16. Check-Valve Backflow
What Happened: Since the through-hull is mounted so low to the waterline, a clever mechanic put a one-way check valve on your bilge pump's exhaust hose to keep the sea out. Too bad it didn't.
What You Should Have Done: Check valves are unreliable and can get stuck open. Route the pump's exhaust hose as high as possible to a through-hull near the rubrail. If it must go to a low outlet, run the hose up inside the boat as high as possible, install an anti-siphon valve at the top of the loop, and run it to a seacock that you can close.
17. Ice in Sea Strainer
What Happened: When it was time to winterize, you put antifreeze everywhere except in the strainer at the raw-water intake. Then you left the boat with the seacocks open. The water in the strainer froze, expanded, and cracked the strainer. Water came in and the boat went down.
What You Should Have Done: Close the seacock and open the strainer's drain plug to empty it of water. Then fill the hose and strainer with anti-freeze, because you never get all the water out and it's better to be safe.
18. Plastic Through-Hulls I
What Happened: The cheap ones that came with the boat got brittle from ultraviolet light and gave way from the weight of the hose. Or maybe the hose barb cracked when you overtightened the hose clamps.
What You Should Have Done: We prefer stainless-steel or bronze fittings below the waterline.
19. Plastic Through-Hulls II
What Happened: The mechanic was in the bilge repairing the engine. While trying to get better leverage to force a rusted bolt free, he wedged his foot against a through-hull. He pushed and it cracked.
What You Should Have Done: Stick with stainless steel or bronze below the waterline. And use a better mechanic.
20. Transom-Mount Transducers
What Happened: You were smart to use bolts instead of screws to mount the transducer to the transom. But over the years the transducer has gotten nudged, hit, and smacked so often that the bedding compound loosened and enlarged the boltholes enough for water to seep in.
What You Should Have Done: Caulking and bedding compounds don't last forever. Check every year and rebed every four years.