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lengths to detail, both in writing and using diagrams, the requirements for exhaust system design and construction. While they don’t tell boat builders how to build an exhaust system, they do provide the parameters the system must operate within. One of the more common errors involves the angle of the mixing elbow and hose connected to it; some engine manufacturers call for a minimum of as much as 25 degrees. The primary goal of this requirement is to prevent water from flowing back into the engine. However, if the angle is too shallow, another problem can manifest itself; while running water will quickly flow to the bottom of the hose, leaving the top of the hose or spine exposed to dry exhaust gasses, which can be as high as 1000 degrees F. In this scenario, the hose overheats and eventually burns, creating a hole through which exhaust, soot, and atomized salt water are discharged into the engine room, a destructive scenario to put it mildly, while the engine itself remains cool, giving no immediate indication of trouble to those at the helm. Having seen the results of such failures, I can attest to the degree

##Typical exhaust temperature alarms are triggered at 165°F. The high temperature measured on this exhaust hose is 217°F, which is cause for concern.

of, and rapidity with which, damage can occur; it’s not unheard of to accrue tens of thousands of dollars in just a few minutes. In addition to ensuring your engine’s raw water cooling and exhaust systems are in good working order, and compliant with the engine manufacturer’s requirements, you can implement one additional measure to stave off disaster: install an exhaust temperature alarm. Not only are these inexpensive insurance

##Restricted exhaust mixing elbows, particularly those made from cast iron, are a common cause of exhaust water restriction and starvation.

against exhaust, as well as engine overheating, they are required for those who wish to comply with ABYC standards. About the Author: With nearly three decades of marine industry experience, former boatyard manager, technical writer, and lecturer, Steve D’Antonio, consults for boat owners and buyers, boat builders, and others in the industry. Find his weekly technical columns at

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