Well, the most interesting and significant figure of speech to my mind in this brilliant poem is the metaphor that compares the sea that the yachts speed over to a restless mass of human bodies that the yachts must cut through ruthlessly. The fact that this metaphor is only introduced half way through the poem has the effect of turning what starts off to appear to be a pleasant poem into something slightly more sinister and disturbing. Consider the metaphor and how it is introduced:
Arms with hands grasping seek to clutch at the prows
Bodies thrown recklessly in the way are cut aside.
It is a sea of faces about them in agony, in despair
The struggle that the yachts engage in can thus be read symbolically to refer to the way in which the struggle in life involves trampling down those who are beneath you or lesser than you to ensure your own survival. The fact that this poem was written in the wake of the 1930s Great Depression gives such an image a rather unsettling picture of what was happening during that time, as the relentless masses were crushed by the rich elite who sailed over them to continue in their struggle of the survival of the fittest.