Smallest steel boat?

Discussion in 'Metal Boat Building' started by magwas, Jul 21, 2011.

  1. magwas
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    magwas Senior Member

    After trying wood (I like it) and composite (not for me), now I am thinking about trying out steel boat building. I try to figure out what is the smallest size which can be built this way.
    I am thinking about building a six chined laser: basically the "laser2" model coming with Carlson's hull designer.
    I figured that using 0.8mm thickness the weight of the boat would not be ridiculous. But what about its strength?
    The construction method would be origami, with the adjustments to increase strength as necessary.
    I am thinking about two such adjustments:
    1. long chines. Origami design tries to minimalise the length of welds, hence the chines. I would rather try to maximalise this length, leaving the strakes connected only to the extent necessary to form the shape without a frame.
    I guess this would help prevent buckling. As there are 6 chines, the chines on the hull are close. But are they close enough?
    2. adding frames where necessary. My suspicion is that the deck would need some strengthening, as it is a big area without chines. What size of framing would be needed there?

    Well, if someone could give actual numbers and calculations as answer, it would be nice, but I don't expect that. Answers like "no, you cannot do this from 0.8mm", "you would need frame spacing on the 10cm range", or "this would work without additional framing" would suffice.

    Thank you
     
  2. hoytedow
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    hoytedow Wood Butcher

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  3. magwas
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    magwas Senior Member

    thank you:)

    Now do we have any saying on what plate thickness would be strong enough for a laser?
     
  4. Wynand N
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    Wynand N Retired Steelboatbuilder

    1.2mm, preferably galvanized....

    Back to your original post. I would rather form the 0.8mm plate in QC planking shape - interlocking channel sections used in building industry for pouring concrete into for upper floors - bend to a size that will suit your chines. Use SikaFlex to glue together the joints.

    Im serious, I still have the fax where Dudley Dix discussed a similar method (1991) with me - he wanted to build a racing steel boat that will be very light and strong by using thin steel plate bend into interlocking sections (this can be rolled any length from coil through die formers - much like galvanized gutters) and glued together with SikaFlex marine bonding compound. Impossible to weld such thin plate hence the gluing. The interlocking joints will form the longitudinal framing / stringers giving it the strength.
    And Dudley Dix was quite serious about this and we discussed it a few times before I stopped building yachts at the time in 1993.
     
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  5. hoytedow
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    hoytedow Wood Butcher

  6. magwas
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    magwas Senior Member

    Thank you both for the help.
    I could not find any information on what "QC planking" is.
    I would guess you are referring to one of the methods in the attached picture.
    Is it the upper one?
    With the upper one I guess there is no actual need for welding because the two sheets can be punched together, so sikaflex would be primarily for water tightness.
    I cannot see why you have written that this material cannot be welded. I have just bought a CO weld machine, and learning to weld 0.8mm steel. My neighbour is a professional welder, he can do it, and I hope I can learn it as well quickly.
    Are you saying it because it is indeed hard to make a watertight weld, or because it makes the material weak?

    In this page there are more lock styles. (And even my grandpa's hand operated crimper machine is there! )
    http://www.americanmachinetools.com/hvac_tools.htm
     

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  7. gonzo
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    gonzo Senior Member

    Welding thin material will distort it quite a lot. You will then need to add a thick layer of fairing compound. I have seen precision welding of beer cans as a demonstration.
     
  8. jehardiman
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    jehardiman Senior Member

    Well.... you could weld it without distortion using a small (10-20 KW) CO2 laser, but not everyone has one of those in thier garage. But gonzo has it right, the thin skin metal racing yachts of the 1930's and even modern aircraft are riveted and glued rather then welded to prevent having to apply lots of fairing.
     
  9. magwas
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    magwas Senior Member

    Thank you all for the insights.

    I have tried the locking method above. It is too cumbersome with hand tools, and my grandpa's machine is lost...

    So I guess I will go for 1.2mm plates as Wynand suggested and origami.

    The current state of the plan is attached.
    I will come back with the developments origamized to ask where I would need additional framing.
     

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  10. gonzo
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    gonzo Senior Member

    Why the chines? There are plenty of metal boats with thin skin. If you give the sheet metal a curve, preferably compound, it will stiffen it considerably.
     
  11. magwas
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    magwas Senior Member

    It should be my lack of knowledge. I know the following steel boat building methods, do you refer to one of them, or ?
    1. framed: build a frame then weld the sheets on it
    2. chined frameless: same as stitch&glue but with steel and welding.
    3. origami: This is what I plan to do. The attached plan is an intermediate one: I will eliminate some chine intervals when origamizing the design.

    Correct me if I'm wrong, but I have the feeling that as the chines and the weld to the deck gives the curve of the boat, with a thin skin I should have the chines closer than with a thick one.
    This is why I went for a 6-chined design. I actually did a 3-chined version of the boat. If I would be confident that an origami based on that made of 1.2mm steel would be mechanically strong enough, I would go for that: less cutting, less welding and smoother shape.
     
  12. magwas
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    magwas Senior Member

    Here is the origamized plan. It needs 8 sheets of 1.00mx2.00mx1.2mm steel.
    (From the dxf only the origami_* and sheets layers are interesting.)

    I was trying to keep the intervals where the strakes are glued together to the minimum, to keep the unchined area minimal. However this means that cross bends are less, hence it might even raise the possibility of buckling. It depends on factors I can't even remotely catch.

    (It would be nice to have some tools which can do mechanical calculations. I have taken a look into freefem (a finite element analysis tool), but it is way beyond my grasp.)
     

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  13. gonzo
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    gonzo Senior Member

    Have you looked at any metal boats in that size? There are several solutions to the problem. However, they are usually built of aluminum because of the weight.
     
  14. magwas
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    magwas Senior Member

    I could not find much useable information on metal boats that size. There are some fishing flat-boats here, but nothing else below 25 feet. And could not find much more on the internet either. I figure because it is not a well-suited size for metal boats.
     

  15. Wynand N
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    Wynand N Retired Steelboatbuilder

    Magwas, there are steelboats below 25ft and the Tom Thumb 24 comes to mind, I had built quite a few of these with custom fin keels opposed to the std full keel - beautiful and fast cruisers.
    I also built a 20ft frameless steel boat of my own design based on the TT - hull 2.5mm plate and deck 2.0mm.

    But my question to you is WHY would you like to build a laser type hull in steel:?:
    For a custom one off I would have gone for strip moulded ply (my favorite boat building material) but since you do not want to go that route, why not simply a GRP hull reinforced with CoreMate sandwich? It would be light, stiff and strong and any shape is possible....
     
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