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  • Krabby

Engine Repairs

“What's that smoke I see, Krabby?” ask the East Coaster from the v-berth.

"It’s the coffee pot. Get up and turn it down and pour me a cup while I make ready to get underway," I yelled back from the cockpit.

"It sure looks like smoke to me," she replied dodging morning coffee detail.

" water!" I belted out as I peered down the companionway at the smoke coming from the engine compartment. I shut down the engine and opened the compartment door to find the dry section of exhaust rise parted in two and the bilge flooded.

"It was smoke, wasn't it?"

"Well, that got you out of the bunk" I replied with my head down in the engine compartment.

“You didn't have to light the boat on fire to get me up – but seriously what's wrong in there?"

“The exhaust pipe has parted, just past the manifold, and that has allowed the raw cooling water to flow into the bilge instead of overboard. This failure must have just happened because I checked the fluids and checked the engine for leaks when I started it this morning." I replied while still trying to make sense of how this happened so quickly.

"Well, this is a fine way to start our East Coast cruise. I was hoping to show you around Block Island this afternoon, but there is not enough wind to even get out Newport Harbor."

"Calm down little Miss East Coast, I can make a temporary fix."

"Ok, how can I help?"

"Great! Grab me your Dad’s tool bag and emergency repair kit and let's see what we can do.”

“All right, here's the tools and a tin can full of old hose clamps," said my repair assistant.

"Any chance there is epoxy repair putty in that locker? It seems to have collected a bit of everything over the many years of cruising." I inquired as I sized up the collection of materials that we could engineer a repair from.

"There's this stuff that looks like two dried up candy bars, but it might be too old," said my partner in make-shift engineering.

"That will work, hand me the coffee can and the shears. Open the hose clamps up to about two inches while I cut out a piece of this can. This stuff is old, but it will work" I said as I needed together the two-part putty "hand me the piece of can and clamps." I asked, as I crawled into the engine compartment and smeared the putty around the broken exhaust pipe. "Tighten the clamps while I hold the can around the putty."

"I think this will work," said my helper, "Let's clean up and have some breakfast as the putty sets up." I agreed, hopeful of my repair.

"The can splinting the broken joint, reinforced with the putty and hose clamps looks strong enough to get us through our cruise." said the East Coaster on our way to Block Island.

"Good thing, it would be a long sail to the Island in this light wind," I said checking our work in the engine compartment."

“The engineer in me wants to know how the exhaust system works and how it failed." She continued.

“Since you asked, I'll go over the basic idea of a marine exhaust system, particularly how it applies to an auxiliary engine in a sailboat. As you can see, exhaust and seawater come out the back of the boat, but the exhaust port is higher than the engine. Sea water is pumped through the heat exchanger to cool the engine, then is pumped into the exhaust to cool the hot exhaust gases and muffle the sound. The issue here is that the engine is below the water line so when the engine is shut down, there is no exhaust pressure and water is free to run downhill back into the engine and flood the cylinders" I started to explain.

"Oh, so that is why the water flooded the engine compartment and filled up the bilge when the pipe parted?" queried the East Coaster.

"Exactly, the engine was running, but the pipe parted so there was no exhaust to force the water out and it ran back down the pipe into the bilge. Even if the pipe didn’t break, water in the system needs to be prevented from running back into the engine (cooling water or water entering the boat through the transom exhaust pipe) - so an air lock type muffler is installed. This is a tank that the exhaust and water are directed into. The exit pipe goes almost to the bottom but the inlet pipe is at the top. Exhaust is trapped between the bottom of the exit pipe and the engine. When the water flows back through the exhaust hose from the back of the boat, it fills the muffler tank to the bottom of the exit pipe before it forms an airlock. This prevents the water from flowing back into the engine."

"Ok, that make sense. Why did the pipe fail when the engine is barely two years old?" She asked.

"Good question. For the airlock to work with a margin of safety there must be 12 inches from the point the cooling water is injected into the dry exhaust and the top of the muffler. In this case, the muffler had to be mounted above the propeller shaft and that made it the same height as the exhaust on the engine. In order to make the exhaust height enough, an extension loop was welded on and anchored at the top. It parted because the distance of the extension from the center of the radius of vibration of the engine was so great, it basically shook the extension until the weld failed. The permanent fix will be to relocate the muffler lower to eliminate the extension or add a flexible joint to the extension."

"So, even that brace could not prevent that length of exhaust pipe extension from failing. It probably helped for a while but eventually, the pipe parted" she added.

"That's correct. Look out there ahead, is that Block Island? Shouldn’t we have a drink to toast our success?" I asked.

"Sure. You know, I still haven't forgotten about that East versus West cruising bet from a couple months ago. Under the circumstances, I guess this one’s on me." Conceded the East Coast navigator.

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