The Submarine Snorkel

The whole device is a tube and one valve that must close before water gets in and open again immediately after.

1. Make a vertical tube with a chamber at the top containing a buoyant float and a seat above it.
2. Arrange the float so that rising water lifts it onto the seat and seals the intake.
3. Test by raising the water level slowly and confirming the seal, then lowering it and confirming the float drops away cleanly.
4. Now raise the level FAST, simulating a wave slapping over the head, and watch the timing.

The valve must be fast enough to beat a wave and light enough to reopen the instant the wave passes. Too heavy and it floods; too light and it chatters shut on spray, cutting the engines repeatedly.

The intake is only half the mast. The exhaust has to push against the sea.

1. Compute the water pressure at the exhaust outlet for periscope depth — a few metres down.
2. Compare that with the exhaust back-pressure a diesel will tolerate.
3. Now submerge a tube discharging air a metre under water and observe the surface.

The engine must push its exhaust out against sea pressure, which costs power and limits how deep the boat can snorkel — a few metres, no more. Deeper and the back-pressure chokes the engine.

Then look at the surface: the exhaust bubbles up as a visible, continuous trail of froth and haze, and the diesel smoke is visible and smellable downwind. A snorkelling submarine is quieter than a surfaced one and it is not hidden.

Every constraint in this blueprint traces to one fact, and removing that fact removes them all.

1. List everything the snorkel exists to serve: the diesel needs oxygen, the batteries need charging, the charging needs the diesel.
2. Now assume a power source that needs no oxygen at all.
3. Cross out every constraint that disappears.

Nearly all of them go. No intake, no exhaust, no mast, no depth limit imposed by back-pressure, no radar-detectable head, no periodic exposure at a predictable interval. The boat's endurance stops being set by fuel and battery and starts being set by food and crew.

What remains is the crew's own oxygen, and that is solved by electrolysing seawater and scrubbing carbon dioxide — using electrical power, which is now abundant.