Proper ballast tanks are the solution (~30% reserve buoyancy). Some additional thoughts on lift bags: 1. It usually takes two to maintain a level condition and cause your hatch to be exposed at the surface. 2. Bags need to be attached very low on the sub, especially when looking at a PSUB the size of a K-350. 3. Lift bags should be fully inflated at the bottom to maintain a controlled ascent, otherwise a. The ascent will be under constant acceleration (i.e. continually speeding up) b. When surfaced rapidly, the bags/sub may broach and the bubble is lost resulting in the sub sinking once again (and potentially injuring the survivors inside). R/Jay -----Original Message----- To open the hatch at -1 ft seems a better solution = drop weight. 20 ft = 6 meter depth - hatch of 2ft diameter has a area of 0,283 m2 so at 20 ft the pressure on the hatch wil be stil 1,7 ts. Means in even a full dry boat with just destroyd mbt you have to flood it and destroy all the interior by saltwater.. "If you have air a to blow an lift bag - means you have still air to blow the mbt" Lift bag is a good thing to have - on shore in store at the car close to the diving spot. vbr Carsten |