SEALED FOR YOUR PROTECTION Case #SAR99-023
"At approximately 0330 hours, a 51' twin-screw yacht was discovered adrift seven miles from shore. Upon boarding the vessel, officers discovered four occupants passed out in the main cabin. Preliminary inspection indicates the cause as CO poisoning. Source of contamination was likely a leaking exhaust hose; a faulty hose clamp was discovered in the bilge."
In this case, during an engine overhaul, the exhaust pipes, which run behind cabinetry, were twisted for easy removal from the manifold. Upon reconnecting the pipes, however, the mechanics failed to inspect the rubber hose connections in the cabinets where the hose clamps had loosened after being twisted. Coast Guard investigators later determined that normal engine vibration caused the failure, which allowed carbon monoxide to enter the cabin. The leak was bad, but the real problem here was that the escaping fumes should have never been able to enter a living area.
If you're considering a double cabin cruiser or motoryacht, know that there's a good chance that exhaust lines will pass through the aft stateroom on their way to the transom. Make sure that access ports are sealed by a gasket or O-ring and if not, ask your dealer or builder to provide them before you take delivery. Inspect all joints or connections at least twice every season. Wet exhaust lines make a crack or leak easy to detect; with the engine running, look for a telltale drip of water. Make certain that any rubber hose connections are held by a pair of hose clamps at each end, rather than a single one. And make absolutely certain the manufacturer has used a rubber exhaust hose (or better yet silicone), designed for marine use. It will be clearly imprinted as Marine Water/Exhaust, SAEJ2006, or UL1129.
Inspect the engine room bulkheads to ensure they are completely sealed against air leaks into the living areas. Ventilation must come from outside the hull or cabin. Pay close attention to any holes used for passing plumbing, wiring, or control cables. Larger holes should be sealed with fiberglass; small holes must be caulked with silicone or polysulfide. As the Coast Guard likes to warn us, don't let anyone tell you that holes in the engine room bulkhead are necessary for ventilation of the framing.
OUT OF SIGHT, OUT OF MIND Case #MC98-177
"A 29' sportfisher experienced an engine room fire shortly after refueling. Cause was determined to be a small leak in the craft's aluminum fuel tank, which allowed fuel to puddle in the bilge. Gasoline vapors were likely ignited by a spark from the ignition."
It went largely unnoticed, but in 1997 the Coast Guard issued a warning about the alarming failure of aluminum fuel tanks in recreational boats. Citing a long-term Underwriters Laboratories (UL) study begun in 1992, the Coast Guard pointed out that 92 percent of the failures were a result of corrosion, particularly when tanks were mounted low in the bilge.
As the UL survey points out, part of the problem is that most aluminum fuel tanks are considered "maintenance-free." With limited space available, tanks are often pushed into the least accessible corners, making regular inspection almost impossible. Although corrosion from sloshing bilge water was the most common culprit, the study also found several instances of abrasion. One boat's fuel tanks were mounted atop a rubber pad, but the staples that held the pad in place weren't recessed - they eventually wore into the tanks. In another case, the survey found brass fittings screwed directly into aluminum tanks, promoting galvanic corrosion. Almost every aluminum tank examined had some form of corrosion, and in every case the common factor was that the tanks hadn't been installed so they could be easily inspected or repaired.
Ask your builder or dealer where the inspection ports are, and determine whether you can see susceptible connections, joints, welds, supports, and restraints. Examine the bilge to see whether water will flow freely past the tank or will instead be trapped under or around it. Also consider the thickness of aluminum tanks. The UL study found that most failures occurred in tanks constructed from 0.090" or thinner aluminum sheet. Or look for boats using polyethylene or fiberglass tanks that are marked to show that they meet Coast Guard and ABYC standards.