Bucket of nails and a giant fan

[Spiff]

Been trying to remember this for a while. It's a movie about a guy who worms his way into a couple lives (if I remember rightly he's actually the child of one of them). There's a fight at the end which ends with somebody throwing a bucket of nails into a giant fan (I think it might have been a swamp boat) with obvious results. Likely to be late eighties or early nineties (but I could be wrong on that)