<< "So how come a ship built in 1969 is sinking because it hit a chunk of ice small enough not to appear on radar?" >>
Umm, because not all obstacles in the ocean are visible on radar? Sheet ice might well not show, but besides that point, it's not at all clear that it *was* ice - The article made clear, if you'll read for comprehension, that object was "unknown." That could mean any manner of obstruction, from a floating cargo container washed off a ship (rather more common than you'd think), to a large log (My submarine nailed a floater like that 150 miles off of Hawaii - made a god-awful noise when we hit it!), to an uncharted rock, to yes, maybe a hunk of ice.
Anyway, M/V Explorer, in at least one, possible two, of the Daily Mail images, was clearly under power - her *own* power, despite the exagerated list. I'm not at all convinced that she's actually due to sink, though she's in dire straits, and a spot of bad weather (very common down thataway) could do for her in a jiffy.