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Old 05-31-2020, 11:05 AM   #1
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Not so Pretty in Pink?

My prop has apparently suffered from some galvanic action. Most likely it was because I spent four months in fresh water without knowing I should have changed my salt-water zink anodes to magnesium. This was probably exacerbated by being plugged into shore power much of the time at marinas having...shall we say "questionable" power installations.


My question is this: Is there any strong reason to replace my prop with a new one at this stage? Clearly it has gone through some de-zinkification, but it leaves me wondering if the prop is still usable, without risk (of a blade flying off, for example...).


Thank you, everyone, in advance for your collective thoughts on this!
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Old 05-31-2020, 11:23 AM   #2
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How bad are your shafts and rudders? I would probably defer to a professional at a propeller shop.

Ted
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Old 05-31-2020, 11:23 AM   #3
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I would recommend having a prop shop expert evaluate your prop. Very difficult to get good, reliable diagnostics of metalurgy online from distant strangers.
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Old 05-31-2020, 11:28 AM   #4
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How bad are your shafts and rudders? I would probably defer to a professional at a propeller shop.

Ted

Shaft & strut are stainless steel. It seems I have no worries there. Rudder is either fiberglass or some type of plastic composite.


I have a few bronze through-hulls, however...which I probably need to take a closer look at.
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Old 05-31-2020, 11:37 AM   #5
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Shaft & strut are stainless steel. It seems I have no worries there. Rudder is either fiberglass or some type of plastic composite.


I have a few bronze through-hulls, however...which I probably need to take a closer look at.
Would expect to have seen some shaft pitting with that much pink. The rudders may be of an alternative material, but the rudder shafts are metal and should be protected. They may be protected by internal bonding. Do the prop shafts have anode brushes on the inside of the boat?

Ted
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Old 05-31-2020, 11:42 AM   #6
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Would expect to have seen some shaft pitting with that much pink. The rudders may be of an alternative material, but the rudder shafts are metal and should be protected. They may be protected by internal bonding. Do the prop shafts have anode brushes on the inside of the boat?

Ted

Hi Ted,
I will have to take a closer look at the shaft when I can manage to travel to my boat. Hopefully, that will be this year!! Regarding Anode brushes - no, unfortunately, I don't have them. They might be something for me to consider!
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Old 05-31-2020, 12:23 PM   #7
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Maybe go to aluminum anodes. They are good for both salt and fresh water. Easy fix and certainly cheaper than replacing props and other underwater metals.
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Old 05-31-2020, 02:58 PM   #8
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I’d run it.
Have a spare onboard if you cruise to remote locations, though.
Before buying a spare , Take time to reassess your prop performance to be certain you’re not overloading your motor. The longer you own the boat, the heavier it gets!
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Old 06-01-2020, 11:22 AM   #9
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I’d run it.
Have a spare onboard if you cruise to remote locations, though.
Before buying a spare , Take time to reassess your prop performance to be certain you’re not overloading your motor. The longer you own the boat, the heavier it gets!

Very interesting comment, Kapnd! I do have a spare that I bought from the factory when the boat was new. I always have it with me, but haven't had to use it yet.



The boat is certainly a lot heavier now than when new, so prop performance could, indeed, be different! This is something that has never occurred to me. Hull speed and my normal diesel cruise speed is ~7 knots. It can do 13 knots with the 165hp turbo diesel, but I almost never run it that hard.



It was my understanding from early reviews on this boat that my 5-blade factory prop is a performance compromise -- in order to perform acceptably (but not necessarily optimally) when running in either diesel or electric mode. The Diesel-only versions of my boat were delivered with 4-blade props as standard from the factory.



I find prop sizing and performance a daunting subject even before throwing "dual-purpose" into the equation. Nevertheless, I am grateful to learn from you that this is something I need to think about as the boat becomes heaver. Thank you!
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Old 06-01-2020, 11:33 AM   #10
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Prop shop. All else is nonsense.
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Old 06-01-2020, 11:56 AM   #11
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Maybe go to aluminum anodes. They are good for both salt and fresh water. Easy fix and certainly cheaper than replacing props and other underwater metals.

Thank you for the Aluminum anode tip, Comodave! I just finished some reading up on this topic on the internet and it seems that Aluminum will, indeed, be the way to go for me for the coming few years. The boat will be 90% of the time in salt water and not sitting idle for long periods.
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Old 06-01-2020, 01:28 PM   #12
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My dad had a saying: "Never ask a barber if you need a haircut" I'm not sure what the alternative but a prop shop is going to want to sell you new props. Even an honest, reputable one. All they look at every day is brand new shiny props, and its not their money.
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Old 06-01-2020, 03:10 PM   #13
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I had our props rebuilt about a year ago. He figured the price and then said let’s use the other computer and see if it comes up with a better price. And it did so we went with the cheaper quote. He didn’t have to give me the lower price but he did. I think I would trust him to give a true answer.
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Old 06-01-2020, 03:11 PM   #14
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Thank you for the Aluminum anode tip, Comodave! I just finished some reading up on this topic on the internet and it seems that Aluminum will, indeed, be the way to go for me for the coming few years. The boat will be 90% of the time in salt water and not sitting idle for long periods.
It saves having to change anodes back and forth as you change water. Just makes life simpler with one less thing to worry about.
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Old 06-02-2020, 02:02 AM   #15
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[QUOTE=ScottCI find prop sizing and performance a daunting subject even before throwing "dual-purpose" into the equation. Nevertheless, I am grateful to learn from you that this is something I need to think about as the boat becomes heaver. Thank you![/QUOTE]

Might be a good question to refer back to the engineers!
Even a good prop shop is not likely to be a great deal of help with D-P.
You could start the ball rolling by making a performance log.
record speed, boost and exhaust gas temp at 2000 rpm intervals for the diesel side, not sure what kind of instrumentation you’ve got on the electric side, but you get the idea.
Actual vessel weight is helpful in prop selection too.
I think the electric side is going to be more lenient on prop parameters than the diesel side, as it can work efficiently over a far wider range.
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