In a world where interstellar travel is just beginning, and is expensive, does such technology make ocean-based travel obsolete? Does the ability to use air/space flight around the world make water based vessels not economical, or are there still reasons to use it?
Did planes make water based travel obsolete? Well, yes and no in the same time.
Before the planes were invented and able to cross Atlantic ocean, the only way to get from Europe to America was to board a ship and spend more than two weeks on the ocean.
Did ships vanish after we invented planes? Well, kind of.
Cargo ships are still in place, because they are really cheap. Cheapest way to get goods from China to America (or from Europe to America) is to load in on ship. Yes, you can use plane, but its costly.
Passenger ships are still in operation, but their goal is not to get you from place A to place B. Rather, current passenger ships aim on holiday passengers who want to visit several holiday destinations and then get home.
So, to answer your question: The ocean ships will be still around even if we travel to stars
We have airplanes, but non-perishable goods still travel the world on huge container ships, because they are simply a lot cheaper per ton transported.
If your spaceships can fly a ton of goods to the other side of the world for less money seagoing transport will be dead.
There will most likely still be ships for other uses: recreation, fishing and lurking nuclear subs.