best material to be used when fairing?

Discussion in 'Fiberglass and Composite Boat Building' started by nevilleh, Oct 20, 2012.

  1. MaxHammer
    Joined: Oct 2012
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    MaxHammer Junior Member

    Hey guys,

    Another noob to join the fray here :). I would like to ask you guys. I see that there are several possibilities that you as a yacht builder can use when making a perfect faring material. Blending sounds good to me as mentioned here before. The softer the result easier to sand. But I was wondering. Maybe a use of better sander tools will solve that problem? I know that there are some tools that can work with curved surface and on large areas making the sanding a lot easier.

    Dont worry and point me in right direction. As I said before. im quite a noob here. Even when it comes to yacht building. But this forum is a good source of knowledge
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    With fairing you have to assume good techniques and materials, more so than tools. A long board is a pretty simple device. Your elbows will hate you, but there's just not much to one. A DA or sander/buffer can be helpful, but it's more about good abrasives and techniques then tools.
     
  3. waikikin
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    waikikin Senior Member

    Neville, given that I haven't seen the tooling & that your "locked in" for this vessel, can't a simple flat melamine sheet be temporarily back screwed/bolted/clamped to the existing wheel house tooling to form & mold your inward facing flange? Surely the cambers etc will match over the width of the flange adequately to bolt down onto probond or similar or are there large radius to perimeter?. Jeff.
     
  4. MaxHammer
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    MaxHammer Junior Member

    I would kill for flexible sander!!Argh...

    Was not around for a while. Thanks for your reply PAR. That sounds good.
    I got another question for you if ou dont mind. It is still about the sanders.

    I must confess, that lately I spent countless nights wake up and thinking, why there are not any flexible electric sanders around. You know something tht would just copy the surface of the hull. I am refiting 72 foot long yacht and I would definitely welcome something like that. Do I live in the land of dreams? Or the electric flexible sander is just too much hard to make? I wonder why such giants as Mirka, 3M and many other great companies did not yet made any flexible sanders. :p
     
  5. michael pierzga
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    michael pierzga Senior Member

    Look around and you will find many flexible sanders.

    This old reliable can be shop made and is very effective for many jobs.

    http://www.epoxyworks.com/33/pdf/Sanding Tricks of the Trade.pdf

    It works but unfortunately it is also very dusty.

    Plywood works fine and is best as a first try until you have proven the design. Prime the ply with epoxy so that common 3M dics adhesive can be used.
     
  6. Frosty

    Frosty Previous Member

    Long boarding makes flat ,--sanding makes smooth --the two dont necessarily meet and ones is not the other.

    In the old days black cars cost more and that wasnt because of paint.
     
  7. midnitmike
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    midnitmike Senior Member

    I realize this has nothing to do with boats, and for the most part nothing whatsoever to do with this thread, but I can't help that. Frosty could you please explain to me what you meant by this comment.

    When I first read it what instantly came to mind was Henry Ford oft quoted line "They can have any color they want, so long as it's black". So I'm left wondering how is it that you came to make such a statement, and what rational are you using to justify such a claim?

    MM
     
  8. robwilk37
    Joined: Nov 2010
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    robwilk37 Senior Member

    MM. cant speak for anyone else, but i remember my neighbor saying you always pay more for a black car. the prep before paint had to go through an extra step because shiny black paint will telegraph the tiniest imperfections in the base material. and he worked for ford...though this was when all the build was done by hand.
     
  9. Frosty

    Frosty Previous Member

    Rob is correct a black car needs extra preparation infact the bodies were picked to be black. What this has to do with long boarding is identical , a flat fairing will show a reflection so if you want it nice and flat a lot of flat boarding is required which is extremely hard work.

    If you paint your boat black and not many do it will need to be perfect also,--- and not just smooth which is all a sander will do.

    If you paint it white it does not need such perfection as white does not reflect the same.
     
  10. midnitmike
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    midnitmike Senior Member

    This is exactly what I was getting at. You will pay more precisely because of the color choice or paint in this case, maybe not because of the higher cost of the paint itself, but because of the greater attention that must be paid to prepping the surface. So when you say that a car costs more in black then in any other color, and that this extra cost is not associated with the paint...well I have to disagree.

    And just so you know....in cold weather climates Black is a very common color for boats. Care to hazard a guess as to why?

    MM
     
  11. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Frosty is absolutely correct and is describing the difference between "fairing" and "smoothing", which are two different things.

    Smoothing is as the word suggests, making the surface smooth. You can have a smooth, yet unfair surface. This is easy to demonstrate, if you look at a car door with a dent in it. The reflections in the paint will clearly show it's not fair (the dent), but the surface can still be smooth.

    Fairing is the "true-ness" of the surface. If it's a flat surface, it has no dips, humps, dents or waviness to it, when you catch a reflection with your eye. Again, looking at a nice shiny car door and catching a reflection with your eye, you'll see a sweet, unmolested, uninterrupted surface. The same with a curved surface that's fair, the reflection will curve without any irregularities along it's length.

    Fairing requires different techniques and usually tools to do properly. You really can't fair things with a DA or palm sander. You need a tool that can bridge low spots and can knock down highs, which "levels" the surface. Smoothing is taking the surface to a finer state, from say (as an example) from a uniform 100 grit to a uniform 220 grit.

    Dark colors, especially black and dark metallics will show up every imperfection on the surface. Your eye is just naturally "tuned" to pick up these reflections better, than on lighter colors. White hides imperfections the best and less gloss or flat finishes also hide imperfections, mostly because they don't have easily seen reflections that draw your eye to them.
     
  12. tunnels

    tunnels Previous Member

    If you cant understand the meaning of that claim you lack the exsperiance and know how of whats required to make a near perfect job to accept a black finish . Its a sign of quality of workmanship !!
    Black is a really hard colour to get to look magnificent and shiney without swirl marks from some one simply rubbing a dry cloth over the paint surface that has dust . the dust acts like polishing compound and leaves bub marks .
    Have only ebe made one black 36 foot yacht and took twice as long to first buff and polish the moulds then hours waxing and making the best possible job of the gel coating to not get any places where there could be patchs of porosity within the gel coat , the first skin of tissue and 225 gram csm glass we also added black pigment to the resin to get an even deeper deepth of colour All this really paid off with the end product and when the boats was ready for the water the glossy finish was so nice and with all the teakwork and gold lettering on a teak transom scroll board was an absolute picture !!
    :D
     
  13. OFFSHORE GINGER
    Joined: Nov 2011
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    OFFSHORE GINGER Junior Member

    [​IMG] I, have spent many years using these machines considering hand sanding or ( long boarding ) is your only option when doing a curved / crowned , surface , and just a quick mention ~ the longer the board the straighter the surface .
     
  14. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Air files are OK for a big shop.

    They use a massive amount of air and are expensive to operate for the small time builder.

    Fairing is always a labour intensive task, If you use the correct bog, apply it correctly and use sharp sandpaper the job goes much better.

    Application is the key. Pro bog men are great to have around on big jobs.
     

  15. Frosty

    Frosty Previous Member

    Yes micheaql is correct those air rasps use a hell of a lot of CFM and --the sandpaper needs to be sharp. I would not use less than 80 and would start with 40 to get the shape and flat then go down for smootheness.

    Then after 80 I wack it with surfacer primer and rub off with 120 then again and 280.

    I never go higher than 400 these guys with 1000 grade might as well use the financial times.
     
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