SS Props getting 'misty'

[Manos]

Some SS props (mainly 4 blade) after operating sometime they lose their shine and become misty. I understand that this is salt deposits and it cleans very easily with vinegar or a spray for bathroom cleaning spray called Viacal.

The question is why these props become 'misty'?

Is it because of the inferior metal qulaity?
Is it because they become overheated?
Is it because they cavitate or vetilate?

What do you think??? Alsois there any way to remedy this?

Any replies and suggestions gratefully received.
Thanks

[Seaharrier]

When we go to the Med, we have the same problem with our prop after 7 days.

Here in Belgium we don't have that problem. During the summer, the boat remained for 3 weeks in the water and the prop is still shiny.

Is it because the med sea has way more salt?

[Manos]

Originally Posted by Seaharrier

Is it because the med sea has way more salt?

No I do not think so. This propblem appears mainly to some aftremarket props all the props we have bought from Mercury or Yamaha never had this problem or if they had it it was only in patches rather than the slat covering the prop.

Very strange .... it must be something to do with the metal and prop overheating IMHO rather than anything else but ...... anything is possible

[UKPOWERBOAT]

Originally Posted by Seaharrier

When we go to the Med, we have the same problem with our prop after 7 days.

Here in Belgium we don't have that problem. During the summer, the boat remained for 3 weeks in the water and the prop is still shiny.

Is it because the med sea has way more salt?

I agree with you, Carly Baby on here has a stainless prop on his drive leg, when we pulled it out of the water here in the UK, it was still relatively shiny having been in the water all summer. After our trip to the South of France with the boat, we pulled the boat out of the water after a week in the Harbour there, and we found the prop had gone all cloudy and "misty.

Also swimming in the sea, the water tasted far more salty than you get in the UK.

[Manos]

What is the manufacturer of these props you are talking about guys?

[Polwart]

I don't think it is likely to be "salt" (sodium chloride) that is causing the problem because:

1. you wouldn't need vinegar to remove it - ordinary tap water would do.
2. the sea isn't anywhere near saturated with salt - so it would disolved off just in sea water
3. the difference in salinity between the belgian waters and the med is not huge - so this wouldn't explain the difference in observations (unless the belgian boat is in say an eastury).
4. it would presumably have been worse on your recent trip to the red sea where salt content is higher
5. mediteranean water is warmer than our water in the north of europe so it would be less likely to be a problem (more salt would disolve in the water / quiker / easier)

The need for vinegar suggests it is probably calcium carbonate (which is a salt, but not what we normally mean when we say salt). Calcium carbonate has an innverse solubility curve - unlike most materials which become more soluble as you heat the water up - calcium carbonate becomes less soluble in warmer/hotter water. calcium carbonate is what causes scaling in kettles, boilers etc.

It seems possible to me that your prop gets hot during use and so precipitates out calcium carbonate from the water.

Why this might be problem for you but not some other people could be related to different calcium carbonate concentrations in water, which can vary with geography/geology, co2 levels in the the atmosphere etc. and of course water temperature.

[Manos]

@ Polwart ... WOW MANY THANKS! This makes sence

[Manos]

One last question.

Would these 'salt' deposits that cover the prop depend also on the type of metal that prop is made of?

I say this becaise all Salt Water Series II Yamaha props (I have all the series by the way ... Isn't taht sad ) as well as the Mercury BRAVO II props as well as the SUZUKI props as far as I know do not (or very rarely) get 'misty', where as other after market props do get 'misty' after a few hours in the water.

[Polwart]

I would assume that most S/S props are made from similar grades of steel and think perhaps this is not the casue of the difference you see. My gut feel, is that if you see a difference it will be because either: (a) the OEM product has been coated or treated to prevent this phenomenon OR (b) there is a difference in the surface finish of the prop.

I don't know if there is any sort of lacquer on the OEM product - that could feasibly prevent adhesion of the precipitated calcium carbonate to the surface of the material. It is also possible that processes such as heating or cooling conditions during manufacture could result in a slightly different surface chemistry which reduces adhesion.

The alternative would be that the OEM props are finished to a higher spec (at the microscopic level), Crystals form a lot easier on little microscopic defects and so if the prop has a slightly different grain structure (in the steel) or the surface finishing is not quite as good it might encourage crystals to form and stick to the prop. Every time you clean it off you may make it a little worse as the acidic vinegar will cause microscopic pitting in the blade.

I guess the alternative is that there is a difference in heat dissipation (either due to material properties or finer points of design) which means the OEM prop surfaces are cooler. Or of course it is a combination of all 3!

[Seaharrier]

Originally Posted by Manos

What is the manufacturer of these props you are talking about guys?

Mercury High Five SS prop and Evinrude Raker