Personally, I would look at a zoom for your everyday lens. Especially on a small boat, where you have limited room to move around in relation to your subject.
I have the Sigma 30mm f/1.4. I like it a lot for people and pets on a crop body camera (which your a6000 is), but I rarely take it on the water. It's a little tight for shooting fish and people pics on the skiff.
For a first upgrade from kit lenses, I'd be looking at a good quality f/2.8 standard zoom, like the 17-50mm Sigma. That's the equivalent of around 27-80mm full-frame. In other words, very similar to the 24-70mm f/2.8 lenses that are kind of the foundation of a good lens selection for a full-frame camera.
You don't really need anything faster than f/2.8 for 99% of outdoor shooting, so I wouldn't be worrying about f/1.4 and 1.8 lenses.
Image stabilization, on the other hand, is a big deal in my experience. I find I'm frequently shooting right on the edge of being able to hold the camera still at dawn and dusk, and image stabilization makes a real difference there.
I used to use the Sigma 10-20mm zoom a ton on crop body cameras. It's great for fish pics and other stuff actually on the boat. But its uses are pretty limited just because it's so wide.
If I could have any three lens types I wanted, it would be an f/4 or faster wide zoom (10-20mm crop or 16-35mm full frame), an f/2.8 standard zoom (17-50mm crop or 24-70 full frame), and an f/2.8 70-200mm, all with image stabilization. If I could add more specialized lenses, I'd start with a longer telephoto, like a 300mm or a 100-400mm, and then a good prime portrait lens like 50mm or 85mm f/1.2 or 1.4.