[jdecoudres]

I let a buddy use a stainless steel prop and when i got it back it wasnt shinny anymore. It had a really thick film on it and u could spray cleaner on it and it wouldnt come off and to to scrap it off. What is this and whats the best way to get it off?

[mikeyt]

Without knowing where & how he used the prop, it sounds like a bit of electrolysis going on. Try using some fine steel wool or even a majic erasor.

[jdecoudres]

ok thanks a lot. so does this happen by leaving it in the water for long period of time

[Firth's Impression]

Yes, leaving it in the water will cause this. I use a product called ON-OFF that is used to take the water stain off your hull. It's powerful stuff (acid based) so don't get it on your hands (at least for too long). I use dish washing gloves and spray it on with on old nozzle out of one of my other empty cleaner bottles. Don't expect to be able to use the nozzle again because the acid based solvent eats away at the valve of the nozzle. Spray it on the prop and the gunk on there will "fizz" up and maybe even turn a bit yellow. Let is sit for about a minute and then take an S.O.S pad and scrub it off (again, don't forget to where your gloves). Not sure if you have S.O.S. pads in the USA as they are a brand name of fine steel wool pads with a soapy detergent interlaces among the steelwool. Used for cleaning stainless steel, etc...Alway hose down the prop and surrounding area with fresh water to be sure that the acid is all washed away.

[mikeyt]

Originally Posted by jdecoudres

ok thanks a lot. so does this happen by leaving it in the water for long period of time

Most of the time yes but not always. If the electrolysis leakage from the boat is bad enough (ie completely worn out or missing anodes), it can happen very quickly.

[Firth's Impression]

Very True.

[jdecoudres]

Ok dumb question. What this anodies and electryoies u guys are talking about and do i need to do anything to fix it

[mikeyt]

No question is a 'dumb' question. I cant pretend to be a scientist but i will do the best i can with this explanation. Anodes are like sacrificial lambs. They're installed so that they handle the electrical currents that are generated when you immerse two (or more) different metals in a liquid (such as water). The anodes are made of a much weaker metal that gets eaten away first (therefore the 'sacrificial') so that your SS prop / white metal / brass fittings / aluminum parts are protected and don't get eaten first. Comprendez?

When the anode gets down to about 50% of its original size, it should be replaced.

Electrolysis is simply the electrical current that is created when the two dissimilar metals are placed in the same liquid. Electrolysis is far more of a problem in salt water as salt water is more conductive than fresh water. Anodes used in salt water applications are different than those used in fresh water applications.

For a more detailed explanation of anodes, cathodes & outdrive protection you can check out this post of mine or the entire thread since 'Dudders' experienced the same problem you had with the discoloration of your SS prop.