A question of burnishing I think

[tangomoon]

Hi,

I have taken my prop off and brass wire brushed it, now I want to make it shine. I am asking this question here, almost in these hallowed halls, because I am sure there is one. or more, among ye who will know how I may set about polishing and then burnishing my prop. No answers from speculators please and we have heard all the jokes. I hope someone will be able to tell me the exact method i should use. Look forward to THE reply.

 

[jhughes]

If you have a bench grinder you can buy polishing mops and pastes quite cheaply, go up through the grades first with wet and dry paper (used wet) and then start on the mops and pastes.
You might be able to get mops that fit into a electric drill if you don't have a bench grinder.
Fairly easy task and the longer you spend on each stage the better the final finish.

 

[ccscott49]

Polish OK, but do you know how to "burnish"?

 

[tangomoon]

Thank you for that

 

[old_salt]

Your prop may be good and true and just a light surface polish may not alter the balance too much but it "is" important to check the balance of your prop so here is a little to keep in mind.

It is quite an important thing is to keep it in balance, an out of balance prop is a beast both in centrifugal out of balance and hydraulic due to the aerofoil section of the individual blades.
So be very careful not to remove too much material from just one blade.
If your prop is of the feathering and dismantling type then you can treat each blade and balance them to match each other in weight a simple beam balance using each blade will do the job if you do not have the use of an accurate weighting machine.
Then assemble and statically balance the prop.
This will require setting it up between centres or on a set up with the shaft running on 4 ball bearings or though 2 bearings very lightly oiled and no dust guards to cause friction it must run very free so the prop shaft can sit on or though them and freely rotate the trick is mark a spot and then spin slowly the set up must be able to stop anywhere.
Use Plasticine to counter balance then when you have a state of equilibrium carefully remove the amount in wight from OPPOSITE the place the plasticine was one lump on one blade means remove equal from the two opposite as two lumps on two blades means remove from one blade.
Then repeat the whole process again and again till it is in balance. At the same time keeping in mind the foil section of the blades one of the multi pin template marking jigs things from B&Q or a tool store will help to check the section of the blades carefully mark the place you are checking with a felt tip on each blade so as to be checking the same place on each blade or make up a simple jig so as to be able to repeat the checks.
To get it right is a slow patient job if done right it will be a joy to you every time you motor.
Even when you come to the final polishing it will still need to be checked for being in balance.
The above is a very brief outline and not to technically worded.
I have a friend who manufactures high speed propellers for the RN and I have worked on steam and gas turbines in the past so this comes with some knowledge of balancing rotating items.
I have balanced and polished yachts props in the past this way and it works.
I hope it does not put you off polishing your prop just go carefully and slow and be patient it will all come together in the end and the benefit will be well worth the effort.
Cheers David.

 

[Aja]

So what you are saying is removing the very old antifouling from my prop with a blunt chisel and rough wet and dry wasn't such a good idea?


Any one want to buy a prop. Sparkly clean....

Donald

 

[old_salt]

No no.
My first comment was:-
Your prop may be good and true and just a light surface polish may not alter the balance too much but it "is" important to check the balance of your prop so here is a little to keep in mind.
________________________________________________

It is the removal of significant amounts of material that would have an effect on the balance and during the job of polishing that can happen if not kept in mind.

That was the point I was endeavouring to put across.
Just as would the added out of balance more barnacle and weed growth on one blade can cause big problems.
In the general run of things I am not to sure if a "super highly Polished" see your face in it prop has any real significance for more than the first few hrs in the water as it then dulls.
Not to happy to splash antifoul on a small prop (carefully done it will be of a benefit) but applied in a ruff manner it will only spoil the effect of good ruining you have endeavoured to achieve by polishing.
I think that is the more important factor of polishing , ie under 18/20ins dia I see no point to antifoul use is the best way to keep it free of unwanted growths.
Un like the highly tuned prop on an offshore racer but then it is not going to be left in the water for the next six months.

 

[Robin]

Wire brushing may well have caused you to have more work overall than cleaning it more gently and taking longer. However the principle is simple enough, you need to remove all the surface scratches with progressively less abrasive means until the final polished finish is achieved. Start with say 360/400 grit wet and dry used very wet, follow that with 600 grit, then 1000 grit and finish with several goes with Brasso. It will tarnish in the open so aim to do a final 5 minute quick final polish just before relaunching. Our prop came out very clean after 11 months afloat, just a light coating of 'slimescale' which I removed with Harpic with limescale remover applied and wiped off after 5 minutes (in our case keep it well clear of the Brunton prop's bearings) followed by a rub down using just the 1000 grit wet/dry then 2 goes with Brasso. The pics below were taken 2 years ago and the prop is even brighter now even though the pics anyway did not do it justice. It took just one hour total to do this year and we went splash yesterday morning. When we bought this boat the prop was antifouled and it took some time to remove this and achieve a good finish, each year since it has got easier.

The bright finish IMO is important because to achieve it you have removed the fine surface scratches that give the crud something to stick to, wire brushing alone gives a surface 'roughened' as if to glue something to it which is not want you want to achieve.

As for upsetting the balance I think that is highly unlikely as you are not removing very much at all, certainly there could be a bigger variation with antifoul thickness on a painted prop, globs of lanolin or any other magic potion in vogue, let alone the odd barnacle.