Preventing Prop Barnacles

[SPIBob]

Here's the procedure for painting the prop that I've had excellent results with for the past seven or eight years:

http://www.yachtpaint.com/USA/boat_pain ... drives.pdf

Careful attention to drying times and application intervals is critical.

[Maine Sail]

Copper based paint can ruin your prop & lead to serious dezincification..

Aren't props supposed to be made of bronze, an alloy of tin and copper? How can there be dezincification in the absence of zinc?

I have painted my bronze props with copper antifouling paint, two coats each time, for more than 40 years with no bad results. After all, the major part of a bronze propeller is copper.

There are some allegedly "bronze" alloys that contain a small portion of zinc, but a decent alloy shouldn't be affected by what amounts to just some more copper.

Cheers,

John V.

John,

A large number of props, including the vast majority of Michigan Wheels, are made of manganese bronze. While called "Bronze" it is really a lot closer to brass than bronze. Manganese bronze can contain upwards of 40% zinc!!! Props are NOT generally made from the same bronze as thru-hulls or seacocks which are usually an 85/5/5/5 or "eighty five three five" bronze.

If you have been painting props that way it is likely you have a NiBrAl prop not a Manganese bronze prop. Nibral props are more expensive yet can still suffer the aluminum content being attacked..

[Joe Myerson]

One year I tried wax. It didn't do a great job.

The next year I tried anhydrous lanolin--it wasn't worth barnacle piss (do they piss?).

The next year I carefully sprayed the prop with zinc primer and added two coats of ablative bottom paint. It wasn't great (the bottom paint was completely gone by the end of the season, but some of the primer was there).

Last year, I stupidly did nothing. I could say that it was the control season in my ongoing experiment, but actually I was in such a hurry to launch that I simply forgot to do anything. In the middle of the season, after the boat sat on the mooring for about 3 weeks, my prop looked like a grapefruit.

This year I put on two coats of Pettit 1792. I also added two coats of Meguiar's marine wax (Mainsail, when I bought it, I thought it was better for boats than their other product). I know that the wax will negate the zinc, until it wears off. But, presumably, the zinc will kick in at that point.

The experiments continue.

--Joe

[Como No Cruising]

Regarding the question of Barnacles on Props. One product that works very well is called "Prop Speed". See propspeed.com.
It is expensive-but it works very well for about 2 years. Best stuff we have seen to prevent growth on props and shafts.

[John Laton]

I also have used a hard copper based bottom paint (not ablative), Over 90% copper (Trinidad Sr.) on my props for the past 9 years with no issues whatsoever. The prop comes out clean at the end of each season and the qt can has lasted years doing my prop and many others in the marina. They all wanted to try it when they saw how clean my prop was at haul out... No brag.. just fact ! Now I'm not plugged into shore power if that would make any difference to the chemists out there.


John

s/y Paradox
CD25D #55
Milford, CT

[Jim Sullivan]

I was told last year by a Pettit technical rep that a bronze prop should be primed before applying their hard copper based bottom paint (non-ablative). I believe the prep was similar to that for Interlux products indicated in the link given by SPIBob. I was told basically the same thing by Interlux re priming. John Laton-- did you apply the Trinidad Sr. directly to the bare metal or did you prime it first? Just curious if you had good results with just applying the paint directly without priming.

I have a bronze prop, bronze skeg and bronze rudder. Previously I applied Super Shipbottom Paint (hard ablative) >60 % Copper to the rudder and skeg without priming. I did not paint the prop and it was also covered with barnacles. Both rudder and skeg were loaded with barnacles last year. This year, I am trying Pettit Barnacle Barrier 1793 again. I had to strip all the old paint off first. If the barnacle barrier is not effective in this area, I will likely for next year, prime (Interprotect 2000E/2001E) my bronze running gear if necessary and then apply a hard bottom paint either Pettit or Interlux.

Thanks,

Jim

[Maine Sail]

This is dezincification of a Manganese Bronze Michigan Wheel caused by copper bottom paint. This prop had been fine for 12 years with zero signs of dezincification then some yard monkeys painted it with bottom paint in a non DIY yard. The paint was on for one season.

Most don't notice it because if the paint is on long enough it turns the entire prop the same color instead of blotchy. If your prop is coppery colored not yellowish it is most likely dezincified.

The prop shop refused to even re-balance this wheel due to liability..

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[tmsc]

Maine Sail that was a great pic of the prop and a fine example.

Back in my boat yard days, we primed all underwater metal parts to prevent dealloying before applying AF. We used Interlux Primocon underwater metal primer with great success. However, barrier coat also seems to work well too. Personally, I use the primer since a small can will last for several years. Good insurance........

[John Laton]

Jim,

The prop was wire brushed with no primer, just 2 coats of Trinidad Sr. , although now after all the discussion and that wonderful picture I would think it a prudent investment to prime first.

In any case I'll strip down the prop this haulout and snap a pic of the prop.. that is if it does not crumble off and disappear this season.. but according to Mr. Vigor I may just have another 30 years left.

John
s/y Paradox
CD25D

[M. R. Bober]

I have a three blade Michigan Wheel prop--on RESPITE--it has been coated with Petit Barnacle Barrier for the past few seasons. Barnacle growth has been minimal. The old prop, a Michigan Wheel two blade model, has been in the basement for at least seven years. There are absolutely no barnacles on that prop.

Following the logic demonstrated by John Vigor, I offer the following: use a two blade prop. I personally favor the "leave the prop in the basement" alternative.

Mitchell Bober
Sunny Lancaster (where the deer and the cantalope play,) VA

[M. R. Bober]

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Mitchell Bober
Sunny Lancaster (where we are working in the data mine,) VA