VP Stainless steel duoprop pitting: electrolysis or casting defect?

[tkrfxr]

I have 6 seasons old stainless steel propellers in dual XDP-B volvo drives. Three years ago I moved from a commercial marina to a club where I can do some of my own maintenance. In 2006 I discovered some pitting on the steel and had the props welded and balanced at a professional prop shop. They found some areas cound not be welded because it could damage the clutch. I posted some pictures and someone recognized the pattern of holes in their own props...he was told it may be a "casting defect".

Has anyone else seen pitting like this? The props seem to function fine, and the shop told me to patch up with epoxy, protect with underwater metal paint, and use the props, that there was no imbalance or vibration....

 

[Texasmark]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

I'm a retired electro-mechanical senior engineer with 36 years with a Fortune 500 company....(whoopee for you hot dog).....calm down a minute. Ok.

Castings are made by pouring molten products into molds, allowing the material to cool and then removing the mold or the product....whichever is the easiest. Best analogy I can offer to what I want to say is the teats on a new tire....you know those little spires of rubber emanating from the carcass. They come from tire rubber that squirts out of the air holes in the castings which are there to allow trapped air a place to exit and doing so, yield a tire with zero defects.

Aluminum castings aren't that forgiving and if air were trapped between the mold and the molten aluminum poured into it you would get things such as you see here. No biggie. Plug it with epoxy if that makes you feel better and get on with your life.

Now, if the product were 30 years old sort of thing then the holes could be caused by sulphuric acid or some other bad critter and all, but you would still have to ask yourself the question: What does this have to do with the operation/performance of this watercraft? If your answer is nothing or I dunno, then forget it and take your wife out to a steak dinner tonight......you'll surely get more out of that than worrying about a few casting PITS that don't hurt a thing.

My 2c.

Mark

 

[TilliamWe]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

...They found some areas cound not be welded because it could damage the clutch....

I don't know exactly what caused the holes in your props, but I find this statement truly baffling. There is no clutch in your props, so could you have misundertood?

 

[hwsiii]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

Tilliam, I am pretty sure they were talking about the rubber hub and he misunderstood their wording.

Mark, that was an excellent analogy, and I would be willing to make a sizeable bet that it came from the casting process and not electrolysis or corrosion. Although I do believe the squeeze casting process creates much better material specs and less of these kinds of problems. LOL


H

 

[TilliamWe]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

Tilliam, I am pretty sure they were talking about the rubber hub and he misunderstood their wording...
H

Only one problem with that, there are no rubber hubs in that prop photoed.

 

[steelespike]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

I think its pretty obvious it is a casting fault.Electrolysis would be over most of the prop.More concentrated in some areas but not a few isolated pits.

 

[hwsiii]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

Tilliam, you are 100 % right, I just didn't look because I didn't know anyone made I/O props without some type of hub that slipped so all of the load didn't transfer directly to the drive itself. I don't believe I would be interested in owning one of those drives personally, as I would be scared I would have to replace an outdrive if I really hit something big and hard.



H

 

[TilliamWe]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

... I didn't know anyone made I/O props without some type of hub that slipped so all of the load didn't transfer directly to the drive itself...
H

Both of the major outdrive manufacturers make props like that. VP on this drive and Mercruiser on ALL the Bravo 3s ever made.

And I also agree, this is not galvanic corrosion, or electrolysis. I have a friend with a Bayliner 2855 with electrical issues, who installed a Bravo 3 drive. After one summer in a freshwater slip in the Illinois River, the edges of his prop(s) blades had holes eaten through them. No reason to expect your props to look different. The holes would form at the thinnest spot in the metal, and that's the blade tips.

 

[jaxnjil]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

Tilliam, you are 100 % right, I just didn't look because I didn't know anyone made I/O props without some type of hub that slipped so all of the load didn't transfer directly to the drive itself. I don't believe I would be interested in owning one of those drives personally, as I would be scared I would have to replace an outdrive if I really hit something big and hard.



H

by the by, for future reference only.

B IIIs dont use any slip mechanism either. they are solid splined too

 

[TilliamWe]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

See my post right above yours jax, where I say that ALL Bravo 3 props are solid hubs.
There are VP DuoProps that have rubber hubs, I have seen them. But obviously not all of them.

 

[tkrfxr]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

Thanks for the replies... The props have a plastic layer between the inner hub and the outer propeller. This will slip if an object is struck with the blades. It is somewhat thin and does not show well in the pictures.

The pits were filled in with epoxy and the props have been painted every spring since... Here is what this one looks like.

 

[jaxnjil]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

See my post right above yours jax, where I say that ALL Bravo 3 props are solid hubs.
There are VP DuoProps that have rubber hubs, I have seen them. But obviously not all of them.

sorry till; i missed that

 

[tkrfxr]

Re: VP Stainless steel duoprop pitting: electrolysis or casting defect?

Only one problem with that, there are no rubber hubs in that prop photoed.

If you look closely, you will see a thin layer of white plastic...