The metal pressure vessels are very negatively buoyant. The bathyscaphe Trieste used 32000 gallons of gasoline to achieve positive buoyancy. Modern DSVs use inc

The metal pressure vessels are very negatively buoyant. The bathyscaphe Trieste used 32000 gallons of gasoline to achieve positive buoyancy. Modern DSVs use incredibly expensive and fragile syntactic foam. A CFRP pressure vessel can be naturally positively buoyant, or much closer to it. Titan's dry weight was less than DSV Limiting Factor, despite having much greater internal volume and carrying 3 more people. Also, being able to load and launch in the water, rather than loading on the deck and needing a human rated crane to launch as most DSVs do, probably saved a lot of money operating Titan.