craschworks

Underwater gliders work by being buoyantly nearly neutral while near the water’s surface, so that they sink slowly down. Very slowly – full steam ahead is under one knot. As they sink, an internal weight is shifted toward the lateral direction the vehicle should go – if you want to go straight, just shift the weight forward to tilt the nose down a bit. Then to rise, pump an oil contained inside the hull into external sacks – this simple maneuver increases the craft’s volume, and thus lowers its density just enough that now the surrounding water wants to push it upward.