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  1. #1
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    Default Steel CB protection

    Shortly I will have a 1/4 in. mild steel center board cut to a plywood pattern that I have made. What can I paint it with to avoid rusting? It will have anti fouling paint over it. That will be the subject of a future topic.

  2. #2
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    Default Re: Steel CB protection

    Quote Originally Posted by ahp View Post
    Shortly I will have a 1/4 in. mild steel center board cut to a plywood pattern that I have made. What can I paint it with to avoid rusting? It will have anti fouling paint over it. That will be the subject of a future topic.
    Couple of options, see my "Need a new rudder" thread. Several here like hot dipped galvanizing, I chose to go with sandblasting and an epoxy barrier coat.

  3. #3
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    Default Re: Steel CB protection

    I sanded it bright with a belt sander then used a steel paint system from a paint supplier. From memory an epoxy primer, undercoat and top coat. About six or seven coats in all.
    still remains to be tested though.
    i was worried about the steel bending in the temperatures used in galvanising.

  4. #4
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    Default Re: Steel CB protection

    I worked for a machine shop that did pumps for municipal water districts where the service life between overhauls was 20-30 years and everything was powder coated from cast from and bronze pump impellers, bowls and volutes to the fabricated column pipes and discharge heads and it would hold up very well and it would maintain it's dimensional stability.

  5. #5
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    Default Re: Steel CB protection

    Here's a wild thought -- make your steel plate the center ply with wood on both sides. Adhere with g-flex epoxy, and shape the wood into a naca or semi-naca. profile??
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  6. #6
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    Default Re: Steel CB protection

    You could also use a reputable rust converter followed by a two part primer and paint system such as Ameron, or Awlgrip. both these companies also make bottom paints designed to work with their systems. They tend to be very effective, the downside is they are also incredibly toxic.

    Nicholas

  7. #7
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    Default Re: Steel CB protection

    "It's a pirate's life for me. Savvy??"

  8. #8
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    Default Re: Steel CB protection

    If you chip the paint by grounding the plate rust will start and run under the paint coating.
    On the other hand the steel cb made for a boat that I built in the '70s and had hot dipped is lying in my yard with no corrosion at all in evidence.
    It really is quite difficult to build an ugly wooden boat.

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  9. #9
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    Default Re: Steel CB protection

    Quote Originally Posted by Peerie Maa View Post
    If you chip the paint by grounding the plate rust will start and run under the paint coating.
    On the other hand the steel cb made for a boat that I built in the '70s and had hot dipped is lying in my yard with no corrosion at all in evidence.
    +1 Without a good corrosion inhibiting coating, the rust will work it's way under the paint. The only exception might be Advanced Polymer Marine Line paint over a heavy grit blast, but it may be hard to source. Whatever you do, the mill scale has to come off, and grit blast is the best way to remove it.

    In order from most to least protective galvanizing (but still very good) base coat:
    Hot dip galvanizing.
    Thermal spray aluminum. (Cold spray>HVOF>plasma>wire arc) If you find an applicator, and once you see the price, you will pick wire arc.
    Wire arc spray zinc
    'Cold galvanizing' paint over grit blast and zinc phosphate. (Devcon Z appears to be gone, Sherwin Williams has some good ones and I've seen good test results for Zinga)

    Whatever primer you apply, if you don't galvanize first, I would apply a phosphate coating. There is one DIY zinc phosphate from POR-15. Most marine primers are good barrier coatings but not really effective corrosion inhibiting coatings. I will leave the specific recommendation to someone else. The only really good corrosion inhibiting primers that I am familiar with are the MIL spec 2 part epoxy primers, MIL-DTL-53022 Type IV and MIL-DTL-53030 Type II. (May be hard to source, $$$. So you will need a good marine paint. Interprotect 2000 (Post 7) sounds good, but since it a barrier coat, not corrosion inhibiting paint, once it is scratched through the rust will work under the paint. Petit Trailercoat might be good, but wait for a second opinion.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  10. #10
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    Default Re: Steel CB protection

    Quote Originally Posted by Peerie Maa View Post
    If you chip the paint by grounding the plate rust will start and run under the paint coating.
    On the other hand the steel cb made for a boat that I built in the '70s and had hot dipped is lying in my yard with no corrosion at all in evidence.
    What he said... always galvanize if you can. No coating can approach the durability. It is self healing if scratched. Generally, hot dip galvanizing is charged by the weight of the material being dipped and spun. Our local high school Metalworking program build's park benches and has them galvanized, then powder coated. Some of my volunteer work with the kids as rewarded with an offer to allow me to throw some parts into the basket I had fabricated for a quick release bowsprit mechanism. It otherwise would have cost me about $50.

  11. #11
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    Default Re: Steel CB protection

    Quote Originally Posted by BrianM View Post
    What he said... always galvanize if you can. No coating can approach the durability.
    If you look at the hot dipped corrosion test panel on the lower right in the first picture, you may want to look a little harder at the zinc rich paints. I can guarantee that if you buy the same paints and run the exact same test again, the results will be a bit different. How different is hard to say. This time hot dip looked bad and next time it might do better.
    zinc only.jpg
    In the same test with the galvanized panel (probably from the same lot) painted and scratched down to the steel and hot dip was the best coating. Note that the Epoxyzen and galvanized swapped places from top to bottom once painted:
    painted.jpg
    EDIT: (not worth a bump)
    Cast iron ballast keels and mild steel corrode at vastly different rates.
    Not exactly vastly in the old NCEL testing on bare metal, but from the picture I'd have to say the paint held up a lot better on the iron. For the sake of... well nothing really, there is a lot of corrosion data here. The testing was at various depths down to 6000 ft and lots of alloys, so as you might expect, it has been too expensive to repeat, so these results are rare. At a depth of 5 feet, A36 (common mild construction steel) corroded at 6.2 mil/yr, wrought iron 4.8 mil/yr and grey iron 2.6 mil per yr. Other sources say mild steel corrodes 10 times as fast as cast iron. Corrosion test results are not all that consistent in detail, but the trend supports Nick's observation.
    Last edited by MN Dave; 04-21-2018 at 12:34 AM.
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  12. #12
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    Default Re: Steel CB protection

    I'me with Nick on this,
    You WILL ground your board and paint will not protect it. Hot dipped zinc is the way. We sold many boats in the early plywood days and always galvanized the plates.
    1/4 inch will be OK from the warping worry.
    A2

  13. #13
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    Default Re: Steel CB protection

    Prime and paint with standard oil paint or Hammerite type enamel. Totally cheap and if you have to have it out for a retouch now and then so what. I say that as pro-metal finishing like galvanising and powder coating, though undoubtedly better, is expensive here, anyway.
    Last edited by jonboy; 04-13-2018 at 04:34 AM. Reason: spellnig
    'C'est la vie' say the old folks it goes to show you never can tell

  14. #14
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    Default Re: Steel CB protection

    Hi,

    You need to remove the mill scale on the mild steel. Sandblasting or hot dip galvanizing is really the only way. My wife did a little write up here on the joys of sandblasting ( http://boatmutts.ca/sandblasting/ ) . You should be able to find somebody locally to do this for you. I don't like powder coating so much, as once it's failed, it's hard / impossible to touch up.

    Cheers,
    Mark

  15. #15
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    Default Re: Steel CB protection

    Hot-dip galvanizing is the way to go.
    Hope for the best, but plan for the worst.

  16. #16
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    Default Re: Steel CB protection

    Idle curiosity. US submarines are black.. What do they use, or are they telling?

  17. #17
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    Default Re: Steel CB protection

    Quote Originally Posted by ahp View Post
    Idle curiosity. US submarines are black.. What do they use, or are they telling?
    Secret submarine stuff aside, hot-dip galvanizing an entire steel ship is not possible. Instead, they are protected with zincs that work on the same principle.

    I wonder if you could design a steel centerboard with a protective zinc?
    I will beg you for advice, your reply will be concise, and I will listen very nicely and then go out and do exactly what I want! (Apologies to Lerner and Lowe.)

  18. #18
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    Default Re: Steel CB protection

    Quote Originally Posted by alkorn View Post
    Secret submarine stuff aside, hot-dip galvanizing an entire steel ship is not possible. Instead, they are protected with zincs that work on the same principle.

    I wonder if you could design a steel centerboard with a protective zinc?
    The bilges of warships used to be flame sprayed with zinc, nearly as good as hot dip.
    As to you question about designing a cb with a protective zinc, That is what we have been recommending - hot dipped.
    It really is quite difficult to build an ugly wooden boat.

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  19. #19
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    Default Re: Steel CB protection

    I will try to find someone around here that will do hot dipped galvanizing.

  20. #20
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    Default Re: Steel CB protection

    Others here - Peerie Maa comes to mind - will know better, but I know that the coatings on modern subs are designed to be low-friction, sound-absorbing, non-magnetic, and uber-expensive.
    Hope for the best, but plan for the worst.

  21. #21
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    Default Re: Steel CB protection

    Another vote for hot dip galvanising. Zinc is remarkably durable, it won't chip or corrode and it's cheap... if that's relevant.
    '' You ain't gonna learn what you don't want to know. ''
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  22. #22
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    Default Re: Steel CB protection

    The hot dip galvanizing is surly a proper coating especially for a centerboard that will see some abuse. I'm in a similar situation wanting to have my rather large tabernacle galvanized. There are several outfits within a reasonable drive that perform the service. So far I have been put off by the large minimum charge. Most of these galvanizers specialize in large architectural or in irrigation applications. For my purposes (little abrasion) I will opt for "cold galvanizing", followed by water-based primer and a LPU top coat.
    http://www.zrcworldwide.com/products...izing-compound

  23. #23
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    Default Re: Steel CB protection

    Quote Originally Posted by bheys View Post
    The hot dip galvanizing is surly a proper coating especially for a centerboard that will see some abuse. I'm in a similar situation wanting to have my rather large tabernacle galvanized. There are several outfits within a reasonable drive that perform the service. So far I have been put off by the large minimum charge. Most of these galvanizers specialize in large architectural or in irrigation applications. For my purposes (little abrasion) I will opt for "cold galvanizing", followed by water-based primer and a LPU top coat.
    http://www.zrcworldwide.com/products...izing-compound
    If you are hit with a minimum charge make enquiries around the fabricators in your area to see if you can put your piece in with their batch and pay them the correct share of the cost.
    It really is quite difficult to build an ugly wooden boat.

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  24. #24
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    Default Re: Steel CB protection

    All the dinghies with centerboards had them hot dip galvanised, also the first Cal Yawl built in The Nethelands. And unprotected it will last 25 years ore more. Dont bother with antifouling.

  25. #25
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    Default Re: Steel CB protection

    The only galvanized near me quoted a minimum charge of $500. So, I plan on cleaning the metal to a shine, Parkerize it with Jasco prep and primer, then applying multiple coats of a zinc-loaded primer. Any paint coating will require close annual inspection, though, no matter how good the paint. Iíll let you know how it works out.

  26. #26
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    Default Re: Steel CB protection

    Quote Originally Posted by JasonD View Post
    The only galvanized near me quoted a minimum charge of $500. So, I plan on cleaning the metal to a shine, Parkerize it with Jasco prep and primer, then applying multiple coats of a zinc-loaded primer. Any paint coating will require close annual inspection, though, no matter how good the paint. Iíll let you know how it works out.
    Maybe tell them that you can wait,or get them to hook you up with one of their customers.
    A guy near me said the same thing,but If I could wait he would slide me in with another order.
    R
    Sleep with one eye open.

  27. #27
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    Default Re: Steel CB protection

    Quote Originally Posted by JasonD View Post
    The only galvanized near me quoted a minimum charge of $500. So, I plan on cleaning the metal to a shine, Parkerize it with Jasco prep and primer, then applying multiple coats of a zinc-loaded primer. Any paint coating will require close annual inspection, though, no matter how good the paint. Iíll let you know how it works out.
    This is a good solution. It is not the best (hot dip), but it is reasonable, not the most expensive and it is available. Jasco is an iron phosphate, which is good. Zinc phosphate is better. Not a show stopper, either will work. https://www.finishing.com/318/84.shtml

    So now all you have to decide is which zinc rich is best. Inorganic, organic, one part, two part... and the answer is... it depends. http://www.elzly.com/docs/Ault_Zinc_Rich_Paper.pdf I would tend to look for one that meets a specification. Someone here might have a good recommendation.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  28. #28
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    Default Re: Steel CB protection

    Any mild steel should be sandblasted prior to paint. It removes the mill scale and provides an anchor pattern for the paint. Good paint starts with good prep.

    Mark

  29. #29
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    Default Re: Steel CB protection

    What did I say? a can of hammerite costs fifteen beertokens... I had a montague whaler with a at least 1/4 maybe more steel dropping centre board as far as I know it was probably never painted, but after fifty years it hadn't gone anywhere and another 50 years probably still not. The boat sat on a mud berth, cb up most of its life, The only issue I ever had was that if the CB had a super smooth pro finish maybe it wouldn't have gathered barnacles and such which did cause it to jam once in a while in the case. but nothing a hefty whack with a lump hammer didn't sort. actually in retrospect I probably wouldn't even bother painting it all. but I did .
    The boat's long gone but I bet there's a hefty 1m2 lump of quarter inch steel gathering mussels at the bottom of some muddy creek and its probably only a couple of thou less thick than when it started .
    'C'est la vie' say the old folks it goes to show you never can tell

  30. #30
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    Default Re: Steel CB protection

    Copper-Nickle instead of steel. near zero corrosion and near zero fouling, greater than zero price but depending on how deep your pockets are it might be an interesting option.
    This is the first lesson ye should learn: There is so much good in the worst of us, and so much bad in the best of us, it doesn't behoove any of us to speak evil of the rest of us.
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  31. #31
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    Default Re: Steel CB protection

    Quote Originally Posted by George Ray View Post
    Copper-Nickle instead of steel. near zero corrosion and near zero fouling, greater than zero price but depending on how deep your pockets are it might be an interesting option.
    You can save some money by using 90-10 CuNi clad plate, but the centerboard might still cost more than the boat. Locating the material can be challenging too.
    It does work well. https://www.copper.org/applications/...corrosion.html
    Idle curiosity. US submarines are black.. What do they use, or are they telling?
    Mare Island epoxy, MIL-DTL-24441.
    The anticorrosive and antifouling coating system used should be in accordance with MIL-PRF-23236, Coatings Systems for Ship Structures, MIL-DTL-24441, Paint, Epoxy-Polyamide, General Specification for, and MIL-PRF-24647, Paint System, Anticorrosive and Antifouling, Ship Hull as specified in Submarine Maintenance Standard (SMS) 6310-081-015 Ė Submarine Preservation and NAVSEA Standard Item (NSI) 009-32. http://www.nstcenter.biz/navy-produc...ull-submarine/
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  32. #32
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    Default Re: Steel CB protection

    Hi Jonboy
    Hammerite is not what it was, since they changed the formula due to eco pressure.

    And, those that sand the plate to 'bright' might want to think again, as paint will work much better on a sand blasted surface.
    A2

  33. #33
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    Default Re: Steel CB protection

    Hey Andrew, «a va ?

    I'd wondered about Hammerite as now it can be thinned with most petro solvents and it used to only be Trichloroethane or carbon tet if I remember
    I used a smooth non hammered version on some stanchions and other bits of scabby iron and its holding up well, maybe three years now. on an old fishing traineira in Nazarť. Topsides only but it is still pretty bright and cleans up nicely.
    'C'est la vie' say the old folks it goes to show you never can tell

  34. #34
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    Default Re: Steel CB protection

    Hot-Dip...

  35. #35
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    Default Re: Steel CB protection

    Canoeyawl, it seems that we have a situation here where the horse has been led to the watering trough, but whether it drinks or not is entirely up to the horse. Making it look repeatedly at the water only tires the groom and irritates the horse...
    Hope for the best, but plan for the worst.

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