Ash-Shuraa 42:32
The verse sets three scenes side by side: (1) the ship floats "like mountains" (ka-l-aʿlām); (2) when the wind stops, the ship remains "rawākid" (stilled) upon the back of the water; (3) sometimes the ship is sunk, sometimes it is pardoned.
وَمِنْ ءَايَـٰتِهِ ٱلْجَوَارِ فِى ٱلْبَحْرِ كَٱلْأَعْلَـٰمِ
And of His signs are the ships sailing the sea like flags
Ash-Shuraa 42:32 · Translation: talal-itani
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The verse's simile (ka-l-aʿlām) is observational in register: a great human-made mass can stand upon water like a mountain. The next clause recalls that this motion is conditional, bound to the wind — greatness is not of itself motion. The third clause opens a moral dimension: floating, sinking, and pardon all take place within the same sea.
Observation
From the side of physics, the standing of a ship upon the water depends on buoyancy: the weight of water equal to the volume a body displaces pushes that body upward. If a ship displaces a volume of water whose weight equals its own total weight, it does not sink — a principle recorded by Archimedes and the foundation of modern naval engineering. Motion is a separate question: a ship advances only through an external force (wind, current, engine). On historical sailing ships the stopping of the wind obliged the ship to stand on its course; the verse's "yuskini-r-rīḥa fa-yaẓlalna rawākid" (He stills the wind and they stand pausing) is the record of this observation. A great load sitting on still water (not sinking + not moving at the same time) is physically the concurrent working of two distinct principles: buoyancy on the vertical axis, absence of thrust on the horizontal. The verse holds both within a single scene.
Exegesis
Classical exegetes particularly stress the verse's phrase "ṣabbārin shakūr" (much-patient, much-thankful): al-Rāzī says patience is the stance taken when the wind stops, and thankfulness the stance taken when it blows — the verse reads the ship as a figure for life. Al-Zamakhsharī underlines that "aʿlām" (signs, mountains) can answer to both mountains and tall masts, and that the verse therefore loads both the sense of visible greatness and of being-a-sign (āya) onto the same word. Al-Qurṭubī notes that the verse's closing line ("aw yūbiqhunna bimā kasabū wa yaʿfu ʿan kathīr") calls to humility — the distance between a ship's floating and its sinking is as slender as the distance between earning and pardon.
Sources
Tafsīr: al-Rāzī · Mafātīḥ al-Ghayb; al-Zamakhsharī · al-Kashshāf; al-Qurṭubī · al-Jāmiʿ li-Aḥkām al-Qurʾān. Science: the Archimedean principle and naval engineering; history of sailing ships; standard literature in classical physics on buoyancy and the independence of thrust.