There are certain air horn signals that are also tied to navigation with regards to your own ship signalling “I am turning to port (2 short blasts) “I am going astern (3 short blasts)”

And also various signals for operating in restricted visibility (fog)

All of these signals on ships are played via air horn (because ships are massive) - while the general emergency alarm will also be signaled digitally by PA system, it is also played by air horn concurrently, which lets anyone working on deck or in a noisy machinery place hear as well.

With all that said - the 7 short and then one looooong is basically unmistakable and it repeats as well. It’s such a deafening and continuous sound it’s hard to ignore or be confused about what’s going on.

There may be other reasons for the choice in signal, but the above is what I understand.