My propeller completely split along the full longitudinal axis (the part that slides over the shaft). I've tried to attach a photo to depict what happened. Any clue as to what could possibly have happened? It's been on the boat for 6 years and, all of a sudden, split. I didn't hit anything and the blades are just fine; no dings or scrapes. I didn't run over any line. It was going just fine and, all of a sudden, split apart. It came from a Beneteau 321 powered by a 27 hp Yanmar. It's a mystery to me. I had to buy a new bronze prop from Beneteau for almost $500.00 and don't want this to happen again.
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It's rotten.
Rick: Your prop rotted. It looks like it may have been electrolysis. Did you have zinc's on your prop shaft?
Rick: Your prop rotted. It looks like it may have been electrolysis. Did you have zinc's on your prop shaft?
Zinc
Well, I thought I had a zinc but when it came apart, it was lost. I've always had them replaced about every 6 months or so. That said, our marina has been plagued with stray current and zincs have been eaten up pretty fast; on the order of every 4 months or so. Is there any way to confirm that it was electrolysis? It it was, why not the thinner edges of the blades rather than the thickest part of the prop?
Well, I thought I had a zinc but when it came apart, it was lost. I've always had them replaced about every 6 months or so. That said, our marina has been plagued with stray current and zincs have been eaten up pretty fast; on the order of every 4 months or so. Is there any way to confirm that it was electrolysis? It it was, why not the thinner edges of the blades rather than the thickest part of the prop?
I would take it to a prop shop.
Rick: I would take the old one to a prop shop for an expert opinion. You probably want to get an expert opinion on the problem before another 500 prop goes down the drain. I would ask the marina to test and see what is going on.
Rick: I would take the old one to a prop shop for an expert opinion. You probably want to get an expert opinion on the problem before another 500 prop goes down the drain. I would ask the marina to test and see what is going on.
Murphy's Law?
Sometimes the unexplainable happens. Why is it not possible you got a bad casting? I used to be a melter at a gray iron foundry and what was good iron on Tuesday was junk on Friday. I made it the same way every day. Yeah, we did spectrometer and Brinnel testing, but stuff was just bad sometimes. The Titanic wasn't supposed to sink... after examination of the steel, metalurgical deficiencies arose. Buy another and go sailing.;D;D;D
Sometimes the unexplainable happens. Why is it not possible you got a bad casting? I used to be a melter at a gray iron foundry and what was good iron on Tuesday was junk on Friday. I made it the same way every day. Yeah, we did spectrometer and Brinnel testing, but stuff was just bad sometimes. The Titanic wasn't supposed to sink... after examination of the steel, metalurgical deficiencies arose. Buy another and go sailing.;D;D;D
Marina says AC current can't do this
I did call the marina to ask them about the possibility that their wiring is the source. They claim that AC power is never the source of electrolysis but that it always comes from bad DC connections on other people's boats. Is that accurate?
I did call the marina to ask them about the possibility that their wiring is the source. They claim that AC power is never the source of electrolysis but that it always comes from bad DC connections on other people's boats. Is that accurate?
From what is visable...
...the leading and trailing edges of the prop look pretty good. Electrolysis would have attacked the outer edges of the prop first. Is there any sign of a lightning strike on your boat, all the electronics functioning?, wiring OK? VHF works? It looks very much like an exit point from a strike. (truth be told it's an entrance point) lightning strikes from the ground up not from the sky down.
...the leading and trailing edges of the prop look pretty good. Electrolysis would have attacked the outer edges of the prop first. Is there any sign of a lightning strike on your boat, all the electronics functioning?, wiring OK? VHF works? It looks very much like an exit point from a strike. (truth be told it's an entrance point) lightning strikes from the ground up not from the sky down.
Rick -- Your marina is wrong.
Bad Grounds from AC wiring can cause rapid deterioration of underwater . Yes its the DC (Direct Current) component "single direction flow of electrons" that cause accelerated Galvanic Corrosion (not really electrolysis -- thats often used incorrectly). But it could be a bad ground circuit in your docks causing it. Or possibly more likely it could be from your boating neighbors. When they have lousy wiring and leak current into the water it can cause you problems. You'd be surprised just a small voltage differential can do lots of damage. This web site explains it a bit http://www.boatus.com/boattech/MarineCorrosion.htm. Does your boat have a galvanic Isolator? If you don't it might help (maybe isolat Please Please !! check your underwater metal thru-hulls. If your prop looks like that it can affect the thru hulls also. But the thru hulls are less likely corroding since many people do not bond them (which I agree I wouldn't do either) and therefore there is no real complete circuit thus less current flow through it. You could always put a rubber shaft spacer that could isolate the shaft from the engine ground
Bad Grounds from AC wiring can cause rapid deterioration of underwater . Yes its the DC (Direct Current) component "single direction flow of electrons" that cause accelerated Galvanic Corrosion (not really electrolysis -- thats often used incorrectly). But it could be a bad ground circuit in your docks causing it. Or possibly more likely it could be from your boating neighbors. When they have lousy wiring and leak current into the water it can cause you problems. You'd be surprised just a small voltage differential can do lots of damage. This web site explains it a bit http://www.boatus.com/boattech/MarineCorrosion.htm. Does your boat have a galvanic Isolator? If you don't it might help (maybe isolat Please Please !! check your underwater metal thru-hulls. If your prop looks like that it can affect the thru hulls also. But the thru hulls are less likely corroding since many people do not bond them (which I agree I wouldn't do either) and therefore there is no real complete circuit thus less current flow through it. You could always put a rubber shaft spacer that could isolate the shaft from the engine ground
I've been told...
that when bronze turns pink like major parts of your prop has, that it is definitely from electrolysis. Yes, stray current in the marina CAN cause what you are seeing. Read through the attachment I sent along for more information.
that when bronze turns pink like major parts of your prop has, that it is definitely from electrolysis. Yes, stray current in the marina CAN cause what you are seeing. Read through the attachment I sent along for more information.
Rick, place two electrodes
in an insulator about two feet a part, connect them to a digital volt meter and lower them into the water at your marina. Then rotate them to see if there is a difference in the potential relative to the orientation. Next drag this contraption around the marina until you find the highest potentail between the electrodes and you will be close to the bad boy that is causing all of the problems.
in an insulator about two feet a part, connect them to a digital volt meter and lower them into the water at your marina. Then rotate them to see if there is a difference in the potential relative to the orientation. Next drag this contraption around the marina until you find the highest potentail between the electrodes and you will be close to the bad boy that is causing all of the problems.
galvonic corosion
Take a close look at the picture. Where is the keyway groove? Look at the edges of the "crack". Do they look like it broke or do they look like rust? The key was probably SS and not bronze and you got that two metals in salt water battery thing going. Now a zinc is going to stop that if it is electricaly connected to both metals. If the zinc is consumed by another process and does not get replaced BEFORE it becomes ineffective, the rest of the system will start to rust. Putting on a new zink at that point will not repair the damage. Do that a couple of times and you gets a busted prop. Also once your let corosion get started you don't have a good electrical connection between the prop and the shaft so a new zink is not going to help. I'd be checking ALL my thru-hulls TODAY!!! I'd also get one of those "fish" zinks that you attach to your grounding system and then throw over the side. These help out your primary zinks and allow you to keep an eye on how fast they are being consumed. As for zinks being consumed in 4 months, that is not right and if everybody is having this problem I'd pull the shore power and isolate myself untill I found out what was going on. There are meters that can test for a bad shore ground. Or it could be that you are moored next to an aluminum hull boat. That is alway a fun thing to have as there is effectively a giant aluminum cathode electricaly attached and in close proxmity to your $500 prop. Aluminum is less noble than zinc.
Take a close look at the picture. Where is the keyway groove? Look at the edges of the "crack". Do they look like it broke or do they look like rust? The key was probably SS and not bronze and you got that two metals in salt water battery thing going. Now a zinc is going to stop that if it is electricaly connected to both metals. If the zinc is consumed by another process and does not get replaced BEFORE it becomes ineffective, the rest of the system will start to rust. Putting on a new zink at that point will not repair the damage. Do that a couple of times and you gets a busted prop. Also once your let corosion get started you don't have a good electrical connection between the prop and the shaft so a new zink is not going to help. I'd be checking ALL my thru-hulls TODAY!!! I'd also get one of those "fish" zinks that you attach to your grounding system and then throw over the side. These help out your primary zinks and allow you to keep an eye on how fast they are being consumed. As for zinks being consumed in 4 months, that is not right and if everybody is having this problem I'd pull the shore power and isolate myself untill I found out what was going on. There are meters that can test for a bad shore ground. Or it could be that you are moored next to an aluminum hull boat. That is alway a fun thing to have as there is effectively a giant aluminum cathode electricaly attached and in close proxmity to your $500 prop. Aluminum is less noble than zinc.
That prop is definately
"de-zincified", as the coloring shows. The zinc in the bronze has been eaten away, leaving the copper behind. The problem may be either galvanic corrosion or electrolysis. As suggested earlier, check the water around your boat for stray current and also check your boat for electric potential between your boat ground (shrouds, thru-hulls, prop shaft, battery negative, etc.) and the water, the marina's ground connection in the power outlets, and between all the gounded parts of the boat and each other, especially between prop shaft and thru-hulls, prop shaft and battery neg, etc. to try to isolate the source. In the mean time, hang a zinc over the side on a copper wire, connected temporarily to the prop shaft. to provide protection.
"de-zincified", as the coloring shows. The zinc in the bronze has been eaten away, leaving the copper behind. The problem may be either galvanic corrosion or electrolysis. As suggested earlier, check the water around your boat for stray current and also check your boat for electric potential between your boat ground (shrouds, thru-hulls, prop shaft, battery negative, etc.) and the water, the marina's ground connection in the power outlets, and between all the gounded parts of the boat and each other, especially between prop shaft and thru-hulls, prop shaft and battery neg, etc. to try to isolate the source. In the mean time, hang a zinc over the side on a copper wire, connected temporarily to the prop shaft. to provide protection.
Change marinas
I had the same type of problem; Martec folding prop was eaten away to almost failure in less than 3 months, got the same line as you did from the marina. I moved the boat and never had any problems after that.
I had the same type of problem; Martec folding prop was eaten away to almost failure in less than 3 months, got the same line as you did from the marina. I moved the boat and never had any problems after that.
Verification
Morning Rick: To verify what everyone else has indicated, get yourself a cheap multi-meter. With your boat hooked up to shorepower, set the multi-meter on DC and then touch one end to a portion of your boat that is grounded and drop the other end in the water. I believe that you are going to fine a considerable amount of DC current in the water. Then switch it over to AC and do the same thing to see what type or reading you get. If your through-hulls are in the same shape as your prop, you have additional problems. By the way, if you get some pretty good DC readings, try the same procedure on your dock mates boats. The closer you get to the offending boat, the larger the DC reading will get. I'm pretty sure that AC will also cause problems, but not to the extent that DC will.
Morning Rick: To verify what everyone else has indicated, get yourself a cheap multi-meter. With your boat hooked up to shorepower, set the multi-meter on DC and then touch one end to a portion of your boat that is grounded and drop the other end in the water. I believe that you are going to fine a considerable amount of DC current in the water. Then switch it over to AC and do the same thing to see what type or reading you get. If your through-hulls are in the same shape as your prop, you have additional problems. By the way, if you get some pretty good DC readings, try the same procedure on your dock mates boats. The closer you get to the offending boat, the larger the DC reading will get. I'm pretty sure that AC will also cause problems, but not to the extent that DC will.
Key or no Key
Rick Does, or did you shaft have a key slot in it? If so the key may have been made out of a different metal (iron) and it took 6 years to eat through your prop. You will never find the key but you may see something left of it on your shaft. Brass being a softer matal than the SS shaft it just gobbled it up. See if your insurance co. will pay for a new one. Good luck
Rick Does, or did you shaft have a key slot in it? If so the key may have been made out of a different metal (iron) and it took 6 years to eat through your prop. You will never find the key but you may see something left of it on your shaft. Brass being a softer matal than the SS shaft it just gobbled it up. See if your insurance co. will pay for a new one. Good luck
I don't blame a SS key (if it was SS)
They are LOTS of boats out there with a Stainless Steel Shaft and Bronze props. Just look at about every single motorboat in your yard. Most everyone of them has a SS shaft and Bronze props. Rarely do you see a Stainless Steel prop. I have a Stanless Steel Shaft and a bronze alloy prop, but I don't get problems like that. Blaming a SS key means you are looking in the worng place. I would put my money on stray underwater electrical currents
They are LOTS of boats out there with a Stainless Steel Shaft and Bronze props. Just look at about every single motorboat in your yard. Most everyone of them has a SS shaft and Bronze props. Rarely do you see a Stainless Steel prop. I have a Stanless Steel Shaft and a bronze alloy prop, but I don't get problems like that. Blaming a SS key means you are looking in the worng place. I would put my money on stray underwater electrical currents
With all of the alloys out
there that are primarilary copper but will have aluminum, tin, silicon, phosphorus, beryllium, manganese and zinc. It is not wise to make broad sweeping statements concerning the cause of a failure of this nature. Usually copper alloyed with zinc is called brass but the terms brass and bronze are often used interchangably today. With a sacrificial anode in place on the propeller shaft there should be no acute corrision problem with a bronze propeller and a non-bronze shaft. I use the terminology because there are several alloys in use for propeller shafts that resemble stainless steel but are much more sophisticated in their content.
there that are primarilary copper but will have aluminum, tin, silicon, phosphorus, beryllium, manganese and zinc. It is not wise to make broad sweeping statements concerning the cause of a failure of this nature. Usually copper alloyed with zinc is called brass but the terms brass and bronze are often used interchangably today. With a sacrificial anode in place on the propeller shaft there should be no acute corrision problem with a bronze propeller and a non-bronze shaft. I use the terminology because there are several alloys in use for propeller shafts that resemble stainless steel but are much more sophisticated in their content.
Pencil zinc
How is you pencil zinc? Do you have a pencil zinc? I would be concerned for my engine also. You need some serious research. Could it have been a reaction with the type of paint that was applied to the prop?
How is you pencil zinc? Do you have a pencil zinc? I would be concerned for my engine also. You need some serious research. Could it have been a reaction with the type of paint that was applied to the prop?
What if the boat isn't bonded??
I'm having a certified electrician check out the problem. I spoke with the marina and their position is that it has to be a "boat" problem and not a marina problem because they believe it necessarily originates from a defect in some DC system. My Beneteau is not electrically bonded so none of my through hulls are grounded. Do you all still think they are at risk. I would assume that electrolysis attacked my propeller because it's connected to the shaft and engine which, of course, are all grounded. Stray current needs a place to enter and to exit so, since by through hulls aren't grounded, there should be no way for the current to leave. I understand that it's when the current leaves the metal that it's at the point of exit that the electrolysis actually occurs. The key to my propeller does appear to be of a different metal (maybe stainless) and that raises the issue of galvanic corrosion but somebody made a good point that there are tons of bronze props with stainless keys. In fact, the new one I bought from Beneteau was a bronze prop with a stainless key. So, it seems unlikely this was the cause although a metallurgist told me this could be prolematic.
I'm having a certified electrician check out the problem. I spoke with the marina and their position is that it has to be a "boat" problem and not a marina problem because they believe it necessarily originates from a defect in some DC system. My Beneteau is not electrically bonded so none of my through hulls are grounded. Do you all still think they are at risk. I would assume that electrolysis attacked my propeller because it's connected to the shaft and engine which, of course, are all grounded. Stray current needs a place to enter and to exit so, since by through hulls aren't grounded, there should be no way for the current to leave. I understand that it's when the current leaves the metal that it's at the point of exit that the electrolysis actually occurs. The key to my propeller does appear to be of a different metal (maybe stainless) and that raises the issue of galvanic corrosion but somebody made a good point that there are tons of bronze props with stainless keys. In fact, the new one I bought from Beneteau was a bronze prop with a stainless key. So, it seems unlikely this was the cause although a metallurgist told me this could be prolematic.
Rick, Problematic, Yes. Totally destroy a prop, No
This isn't some average everyday galvanic corrosion here. This is a full blown catastrophic failure. Ross, yes you are correct, I was not trying to over explain and throw too many variable in, but you are correct, there are many different types of "bronze" and "SS" alloys. But any decent shaft be it AQUAMET® 17,18, 19 or 22 would never cause that kind of damage alone I would highly doubt that prop was more a "copper" or "brass" type alloy than a good bronze alloy used for marine applications.....who would make one like that anyway...
This isn't some average everyday galvanic corrosion here. This is a full blown catastrophic failure. Ross, yes you are correct, I was not trying to over explain and throw too many variable in, but you are correct, there are many different types of "bronze" and "SS" alloys. But any decent shaft be it AQUAMET® 17,18, 19 or 22 would never cause that kind of damage alone I would highly doubt that prop was more a "copper" or "brass" type alloy than a good bronze alloy used for marine applications.....who would make one like that anyway...
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