removing swirl marks and scratches from bare aluminum hull

Discussion in 'Metal Boat Building' started by Pen Gwyn, Mar 7, 2020.

  1. Barry
    Joined: Mar 2002
    Posts: 1,313
    Likes: 149, Points: 63, Legacy Rep: 158

    Barry Senior Member

    These particular discs are rigid flap discs for cleaning up inside fillet welds. They have many other abrasives, as well
     
  2. Pen Gwyn
    Joined: Mar 2020
    Posts: 10
    Likes: 0, Points: 1
    Location: Belgium

    Pen Gwyn Junior Member

    Hi all.
    A few photo's of other boats from the yard.
    This is the standard level of finish leaving the yard.
    The picture of the boat in the water, is what is intended as an end-result.
     

    Attached Files:

  3. Pen Gwyn
    Joined: Mar 2020
    Posts: 10
    Likes: 0, Points: 1
    Location: Belgium

    Pen Gwyn Junior Member

    Some owners take to sea without finishing.
    Over time it seems all marks also disappear.
    But since I have a few months ahead of me while they are finishing the interior, I prefer to give it a more finished look before launching.
     

    Attached Files:

  4. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,951
    Likes: 604, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Looks scheissenhausen to me. I don't think you be in business long presenting products like that in the modern world.
     
    fallguy likes this.
  5. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    I can't understand why would anyone do that to a hull.
     
    fallguy likes this.
  6. fallguy
    Joined: Dec 2016
    Posts: 3,343
    Likes: 440, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    Run Forrest, Run!

    Do not allow them to touch the finish.
     
  7. fallguy
    Joined: Dec 2016
    Posts: 3,343
    Likes: 440, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    OP

    please read this post to yourself about 3-6 times

    the yard is almost certainly doing this to hide weld marks or handling marks or because noone hollered at them or to speed corrosion or some set of them; deep scratches increase the surface area which mean more surface to corrode; not less

    consider asking the linked public forum for some world class advice

    they may suggest a chemical; ask them about sun bleaching; I don't know how to faster achieve your dull look, but a chemical may be better and faster done safely

    Finishing: Anodizing, Plating, Powder Coating, & Surface Finishing https://www.finishing.com/index.html
     
    Last edited: Mar 8, 2020
  8. fallguy
    Joined: Dec 2016
    Posts: 3,343
    Likes: 440, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    There is a fellow I know who says anything unfinished is 'industrial' looking. I'd say the yard runs a Festool hogger over the thing once to speed their involvement in making it appear super shiny and polished. Polishing takes considerable effort and now will take even more effort.

    What bothers me about the approach is how much corrosion is invited; not to mention the ugliness.

    I would start with a few hundred sheets of 180 black oxide with a medium density pad. No lubricant. Run until it removes most of the gouges; and if needed step to 80 or 100 grit in between, but only if absolutely needed to shorten the work. I like to do a test area and determine time per square foot. The first one will be quite a bit to undo the damage.

    But I am used to a polished look; not the dull gray..
     
  9. Pen Gwyn
    Joined: Mar 2020
    Posts: 10
    Likes: 0, Points: 1
    Location: Belgium

    Pen Gwyn Junior Member

    Guys, thanks for all the input. However, and apologies if this may come across as blunt, ...
    ... what I am asking for is technical support. Not opinions on esthetics.
    Whether you like the final look or not, is a question of personal appreciation.
    So, let's not go there.

    The picture "hull in water" is the same boat as the pictures "hull yard 1-5".
    You may not like the 'military look', fine. But for me the unpainted look of "hull in water" is more than adequate.
    The esthetics do not determine the performance and seaworthiness of the boat. The design and the build do.

    All these boats have been in the water for years, some for several decades. Having made great voyages.
    The impetus here is on sailing and traveling, thus low-maintenance.
    And it is undeniable that not painting the hull makes for a much more low-maintenance boat.

    The question at hand is how to go from "hull yard" to "hull in water".
    In the most efficient way, and without doing unforeseen damage by applying a faulty procedure.

    You've given me already things to work with, and will start with that tomorrow.
    Keep you posted.
    In the meantime further technical comments are welcome.

    Thanks
    Philippe
     
  10. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Technically, the only problem is increased corrosion. You, however, are asking about aesthetics since the question is about polishing it. The main problem is the amount of plating that needs to be removed. Hull plating is designed thicker than necessary from the structural requirements to account for corrosion and mechanical damage. By polishing, there may be no safety margin and could end up thinner than the minimum structural requirement.
     
  11. Barry
    Joined: Mar 2002
    Posts: 1,313
    Likes: 149, Points: 63, Legacy Rep: 158

    Barry Senior Member

    I mentioned earlier that if you want to reveal the scratches, which you don't, you can use a thin spray coat of a GLOSS paint.
    If you want to paint and hide imperfections, then a flat or ultra flat paint will give the look of a smooth finish even though the scratches are still there

    From a short distance away, over time the, the flat finish when the aluminum develops its natural corrosion resisting oxide, as the pictures of the boats that you provided show.

    So to get to the flat finish albeit with scratches you can experiment with an acid etch. Almost all paint jobs on aluminum require an acid etch prior to applying a primer. (certainly there are etch primers available but our experience with them
    was not stellar). This goes back awhile but I believe with the International Paint products which were incredible, we used a product called Alodine ###. We brushed this one, then rinsed it off, as soon as it dried, we primed the surface before
    the primer was applied.

    Right after the rinse, the aluminum possessed and extremely flat finish.

    You might give this a go on a sample piece. There will probably be a safety sheet on its application, ie minimum eye protection and probably a respirator, lots of ventilation

    Another product, but you should experiment again, is vehicle aluminum rim/wheel cleaners that are used prior to polishing.

    The scratches will still exist, but they will not be too visual

    The boat builder builds some very nice looking hulls. If they want this initial scuffed surface knowing that in time it will disappear, they should just use a higher numbered grit.
     
  12. fallguy
    Joined: Dec 2016
    Posts: 3,343
    Likes: 440, Points: 93, Legacy Rep: 10
    Location: usa

    fallguy Senior Member

    I can't think of a single builder here in the US that builds in that fashion.

    Perhaps the most typical and known aluminum builder is Munson Boats. And I have never seen a Munson done this way.

    So, you are making a cultural leap to want to go to gray we are not accustomed to.... hopefully you can understand.

    I honestly think a better approach to go to gray would be a 180 grit etch followed by a chemical wash (of some kind). Of course, the chemicals would need to not attack other sections of finished hull. And driving gouges into a surface speeds corrosion and lowers service life; so another reason we would not see it as desirable.

    I strongly recommend you ask the people at finishing.com. Really great forum.. kindest regards
     
  13. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,951
    Likes: 604, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    The OP is starting to become an annoyance, if you are the buyer of this boat, take your concerns up with the builder of it, to read that he isn't concerned with aesthetics, is laughable, if it is purely a concern with durability compromised by scored plating inviting corrosion, why haven't you challenged the builder about a product not delivered in properly finished form ?
     
  14. Ad Hoc
    Joined: Oct 2008
    Posts: 6,609
    Likes: 617, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    There is a lot of useful info given already. But, what you need to understand is the difference between standard aluminium fabrication results v end result expectations.

    All aluminium fabrication, when done properly will have those score marks you show. Here is one example of a vessel post repair:

    upload_2020-3-9_8-30-27.png

    And another new build:

    upload_2020-3-9_8-31-26.png

    What you're asking is to just go to a "smooth" surface for aesthetics and presentation.
    Which means you're left with 2 choices:-
    i) An ever decreasing grinding disc roughness to make the surface smoother with each iteration
    ii) leave it as it is.

    It seems you're getting frustrated with the progress of i). Thus just leave it as it is. Bare aluminium oxides rapidly. Over a short period of time you will no longer notice those swirls and score marks (assuming them to be not deep and general fabrication ,as noted above). The only down side it will be a matt look, not a glossy look. If you want a glossy bare ally look, you'll need to do a bit of i) and then coat with a clear epoxy.

    Leaving the hull bare unpainted is nothing new and is far more common than many posting on this thread would appear to suggest.
    Technically, there is no reason to paint an aluminium hull, it is oddly, for aesthetics only. Aluminium's natural oxide layer protects the hull far better than any paint.
     

    Attached Files:


  15. gonzo
    Joined: Aug 2002
    Posts: 14,507
    Likes: 659, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Are you used to seeing the scuff marks with a grit as coarse as #40? I am used to a much finer grit finish.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.