Trying to make aluminum flat bottom 16 foot there is a form machine to strenghten hull what is it?

Discussion in 'Boat Design' started by Keith777, Jun 1, 2019.

  1. Ilan Voyager
    Joined: May 2004
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    Location: Cancun Mexico

    Ilan Voyager Senior Member

    Thanks Angelique for the laugh...
    Riveted aluminium boats are born after WWII taking the methods and tooling for fabricating airplanes. By essence it's an industrial method of building boats as it requires a lot of tools and a few skilled workers. It's also rather lengthy as hundreds of holes and rivets are used. Traditionally these boats are made in 6061, an easy to work alloy and found rather cheaply everywhere and these boats are designed for use in fresh water.
    Riveted alu it's not the easiest nor the cheapest method for a single DIY flat boat 16 feet...
    Alu has another drawback for a small boat; density 2.7 kg/liter. While GRP is about 1.5 and plywood 0.6 to 0.7. That means that for the same weight for a square meter a plywood skin is around 4 times thicker than the alu one and its rigidity is 4^3 times higher.
    A piece of 12 mm plywood is far more rigid (I do not mean stronger) than a 3 mm alu so it needs far less structure. I won't enter in the arcanes of weight/rigidity ratios in structural boat engineering and thus the superiority of thick lightweight skins as composites sandwiches and honeycombs.
    Plywood is worked with simple home tooling, can be glued, nailed and screwed in all meanings of the word in a humble garage. It can be made dirt cheap if destined for a small river boat, for a Sunday holidays use and kept dry in storage.
    In France the CTBX grade plywood is perfect for such little boats.
    Angélique likes this.
  2. Angélique
    Joined: Feb 2009
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    Great post Ilan, I'm waiting for some input by the OP about his heading, there's plenty of good cheap planks in BC to DIY build a very cheap Jon boat the old fashioned way I'll think (eg. like some on the thread boat side angle), marine grade plywood may need to be imported and expensive in the PNW where some trees still grow for free . . .

    BTW, a bit back on topic, is there a good and simple and cheap way to build a single DIY 16' × 6' flat bottom aluminum boat . . ?
  3. Barry
    Joined: Mar 2002
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    Barry Senior Member

    The OP was trying to find a method to put channel profiles into 1/8 inch aluminum to stiffen the bottom of the hull
    A big enough swag former as some contributors presented will work but will take multiple passes to get a high profile. We built ours with a 4 foot throat only to roll a small channel into the sides of the hull sheet to stiffen the sides and the profile was slight.
    The channels shown on the riveted boats are not enough by themselves to stiffen the hull and the builders employ many cross members riveted in to assist in stiffening the floor by
    connecting across the channels in the bottom of the hull to the sides
    Of course they are not using 1/8 inch material so welding is not a realistic option

    For the OP, if you want say 1 1/2 inch high by 3 inch channels in the bottom, the easiest way would be is to rent some brake time. If you lay out both sides, a couple of guys should be able
    to form the single sheet in about an hour and a bit, certainly not more than 2 due to the size. So for maybe $300, you might get a sheet formed.
    You will still need some floor reinforcement though meaning more aluminum so the alternative that I would consider is using the hull stiffener made from channels 1 1/2 by 3 and weld them to the outside of the boat. As the hull is flat, you do not have to weld full length. I would weld these to the outside at say 16 inch centers and to the inside at the same mirror image so that in essence you would have a 3 inch by 3 inch set of exterior strakes ( using the term loosely) and a set of interior ribs

    In order to get high profiles, a roll former changes the shapes in stages
    Angélique likes this.

  4. JSL
    Joined: Nov 2012
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    Location: Delta BC

    JSL Senior Member

    Nothing wrong with 'forming' (bending, swaging, etc) - similar to corrugated panels for roofing etc. Some ships and barges use a similar technique for bulkheads etc.
    But, keep in mind that the 'stiffener'/'stringer' is now proud of the main panel and therefor exposed and vulnerable to puncture: landing on a rocky beach may require care & caution and the panel 'stiffness' could be compromised by the damage.
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