsuit loses about 9 lb. (4 kg) of buoyancy at 100 feet (30 m). Meanwhile, an 80 cf tank is approximately 3 lb. (1.3 kg) negative when full; that tank will be about 3 lb (1.3kg) positive when empty. So, when wearing an Al 80 tank and a ¼ inch (5 mm) Farmer John wetsuit, the variation in buoyancy from the start of the dive (at depth with a full tank) to the end of the dive (at 10 ft./3 m with 500 psi/35 bar) will be about 15 lb. (6.8 kg). Divers using such a configuration and weighted to be neutral at the end of the dive could need to add approximately 15 lb (6.8kg) of gas at depth in order to be neutral. Please note there are a range of factors that can affect required buoyancy. Divers should seek appropriate training to ensure they understand these variables.
Given that most divers would prefer to be more than just neutral at the surface, doubling their variable buoyancy requirement is one way to support additional surface floatation. In this case, one might select the Eclipse 30. There are a few other factors that can increase your lift requirements. One is a desire for your BC to float your gear without you in it. It is not necessarily a requirement, but it can be of benefitparticularly for divers that dive from inflatable boats or don their gear in the water. You will determine this lift requirement by adding together the lift needed to float the specific tank you use and how much weight is on the system.
As with any change in ones diving equipment, it is recommended that all divers make a few dives with their buddy in controlled conditions while establishing how these changes will affect in-water performance. Careful wing selection, together with proper training will help ensure adequate lift capacity while avoiding the excessive drag and instability caused by unnecessarily large or buoyant systems. Poorly chosen systems can be very detrimental to buoyancy and trim control while decreasing efficiency and increasing effort while diving.
