We were trying to leave Marathon but the boat had other ideas. The generator had been a little finicky more than once, and just before we were going to leave it started belching out black smoke again, then threatening to die. We didn't really need the generator while we were on the move, but we had a world renowned diesel mechanic, the aptly named Diesel Don, as a neighbor. As we proceeded up the coast who knows what kind of tech support we would find? As it turned out - good, but that's another story.
We decided to stay and fix it now. This thing is buried deep inside our starboard lazerette (normally under a ton of crap we have stored in there), which is in turn inside a sound enclosure. The valve cover is off in the picture below, and Don tsked the state of our valve adjustment, but moved on to our primary problem. This was a little gadget in the lower right hand corner of the picture, below the black hose.
Since people started putting engines on boats a fundamental issue has been what to do with the exhaust, which is at fire starting temperatures. There is the dry stack approach used for bigger boats, where you treat it like a chimney, and direct the heat out of the boat with as little loss into the boat on its way. Smaller boats like ours tend to use simpler process with one big side effect (well, two but that's for later). To cool the exhaust the raw (sea) water first goes thru a heat exchanger for engine heat, what would be a radiator in a car. Instead of transferring engine heat to a coolant then into the air, the heat exchanger takes the hot coolant and transfers it to a steady stream of sea water pumped into the boat for that purpose.
Anyway, after exiting the heat exchanger the sea water is warm, but it still has one more job to do. A cast elbow forms the first part of the engine exhaust. The sea water is sprayed into the exhaust, cooling it dramatically. Now you just have relatively cool exhaust gas and warm water that collects into a muffler, which then uses the back pressure to gurgle out the collecting fluid every few seconds. This is a pretty elegant solution except for the horrible life of that exhaust elbow. Exhaust at hundreds of degrees mixed with a very corrosive sea water and steam mix doesn't add up to a very long life.
In fact they're only supposed to last for 500 hours of operation or five years or so. Now that Don is taking things apart ours appeared to be the original with over a thousand hours and more than a decade old. Oops. After one of the nuts which had corrosion welded in place was surgically removed the elbow was off. Pieces were falling off, so we were just in time to prevent at least a big mess, if not a fire, as exhaust would start to find its own way out of the boat.
Below is the shiny new exhaust elbow for the low, low price of of $330. Who knows where we will be 500 hours and or five years from now.
Installation went much faster than teardown, and after a quick valve adjustment and a swap out of the air filter we were back in business. The generator is actually much better than we ever knew, and with everything on the boat switched on, including the battery charger and two air conditioners, the generator chugs along just fine. Like many things, it turned out to be nothing that money couldn't fix. In Don's case, cash only.
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