That’s not a good comparison, sailing, to space travel. The distances are orders of magnitude different. A sailor could leave harbor and arrive somewhere within their lifetime, and have enough of it left to set up shop and build some kind of life. With current propulsion technology you could leave earth today and not arrive at our closest neighboring solar system (Alpha Centauri) in 372 generations (assuming EVERYONE lived to 100 in every generation). That’s 37,200 years one way. Think about it this way, the humans that left on a generation ship for Alpha Centauri, would leave humans, and very possibly arrive as a different branch in our developmental tree. That’s how much time it would take without some super luminal propulsion.