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Old 06-29-2020, 06:26 PM   #1
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Shredded impeller.

This last weekend I had my first taste of a shredded impeller in the cooling system.


Impeller was just shy of 2 years old.

For only the 2nd time in my boating life I left the dock with the raw water seacock closed.


Shortly after leaving the dock my wife mentioned a different exhaust note. Sure enough, I went back to the stern and listened and it sounded like a dry stack exhaust. We were headed to the pumpout dock so we continued, docked, emptied the holding tank and went back to our dock. Maybe about 10 minutes at idle each way.


When I opened up the impeller cover the impeller essentially had no blades left.


I had to take apart part of the pump and disconnect the hoses to get all the pieces out. I "think" I got all the pieces out.


So, next time the impeller will be checked at a year instead of two.
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Old 06-29-2020, 06:34 PM   #2
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Some have done, some will. Glad for you that the consequences were minor.

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Old 06-29-2020, 06:35 PM   #3
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Been there and done it , maybe more than once.
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Old 06-29-2020, 06:37 PM   #4
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When I shredded an impeller it had NO lobes left!
I had good luck using a shop vac... first sucking at the pump then exhaust blowing into far end of heat Xchgr, back to sucking at pump, etc. Etc until I got no additional pcs.
Some back flush w a hose but I'd guess that's a lot messier to clean up.
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Old 06-29-2020, 07:37 PM   #5
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Take the ignition key and put a loop of string or a tie wrap on it. When you close the seacock, hang the key on the handle.

On my boat I have a simple rule, whenever the engine must not be started, take the key out of the ignition. Oil changes, closed seacock, doing a repair on anything in the drivetrain, pull the key before you do anything else.

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Old 06-29-2020, 07:55 PM   #6
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Dave, it can happen. We all "forget" things so don't be too hard on yourself. Ted mentions a good idea.
However, I don't understand how checking or changing the impeller at the one year mark would have helped you in the situation of not opening the sea cock. Even brand new, it would have been "toast".
Coming from a sailboat where my raw water was expelled above the water line right next to where I would sit to drive the boat, I was terrified at first that I would forget the thru hull and not know. To solve that, I installed a raw water flow alarm (Aqualarm) before the raw water pump. Not only will it alert me should I leave the sea cock closed (not yet), but it would alert me to a blockage like a plastic bag for example. Not all that expensive (about $100 or so)., and simple to install.
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Old 06-29-2020, 08:12 PM   #7
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I second Tom’s suggestion. The Aqualarm Flow Alarm is a great idea that might not only save your impeller but your engine as well. I’m surprised that more boats don’t use them.
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Old 06-29-2020, 08:14 PM   #8
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Quote:
Originally Posted by dhays View Post
This last weekend I had my first taste of a shredded impeller in the cooling system.


Impeller was just shy of 2 years old.

For only the 2nd time in my boating life I left the dock with the raw water seacock closed.


Shortly after leaving the dock my wife mentioned a different exhaust note. Sure enough, I went back to the stern and listened and it sounded like a dry stack exhaust. We were headed to the pumpout dock so we continued, docked, emptied the holding tank and went back to our dock. Maybe about 10 minutes at idle each way.


When I opened up the impeller cover the impeller essentially had no blades left.


I had to take apart part of the pump and disconnect the hoses to get all the pieces out. I "think" I got all the pieces out.


So, next time the impeller will be checked at a year instead of two.
In your case it is more check seacock before firing the engine than check the impeller yearly.
On my boat I have to put the flybridge throttle lever down to setup the fabric cover properly, I have put a label on the lower helm in big bold letter "check flybridge lever before starting the engine". Knowing how much silly I am it is a cheap simple insurance

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Old 06-29-2020, 08:25 PM   #9
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Good suggestions.

On my sailboat, I closed the seacock every time we left the boat. I always hung the key over the seacock handle.

On this boat I donít normally close the seacock when we leave the boat. It was closed this time because I had gotten out of my normal routine and had gone down to the boat just to do a fresh water flush on the engine. I forget to open the seacock after I did that.

I like the idea of a flow alarm, but Iíve only done this once before, two boats ago it may be a solution in search of a problem.

Checking the impeller more often is likely a good idea. Changing the impeller is a PITA, but checking the impeller isnít too tough.

I also was once again appalled at the cost of a replacement impeller. The things are ridiculously expensive.
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Old 06-30-2020, 05:37 AM   #10
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Plan B is as simple as installing a Y style strainer AFTER the sea water pump.

It will catch debris , even tiny chunks so worry about clogging the system are gone forever.
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Old 06-30-2020, 07:10 AM   #11
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Can't remember the last time I closed either the engine or generator seacock.
That's in 30 years of boating.
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Old 06-30-2020, 08:50 AM   #12
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I cycle mine every few months, keeps them free and gives me a chance to inspect. But otherwise they are left open.

If I have the engine in some sort of non-operational condition I take the ign key out and blue tape it to something nearby.
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Old 06-30-2020, 09:23 AM   #13
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When I close the sea cocks I use a business card with "sea cock" in red written on it, cut a slop in it and place the key through it and leave it in the ignition.

Typically I seem to relearn this trick at some point on every new boat we buy. On the current boat I forgot to open them and to add insult I forgot to flip the breaker on for the engine alarm circuit.. which would of notified me of my boneheaded move.
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Old 06-30-2020, 09:47 AM   #14
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congratulations to your wife on being alert for a louder exhaust.
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Old 06-30-2020, 12:00 PM   #15
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Quote:
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Plan B is as simple as installing a Y style strainer AFTER the sea water pump.

It will catch debris , even tiny chunks so worry about clogging the system are gone forever.

I like that idea... I don't know that I have the space for it, but I really like that idea...
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Old 06-30-2020, 12:01 PM   #16
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congratulations to your wife on being alert for a louder exhaust.

Yeah, it impressed me. I may not have noticed it until the temps increased and by then we would have been well out of the harbor.
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Old 07-01-2020, 11:46 AM   #17
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Old 07-01-2020, 04:05 PM   #18
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Dave,
"I like the idea of a flow alarm, but I’ve only done this once before, two boats ago it may be a solution in search of a problem."
Just to point out the whole potential benefit; but a flow alarm will not only alert you in case you forgot to open the sea cock, but will alert in the event of an unexpected problem like blockage. Mine has gone off a couple of times when mussels have partially filled the on hull "clamshell" strainer for the main engine, or when a fish was sucked into my generator through hull blocking almost all flow. This inexpensive, relatively easy to install early warning could save you from potential major engine damage due to overheating due to reduced or no raw water flow. Think of it as "insurance" for your engine. Hopefully, just like insurance, you never really need it.
Personally I would think that the fact that your impeller is difficult to install would be all the more reason to install this alarm
Just a suggestion, that I feel is a good idea.
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Old 07-06-2020, 10:38 PM   #19
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checks

My routine is check oil,check header tank,start engine,walk aft to check exhaust water flow
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Old 07-07-2020, 12:44 AM   #20
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Quote:
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Good suggestions.

On my sailboat, I closed the seacock every time we left the boat. I always hung the key over the seacock handle.

On this boat I don’t normally close the seacock when we leave the boat. It was closed this time because I had gotten out of my normal routine and had gone down to the boat just to do a fresh water flush on the engine. I forget to open the seacock after I did that.

I like the idea of a flow alarm, but I’ve only done this once before, two boats ago it may be a solution in search of a problem.

Checking the impeller more often is likely a good idea. Changing the impeller is a PITA, but checking the impeller isn’t too tough.

I also was once again appalled at the cost of a replacement impeller. The things are ridiculously expensive.

Dave:
It is all about systems.
You decided to deviate from your normal systems and do something out of your normal comfort zone and that led to forgetting to re-open the thru-hull.
Every time I deviate from my normal system I forget something. Mostly of no consequence, but your experience convinces me that should I deviate again, I should be very careful to check all of those items that could come back to bite me.

In my boat, the thru hulls, especially the ones that allow the engine to get cooling water, get exercised twice every 7 years. the first time is when I schedule my regular insurance survey, the second time is when the surveyor exercises them in the survey, always with a comment like "most of the thru-hulls I see are seized". In our local waters, for which I include where you are, there is no danger whatsoever of freezing, so you don't need to close the thru hull when you are away from your boat. You will see the condition of your hoses whenever you are doing regular cleanups or any other maint in the ER, so don't need to worry about a hose deteriorating, and face it, your boat isn't old, so that isn't going to be an issue for decades. Too bad you decided to do a flush. Way out of your comfort zone......Why would you need to do a flush on a boat that is as new as yours? What is in the water where you moor that you are afraid of? As you now know, the consequences of not doing a flush are way less than the consequences of doing one and forgetting to re-open the thru-hull!
As for flushing, if you have zincs in your cooling system, you don't need to replace the salt water with fresh. If you don't have zincs, you might benefit from having some fresh in the cooling system, but the jury is out on that, as several engines commonly used in salt water don't even come with zincs. I found this out when my son bought a Monaro 27, built in Richmond BC ( on or almost surrounded by salt water) and went to replace zincs in the engine Heat exchangers, only to find that there are none. Nothing on the boat to suggest he ought to be flushing with fresh.

If you can develop systems that work, don't be quick to deviate from them.
If it isn't broken, don't try fixing it.
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