The raw water impeller gave up today because I ran the engine for too long with the raw water seacock closed. It ate itself and jammed the tiny pieces down the plumbing toward the heat exchanger. I spent an hour laying on my belly on the floor pulling the pieces out. Not a fun chore but completely necessary because there was no cooling water for the engine and it could have seriously overheated. If I’d have replaced the impeller annually as is recommended in many maintenance schedules it probably wouldn’t have thrashed itself. Live and learn.