Pressure lock marine horn

1. A marine horn comprising a housing having a horn path from a sound source to an outlet, said horn path having a pressure lock chamber blocking water which has ingressed said outlet from reaching said sound source along said horn path, wherein said horn path is a tortuous path extending from a first upper segment at said sound source to a lower segment and then to a second upper segment at said outlet, said lower segment being gravitationally below each of said first and second upper segments, said pressure lock chamber being between said lower segment and said first upper segment, wherein said outlet is gravitationally above said lower segment and second upper segment, such that water ingressing said outlet flows gravitationally downhill to said second upper segment and said lower segment without climbing uphill to said second upper segment nor said lower segment.

2. The marine horn according to claim 1 wherein said housing has a water drain port at said lower segment draining water therefrom, wherein said outlet is gravitationally above said water drain port.

3. The marine horn according to claim 2 wherein water ingresses said outlet and flows to said lower segment and compresses air in said horn path until stopped by pressure lock, whereafter water drains through said water drain port from said lower segment.

4. The marine horn according to claim 1 wherein said horn path is a spiral trumpet horn path.

5. The marine horn according to claim 1 wherein said lower segment collects water which has ingressed said outlet, which water at a given level spans transversely across said horn path and closes and pressure locks the section of said horn path from said given level to said sound source and provides said pressure lock chamber therebetween.

6. The marine horn according to claim 1 comprising an acoustically permeable membrane covering said outlet and blocking some water, including at least one of low pressure water and low speed water, from ingressing said outlet.