So they sent the deck only, not the hull. When I unscrewed and removed the damaged deck, I discovered two further bits of damage:

On the left is the hull, showing a bit of broken off underdeck, as well as a broken screw hole. Middle is the faulty deck, with the broken off place visible around the screw hole. Right is the replacement deck.
(Note how surprised they all look. I imagine they are rarely exposed to scrutiny in quite this fashion.)


Two closer shots of the hull, showing the broken screw hole more clearly. 

To glue the screw hole back together, I had to take out the styrofoam and hold! Here's what the metal ballast looks like.
I got it all back together and am now the proud owner etc. Will go into the duck lake at Laurelhurst Park in a week or two, hopefully with pics and video to follow. 
I must say, the rigging is a devil to tie properly.