boatdrink,
When I bought my Funship last summer.......the sink bottom was broken just like yours is..........I ordered a new one from Four Winns..........cost was about $40...........there is a bulk head in my head compartment that is held in by a couple of trim screws.......removing those screws allowed me to get the bulk out and get under under the sink to remove the sinks tail piece............just like Sounder said.......the sink itself is silicone sealed to the hull of the boat..........just home depot variety caulking gun tube silicone.......after removing the old sink I scraped the silicone and then put a bead under the new sink and dropped it in place......I waited a day for it to dry to hook up the drain hose so it would not tug at the sink before the silicone cured up........
Here is the company that makes the sinks for Four Winns........
http://ssicustomplastics.com/I hope helps........