bpyhullgen silver bullet 4.8

Discussion in 'Boatbuilding' started by zukobo, May 6, 2021.

  1. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    The majority of the structural members are placed low to provide a low center of gravity. Previous two hull designs were very similar and demonstrated good static and dynamic stability in real world tests.

    stability_test_a.gif
    No extra ballast was used in these tests - but additional ballast could lower the center of gravity even further if desired.

    stability_test_b.gif
    In this bathtub test - when I pushed it down further so water came in through the window it did sink quickly and was a bit scary how fast it went under. It hit the bottom with a clunk. This got my attention enough to have flotation foam on the list of things to do before it hits the water.
     
  2. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    5cm foam installed on the top half of the interior would provide some insulation as well as safety in the event of an accidental rollover event.

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    This is what 5cm foam would look like. It's rendered on the outside so you can see the approximate location and size in relation to the hull but would be installed on the inside. The 5cm foam in these renderings has a total volume of 0.29 cubic meters enough to displace water - slightly more than the dry weight of the hull. In the event of a rollover it should float on the surface with the hatches facing upright so it's not a deathtrap. You might get wet but won't be trapped inside.
    [​IMG]
    Cutouts in the top around the approximate location of hatch areas.

    [​IMG]
     
  3. zukobo
    Joined: Sep 2019
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    zukobo Junior Member

    A displacement simulation using bpyhullsim shows the waterline location with various loading conditions between dry empty weight and 2000kg. 2000kg is way beyond any expected operating load - I just wanted to see what it looked like and where the waterline would be at 2000kg displacement. I anticipate the payload to be less than 250kg for this build under normal operation.
    displace_20210513.gif
     
  4. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    Bulkheads welded together.

    [​IMG]
    The material is 3/16 inch (4.8mm) 5052 Aluminum. It was CNC waterjet cut. I know many builders prefer 508x series for boats because it's tougher but it's more expensive and supposedly a little bit harder to weld. For this size boat I think it's plenty strong.

    [​IMG]
    So my idea was to make a self jigging frame. It all fit together perfectly and I used clamps to hold it from moving around for the welding. There is no jig or additional braces - just the frame.

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    The order of assembly was sides first then upper sides. I used clamps to hold the sides onto the bulkheads once they were aligned prior to welding.

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    View from inside showing side and upper side plates tack welded. I got a little bit of black soot on the beginning and end of welds. I spent almost a day and a half trying to debug this problem with test welds on scrap. Some of the things I tried to solve this problem:
    * Check for air leaks in lines (soapy water)
    * Disassemble and reassemble spool gun (two times)
    * Alternate argon gas bottle from different supplier
    * Different filler wire size
    * All different spool gun angles
    * Different flow rates
     
  5. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    Clamp holding aft side plates to frame prior to tack welding. Bricks were nice and stable to prevent the clamp from sliding off the back.

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    Top plate tack welded on. If you look very carefully at the top chine on the side plate the edge is not 100% perfect. This is because I exported the DXF file as a series of line segments. Is it perfect? No. Does it work? Yes. For a long curve this big you can tell if you look closely and know what to look for but it fit up really nicely and welded great. After welding you can't tell.

    Some of the side plating we were a bit hurried with the alignment - the top plate is slightly too far aft. There is a function on the CNC waterjet machine and also most CNC laser machines to do a low power etching pass to add some alignment marks. I don't have alignment marking capability added to bpyhullgen yet but this highlights the importance of that feature. I'm working on adding this feature. On my next build I'll spend more time and care on alignment. It's not perfect but it welded up nicely and I'm quite confident it will be watertight.
     
  6. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    Hull turned upside down for welding inside. I welded inside seams before closing it up while good ventilation was available.
    [​IMG]
    I'm wearing a Miller LPR-100 respirator underneath the welding helmet. It worked quite good but I could smell a bit of argon.
    [​IMG]
    Doing full welds on the keel to bulkhead seams.

    [​IMG]
    Trying to do as much welding as possible on the interior seams before closing it up. In this view you can see the curve on the side... You can't really tell it's a series of line segments.
     
  7. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    For the nose I tried something different - angles clamped to the side plates to give the long red clamp something to grab onto. It worked quite well... Some of the stuff on the ends I did with a TIG torch.
    [​IMG]
    View of nose tack welded together with big clamp removed. You can see some stitch welding on the side chines...
     
  8. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    View of interior welds. I could have done a better job on the corners. I know from some boat building books people sometimes cut out the corners of the bulkheads so you can do continuous welds on the interior chine seams. I was worried because of the small size of the boat and the size of the bulkheads there wasn't enough material to cut away to give me full access to the inside seams. It is what it is... any suggestions welcome.
     
  9. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    Nose welded up a bit more and hook plates installed... These plates could be thicker but I used the same sheet of material as the rest of the build... I can always reenforce them later. I guess you could argue that if the force exceeds these eyehooks it will bend the eyehook plates rather than bend the hull. For vertical loads it's plenty. For side loading it is a weak point. They worked great for holding onto with your hands and we could roll the boat over easily with two people - one person on each end of the boat.
     
  10. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    I rolled the hull around to make inside welding easier... down or side is easier than upside down.
    [​IMG]
    Looking at the bottom of the hull... There are some longitudinal supports missing, I left them out so it's easier to get in and out for welding. They were added later. You can see all the extra weight on the bottom compared to top.
     
  11. zukobo
    Joined: Sep 2019
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    View of chine edge fitup. Not perfect but worked well and welded nicely.
    [​IMG]
    Fitting up bottom plates - getting ready to weld bottom.
     
  12. zukobo
    Joined: Sep 2019
    Posts: 53
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    Location: taiwan

    zukobo Junior Member

    [​IMG]
    I used a battery powered circular saw for back chipping so seams would get continuous good penetration and be watertight. Sometimes I would have a bead at the start end of my weld line (cold start). The welder I have doesn't have hot start feature or I've heard of some other features to prevent this. I always got a bump at the beginning of weld lines and I don't have a variable feed control on the spool gun. You set it on the machine and what you set is what you get.
     
  13. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    Wow looks very nice. Thanks for sharing your build pictures.

    How wide are the ribs?
     
  14. zukobo
    Joined: Sep 2019
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    zukobo Junior Member

    Rib width 15cm
     

  15. Dejay
    Joined: Mar 2018
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    Location: Europe

    Dejay Senior Newbie

    Intuitively, as a totally uneducated opinion, you could probably cut them down to 5cm at least above the waterline. I mean how could anything move after you welded it all together?
    You could also cut out large sections on the top and turn them into plexiglass windows to save a bit of weight / stability.
    Also if the water is cold it's probably more worthwhile to insulate the bottom half for camping on the water. The water must act as a giant heat sink.

    Any thoughts on how much HP / kW motor power you'll have?
     
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