The only 'ritual' involved in Fredo's reciting of the 'Hail Mary' was the one he had used since he was a kid fishing with his father & brothers...as he had explained to his nephew in an earlier scene. Every time he said the Hail Mary, he caught a fish.

That's all it meant to him, this last time too...it was NOT a gallant facing of the moment of his death...since he didn't know it was coming.

When Connie called Anthony off the boat, he promised the boy they'd go fishing again 'tomorrow'...and that he'd catch a fish using their 'secret'.

If Fredo had even the slightest inkling that his life might be in danger once left along with Al, he would've gotten off that boat as quickly as he could. He trusted Al, he trusted Michael...he thought he was forgiven.

Nothing 'came together' at the moment Anthony was called away. If we just look at Fredo in just about every single scene, from both Parts I and II...leading up to this last one, it is so clear that he just did not have it in him to face and accept death so calmly and bravely.

Get with it, folks...he did not know.

Best,
Apple