Boats is a tiny poem built around one extended metaphor. A woman's heart is pictured as the ocean, and the man she loves is a boat moving across it. Love itself is the captain, the one in charge who keeps that boat from sinking.
The speaker seems to see love as something steadying rather than wild. An ocean can be vast, deep, and unpredictable, and the poem hints that a heart can be like that too. The boat on its own might drift or go under, but love steers. That gives the lines a hopeful, reassuring feeling, as if the relationship survives because of something bigger than either person.
The mood is gentle and simple. The short lines rock back and forth a little like waves, and the rhyme of "boat" and "afloat" closes the poem with a calm, satisfied click. It reads like a small, sincere image of devotion.