I found it in a publication here:
Few people know where it came from that the third toast is drunk for those who are in the sea. The fact is that there was no such connection before as we have now. They drank the first toast for the living, the second toast for the dead, and the third toast for the sailors, because they did not know whether they were alive or not.
The sailors of Schrödinger, their mother. Where to get a cat...