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Aluminum hull bottom paint

Discussion in 'Chris Craft Roamer Yacht' started by q240z, Apr 1, 2008.

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  1. q240z

    q240z New Member

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    So many choices...

    In late April we'll be blasting & painting the hull on our 46 Roamer and I'm looking around for bottom paints. ePaint's online calculator says I need 8 gallons to do the job, which is quite a bit more than I've ever used in one go on our 52' Connie. The Pettit calculator says 3 gallons will do the job. Here's the current line-up of brands I'm considering:

    Petitt-- Vivid Free ($169/gal) [zero copper, active ingredient Zinc Pyrithione .....4.95%], Alumacoat SR ($159/gal) [zero copper, active ingredient Zinc Pyrithione .....4.95%]; Vivid ($149/gal) [contains Cuprous Thiocyanate and 2.% Zinc Pyrithione but is recommended for AL hulls.]

    ePaint--EP-ZO ($179/gal) [zero copper, active ingredients are Zinc Pyrithione 4.8%, Zinc Oxide 36%; ]; EP2000 ($209/gal) [Proprietary Algaecide 4.7% and not compatible with other bottom paints]

    Interlux--Trilux 33 ($198/gal) [still contains some copper (Cuprous Thiocyanate) and is formulated for fast boats]

    As I understand it, Trilux 33 is what Marinette Yachts applies from the factory even though it does contain some copper. EP-ZO looks interesting because it's got relatively more Zinc AND produces hydrogen peroxide. Pettit's copper free paints look pretty good as well. It's like I said...too many choices. :p

    Any thoughts? What do you use for your aluminum hull?
  2. Redhook98

    Redhook98 New Member

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    I have a Marinette (for sale right now), and I have been using Trilux-33. Seems to be the best for aluminum boats. It took a gallon for each coat on that boat (32-ft). Recommend at least 2-3 for any boat.

    HOWEVER.... If you take it down to bare aluminum with a good media blast, etch and prime it properly, then put on a barrier coating (IP-2000 is perfect) then you can put whatever paint on there you wish. The key is absolute isolation from the aluminum hull. A good quality barrier coat does just that. It is expensive the first time (and only time), and should last the life of the boat after that. This is providing you have everything that should be isolated (shafts, rudders, etc) from hull as they should be.
  3. q240z

    q240z New Member

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    Redhook98, I've been thinking about Trilux 33 and the other paints with "Cu anything" as the active ingredient. I understand that the Cu is rather tightly bonded in these molecules, but have to wonder if it isn't a matter of "best practice" to reduce to the extent possible and practical the amount of Cu that's in close proximity to my 40-year old aluminum hull. I dunno...relying on a barrier coat just sounds like relying on a condom to protect yourself from HIV or some other STD. Isn't it better to simply avoid risk than to hope that a prophylactic does its job?

    In retrospect, herpes might have been the most appropriate example...

    Anyway, our hull will be etched etc. appropriately. I'm just looking for thumbs up or down about bottom paints for AL hulls. How has Trilux worked for you? Does it last long or are you having to repaint annually? Are you covered with barnacles each time or does everything pretty much just powerwash off? Do you scrub your bottom once or twice a year or is that even recommended with Trilux?

    Cheers,
  4. Redhook98

    Redhook98 New Member

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    To do it the right way, you should barrier coat it. But barring that, taking it down to bare metal, etching and then priming it, then followed by several coats of Trilux-33 is what I would do. The last coats I put on mine was back in August. It was previously coated with Trilux more then 2 years previously. Bottom was not to bad and a simple power wash took everything off. Very few barnacles.

    Since it was coated in August, there is no growth to speak of. Of course the water has been a lot colder for the past 6 months since it was painted. I am also in brackish water and in a covered slip. I bring up the covered slip thing because there is only a limited amount of sun on the hull that way. The lack of sunshine tends to inhibit the worst growth which is usually along the water-line, extending down 6-8 inches. Extra paint should always be applied there anyway for that reason.

    I have no experience with the other paint you spoke of. The Marinette community though seems to be mostly Trilux-33. Most seem to use that.

    Hope this helps.
  5. q240z

    q240z New Member

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    That's an interesting point about the covered slip. As I understand it, EP-ZO is formulated to release H2O2 when the paint is exposed to sunlight in oxygenated water (http://www.epaint.com/questions/#1). I suspect it would be less effective in your circumstances. My boat is out in all kinds of weather, so it should function as designed.

    Then again, the fact that you're getting lots of growth near the waterline seems to indicate that adequate light is getting through. Time to hit the laboratory!!! lol

    But I'm still not sold on the idea of using paints containing any amount of Cu for old Al boats, though I can see how it would be a lesser concern on new hulls. For these old Roamers, where 40 years in the water have left their share of pits (barrier coats notwithstanding), my gut tells me Cu-free might be best.

    Have you ever asked Marinette why they use a bottom paint that contains CU when CU-free alternatives are available? If they've got data showing that the Cu is so tightly bound in Trilux that it doesn't pose a problem even years down the line (on old hulls that do a few hundred hours/year), I'm willing to read.
  6. Alanglois

    Alanglois Member

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    When doing the botton "top to bottom" so to speak, what lengths need to be gone to to ensure that the rudder and shaft log interiors are treated as well. These areas will be exposed to the water and if left untreated could cause issues couldn't they? Not sure how this was done at the factory but I will be doing the same bottom job this spring and just don't want to miss anything! It's an issue as one would have to remove both the shatfs and rudders to reach these areas.

    Al
  7. q240z

    q240z New Member

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    An interesting point, Alanglois. I would think you'd want to paint the log interiors as well the next time you have the shafts and rudders out. The problem, of course, is prepping those areas to accept and hold paint. We're using the Farrow System of low-pressure blasting, but I don't see how even that system could remove Al2O3 from inside the old logs.

    On our 46 we're going to cut out and replaced the rudder logs with new, and I intend to epoxy in a delrin bushing that's sized for the new SS rudder shafts. That should completely encapsulate the Al.

    I'm not sure how we'll deal with the shaft logs...
  8. crewzin

    crewzin New Member

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    According to the Painting Instructions for Roamer Yachts, revised 1-1-63 (that I happened to get when I bought my boat), the boats were painted at the factory with Glidden products. The 5 page document does not say you cannot use copper anti-fouling paints, but it says that you must "insulate steel and aluminum from copper bearing anti-fouling paint." Continuing, "NEVER APPLY ANTI-FOULING PAINT OVER BARE STEEL OR ALUMINUM."

    Like you, I am also currently investigating the paint selections. I work in an industry where we paint a lot of aluminum (aviation) and am working with one of our paint supplier's marine division to get the best product selection. I cannot give you more details today, but in the coming weeks I can pass more on.

    I hope this helps!
  9. q240z

    q240z New Member

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    The approach in that manual sounds very similar to what Marinette says about their new boats, crewzin.

    I spoke to a former USCG naval architect and ship inspector this evening. He confirmed what we all know: Cu directly over Al makes a fizzie [I'm paraphrasing, of course]. He also said that he would never recommend using any bottom paint containing Cu over an aluminum hull, even if it had a barrier coat. His example: imagine tapping a log while underway and knocking off a bit of paint and barrier coat. In the process, you've exposed the Al and potentially mooshed a bit of that Cu-based bottom paint up against it. That's a recipe for pitting. Take the Cu out of the equation though, and all you've got is a spot in the primer coat and bottom paint that will need a touch up on the next haul-out.

    Keep us updated on what you learn, crewzin. Maybe it's all much ado about nothing. Then again, with welders at $90/hr and hulls being kind of a critical system...
  10. Alanglois

    Alanglois Member

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    Can anyone share specifics on the etching and priming stages of the process such as what exactly is used or should be used to etch and timing between etching and priming. Also what primers have you all used (composition and brand names etc...). I am trying to make sure the marina that is doing this work is actually doing this the way it should be done.

    Thanks in advance...
  11. q240z

    q240z New Member

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    Alanglois, the process can depend on what brand of paint you use. Some are not compatible with certain primers, etc. After looking everything over, I'm inclined to go with epaint's products. For my 40-year old hull, no copper at all in the bottom paint is a must.
  12. artwork

    artwork Member

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    aluminum prep

    Alanglios, I've attended a couple aluminum paint seminars at IBEX (Internat Boatbuilders Exhibition) and they are consistent in their proceedure. For new or bare aluminum - sandblasting is best - not soda or walnut shell, but medium grit sand. If blasting is not practical, sand with 80 grit, this gives the best 'profile' for paint adhesion. Then prime with an epoxy primer to build a barrier coat - this could be up to 4 or 5 coats, then a non-cu bottom paint. If you have pitting and want to fair it out. The fairing goes on after the first epoxy primer. The epoxy fairing compound chemically bonds to the primer.

    The VERY critical part of this process is time. Get the primer on IMMEDIATELY after sanding. The boatbuilders and paint people concurred - what you sand in the first half of an 8 hr shift, you must paint in the second half. If you can be painting within an hour, all the better. The aluminum will start oxidizing that fast. If your yard sands one day and paints the next, it's too late.

    As a sidebar, there was a fellow attending the seminar who worked in the paintshop of a megayacht builder who said they no longer sandblasted, but used the chemical etcher -Alumiprep. I sandblasted the bottom of my 58 and zinc chromated it as a holding coat. This took a bit over three tons of sand, at least half of which is still in my boathouse, but the topsides are too big of a job to imagine doing this again, so I'm thinking chemical. I spoke to International paint and they admitted that the 'old standby zinc chromate' is as good as any primer, just sand it (80 grit) when I'm ready and begin the epoxy coatings.
  13. Alanglois

    Alanglois Member

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    Ok - Am I missing something here? Is the primer you mentioned a self-etching primer? It was my understanding that the bare aluminum needed to be etched then primed. I guess I am a bit confused as to the function of the sandblasting and the etching - do they accomplish the same thing as long as the primer is applied in a timely manner? Or does the blasted aluminum need to be etched then primed (or both steps handled in one coat with a self etching primer)?
  14. 9lives

    9lives Member

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    Hull painting

    Al as you know we did paint the hull and all exposed aluminum after sandblasting. I cannot remember the chemical used to etch or prime the aluminum after blasting but it was done. Next came a layer of zinc chromate followed by a 2 part coal tar epoxy and the layers of bottom paint were last.

    It has been 3 years since repainting and there is no issue whatsoever with any fairing cracking, or bottom coat peeling away.

    As you know we are re-shafting to 1-3/4" this spring. To clean the tubes and paint the interior was a perfect fit for this project. I used a sanding pad disc made of many sheets of paper mounted on a long shaft to my portable drill and cleaned out the tube. I then ran a paint pad pulled by string through the tube soaked in acetone to pull all residue out. I gave it 5 minutes to dry and the pulled another sponge soaled in sinc chromate. I pulled it from both ends so it passed by all points 2 times. I repeated it with the coal tar epoxy and made it a 2 coat application. I will not use a bottom coat inside the tubes. Good luck with your job!
    Mark
  15. artwork

    artwork Member

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    etching aluminum

    Al, the short answer to your question is that sandblasting IS etching. Chemical etching can be done in leiu of sanding (though the finished 'feel' is not the same). If a yard blasts first and still uses a chemical etching - all the better.

    After my post yesterday, I read up on the Alumiprep and Alodine products - some nasty stuff. The Alumiprep is a phosphoric acid and the Alodine is a chromium oxide - warnings of chemical burns, blindness, desease. Geez, if you use this stuff, where a rubber suit.
  16. Alanglois

    Alanglois Member

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    Mark, as usual always great information! Artwork, thanks to you as well and all who have posted to this thread as I'm sure it will be helpful to future hull adventurers like us! Just blasted the hull bottom this morning and all looks well. The primer is going on as I write this. The blast revealed that the original barrier coat was intact (and still is) on 95% of the boat. We went down to the aluminum on the other 5% (maybe less) and we need to do some fairing repair in these areas. Otherwise I was pleasently surprised. Boy the factory used a lot of fairing in some places just to get the right line - impressive. I'll post again as we move along.

    Al
  17. 9lives

    9lives Member

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    bottom painting

    Al, now you know what I meant that the orange urethane bottom barrier coat was impressive! Like yours, we left 95% intact as well.
    The worse places were on the hard chines about directly under the gate areas.

    What are you using as a new barrier over any zinc chromate?
    Mark
  18. q240z

    q240z New Member

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    Art, interesting point about fairing over the barrier coat. I suggested that to my painter a few weeks back and he said the fairing compound goes on first. Then he invited me to look at what Chris Craft did back in the day. Sure enough, they appear to have faired over aluminum then hit it with the orange primer coat.