Publish Date: Wednesday, March 11, 2009
Location: Crossing the Exuma Sound, Bahamas
Our floating home is an compact engineering marvel, making us almost as self-sufficient as a small city: we generate electricity; make drinking water; maintain a local-area network; manage waste (both trash and human waste); and occasionally, run a movie theatre (see Ayla’s blog). This off-the-grid independence is very satisfying, and it gives me confidence that we can actually live aboard this platform for several years.
To support all these systems, we normally run our generator twice per day for 2-3 hours. This allows us to charge our battery bank, make fresh water, do laundry, make ice, and heat water. I’ve diligently done the normal maintenance required to keep the generator running (check the coolant level, check and change the oil, check and change the fuel filters, etc.), so it came as a bit of a surprise the other day when the generator abruptly shut down. At that moment we realized just how dependent we are on our generator: if we couldn’t get it working we would have to tie up in a marina and use shore power — our independence was gone.
The good news is that the generator was smart enough to shut itself down because it was overheating. We learned about this brilliant feature when were were reading the manual trying to diagnose the problem. The overheating symptom also allowed us to narrow the problem down to something with the oil or water. A visual inspection didn’t show any oil disasters, and after a few other water-related inspections I was zeroing in on the water pump impeller. I was pretty sure I had a spare impeller, but there was a ten-minute period during which I was looking for the spare that I was a little panicked that we would be without a generator for awhile.
I had never changed an impeller before, so I radioed a friend on another boat to review the procedure — it sounded like something I could handle. I pulled the cover off the impeller housing, and sure enough, the impeller was shredded to almost nothing. I installed the new impeller, and the generator has been running perfectly ever since. I was also able to find another spare in Spanish Wells, so all is well. While this was a relatively minor repair, there was a certain satisfaction to being able to diagnose and fix the problem. And better yet, we didn’t need to go into a marina.
Congratulations on passing your first test in diagnoses, repair, and restoration.
Hey David,
A failed generator impeller has happened to me as well. Actually, I had just purchased my vessel (new) and had about 70 hrs on the main engines and perhaps 120 hours on the generator. Everything was working well as I kept up with routine checks of the generator; the assigned mechanic had given the generator oversight and care on several post-delivery inspections in the preceding weeks leading up to my incident. Low and behold one morning I started the generator in my slip and it ran about five minutes before coming to a halt. Efforts to restart the generator witnessed it run for five to ten seconds and then stop again. I went through the same diagnosis you did and drew conclusion on the impeller. Unfortunately I did not have a spare on board but then again I was only going out for a local cruise anyway and returning in a few hours, so there was no consequential impediment to our well being.
Later the mechanic met us on arrival with an impeller in hand. He pulled off the impeller housing and the blades were in pieces. How could this be I asked? The theory was a barnacle “piece” may have come though the water intake screening – we don’t know for sure but the lesson learned for me is carry a spare impeller (for the engines and air conditioner as well) and keep all the water intakes clear/clean through very routine scour efforts by a qualified and caring bottom diver.
However, the lesson continued and I’ll share it with you to emphasize the importance of keeping the water intakes as clear as possible in salt water. Recently my air conditioner would fail whenever the vessel was coming on or off plane; the system would shut off after generating a high-pressure alarm and, as you probably already know, the shut off function in this type of condition is intentional to protect the compressor from over-heating. Keep in mind, this would only occur whenever the vessel was coming up on plane or falling off of plane. As investigation would find it, blockage had occurred within the air conditioner water intake, about seventy-percent (so much for the qualified and caring bottom diver, eh?). This blockage caused aeration within the feed and then plenty of cavitations around and aft of the bronze impeller. As you might be anticipating in this story, these cavitations cause the same damage to an impeller as they do to an improperly pitched or tuned propulsion propeller. The significance for the air conditioner on my vessel was the minute air bubbles began to pit the bronze impeller. This “pitting” caused even more cavitations within the air conditioner pump and contributed to the high pressure alarm even more.
Clear the blockage – change the bronze impeller (read: expensive) and all was back to normal. The lesson again for was the impact sea growth, barnacles in particular can have on the function of our needed peripherals. Again, sea organism had likely caused another unexpected maintenance issue despite a bottom diver’s regular cleaning efforts. Ughhhh….
I’m not sure how you’re addressing cleaning of the vessel bottom and the water intakes in your travels but thought you might benefit from my story.
Love you blogs – safe voyages and look forward to chatting as you round out your Bahamas adventure and head for Florida.
Jim
David,
In our gas boat engines it is very important to try and find all the rubber impeller pieces in the cooling system after they break off. If you do not, they can end up causing more problems or blockages. Not sure what the cooling system looks like on your GenSet but you might want to inspect any downstream hoses/thermostats/passages/etc. Would hate to have a floating impeller piece to come back to haunt the unit later on. Just a thought. Cuz Jon
Hello Dave, nice job on the impellor. Being that I have been in the maintenance business my entire career, with a job as critical as this I would ask what caused the impellor to shred???? Was the impellor plastic or metal? Most impellor malfunctions are caused by contamination or cavitation? Either way, know the cause and correct accordingly. Good luck JOHN