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Old 15-02-2018, 19:02   #1
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New bronze 3 blade prop

I bought a new bronze 14"RH12 and am looking for advice on whether or not to skuff/paint (not bottom painting) the prop before painting with just bottom paint.

Also, the shaft and prop are 7/8" and am curious if putting a dielectric on taper before installing prop??

Thanks,

GLC
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Old 15-02-2018, 19:12   #2
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Re: New bronze 3 blade prop

Nothing at all on the taper.

Why are you painting it?
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Old 15-02-2018, 19:34   #3
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Re: New bronze 3 blade prop

I saw several boats in the yard that had epoxy painted their prop and was curious as to how many boaters (sail) paint their props.
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Old 15-02-2018, 19:36   #4
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Re: New bronze 3 blade prop

Before installing the prop you should lap the prop to the shaft with very fine lapping compound to be sure the tapers match. Then clean the shaft and prop and install the prop without the key and snug it up slightly and make a mark on the shaft to indicate the maximum installed position of the prop on the shaft. Now remove the prop and install the key in the key way and reinstall the prop. Use a very light coat of lubricant like wd40 on the taper. Make sure the key doesn't ride up the key way as the prop is installed. Tighten the prop nut and make sure the prop reaches or passes the mark which you made previously on the shaft. If the prop doesn't reach the mark, the prop is riding on the key and not the shaft taper and the key needs thinning. If your installation uses a thick nut and a thin nut, install the thin nut first and tighten it fully, then install the thick nut and jam it against the thinner nut. Then install the cotter pin and fold the legs back.

Bottom paint rarely stays on props very long because the blade pressures are too high and the paint is too soft. Coatings like " prop speed" work well for a period of time, but eventually it just comes down to scraping the prop clean periodically.

DougD
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Old 15-02-2018, 20:39   #5
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Re: New bronze 3 blade prop

Very good advice Doug! Thank you! I realized ablative paint would not last long but it almost made sense to epoxy and place bottom paint over.

Thank you!
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Old 16-02-2018, 08:20   #6
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Re: New bronze 3 blade prop

Quote:
Originally Posted by DougR View Post
Before installing the prop you should lap the prop to the shaft with very fine lapping compound to be sure the tapers match. Then clean the shaft and prop and install the prop without the key and snug it up slightly and make a mark on the shaft to indicate the maximum installed position of the prop on the shaft. Now remove the prop and install the key in the key way and reinstall the prop. Use a very light coat of lubricant like wd40 on the taper. Make sure the key doesn't ride up the key way as the prop is installed. Tighten the prop nut and make sure the prop reaches or passes the mark which you made previously on the shaft. If the prop doesn't reach the mark, the prop is riding on the key and not the shaft taper and the key needs thinning. If your installation uses a thick nut and a thin nut, install the thin nut first and tighten it fully, then install the thick nut and jam it against the thinner nut. Then install the cotter pin and fold the legs back.

Bottom paint rarely stays on props very long because the blade pressures are too high and the paint is too soft. Coatings like " prop speed" work well for a period of time, but eventually it just comes down to scraping the prop clean periodically.

DougD
Usually, no paint or coating will adhere for long, mainly the edges wear off first.
I've used a high zinc gutter paint, spray on several coats, available at Home Depot, or Ace Hardware, Lowes.
SV Cloud Duster
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Old 16-02-2018, 08:37   #7
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Re: New bronze 3 blade prop

I usually paint the prop with bottom paint. As mentioned it doesnt last that long on the edges. But the high velocity at the edges keeps the barnacles down a bit anyway. My take is it helps a bit for a while. I dont remember priming the prop first.
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Old 16-02-2018, 08:49   #8
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Re: New bronze 3 blade prop

I saw several boats in the yard that applied epoxy first. What really got my attention was a guy building a metal 44' sailboat. When he saw my prop, he told me to skuff and he would mix up some 2 part and spray it for me. Just thought perhaps it might hold ablative bottom paint longer.
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Old 16-02-2018, 10:04   #9
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Re: New bronze 3 blade prop

Use PropPurr™ on a bronze prop. It is the only coating that chemically bonds a thin silicone coating to the copper in the bronze. No primer coat are needed. Just lightly sand to expose fresh copper. Then remove any residue and oils from the surface. Never rough sand and never use an acid etchant. PropPurr does not work by mechanical bonding. Once clean, wipe on PropPurr. No rush, it's easy. PropPurr usually dries within an hour and you are ready for the water.

Because the surface of the prop, when coated with PropPurr, is silky smooth and slippery, marine life can't get a mechanical bond started. It can usually be wiped off with fingers, a mesh coated sponge, or by prop rotation.

We haven't seen the coating wear off at the blade tips, but we are a sailboat. We don't run the prop so hard that there is cavitation and we don't operate in silty water.
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Old 16-02-2018, 11:01   #10
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Re: New bronze 3 blade prop

Good advice from DougR, but do not make the mistake of leaving the prop in the sun before installation. It will expand with the heat and when installed and cools, you will have a shrink fit that will be very, very difficult to remove later. Prop and shaft should be the same temperature when prop is installed.
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Old 16-02-2018, 12:46   #11
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Re: New bronze 3 blade prop

dear GLCALAHAN
The last time I got to see my prop I remember someone said to paint it with a special additive called STP. it is a thick kind of oil that will, supposedly, keep all growth off it.
Please look into it. Best regards, John.
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Old 16-02-2018, 14:37   #12
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Re: New bronze 3 blade prop

STP......Engine Oil additive??
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Old 16-02-2018, 14:53   #13
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Re: New bronze 3 blade prop

Bottom painting a prop works OK if you can keep it on. Priming the bronze first with an epoxy primer is a good step for the best adhesion. Don't use soft ablative paint though. Use the hardest bottom paint available to you like Unepoxy or Trinidad. It will last a bit longer and you can use a scrapper to get the hitch hikers off if necessary.
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Old 16-02-2018, 15:14   #14
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Re: New bronze 3 blade prop

Thanks kenbo.....I think I will lightly skuff the prop and put on 2 part epoxy paint then lightly sand and put Trinidad before splashing.
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Old 16-02-2018, 15:20   #15
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Re: New bronze 3 blade prop

Not trying to be too fussy here but the epoxy primer really should be for underwater metals. There are many 2 part epoxies that are not rated for underwater use.
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