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Prop spots and discoloration

Old 01-12-2019, 08:26 PM
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Originally Posted by maintenanceguy View Post
There are lots of different kinds of stainless steel and almost all (maybe all) fall into two broad classes.

300 series contain iron, chromium, nickel, and molybdenum. 300 series are typically not magnetic. 300 is also more corrosion resistant than the 400 series.

400 series contain iron, chromium and manganese and is magnetic.

There are lots of different types of 300's and lots of types of 400's and they all vary in how magnetic they are and how corrosion resistant they are. 318 is the stainless that is most commonly found in quality marine items. But, I'm sure there are a dozen or more that are also suitable.
Thanks for the information!
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Old 01-12-2019, 09:05 PM
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I would clean/polish them or have a shop do it. Since they have been that way since you got them, the cause could be anything.

Oops, a more recent post from the OP says that they were not always like this while he owned it.

Last edited by GaryDoug; 01-13-2019 at 07:35 PM.
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Old 01-12-2019, 09:46 PM
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Wow - definitely unusual in the time frame stated. Did you ever have the hull acid cleaned?
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Old 01-13-2019, 01:42 PM
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After an argument about magnets on stainless props with a friend of mine,
i tried it on his ss prop and it didn’t stick. Better grade and no rust.
It was not aluminum btw
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Old 01-13-2019, 02:24 PM
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Originally Posted by whorrall View Post
I probably should have just left it the way I was initially thinking of saying it:

Stainless steel isn't.
But it is. Stainless stains less. Less than other steel alloys. But it still can stain.

How stainless came to be thought of as stainfree is unknown to me.
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Old 01-13-2019, 02:26 PM
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Originally Posted by Dacman View Post
After an argument about magnets on stainless props with a friend of mine,
i tried it on his ss prop and it didn’t stick. Better grade and no rust.
It was not aluminum btw
The argument seems to be based on the myth that all stain less steel is non-magnetic. A myth that can be perpetuated here on THT. Where myths becomes facts.

Some better grades of stain less steel are magnetic. Depends upon what the objective of the steel maker is.
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Old 01-13-2019, 03:27 PM
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replace the props, rinse and wash after every use.
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Old 01-13-2019, 04:08 PM
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Clean and polish and they will not rust as quickly. One might even consider powder coat if not in a high proformance situation. Hell i would even consider scuffing them with scotch brite and painting them with good quality black spary paint. I know you would have to hit them every so often but it would be cheap enough it would not matter.
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Old 01-13-2019, 04:33 PM
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Originally Posted by alloyboy View Post
The argument seems to be based on the myth that all stain less steel is non-magnetic. A myth that can be perpetuated here on THT. Where myths becomes facts.

Some better grades of stain less steel are magnetic. Depends upon what the objective of the steel maker is.
Not only that but normally non-magnetic stainless can become magnetic due to cold working of the material.

https://www.assda.asn.au/technical-i...ainless-steels
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Old 01-13-2019, 06:16 PM
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Originally Posted by TeamBalla View Post
replace the props, rinse and wash after every use.
Flushing. Always the answer. After spending 1400 bucks.

I blew through a mud bank back in July and ended up with similar spots about a week later. Did it rip some oxidative layer off the stainless for a brief period? Maybe. Who cares?

Last edited by pstephens46; 01-13-2019 at 06:22 PM.
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Old 01-13-2019, 07:03 PM
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I do flush every time and I also hose the props down good. I looked at a few pictures from when I bought the boat in May of 2018, and the spots are way worst now. I am starting to think it is some type of stray current. How ever I always shut off both battery masters and never run anytype of AC up to the boat, not even a battery tender. I also unplug my boat lift as soon as it is loaded or not in use, so that really does not make sense either. I know none of my neighbors have have lifts or anything plugged in close to the water.
Here is a pic from May of 2018 when I bought the boat. I have put on 10 hours since I bought it.



And Jan 2019

Last edited by mikeloew; 01-13-2019 at 07:14 PM.
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Old 01-13-2019, 07:34 PM
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Originally Posted by mikeloew View Post
I do flush every time and I also hose the props down good. I looked at a few pictures from when I bought the boat in May of 2018, and the spots are way worst now. I am starting to think it is some type of stray current. How ever I always shut off both battery masters and never run anytype of AC up to the boat, not even a battery tender. I also unplug my boat lift as soon as it is loaded or not in use, so that really does not make sense either. I know none of my neighbors have have lifts or anything plugged in close to the water.
Here is a pic from May of 2018 when I bought the boat. I have put on 10 hours since I bought it.



And Jan 2019
Looking at pic. Are they pitted? Or just discolored? Looking again it appears to be pitted. Not normal.

Last edited by pstephens46; 01-13-2019 at 07:40 PM.
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Old 01-13-2019, 07:44 PM
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Flushing was sarcasm.....do you have any extra added battery charging devices on the boat? strange that the aluminum appears to be perfect. All stock bonding wires should be connected. Beyond me.....
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Old 01-13-2019, 08:01 PM
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Originally Posted by pstephens46 View Post
Flushing was sarcasm.....do you have any extra added battery charging devices on the boat? strange that the aluminum appears to be perfect. All stock bonding wires should be connected. Beyond me.....
No, just three batteries, no external charger.
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Old 01-13-2019, 08:15 PM
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Originally Posted by mikeloew View Post
No, just three batteries, no external charger.
i have called for back up.
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Old 01-14-2019, 05:49 AM
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I don't think that this is a bad batch of Yamaha propellers as Yamaha uses high quality materials for their outboards and propellers.
Rusting propellers could be stray currents, in your case probably a bad connected negative cable so the engines uses the lower unit as ground.
If the rusty spots are pitted then the problem is serious, if only superficial rust you can polish them with a SS cleaner and they will turn new again.
However, you should investigate this problem as it is definitively not normal and may ask the dealership where you bought the engines/propellers
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Old 01-14-2019, 08:56 AM
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They look like they were once Black SS Yamaha Props, polished off to look Shiny. Looking at the Rakes, and Exhaust Flutes, and No Exhaust Vent Holes or Names stamped in them.

Sub Stainless is most likely why Yamaha painted their SS Props in the first place.
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Old 01-14-2019, 09:55 AM
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Am I the only one seeing the black soot on the Port motor hub?
May just be carbon build up but the inside of the hub should not be black like that.

As far as the rusting, those all appear to be superficial surface spots. It looks like the seller used the wrong products to clean the prop for resale.

Personally I would take them to the local prop shop. Ask them what they think, if it's just surface spots have them polished. Now you are at a "known good" state.
If they start rusting again after the professional polishing then you know to dig deeper.
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Old 01-14-2019, 10:28 AM
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Originally Posted by maintenanceguy View Post
There are lots of different kinds of stainless steel and almost all (maybe all) fall into two broad classes.

300 series contain iron, chromium, nickel, and molybdenum. 300 series are typically not magnetic. 300 is also more corrosion resistant than the 400 series.

400 series contain iron, chromium and manganese and is magnetic.

There are lots of different types of 300's and lots of types of 400's and they all vary in how magnetic they are and how corrosion resistant they are. 318 is the stainless that is most commonly found in quality marine items. But, I'm sure there are a dozen or more that are also suitable.
316 is the most common not 318, I’m sure that was a typo. 304 is also fairly common and is a little harder but not as corrosion resistant. It is also called 18-8 stainless.
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Old 01-14-2019, 10:48 AM
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Originally Posted by mikeloew View Post
Anyone have an idea what would cause my Yamaha SS props to spot like this? My boat is on a lift so I can not reach them to feel the spots.
The motors only have 110 hours on them and were this way when I bought the boat.
You're not the original owner?
How do you know they are "Yamaha" props ?
Given the zincs & aluminum, (plus you keep on a lift) drives look ok I suspect they are off brand props.
The safe move would be to have a good prop shop check them out. I once had a prop condemned due to a (smaller then hairline) crack creating risk the blade could snap & fly off.
My Yamaha props have 0 rust although one is shinny-polished looking and the other dull. Always kept on lift.
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