ease of fairing of larger boats

Discussion in 'Metal Boat Building' started by Tzuriel, Nov 11, 2006.

  1. Tzuriel
    Joined: Oct 2006
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    Tzuriel Junior Member

    Is there any difference in the ease of fairing a larger boat than a smaller boat? Using a 40' and a 55' for example ... because of the larger size of a 55' which seems to have more sq. ft. of "flatter" plates and less bend in the radius ... is it easier to look more "professional" because of this?

    The one thing that scares me is as a beginner is that the hull might not turn out as smooth as I'd want it to be. So, assuming I am skilled at welding and understand how to handle heat, distortion, etc... in the plates, is there a difference is size and ease of a faired hull?

    Also, I've seen boats with lots of "paint" like lines around the seems and in big patches in some areas. I think it's like a filler (which doesn't seem like the building went correctly when having to add it in large patchy areas). How does this hold up over time on top of steel? Seems like you lose the benefits of strenth in these areas (at least, on the filler portion). What is it?
  2. timgoz
    Joined: Jul 2006
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    timgoz Senior Member

    The filler can be several different types I think, from car like bondo to epoxy based pastes.

    One of the major steel boat builders, Custom Steel Boats, I think, boasts of how very little filler they have used over many years. Personally I would get the hull as fair as possible w/o filler and leave it at that. But cosmetics beyond a certain point do not interest me - "function in beauty".

    An area distorted to the degree that one sees a need for filler may have some structural stresses that would lower strength. Each case would differ. I would think most cases would not be significant as to strength reduction.

    If both the 40ft. & 55ft. boats were laid out correctly, I would think the larger boat with heavier plating & frames would be more likely to come out fairer. This is a guess though.

    Take care.

  3. M&M Ovenden
    Joined: Jan 2006
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    M&M Ovenden Senior Member

    The boat sizes you are talking about could have hull plate thickness anywhere between 10 ga and 3/16 inch, it makes a big difference in plate weight. The weight of the material is a big deal in the ease of handling it, mostly if you are working on your own and without professional lifting devices. Everything, not only materials but also tools, get heavier for heavier boats, so difficulty and time adds up that way. Steel plate behaves like some wet noodle, bigger the area more noodly it is, so as there is a limit to how a big of a plate one can handle, the bigger boat can also end up having more plate seams then a smaller one. Mentioning seams, when you decide what size boat you want, if your size idea is not set in stone, consider the plate dimensions easily available (and handleable) where you want to build. In our case, the biggest plate size easily available (and handleable) where 5 by 10 feet. If the boat had been so big I needed some plating wider than 5 feet I would of added some longitudinal seams, therefore increasing the plating difficulty.
    If you want ease of plating a fair boat, don't consider as much the the size than the design. If a boat has been designed to be fully developable, the plate, no matter the size of it will happily work with you. As soon as the shape of the hull requires forming you add to the difficulty level to obtain a perfect shape independantly from the size.

    Where I think the size of the boat makes a difference for ease of building is for the construction of the inside accommodations. Bigger boat means more room for strait edges, it gets easier to fit blocks. As a persons size doesn't change each part of the inside is proportionally smaller to the boat therefore easier to fit.

  4. Wynand N
    Joined: Oct 2004
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    Wynand N Retired Steelboatbuilder

    bigger the easier.... Less tighter curvature and hence easier to build an extremely fair hull if care is taken, especially with the welding procedure.
  5. mastcolin
    Joined: Jun 2005
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    mastcolin Senior Member

    The fairness of the hull will depend on the how good you build it/cut it/bend it. I'm not sure size comes into it really.

    A curve will look less unfair than a slab side for pure reason your eye gets thrown by the curve.

    I work with paint applicator in NL - we paint everything from 10m steel hulls to 90m. We see good and we see bad - it depends on builder and hull form more than size I'd say from having to apply filler to them.

    Even a uncut sheet from Corus is +/-3mm spec. Your frames will be every 50cm, the welding distorts the plate, the build distorts the hull.

    You have preformed plates or are you having to form them yourself? I presume latter. For you bigger,flatter will probably be better. Some big fat hard chines will make life easy.

    The lines you see I suspect is someone having just filled patches - badly.

    We'll do it if you want - 700euro a square metre:)

    ps don't worry about filler system. It's sticks like the proverbial if it is epoxy system. I was involved with Challenge Business yachts (the 1st 67footers from early 90's) and they've been slammed through Southern Ocean twice. The plates were deformed - the filler and paint was still there.

    pps paint it cream colour - this shows up unfairness less than a purer white. Do not make it dark colour.
  6. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    Definately, the bigger the boat the easier to build her apparently fair.

    I too would stress that the welding procedure is very important, not hard but you need to strictly adhere to it.

  7. alaskatrawler

    alaskatrawler Previous Member

    The plate thickness also helps in keeping the vessel fair. When I built Balto I used 1/4" plating for the hull and 3/16 on the house. Also a vessel design with a hard chine can also contributes to a fairer hull especially if your experience level is more at the beginner stage. Thicker hull plating for sail vessels may not be a viable way to go but on a displacement trawler it make sense. As for fairing I used awl fair by awlgrip in the 2 gallon kits. I will warn you a good quality epoxy fairing compund is not cheap and to see it being sanded off knowing what you pay for it kinda hurts a bit but you get over it if your fairing job turns out well.
    As for the size of vessel..... and I am not speaking of sailing vessels but hard chine trawler stlye vessels the difficulty in fairing really does not matter with the size. Currently I am building my radar mast and am fairing the weld seams as I want a seamless appearance. I will say that I have seen some very nicely welded hulls where the welds are like works of art and contribute to the looks of the vessel.

    Dan Walsh
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