3. Identify an example of metaphor: explain which two things are being compared

in this poem:
The shadows of the ships
Rock on the crest
In the low blue lustre
Of the tardy and the soft inrolling tide.
A long brown bar at the dip of the sky
Puts an arm of sand in the span of salt.
The lucid and endless wrinkles
Draw in, lapse and withdraw.
Wavelets crumble and white spent bubbles
Wash on the floor of the beach.
Rocking on the crest
In the low blue lustre
Are the shadows of the ships.