ScottC
Guru
- Joined
- Nov 2, 2019
- Messages
- 1,528
- Location
- SWEDEN
- Vessel Name
- ABsolutely FABulous
- Vessel Make
- Greenline 33 Hybrid (2010)
I would be grateful for anyone that may have some thoughts on this…
Background
I have a wet exhaust system with a Vetus muffler and outlet under water at the extreme aft end of the boat. Exhaust elbow is “new”. Replaced at the beginning of 2022.
About 8 years ago, I had my yard install a Vetus exhaust temperature alarm. Simple (75 C) sensor in the hose about 2 feet after the exhaust elbow. Connected to a siren.
Until last week, this alarm has never sounded.
Fast-forward to last week
I was idling around in choppy seas near the entrance of a large VTS controlled bridge in the Gulf of Patras. Of course, just as the bridge told me I could proceed, my exhaust alarm sounded. First thing I checked were my two engine water temperature gauges. Both expressed happiness.
I shut off the diesel engine and proceeded using my electric motor. I placed a friend at the helm while I flipped up the engine hatch for a quick inspection. I could hold my hand on the exhaust elbow. All looked fine. All smelled fine.
Started the engine again, checked that I could see water moving in the raw-water strainer and proceeded at 7 knots (1850 rpm) for the next few hours until we reached our destination. I concluded that I must have picked up a piece of plastic in the rather polluted Patras harbor that was blocking my water intake until I turned off the diesel engine.
Fast-forward to yesterday
I was idling around in VERY choppy seas at the entrance to the Corinth Canal awaiting permission to enter. Alarm sounded again (!). I switched to electric propulsion to maintain position and performed checks once again. All fine. Engine water temp fine too. Started the diesel engine when we were called to enter the convoy going through the canal, checked the raw water strainer and all was fine. Ran 7-8 knots through the canal and then 7 knots for another 3 hours after that to our destination. All fine.
Today
It occurred to me that if my water pump impeller is beginning to fail, it might produce insufficient water to keep the exhaust cool at low rpms, but adequate amounts at higher rpms. So today, while at the city quay in the Epidavros, I ran the engine at idle speed (850 RPM) for 75 minutes trying to replicate the phenomenon. No alarm. I then revved it up a bit to 1200 RPMs for an additional 15 mins. Still no alarm. In both prior cases, where the alarm sounded at idle-ish speeds, it happened within 30-45 minutes from starting the engine.
My conclusions thus far
Any thoughts or ideas??
Background
I have a wet exhaust system with a Vetus muffler and outlet under water at the extreme aft end of the boat. Exhaust elbow is “new”. Replaced at the beginning of 2022.
About 8 years ago, I had my yard install a Vetus exhaust temperature alarm. Simple (75 C) sensor in the hose about 2 feet after the exhaust elbow. Connected to a siren.
Until last week, this alarm has never sounded.
Fast-forward to last week
I was idling around in choppy seas near the entrance of a large VTS controlled bridge in the Gulf of Patras. Of course, just as the bridge told me I could proceed, my exhaust alarm sounded. First thing I checked were my two engine water temperature gauges. Both expressed happiness.
I shut off the diesel engine and proceeded using my electric motor. I placed a friend at the helm while I flipped up the engine hatch for a quick inspection. I could hold my hand on the exhaust elbow. All looked fine. All smelled fine.
Started the engine again, checked that I could see water moving in the raw-water strainer and proceeded at 7 knots (1850 rpm) for the next few hours until we reached our destination. I concluded that I must have picked up a piece of plastic in the rather polluted Patras harbor that was blocking my water intake until I turned off the diesel engine.
Fast-forward to yesterday
I was idling around in VERY choppy seas at the entrance to the Corinth Canal awaiting permission to enter. Alarm sounded again (!). I switched to electric propulsion to maintain position and performed checks once again. All fine. Engine water temp fine too. Started the diesel engine when we were called to enter the convoy going through the canal, checked the raw water strainer and all was fine. Ran 7-8 knots through the canal and then 7 knots for another 3 hours after that to our destination. All fine.
Today
It occurred to me that if my water pump impeller is beginning to fail, it might produce insufficient water to keep the exhaust cool at low rpms, but adequate amounts at higher rpms. So today, while at the city quay in the Epidavros, I ran the engine at idle speed (850 RPM) for 75 minutes trying to replicate the phenomenon. No alarm. I then revved it up a bit to 1200 RPMs for an additional 15 mins. Still no alarm. In both prior cases, where the alarm sounded at idle-ish speeds, it happened within 30-45 minutes from starting the engine.
My conclusions thus far
- Could it have been due to back-pressure caused by some rather heavy waves hitting me from astern while I was trying to maintain position/not move forward? I’m sure in some cases, the exhaust outlet was briefly exposed due to the somewhat unusual wave action. On both occasions where the alarm sounded, I was experiencing heavy waves from astern while trying to hold position / not move forward.
- I feel it’s unlikely a faulty sensor, as it’s a very simple sensor and it does not sound immediately upon starting.
- I guess it could have been plastic blocking the intake. But TWO times in one week??? Hmmm….
- I feel that if the impeller is failing, I should have been able to reproduce the problem with my tests at the dock this morning. I couldn’t. Furthermore, the engine water temp remains always normal.
Any thoughts or ideas??
