The Intrepid is a two-person sub with a lot of windows.   The hull thickness is 0.25 inches and has saddle bag type ballast soft tanks on each side.   Batteries are carried in pods on each side.   They are 6 volt golf cart batteries with no Hydrocaps at present.   The windows are 0.5 inch Lexan and have a fairly large unsupported diameter.   The ascent-decent is done with a central tank with a 12-volt gear pump that pumps water in and out.   It has dive planes but Harold said that they are useless because of the slow forward velocity.   Thrust is vectored via hydraulic cylinder that is in-turn driven by a motor gear-system inside the hull.   Thus all steering is done electrically.   The hatch seal is a single O-ring groove 3/16 inch in diameter.   He has a small viewport on the hatch, has made over 100 dives and has taken the boat down to 100 feet.   He has external lighting that he designed using test tubes filled with halogen bulbs; strange but it works well for him.   He uses an external flux-gate compass.