What unusual aspect of the sailing ship do the sailors notice?

In the poem "The Rime of the Ancient Mariner" by Samuel Taylor Coleridge, the poet describes the sailing ship as "as idle as a painted ship upon a painted ocean". This sentence highlights the unusual fact that the sailors notice that the wind has completely stopped blowing. The sailing ship has now reached the silent sea. As a result, the sailing ship appears to be stuck at one place and not to be moving at all and is as still as the painting of a ship.