New Bronze Prop Protection

[stevd]

I have just put a new propeller on my boat, as the one that came with the boat had de-zinced. I have bought a new one from T-Norris. What sort of protection do I need to stop the new prop from corroding like the old one. Is a simple shaft anode sufficient, or are there specific anodes for props?

I also need to drill the new bronze prop nut to put a split pin through, is a stainless steel pin ok, or will that encourage corrosion?

Many thanks

 

[VicS]

I have just put a new propeller on my boat, as the one that came with the boat had de-zinced. I have bought a new one from T-Norris. What sort of protection do I need to stop the new prop from corroding like the old one. Is a simple shaft anode sufficient, or are there specific anodes for props?

I also need to drill the new bronze prop nut to put a split pin through, is a stainless steel pin ok, or will that encourage corrosion?

Many thanks

A good quality bronze ( manganese bronze?) prop should not need any protection.

As a precaution the simplest thing is a shaft anode if there is sufficient exposed shaft.

The alternatives are a hull anode boned to the engine/ gearbox, but any flexible coupling will have to be bridged, or connected to a brush system running on the shaft inboard of the stern gland eg MGDuff's "Electro-eliminator"

 

[vyv_cox]

Unfortunately manganese bronze is just another brass. I believe the manganese alloys with the copper to give some solid solution strength, that's what happens with the tin in Naval Brass, but I am not certain. The vast majority of props are made from manganese bronze and plenty of them dezincify, although it is usually a lengthy process. A shaft anode is the primary measure to slow the process down but a prop anode, one that screws over the threaded end beyond the nut, will help. Paint is good protection, i have written several times about Hammerite Special Metals primer, which seems to adhere very well. You could then antifoul with one of the special paints, Velox has worked well for me.

A stainless steel split pin is always used AFAIK. The anode will protect the very small galvanic action.

 

[stevd]

I have a very little amount of thread left after the nut has been put on, I dont think there is enough thread left to attach a screw on anode, I can try though.

I must admit I was thinking about painting the prop, but it is the only shiney thing on the boat

Does painting the prop make it less efficient at all? are there any downsides to painting it?

Cheers

 

[Tranona]

The problem with paint is getting it to stick to the prop. You stand a reasonable chance with a new prop. I have had success with Trilux on a new prop - convenient for my boat as it is used on the saildrive housing as well. As you have had problems with dezincification in the past it makes sense to fit an a node and see how it goes. A shaft anode is obviously the easiest if you have sufficient exposed shaft, for example in front of a P bracket. With a conventional stern bearing there is often not enough exposed shaft so the only ways of attaching an anode are those VicS suggests. An anode on the prop is attached to a special nut which replaces the existing nut and you may have space to fit that, although the resulting anode is small compared with alternatives.

 

[stevd]

so a shaft anode in front of the p bracket wont do the job? it has to be in direct contact with the prop? From memory, I dont think there is much room aft of the p bracket either.

I really dont want the expense of a new prop next year!

It is a maganese bronze.

Thanks so far

 

[Tranona]

so a shaft anode in front of the p bracket wont do the job? it has to be in direct contact with the prop? From memory, I dont think there is much room aft of the p bracket either.

I really dont want the expense of a new prop next year!

It is a maganese bronze.

Thanks so far

Yes - that is what has been suggested. in front of the P bracket leaving space for water to flow into the bearing. The requirement is for it to be electrically bonded to the shaft/prop which it will be. Make sure the anode is exactly the right size and has a steel lining that clamps on the shaft (some cheap ones don't and come loose).

 

[stevd]

Perfect, I shall do it that way.

Cheers

 

[Graham_Wright]

I have bought a new one from T-Norris.

Make sure the new one is not brass. They sold me a brass stern tube (which they eventually admitted to).