Answer: foundering

AnswerCrossword Clue
FOUNDERINGSinking fast
founderingFOUNDER, to become disabled
foundering(of a plan or undertaking) Fail or break down, typically as a result of a particular problem or setback
foundering(of a ship) Fill with water and sink
foundering(of a hoofed animal, esp. a horse or pony) Succumb to laminitis