percussion from below? (like cracking an egg)
Likely extremely high waves that had a wavelength that exactly matched the length of the ship - the bow and stern got propped up by waves, with the center of the vessel out of the water, and it cracked.
So people do realize that there is precisely NO actual evidence there are any arms for Syria on this vessel?
Likely someone just saw the news of the incident and dramatic pictures and simply embellished the story.