[PSUBS-MAILIST] Ambient pressure design considerations

My intent is to build a small ambient pressure dry sub for recreational use in the fresh water lakes of my area. The conceptual design would be limited (by pressure switch) to a depth of 33 feet (aproximately). I need to keep the sub as small and hydrodynamic as possible to minimize power requirements. The sub will remain slightly positive in boyancy and will power-dive using dive planes which will be linked via a mechanical mixer to provide both pitch and roll control. A control stick and rudder pedals would be incorporated as in an airplane (like flying under water). If the craft exceeds the depth of 33 feet the pressure switch will deactivate the motor thereby forcing it to ascend back into its window of operation. An emergency override switch will allow the use of power beyond the 33 ft. limit. My plan is to breathe compressed air through a two-stage regulator (scuba) with an exhaust duct to carry exhaled gasses to the outside of the sub.

By exhausting the exhaled air to the outside I hope to minimize moisture condensate and CO2 buildup inside the sub, however, I realize in order for this to work it is absolutely essential that the air pressure inside the sub remain ambient to the pressure outside the sub.

I have to go for now, but I have more questions relative to ambient pressure and boyancy to come in another post. I'm not looking for ridicule, but if you have some constructive criticism or see cause for concern with my plans thus far, I would value your input.