Prop anti-fouling

[simplyred]

Hi
I had a Brunton varifold prop fitted to the saildrive on my beneteau 31.7 last year, the prop when fitted was a thing of engineering beauty and maybe should have been mounted in a glass case and hung on the wall... but I digress.
When I had the boat lifted to overwinter, my pride and joy prop looked a hundred years old, heavly pitted and some quite large areas where the brass had been eaten into.
Was I the cause of this. when it was fitted new I painted it with Seajet shogun standard antifouling, having thought about it a bit should I have used primer first?

I know it'll take a fair bit to polish any pitting out and fear that I could unbalance the blades if I'm too agressive.
Does any forumite have any comments to make ..advice to offer etc etc
Regards
John

 

[simplyred]

yes,
one on the prop unit and one on the saildrive leg, although the one on the prop was very well worn after 7 months afloat.

 

[DJE]

Did it have an anode fitted?

 

[VicS]

Varifold should be nickel aluminium bronze not brass.

Brass will dezincify but Ni Al bronze is one of the more corrosion resistant alloys used for props.

Even so other makes of folding prop made of Ni Al bronze stress the importance of maintaining and replacing the anode when necessary.
I'd suggest that you replace the integral anode when necessary ie more than 50% worn. (I dont under stand though why these Ni Al bronze props need anodes) Fixed to a whacking great chunk of copper alloy you'll expect the anode to waste away pretty quickly hence the need to inspect regularly

Do not neglect the leg anode or the leg will corrode as well.

If you are marina based and leave a shorepower connection plugged in (not necessarily in use) then a Galvanic isolator is just about essential.

Why antifoul a copper alloy prop. Some people go to great expense to apply a copper rich coating to the boat's bottom instead of antifouling.

 

[murraynorth]

Sorry to hear about your corroded prop - firstly, never paint or anti-foul any part of the prop or prop body or bowthruster props if you have one (it can badly affect the balance), secondly never leave a prop anode uninspected for more than 3 months; my Maxprop anode only lasted just over 2 months last summer in Pwllheli marina!). Depending on the severity of the pitting, I suspect you will need new blades. Bad luck but happy sailing in 2010.

 

[OGITD]

Corroded Prop

I will endeavor to take some photos of certain props in our compound to provide examples of various conditions and protection of.

http://www.ybw.com/forums/showthread.php?t=224236

Unless you are an expert in everything nautical, I think it is always a good idea to take note of proven methods and procedures applied by others, which I suppose is what this forum is all about….eh!

 

[lw395]

Sorry to hear about your corroded prop - firstly, never paint or anti-foul any part of the prop or prop body or bowthruster props if you have one (it can badly affect the balance), secondly never leave a prop anode uninspected for more than 3 months; my Maxprop anode only lasted just over 2 months last summer in Pwllheli marina!). Depending on the severity of the pitting, I suspect you will need new blades. Bad luck but happy sailing in 2010.

Because your blades are bare, they generate a greater anode current than if they were mostly covered by an insulator. Hence your anode is quickly gone.
Personally, I tend to epoxy prime and antifoul the prop, as our harbour has a mixed reputation for corrosion. Shaft anodes last me at least 2 years and when replaced still weigh at least half the original.
YMMV.

 

[NormanS]

Sorry to hear about your corroded prop - firstly, never paint or anti-foul any part of the prop or prop body or bowthruster props if you have one (it can badly affect the balance), secondly never leave a prop anode uninspected for more than 3 months; my Maxprop anode only lasted just over 2 months last summer in Pwllheli marina!). Depending on the severity of the pitting, I suspect you will need new blades. Bad luck but happy sailing in 2010.

Is this gospel, or just an opinion? I would have thought that a crop of barnacles on a prop would have much more effect on the balance, than a coat of antifouling paint.

 

[pagoda]

Is this gospel, or just an opinion? I would have thought that a crop of barnacles on a prop would have much more effect on the balance, than a coat of antifouling paint.

I think at the radius involved - random barnacles would have vastly more influence than some heavy handed paintwork. Up to spring 2009 my prop was a little barnacle infested, and nothing was terribly untoward. For 2009 we had International Uni-Pro on the hull - and prop. Both stayed pretty clean in the Clyde. I think I'll clean the prop and re-do the same A/F - not too heavy a coat either . If my prop was doing 5000RPM I might be worried about balance, but I'd be thinking about dynamic shaft/prop balancing if that were the case - and most yacht shaft bearings ain't up to that either!
I've read some pleased accounts of using black indelible marker on top of a spotless prop... but I haven't tried it yet.
You pays your money...

Graeme

 

[simplyred]

I spoke to one of the guys at Hemple paints and said that using their product from a spray can gives a better more even covering of paint, thus eleviating the balance problem... so thats what I'll do then.
he did point out that it's best to put a good few coats of primer on.

Regards
John



I read in the paper that drinking was bad for you.... so I've stopped reading papers now

 

[OGITD]

Propeller Antifouling / Protection.

As promised here are the photos of two props. The first is over six years old and only comes out of the water every second year. The second has been polished then the modern equivalent Black-Lead applied.
The first is as it came out of the water with nothing more that a quick pressure wash.