Steel CB protection

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • FF
    Senior Member
    • Oct 2005
    • 1299

    #31
    Re: Steel CB protection

    Originally posted by Canoeyawl
    I wanted a steel centerboard Hot Dipped for a customer (in Maine) There was no shop that would do it in Maine or at least I couldn't find it. All the local yards said; "No one does that anymore, you need to..." powder coat, paint, epoxy or roofing tar, you name it, anything but the dreaded "Hot Dip". It was discouraging to listen to such ignorance, and many of them took it as an opportunity to rant about government for some phantom "regulations" that do not exist. Don't believe everything you are told.

    (Originally this thing was hot dipped and it was still pretty good but getting thin some 30 years later, and it was out of the boat for work on the case. About 400 lbs, I loaded it into the back of a pick-up, took it to Boston and bingo! "Come pick it up next week, about $200" so it is done, back in the boat, sailing and I won't hear about it again my lifetime. And I even found a pal that was commuting to Boston to bring it back).
    I was once put of for the initial cost was prohibitive. Later I somehow got a tabernacle mixed up with a large amount of steel fittings, and had it for free so they did not have the nuisance of writing a bill. Nowadays I will go to a steel worker and let him handle it.

    Comment

    • Dave Hadfield
      Senior Member
      • Apr 2000
      • 7461

      #32
      Re: Steel CB protection

      You don't have to pay that much for galvanizing. Find welding and metal fabrication places. They store up projects that need it until they have a bin full, then get it all done at once.

      Have yours added to the batch.

      I did this 10 years ago when I replaced Drake's CB. Worked great and cost squat.

      Comment

      • johngsandusky
        Senior Member
        • Dec 2003
        • 5557

        #33
        Re: Steel CB protection

        I've had two boats with iron keels. Both were primed and painted originally and held up well. On one I scraped scaled and sanded it by hand, primed with zinc paint, and copper bottom painted. That was over 20 years ago, it still looks good. I have no doubt that galvanizing is best, but many thousands of steel ships travel the world with no more than paint and primer on the hull. Many many classic boats have iron keels that are just painted too.

        Comment

        • Peerie Maa
          Old Grey Inquisitive One
          • Oct 2008
          • 62453

          #34
          Re: Steel CB protection

          Originally posted by johngsandusky
          I have no doubt that galvanizing is best, but many thousands of steel ships travel the world with no more than paint and primer on the hull. Many many classic boats have iron keels that are just painted too.


          Cast iron ballast keels and mild steel corrode at vastly different rates.
          It really is quite difficult to build an ugly wooden boat.

          The power of the web: Anyone can post anything on the web
          The weakness of the web: Anyone can post anything on the web.

          Comment

          • MN Dave
            Banned
            • Jul 2011
            • 3120

            #35
            Re: Steel CB protection

            Don't forget the zinc anodes or impressed current systems on those thousands of ships:
            Originally posted by johngsandusky
            I have no doubt that galvanizing is best, but many thousands of steel ships travel the world with no more than paint and primer on the hull. Many many classic boats have iron keels that are just painted too.
            Originally posted by Peerie Maa


            Cast iron ballast keels and mild steel corrode at vastly different rates.
            This links to a pdf that has the results of testing done on zinc rich primers, followed by tests on rust converters.

            Zinc rich paints:
            1. Zinga Organic epoxy primer 96% Zn
            2. Zinc Clad IV Solvent-based 85% Zn
            3. Zinc Clad XI Water-based inorganic Zn silicate with no VOC and 90% Zn
            4. N-5751M2 Solvent-based moisture cure 90% Zn
            5. Intershield 300V Aluminum-rich epoxy
            6. Epoxzen Organic epoxy with 90% Zn

            Rust converters:
            1. Gempler’s (water-based, tannic acid)
            2. Loctite rust treatment (polymeric-based, barium sulfate)
            3. Total Solutions (water-based, tannic acid)
            4. Phoscote (phosphoric acid – current USMC product) <>>
            5. VpCI CorrVerter (combined rust converter and primer)
            6. Corroseal (water-based, tannic acid with primer)
            7. Gem Rust Killer (under test)
            The rust converters were coated with a non-corrosion inhibiting epoxy primer and a polyurethane topcoat. While they are good paints, there was no chance that the rust converters would look good in these tests. It is unfortunate that they didn't compare to a sample without a converter. All I can say is that none of the rust converters looks bad, since all they do is help the paint stick to the metal.
            Last edited by MN Dave; 04-16-2018, 11:52 AM.

            Comment

            • alkorn
              Senior Member
              • Jun 2006
              • 504

              #36
              Re: Steel CB protection

              Originally posted by ahp
              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.)

              Comment

              • Peerie Maa
                Old Grey Inquisitive One
                • Oct 2008
                • 62453

                #37
                Re: Steel CB protection

                Originally posted by alkorn
                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.

                The power of the web: Anyone can post anything on the web
                The weakness of the web: Anyone can post anything on the web.

                Comment

                • Phil Y
                  Banned
                  • Apr 2010
                  • 21066

                  #38
                  Re: Steel CB protection

                  Originally posted by MN Dave
                  Don't forget the zinc anodes or impressed current systems on those thousands of ships:



                  This links to a pdf that has the results of testing done on zinc rich primers, followed by tests on rust converters.

                  Zinc rich paints:
                  1. Zinga Organic epoxy primer 96% Zn
                  2. Zinc Clad IV Solvent-based 85% Zn
                  3. Zinc Clad XI Water-based inorganic Zn silicate with no VOC and 90% Zn
                  4. N-5751M2 Solvent-based moisture cure 90% Zn
                  5. Intershield 300V Aluminum-rich epoxy
                  6. Epoxzen Organic epoxy with 90% Zn

                  Rust converters:
                  1. Gempler’s (water-based, tannic acid)
                  2. Loctite rust treatment (polymeric-based, barium sulfate)
                  3. Total Solutions (water-based, tannic acid)
                  4. Phoscote (phosphoric acid – current USMC product) <>>
                  5. VpCI CorrVerter (combined rust converter and primer)
                  6. Corroseal (water-based, tannic acid with primer)
                  7. Gem Rust Killer (under test)
                  The rust converters were coated with a non-corrosion inhibiting epoxy primer and a polyurethane topcoat. While they are good paints, there was no chance that the rust converters would look good in these tests. It is unfortunate that they didn't compare to a sample without a converter. All I can say is that none of the rust converters looks bad, since all they do is help the paint stick to the metal.
                  Unfortunately I don't understand most of that! My boat is strip planked and glassed on the outside. The has 2 skegs and rudders. The skegs are steel. The rudders are stainless. In between them of course is a bronze prop. My own little power generation plant right there. At about 50 years old there is considerable corrosion in the skegs, and having had the boat for about 7 years now I've not yet found a paint system for the skegs and rudders that doesn't come out looking very much like a failure at the next haul out. Might be time to remove the skegs, get them thoroughly sand blasted and hot dipped by the sounds of it. But next best is probably sand blast in place and a zinc rich primer. I don't know what sticks to stainless though.

                  Comment

                  • ron ll
                    Seattle WA USA (Ballard)
                    • Oct 2005
                    • 24289

                    #39
                    Re: Steel CB protection

                    I notice the chandleries around here are phasing out zincs in favor of aluminum anodes. Evidently all the zinc we are putting into the water is not very healthy.

                    Comment

                    • Phil Y
                      Banned
                      • Apr 2010
                      • 21066

                      #40
                      Re: Steel CB protection

                      Oh great, now we can't have decent antifouling or corrosion protection. And heaven forbid you might want to create any sawdust in your berth.

                      Comment

                      • MN Dave
                        Banned
                        • Jul 2011
                        • 3120

                        #41
                        Re: Steel CB protection

                        Originally posted by Phil Y
                        Unfortunately I don't understand most of that!
                        Wow! somebody tried to read one of my links! Sorry, it was a bit obtuse. Unfortunately, that wasn't as clearly written as it could have been, but wasn't much worse than the better articles. Welcome to my world. One thing about corrosion testing to remember is that corrosion tests are like an old army mule, they don't reproduce very well.
                        Might be time to remove the skegs, get them thoroughly sand blasted and hot dipped by the sounds of it. But next best is probably sand blast in place and a zinc rich primer. I don't know what sticks to stainless though.
                        Wait a minute, you did understand the link. It also said that painting the galvanized or zinc rich coating is a good idea.
                        As for what sticks to stainless steel, based on my observations of my stainless frying pan, eggs stick really well, followed by just about everything else, except paint.
                        Stainless needs to be really clean. it will help to lightly grit blast with a fine clean aluminum oxide grit that has never been used on steel. It also helps to clean with something like Alumaprep 33, which is pretty much Ospho with some degreaser. If your water is hard or high solids, rinse with RO or distilled water.

                        Do not galvanize or use cold galvanizing on stainless. The corrosion prof at MIT explained the effect on corrosion potentials to me and the part that I understood was that it it's bad to galvanize stainless. The details -- arrgh.

                        There are primers recommended for stainless that are also good for galvanized surfaces. Etching primers are good. I hate to recommend a chromate primer, but Pettit 6455 is good (apply thin, if you can't see through it, the paint will peel.) It is a version of the old DOD-P-15328 polyvinyl butyrate. I would also recommend an easier to use, less hazardous primer like Pettit 6980 Rustlok. The reason to paint stainless not to protect the stainless, it is to protect the other metals nearby. Painting stainless will reduce the large exposed area of cathode that causes galvanic corrosion of everything else.
                        Originally posted by Phil Y
                        Oh great, now we can't have decent antifouling or corrosion protection. And heaven forbid you might want to create any sawdust in your berth.
                        Aluminum anodes are better than zinc.
                        Zinc Again: So you think you know the difference between zinc and aluminum sacrificial anodes?

                        Surprisingly, aluminum anodes are often no more costly than zinc ones. Also, because most are cadmium-free, aluminum anodes are less of a hazard to the marine environment. So, regardless of what a diver, boatyard manager or other industry pro tells you, there are several advantages, and no drawbacks, to switching to aluminum anodes.

                        Comment

                        • Phil Y
                          Banned
                          • Apr 2010
                          • 21066

                          #42
                          Re: Steel CB protection

                          Thanks Dave, etching primer it is then. For the stainless. Of course the other reason to paint stainless, is to stop stuff growing on it.

                          Comment

                          • BrianM
                            Wood-And-Boats
                            • Sep 2002
                            • 1237

                            #43
                            Re: Steel CB protection

                            Originally posted by Peerie Maa
                            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.

                            Comment

                            • BrianM
                              Wood-And-Boats
                              • Sep 2002
                              • 1237

                              #44
                              Re: Steel CB protection

                              Steel Centerboards.... a comment was made on how to fair the board to give it a lifting profile. I had a piece of 5/8" boiler plate my dad pulled from the scrap bin at work and gave me when I was building a sailing dory. I machined the edges square, then made some hardwood leading and trailing edges. I drilled and tapped the front and read edges of the boiler plate and after painting (I was in high school, so did not know about galvanizing) and simply attached the fairings to get a little better efficiency. NACA lifting foils are the ultimate solution, but the shape is impractical for a centerboard in terms of width and they have not flat surfaces to bear against a centerboard trunk.

                              Comment

                              • Jay Greer
                                Senior Member
                                • Nov 2004
                                • 14425

                                #45
                                Re: Steel CB protection

                                Originally posted by Phil Y
                                Oh great, now we can't have decent antifouling or corrosion protection. And heaven forbid you might want to create any sawdust in your berth.
                                Yes, Newport Harbor CA has that rule! Madding if you are, merely, sanding varnish without draping the area! Sanding a mast on the beach is a no no as well!
                                Jay

                                Comment

                                Working...