Normally a person flounders in water and a ship founders. A ship could also flounder, though you have to suspect this was a malapropism in the report. It's hard to imagine a person foundering, and I wonder whether a flounder could do either.

Pre-prepared is one of these things that looks pleonastic but does make sense. You prepare a meal at 6 o'clock to serve it at 7, or you can prepare it beforehand, in the morning or the previous day perhaps. I agree that though there may be a temptation to say pre-prepare, a longer-winded form would be better.