Hello we bought a folding prop from Kiwi Prop (out of Marina Del Rey, but was shipped here from NZ) They have refused to honor any warranty basically and just downright unhelpful so far. The keys/hardware are already showing severe corrosion which makes me question the workman ship for a $1700 propeller! Has anyone had any luck with using these for the longer term? any advice on how to keep from corroding? Or better yet any advice on how to hold manufacture accountable here?
Kiwi Folding Prop- Already corroding after 6 months of use! What shall I do?
- Thread starter califun1
- Start date
The warrantee on the website specifically says that wear and corrosion are not valid warranty claims. They also suggest painting the unit with non-copper antifouling. Doing that might reduce corrosion. The blades don't look like they're about to fall off. How long have you had it?
Are you able to add additional zincs to the prop shaft ? The more cathodic you can make the shaft and it's in good electrical contact with the prop, the more corrosion resistance the prop will have.
You can also install an external zinc which is submerged, close to the prop, and in good electrical contact to the engine block and the prop shaft as measured inside the boat. You're looking for a reading of near zero Ω through the electrical wiring.
The overboard zinc is put in place when the boat is at rest in the home marina.
You can also install an external zinc which is submerged, close to the prop, and in good electrical contact to the engine block and the prop shaft as measured inside the boat. You're looking for a reading of near zero Ω through the electrical wiring.
The overboard zinc is put in place when the boat is at rest in the home marina.
Last edited:
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,742
It looks like Kiwi used 304 or 18-8 hardware, these are less corrosion resistant then 316. You could replace them with 316 hardware. I don't see a "severe" corrosion, just some surface rust typical of 304 hardware.
Most of this prop is plastic, so corrosion shouldn't be an issue. Just the hub and hardware are not plastic. The hub is bronze.
Most of this prop is plastic, so corrosion shouldn't be an issue. Just the hub and hardware are not plastic. The hub is bronze.
It is a feathering prop, not a folding prop. I flicked through the photos looking for corrosion, and had to go back again to scrutinize them to see what your complaint was. There is hardly anything at all a problem there. Just a bit of staining around some stainless fasteners. This is not in any way "severe corrosion", and is completely normal - even 316 fasteners will do this. Take them out, clean them up, soak them in citric acid, and put back in with either locktite or tefgel, depending on what the manufacturer states.
It does look like cast SS, however I got the bronze info from the Kiwi website. The cast hub has not been finished very well, it is a rough casting.
You can verify the SST material with a small magnet. 316 SST is not magnetic. 304 SST will be slightly magnetic. I worked in the mining industry and we would get hardware that claimed to be 316 SST. It would either be low grade or 304 SST. The magnet test works.
The slight amount of corrosion can sometimes be caused by contact with non SST. For example the slots in the screws can show rust from a non SST screwdriver. An extreme example is using a standard wire brush to clean SST.
SST gets its corrosion resistance from a passive oxide layer. I don't know this for certain but in theory coating or painting it would not be helpful as SST needs exposure to oxygen to maintain that passive layer.
The slight amount of corrosion can sometimes be caused by contact with non SST. For example the slots in the screws can show rust from a non SST screwdriver. An extreme example is using a standard wire brush to clean SST.
SST gets its corrosion resistance from a passive oxide layer. I don't know this for certain but in theory coating or painting it would not be helpful as SST needs exposure to oxygen to maintain that passive layer.
What years did you work in the mining industry? I ask because before about 1990, the magnet test - while not very good the either - was somewhat useful. With the advent of modern stainless steel manufacturing ( long story) it is no longer a reliable test.
Painting stainless is typically not a good idea as you say, but coating, that depends upon the coating system.
Completely agree with the screw driver explanation and wire brushing.
dj
In the 1980's and before, the mills would make separate mill runs for 316 and 316L. At that time 316L was more expensive to produce because the control of carbon was difficult. Then they came up with some new methods in the smelting that made the control of carbon easier. Mills went to producing what is called dual certifiable 316 meaning that the chemistry met the 316L requirements and the mechanical requirements of 316. The mechanical requirements for 316 are higher than 316L. In order to achieve the higher mechanical properties, mills would induce cold working into the base material so all runs would meet both the chemistry requirements of 316L and the mechanical requirements of 316.
In todays world, it's very difficult to purchase 316 that runs high enough in carbon content to be strictly compliant to 316. Now instead of running a mill run for 316 and a separate run for 316L, they simply run where the requirements of both are met. The carbon content is listed as a maximum, and the mechanical properties are listed as a minimum. Producing this alloy that meets both requirements today is the standard method of producing these.
In order to make 316L chemistry meet 316 mechanical properties, they induce cold work in the mill such that the alloy produced can be certified as either 316 or 316L. Often times they will cert to both, sometimes just one or the other. However, since cold working causes this material to have a noticeable magnetic attraction, pretty much all 316/316L alloys available today will have a magnetic attraction. This attraction will vary by mill, but sometimes it is quite high. Sometime in the 1990's this became increasingly common. Today, it is pretty much industry wide.
I used to oversee a production line using 316. We were producing a product with much higher mechanical properties that what this alloy has as manufactured. We produced those mechanical properties through cold working. In the '90's we started to have problems with our product. 316L and 316 respond differently to cold working. 316L does not increase in mechanical properties through cold working as much as 316 does. We started having product that was not meeting our required mechanical properties. It took us awhile to figure out what was going on until we finally traced it back to the mill. It was a big deal as we had to change all our starting stock sizes, tooling and production schedule to accommodate the 316L chemistry.
dj
I wouldn't call this a marketing thing. It's really a way to remain competitive in a very competitive market.
I always buy material that has certs. Since I know how to read them, I will check the certs to.make sure what I'm getting. It is possible to find 316 that doesn't meet the 316L chemistry but it's not so common. If I'm buying material and will be welding it, can only find 316 material, I'll ask for the certs and it will usually meet the 316L chemistry - then I'll buy it and use it. Does this make sense?
dj
Yes. I was just wondering why certain items are listed in both 316 and 316L if they were the same thing.
I understand the manufacturing reasons why these two would be the same. It is similar to something I experienced with Maggi chain, where their G3 chain in certain sizes was actually G4, because it was less expensive to manufacture only G4 chain, but to continue to sell two price point versions under different grade labels. I got this info directly from Maggi technical.
Mark
316 and 316L are not the same thing. 316L was developed specifically because during welding a metallurgical condition can be created called sensitization creating a region susceptible to corrosion. If desired, I can give a detailed explanation...
The way the standards are written 316L states carbon is a maximum of 0.030%. and 316 has a maximum of 0.08%. Hence as you can see, if the carbon is say 0.028%, that carbon content meets both requirements. However, the mechanical properties for hot-finished 316 is a minimum of 75 ksi UTS while the minimum for 316L is 70 ksi UTS. So if you produce the product to say 80ksi (done through cold working in the processing) that meets both mechanical requirements. The output of this now gives a product that can be certified as 316 or 316L.
Modern day certs will now often simply list the product as 316/316L - dual certified.
These numbers are coming out of ASTM A276 - there are other standards these alloys are produced to but as far as I remember (I'd have to check) the carbon content is pretty much the same, there may be slightly different requirements. A276 is a commonly used standard. This is for hot-finished product. But most of the stainless produced today is done to a cold-finished requirement. Cold-finished product on sizes up to 1/2" require the UTS to be 90 ksi. That means most of the product we are using will have had a notable amount of cold work induced at the mill. As most will meet the 316L chemistry, that requires more cold working to meet that 90ksi than 316 so the products we will be buying will likely have a noticeable magnetic attraction. Not necessarily always, it's a kind of weird hit or miss. But it does make using a magnet today to distinguish these alloys unreliable.
Probably more than you ever wanted to know... LOL
dj