Thanks for that, 3 holer. Some super stuff there by me, and I'm in complete agreement with everything I say. There's one matter that's not covered in the passages you have selected, which is that Mahon was idiot.
But putting the idiot to one side (which is where he was from the outset): Were they VMC when they hit the mountain:
(a) As a matter of fact, or, if not:
(b) According to the captain's genuine belief ?