Propellor fouling

[cookjwm]

my old two blade folder of indeterminate make -cheapo italian I think , did not pick up barnacle growth to any signifcant degree.
My new super duper autprop does -badly.
Anyone know why? I presume its to do with the casting composition but......?

 

[Norman_E]

If your old prop was bronze the copper content in it was effective against quite a bit of marine growth. As an aside real bronze is a copper / tin alloy, both constituents having antifouling properties. Many props are however "Admiralty Bronze" which is in fact a type of brass, i.e. a copper / zinc alloy.
If your new prop is one of those made from stainless steel, I am not surprised if it gets fouled.

 

[cookjwm]

No ,its bronze , thats whats making me wonder -is it metal quality?

 

[Norman_E]

Could be metal quality, but also possible that it was laquered to make it look nice and shiny in the shop! Clean it back to bare metal, and see if it is any better next season. My own "bronze" prop gets some fouling, but not too bad, and I am not sure if there is anything you can paint on that actually improves the situation.

 

[Robin]

We have an older Autoprop but probably the same bronze material as yours. We removed the antifoul from it when we bought the boat 5 years ago because it hadn't worked and then we bright polished it. That is to say BRIGHT polished it! Started with wet/dry about 360, then 600, then 1200 then several goes with Brasso until you could see to shave in it. Subsequent years all that is necessary on lift out (we are there for it) is we use a plastic scraper to push off the limescale whilst it is still soft and the bright surface is revealed, there will be a few barnacles in the root of each blade and on the hub, but not many. All that is needed then is a rub down with wet/dry 600, then 1200, the Brasso with a final Brasso buff as we launch. It is quite a therapeutic satisfying job really but then I am a bit of a saddo!

We or our friends have tried all the usual ideas over the years and come back to bright polish. Even the guy locally that sells one of the very expensive prop antifouls agrees it is useless and now polishes his!

Where polishing doesn't work (nor does anything else tried so far) is on the exposed S/S shaft, so this gets scraped as and when I go for a swim off the boat.

 

[Norman_E]

Thanks for that reply, I had wondered what to do with mine, and have only wire brushed it clean on lift out. I will try the polishing method next spring.

 

[npf1]

Robin - very interesting. I have the same prop as you and this year tried a really good coating with lanolin after heating up the prop. Bloody useless - barnacles after 4 months and that was with very regular use of the boat. Looks like the polishing is the next thing to try. How long did it take you to polish it? And how did you cope with the tighylu curved areas of the central boss?

 

[Miker]

As I was losing about 1kt and 600 revs on the engine, and my autoprop was covered two to three deep in limpets etc, I spoke to Bruntons about it. I had always burnished the prop, not using Brasso admittedly, and had not suffered excessively before from such buildup. Bruntons confirmed that the loss in performance was probably from the limpets and advised the use of lanolin, not antifouling, saying that other customers had found it beneficial. You pays your money and you takes your choice?

 

[Robin]

The first time is the worst. Once the prop is clear of antifoul or lanolin it probably takes about an hour? I might be wrong as I tend to do one or two blades, then do something else, then go back and do a bit more. The fist time of course you have to remove scratches from previous scrapings and so on, hence the need for say 360 wet/dry on the bad bits. The 600 then 1000 doesn't take that long really because you are merely flatting the scratches from the previous coarser papers, but keep the paper very wet. Getting into the tight radius by the boss is a pain, I use finger pressure with a strip of paper, around the boss is easier with a strip see-sawed back and forth. In reality I don't worry about perfection right in the corners, just on the blades. Brasso works very well, I do it a couple of times initially then do a quick last one in the slings as we lift in to take off any tarnish.

Oh and mind your fingers when the Brunton blades swing round, the older ones like ours with open bearings have very free rotating blades, not to mention we have a Stripper cutter fitted!

 

[cookjwm]

Thanks all, it seems hard work the only answer -but was interested to hear others had same issue with autoprop