What would be a good thesis for an analysis of the poem "Fog Galleon"?
A thesis is an answer to a good question, so you need to start with a good question. For this poem, it might be something along the lines of: "What is Komunyakaa arguing for/against?"
The poem is about a town in his native Louisiana. He is returning to it and seeing it is all its non-glory. It's swampy, cloudy, and smoggy. The colors are generally grey and black, depressing. It has a paper mill, which emits a sulfurous smell that is, over time, toxic to humans. The mill--and everything else--has "scabrous residue." What he also sees is how the people who live there seem to be carrying on their day-to-day lives as though everything is all right, oblivious to the chemicals they inhale and ingest that are not only connected to their livelihoods, but which will also someday kill them.
He is disgusted, clearly, and perhaps a bit angry. What causes this sort of toxic life? Commerce and industrialization. There may even be a case to be made for "big money" as being his ultimate target--big money that doesn't care about the "little people" it has to kill to keep making profits.
I'd probably argue that he's targeting the rich who not only use the poor who are trapped there, working at the paper mill, but who are also slowly killing them.