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Prop spots and discoloration

Old 01-10-2019, 04:06 PM
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Default Prop spots and discoloration

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.

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Old 01-10-2019, 04:50 PM
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are you rinsing the motors off after use? looks like corrosion and rust from where salt is left after the water has evaporated
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Old 01-10-2019, 04:59 PM
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yes I flush the engines and hose the whole boat and engines down. I have had many boats with SS props and have never seen this before. Also the props are 3-4 foot out of water.
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Old 01-12-2019, 08:48 AM
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anyone else?
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Old 01-12-2019, 09:00 AM
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Maybe a bad batch of stainless
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Old 01-12-2019, 09:56 AM
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Over spray from some cleaner being used near the boat that's reacting with the stainless?
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Old 01-12-2019, 10:12 AM
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My stainless steel yamaha props are starting to look like that. No cleaners involved but it could be air pollution like the crap collects on top o car and stuff left outdoors.

it could be acids in canal wasser.

Last edited by solarfry; 01-12-2019 at 03:01 PM.
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Old 01-12-2019, 10:18 AM
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I would guess a cheap grade off stainless steel used to make them. I had one stainless prop on a previous boat that I used in saltwater and fresh and kept it trailered always. Washed it down after use etc. It rust spotted like yours to a degree, not quite as bad.
I don’t know the brand it was but was on a OMC. Ran great though .
You could get a prop shop to tune them up, polish and coat them.
Or just run em.

I remember that a magnet stuck to mine very well so there was a lot of ferrous metal in it.
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Old 01-12-2019, 10:21 AM
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I know what it looks like. Only you can figure out if there is a chance that it is.

I've seen stainless do this when some other metal cutting or grinding was going on nearby and the red hot sparks (embers) flew off and stuck to the stainless.
Then you get near saltwater and the little non-stainless pieces that have essentially been "soldered or welded" in place, start to rust and stain.

Believe me it don't take much, even if you steel wool something and don't vacuum and wash thoroughly afterwards, you will have mysterious rust stains everywhere soon after.
8 is enough and toy box like this.
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Old 01-12-2019, 10:54 AM
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There are many different grades of stainless steel. Steel (and stainless steel) is not a uniform material. It appears that there are localized areas within this stainless that are different in composition from the rest and that these areas are rusting. I suspect that these regions are all small enough that the rust is limited to these small localized spots and hasn't made it into the bulk of the material. I think you're okay.


It's also possible that whatever polishing operation was done at the factory introduced tiny particles of regular steel into the surface.
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Old 01-12-2019, 11:15 AM
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I would try a good cleaning with barkeepers friend and a green scrubby pad to see if it is contaminants.
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Old 01-12-2019, 11:31 AM
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I bought my stainless prop at a discount because it was NOS and had become blemished by just sitting.

Stainless steel isn't stainless.
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Old 01-12-2019, 03:50 PM
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Originally Posted by whorrall View Post
I bought my stainless prop at a discount because it was NOS and had become blemished by just sitting.

Stainless steel isn't stain free.
Fixed it for you. You are welcome.
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Old 01-12-2019, 03:56 PM
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Originally Posted by alloyboy View Post
Fixed it for you. You are welcome.
I probably should have just left it the way I was initially thinking of saying it:

Stainless steel isn't.
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Old 01-12-2019, 04:03 PM
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Originally Posted by Dacman View Post
I would guess a cheap grade off stainless steel used to make them. I had one stainless prop on a previous boat that I used in saltwater and fresh and kept it trailered always. Washed it down after use etc. It rust spotted like yours to a degree, not quite as bad.
I don’t know the brand it was but was on a OMC. Ran great though .
You could get a prop shop to tune them up, polish and coat them.
Or just run em.

I remember that a magnet stuck to mine very well so there was a lot of ferrous metal in it.
Hey not to derail the thread here but I've heard this about nonmagnetic stainless steel before, and i don't understand. The other day i was playing with my big rare earth magnet and noticed that stainless bolts stick to it, but not as well as regular bolts. Ferrous = iron containing, right? And steel is any alloy that contains iron, correct? So any stainless steel will stick to a magnet right? Or no?
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Old 01-12-2019, 04:18 PM
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Interesting to see all the comments about SS props.
To the OP, well, that sucks and hopefully they will serve you for a long time.

I was going thru another thread and saw the yammies SS props in this picture. I have never seen that.
This in the new Yammie V8 engines. Two look weird, the third one is getting there... considering these are 2018 engines with less than 100hrs, there's something in that SS that is not right, at least in my untrained eyes.
And I don't think it's stray current...

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Old 01-12-2019, 04:36 PM
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I’d be slightly concerned with stress corrosion cracking if it is indeed corrosion. Typical corrosion spots induce stress, stress induces micro-cracks, micro-cracks propagate and well..you know the rest of story. Perhaps bring them to prop shop and have them cleaned and inspected.
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Old 01-12-2019, 04:40 PM
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Originally Posted by Grunts N Grits View Post
I know what it looks like. Only you can figure out if there is a chance that it is.

I've seen stainless do this when some other metal cutting or grinding was going on nearby and the red hot sparks (embers) flew off and stuck to the stainless.
Then you get near saltwater and the little non-stainless pieces that have essentially been "soldered or welded" in place, start to rust and stain.

Believe me it don't take much, even if you steel wool something and don't vacuum and wash thoroughly afterwards, you will have mysterious rust stains everywhere soon after.

I saw that happen on my old sailboat’s fiberglass after I cleaned some of it with steel wool
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Old 01-12-2019, 05:55 PM
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Originally Posted by whorrall View Post
Hey not to derail the thread here but I've heard this about nonmagnetic stainless steel before, and i don't understand. The other day i was playing with my big rare earth magnet and noticed that stainless bolts stick to it, but not as well as regular bolts. Ferrous = iron containing, right? And steel is any alloy that contains iron, correct? So any stainless steel will stick to a magnet right? Or no?
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.
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Old 01-12-2019, 06:03 PM
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I h ad some discoloramd rust spots on mine, took some Rust away spray, cleaned with a bronze pad, then polished to a mirror finish with some flitz and a wheel. Salt is moslikely the culprit. I’ve heard sharkhide works well in preventing this or at least slowing,
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