Two men are in blue life jackets and sitting on innertubes with 'Crusher' written on them in the middle of a body of water.
Two men sit on innertubes in the middle of a body of water.
Sit and sitting are equivalent terms in this situation; each man is on an innerrtube.
Two men in blue life jackets are a type of two men.
Sit on innertubes is a rephrasing of sitting on innertubes