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. 

What is a good thesis for Yusef Komunyakaa's poem "Fog Galleon"?

In 24 lines, Yusef Komunyakaa writes with unveiled disgust of the pollution caused by commerce and industrial waste. He clearly condemns the filth and poison that floats in this dreary, swampy area. (As it is a swamp, the waste will hang in the humid air, slowly poisoning the inhabitants.) The "phantom ship" he speaks of is the paper mill, which emits a sulfurous gas; the air smells of rotten eggs (he says it "smells like the world's oldest anger"), and long exposure to this gas causes respiratory problems, as well as eye irritation, even at low levels (higher levels can cause nerve damage). 

He is in a taxicab, "interfaced / With a dead phosphorescence." Phosphorescence carries a double meaning here: it is both light that is emitted from something without any discernible source of heat and latent radiation. In the first case, the city he's watching is black and dreary, and the people have been lulled into acceptance; the city's and the people's "phosphorescence" is dead. With the second meaning, he implies that the town is as deadly as though it were radioactive.

At the end, he speaks of

chemicals
That turn workers into pulp
When they fall into vats
Of steamy serenity.

The workers whose labor produces the pollution collect their paychecks and go about their lives, oblivious to the fact that they are killing themselves.

What Komunyakaa is telling society is that we are destroying ourselves with our own pollution. This poem is a call for us to help ourselves.