If the staining has not wicked up the hatch boards too far, one can remove the offending area and replace it with a section of solid teak. This was a fast and satisfactory solution for me that has lasted for several years. It has the added advantage of sealing off the lower end of the board(s) to prevent moisture wicking up the plywood.
In addition, I have a pair of heavy clear lexan boards (to keep out the wildlife) that are used when varnishing the teak boards. They are useful when I need more light and less privacy. I am told that they will stop bullets, but have not had occasion to try!
As Thor has done, I replaced my hatch boards with smoked plexiglass.
It admits a lot of light, but is hard to see into the cabin from outside.
It also ignores water.
Just find a good plastic fabricator, and dont forget to bring the old boards as a template.
You will wish to put a small overlapping piece on the inside where they join, and have them bevelled where they meet so water drains outward.
I also put a 4" square reinforcing piece where the door lock attaches.
I think that my hatch boards are 1/2", but they are the same as the plywood they are replacing.
I used P&A Plastics at 150 Main St, Hamilton, and was very happy. I think they charged around $350 but ask first.