Advanced aluminium extrusions for boatbuilding?

Discussion in 'Metal Boat Building' started by simon, Jan 1, 2008.

  1. simon
    Joined: May 2002
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    simon Senior Member

    Most of the sources mention flat bars, L-, T- or bulb aluminium extrusions for the use of longitudinals. But are there other types of extrusions, for example like a D-shaped, that will distribute the load more evenly and will reduce the unsupported panel area, not being heavier, faster to build?

    In shipbuilding new extrusions for decks have come up that simplify the construction process.

    What is the potential for use of specialized aluminium extrusions in boatbuilding?
     
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  2. kmorin
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    kmorin Senior Member

    New Extrusions

    simon,

    In the NW new extrusions can be done several ways. One is to pay the die charge to design and machine the extrusion plate and also buy the minimum wt order - as 1000 lb of material. The second is to OWN or hold rights to the plate's output in addition to the above.

    The latter method resembles a patent, or copyright but if the extrusion mill finds lots of customers for your shape-well you'd need some good prior agreement to defend your proprietary shape.

    I've done this a few times over the last few decades- design an extrusion- my first was the 1/2 pipe now one of the most common shapes sold in 6061 for wrapping the gunwales without splitting whole pipe.

    The second time was a much more complex shape- still very simple compared to 80/20's bar stock, but again if you don't have dialog with the extrusion company your idea becomes their property and they can sell it to whomever they'd like.

    1000 at $2.50 to $3.00lb for the metal order and another 2- 5K for the plate seem to be about the likely costs. All these numbers could be off if the alloy was not 6061-T6 or something similar since that is what the example is based on.

    If the framing members (extrusions) are larger than four inches in one direction(?) it would probably be more economic to bend sheered plate into tall "L's" rather than extrude.

    Depending on the boat size and the orientation of the structural elements bending is extremely cost effective. Building open skiffs for commercial fishing I used to bend 1/8" 5086 into an 8" tall 8" wide U where the legs were not parallel but 15degs spread. This was fit to the bottom of the skiff transversely. The resulting fully welded box was an 8" x 8" hollow member holding a 3" convex camber in the bottom. These "rib's" were light, stiff and kept the load from shifting fore and aft so they did lots of 'work' in the overall design.

    The folded sheet was much less expensive than an extrusion of a similar section.

    An extrusion that is 2" x 3" x 1/4" of a similar cross section described above is available - I've only heard it referred to as "Hull Stiffener" I don't know the extrusion order number. I've used thousands of feet of this material to stiffen hull panels in lots of different boats.

    Cheers,
    kmorin
     
  3. FAST FRED
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    FAST FRED Senior Member

    I wonder if someone would be kind enough to publish current (JAN 08) per pound prices for aluminum for a common hull build .

    say 1/4 , 3/16 plate and the price of appropriate T and L stock? 5083 ? or whatever would be a good choice.

    Close $$$$ costs would be great , Thanks!

    FF
     
  4. kmorin
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    kmorin Senior Member

    Aluminum costs in Alaska

    FAST FRED,
    I just called the supplier in Kenai Alaska and 6061 extrusions are from $3.75 to $4.03 /lb depending on shape.
    5052 is $3.88 to $4.10/lb. - larger sizes have a handling cost with crating to our location.
    5086 is $4.70-$4.85 lb larger sizes carrying similar extra burden for handling and crating.

    Costs can usually be reduced (5-15%) by buying >10k lb. in a single order and accepting delivery directly off the shipping flat instead of having local distributor handling material as inventory. Savings is in quantity break (volume), handling along the way (multiple crates vs one) , local loading and handling costs (who's employees move the goods) and bulk customers generally receive better (lower) distributor margins.

    All of this material is shipped barge to Anchorage or Seward from Seattle- and trucked on to Kenai- so freight costs are very likely higher than in the contiguous states (the Old Country).

    Cheers,
    kmorin
     
  5. Seaboater
    Joined: Jan 2008
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    Seaboater New Member

    Aluminum Extrusions

    You may want to look at the features page of the Duroboat website. It has a sketch of the extrusions they use to build aluminum boats without rivets or welds.
    www.duroboat.com
     
  6. kmorin
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    kmorin Senior Member

    Duraboat methods

    Seaboater,

    It looks like the patented Duroboat extrusions wouldn't be available to the general market? Plus they look to require some hull panel edge treatment that might be out of scope for less than a manufacturing plant investment.

    From their site; it seems the panel edges are 'wedged' into the extrusions in a jam fit with an extruded plastic gasket filler that locks into a precisely cut groove in the hull panels. It may work for them but I'm not confident a one-man shop could get this type of system to be effective?

    I may not understand the joint's seal and lock method but that is what the site implies to me.

    Cheers,
    kmorin
     
  7. Thunderhead19
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    Thunderhead19 Senior Member

    There are a number of mills out there (the majority) that retain the dies when someone special orders an extrusion. Generally if the mill can sell more of the extrusion to other customers, they refund part of the die tooling cost to the original buyer. Check with some of the bigger mills and see if they have a catalogue, or a tool similar to what you want. Some of our local suppliers have contacts in Asia that charge next to nothing for tooling, and can crank out 500ft of specialty extrusion AND ship it to Vancouver or Seattle for less than what we can get it for domestically. Go figure.
     
  8. petereng
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    petereng Senior Member

    Hello Simon,
    You ask about advanced boatbuilding then discuss aluminium. Fiberglass construction will produce lighter and stronger boats then aluminium and you can make any shape you like on site. If you go to sandwich construction the boat will be significantly lighter then aluminium can can produce. I suggest you sidestep the aluminium path and go straight to composites. Military shipbuilders are going this path so must be OK.
    Cheers Peter
     
  9. Thunderhead19
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    Thunderhead19 Senior Member

    Who wants to work with FRP...Stiiiinky poooo.
    Just kidding...well, no not really.
     
  10. petereng
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    petereng Senior Member

    Haven't you heard of Infusion or VARTM. No fumes, can take as long as you like to lay dry fibre, then you get excellent engineering properties, lightweight super strength (much much stronger then aluminium) no corrosion, easy to repair (no welding), can make any shape yopu want... the list goes on.

    Peter
     
  11. Jratte
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    Jratte Junior Member

    I gotta say after spending nearly the last year and a half building aluminum ships, I certainly wish we used fiberglass for certain pieces, especially lately. Some of the complex curves they have designed would be much better suited to glass, especially since many of them don't serve a structural purpose.
     
  12. Thunderhead19
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    Thunderhead19 Senior Member

    Infusion works great except for the cosmetic part. I'm sure someone has this figured out already, but the last time I was involved with infusion, we had to lay down our cosmetic layer and some mat and a print barrier before we were even ready to set up the infusion equipment...and it was stinky. Okay...I'm just bitter because my first day on the job I slipped and fell into a mass of uncured FRP.
     
  13. petereng
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    petereng Senior Member

    To get good cosmetics from styrenated resins you need to use a "finishmat" type product or you can use CSM for the outer layers. If an oven (or heated mould) is available the part can be post cured in the mould and the cosmetics will be perfect. Print through with epoxy is not a problem as it dosn't shrink as much. Since the resin consumption in infusion is well down compared to conventional processes and since this thread was "kicked off" by "advanced boatbuilding" I'd be using epoxy for various reasons anyway so all of your concerns would be covered.

    The best practice is as follows;

    1) Gel coat (0.5-0.75mm)
    2) Barrier coat (0.5 - 0.75mm)
    3) felt mat of suitable thickness (laid dry) infused thickness can be from 0.3mm for lantor finishmat up to 1.0mm for other products behind heavy laminates
    4) 200gsm layer of needle punched CSM (laid dry)
    5) structural laminate
    6) Infuse, let exotherm peak under vacuum
    7) Post cure on the mould under vacuum, to resin suppliers spec

    If the laminate is very light use epoxy.

    Cheers
    Petereng
     
  14. simon
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    simon Senior Member

    OK, we are back to fundamental discussions and are writing about laminates in the metal construction area.

    So you cracks, give me a solution to my wish. I want a low maintenance surface, no fairing, no painting. I sometimes bump into things and my fender is not where it should be, or other boats are hugging mine, like recently a catamaran that had it's laminate ( on the water level, so reapairs are quite difficult without drying out) beaten down to the core while my (5mm)aluminium hull has some scratches.

    I hit big iceblocks and broke through solid ice surface for hundreds of meters.
    Tell me how you are going to do this with your shiny, awlgripped topsides?

    I might be a bit sloppy about paint maintenance, I do not want to spend any sweat on fearing for my precious paint job.

    I want a construction that will not need hundreds and thousands of hours of sanding.


    Any suggestions about using a prefabricated top layer (any material) that will bring these qualities.

    Anyone has seen aluminium used as a top layer on a cored hull. How can I combine the best of both worlds?

    So you composite cracks, lets see your answers
     

  15. SeaSpark
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    SeaSpark -

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