I have a 246 diesel. Yesterday the water impeller failed, nearly taking out the whole boat. Luckily we were just departing from home and had just gotten on plane when I noticed billowing white smoke coming out the back. Did a quick shutdown and found all gauges to be normal. Popped the engine cover open and found the exhaust tube to have a hole melted through it just behind the elbow. It appeared to be burning inside. I hosed it down with the wash-down pump through the hole and the smoke seemed to stop. We deployed the trolling motor and slowly made our way back to the dock. Once on the dock I started taking a close look. I found the bilge pump was cycling on a few times and there was a leak at the exhaust tip at the stern. I lifted it out of the water and started taking things apart. When I removed the exhaust tube from the elbow, the tube fell out of position and literally fell off the exhaust tip on the back. The exhaust tip had deformed/shrunk so much that the clamps on either side of it were useless. If the arrangement of the exhaust hose wasn't just right, it would have easily fallen apart while on the water. That would have been a big challenge to overcome. I am upgrading it all to a silicon tube and a 4” stainless exhaust tip. This plastic stuff below the water line is a real joke. The impeller by the way was 2 years old according to previous owner. Im not gonna take a chance on that part again. The day before yesterday we were offshore all day.