I never tried it solo but I imagine not. One of the coolest parts of the game is how the crew synergizes and how everyone gets to do different things to help out. For instance, I was playing with my mate and manning the ship while he was in the crow's nest guiding where I was going.
At another point, we found an island with buried treasure but needed a vantage position to spot exactly where they chests were so anchored the ship next to the shore. I went on foot and he remained on the crow's nest and was telling me where to dig.
We also sank on our ship's maiden voyage.
It might be fun solo but the appeal is really to be part of a pirate crew. Even just two is a lot more fun. A whole crew (6-8 people) is honestly a blast.
Also, yeah, sloops are for 1-2 players but are still easier to manage with two.