bottom paint on metal parts

[sail410]

Are the rudder, trimtabs and prop the only metal parts on a 28te that need special consideration when bottom painting or am I missing any?
Thanks in advance,
Bill

[joe.baar]

Our '95 has a bronze shaft gland housing - about 4" diameter at the after end and about 12" long - with a flange to attach it to the skeg; a bronze thru-hull underwater for head overboard discharge; and at least four bronze strainers for all kinds of intakes - one for the head, one for main engine cooling, one for exhaust cooling, and one for the bait tank on the transom. There's also the large shoe from the bottom of the skeg that holds the rudder pintle. I've used transducer paint in the past with good success at keeping away barnacles. Previous owners had painted several of the strainers with plain ol' bottom paint which caused a lot of pitting and thinning of the sections and I've removed all the old paint. For heavy, rough items like the shaft gland housing and the skeg shoe there isn't so much concern, but I've stripped these also. This season I left everything bright just to see if the barnacles care.

[DougSea]

The only metals I've paid special attention to are the prop (and shaft), rudder, tabs and the thruster. The paint always comes off the prop and much of the rudder during the season but I figure, based on minimal fouling, that the paint at least slows down the little critters growth. I clean the metal with a wire wheel in an angle grinder, prime it, and then paint with two coats of bottom paint.

The remaining thru hulls were primed and painted with normal bottom paint. It's worked well for me in the past. I have the same shaft fitting Joe mentions above and it also just got primed and painted.

I should add that this last season I stripped EVERYTHING off of the bottom and used Interprotect 2000 barrier coat (4 coats) on all of the hull and fittings. The bottom looked great when she was hauled this fall, very little work to get her ready for her next owner.

[Cape Codder]

Although already mentioned by joe.barr, special attention to raw water intakes. Both inside and ouside surfaces can be plagued by barnicles.
Before treating properly, my raw water intake for cooling the Yanmar was covered inside and out with them crusty critters.
Now....clean as a whistle......

[special k]

what is the preferred treatment of our running gear and other sub-surface metal parts such as thru hulls, strainers, tabs, even t-ducers.. i always used my bottom paint without noticing any harm.

can bottom paints harm bronze or stainless steel?

[joe.baar]

SpecialK - Many bottom paints contain a lot of metal, usually copper in some form. Galvanic corrosion can occur between the fitting and bottom paint because the metals are dissimilar, that is they will produce an electrical field in salt water which will cause corrosion.

In general corrosion will occur to the more "active" metal in any couple, which means your copper bottom paint will pit first, then your bronze, and finally your stainless. The short answer is, bottom paints probably won't harm bronze or stainless steel but the paint's surface on fittings is likely to become rough over the course of a year. This might not be a concern.

[special k]

good answer. it sounds like the anti fouling paint will break down first. should explain why i get more barnacles at the fittings. thanks

[Cape Codder]

Actually, the way it was expalined to me by Pettit paints is the following:
The dissimilar metals in salt water form and electric current, no news here.
Zincs do a great job in being less noble and sacrafice to protect the other metals.
But the copper in the anti-fouling paint is unable to leach out due to this weak current, rendering the paint ineffective. Therefore the barnicles attach.
Pettit recommends getting metals bare, coat with a 2-part epoxy (1 coat) and 2 coats of tiecoat (rubber) paint, THEN the anti-fouling paint (they recommend Vivid on matals) and your done.

I can truly attest, this system works!! This was the first season with NO barnicles.

[special k]

so a barrier between the metals and the paint must be created, therefore preventing the galvanic reaction.

sounds logical, may give it a try or just dive down during my short CT season for some barnicle abatement.