This is an old saying dating back to the times when you would sail from England to India on a clipper, the fast ships that carried people and spices back and forth between the two countries.
And by the way, the clipper cabins are where the modern words Starboard and Portside for respectively right side and left side of the ship come from.
Clippers berthed alongside berths on their left side. Cabins on that side would just see the port from their windows or portholes, while at port. Whereas cabins on the right side would have a much freer view of the bay and the stars at night. Hence the words Portside and Starboard!
OK, so what about Booking one’s Sailing to Bombay? It’s a colloquial way to say that you commit to something such as a long journey to a far off destination.
Well, I’m committing, however I will not tell to what yet. Suffice to say that my trip will last exactly until my birthday thee months for now, and I want to accomplish something pretty challenging by then. I might flounder along the journey. The probability of success is tiny, yet the objective is big enough to inspire me to do all I can and some, just for its own sake.
I might fail, but being in the journey will have been enough to repay me without regrets. See you in Bombay!