DON’T TRY TO BE TOO COOL

There’s another plumbing issue that might lead to the engine flooding. A traditional propeller-shaft stuffing box needs a slight bit of water—drips, really—to cool it while the engine is running and the shaft is turning, but none when the shaft is at rest. Tightening the nut on the stuffing box will adjust the rate of dripping.

Some boat owners anxious to keep the stuffing box really cool add a small hose that, via a T fitting, carries water from the raw-water cooling loop and exits underwater along the shaft into the stern tube. This, of course, allows another opportunity for seawater to siphon back into the engine. The stuffing box’s cooling waterline also has to be looped high above the waterline with a vacuum break valve at the top.

Unless your sailboat has a super-high-rpm engine, this extra cooling is quite unnecessary. Truthfully, I’d rather live with a slight drip into a bilge equipped with an automatic bilge pump. Just make sure the bilge pump discharges well above the waterline or you will need another loop provided with a vacuum break valve.

Other schemes that can stop the propeller shaft from dripping entirely are complex setups of precision seals, rubber bellows and, of course, the absolutely vital cooling waterline. The consequences of these systems failing—and they do, often unexpectedly—might include rapid sinking. Only very fast powerboats might really find them necessary.