How a proa works / I'm making a 45ft one in Aluminum

Discussion in 'Multihulls' started by SV Pororoca, Jan 8, 2020.

  1. SV Pororoca
    Joined: Jan 2020
    Posts: 4
    Likes: 1, Points: 3
    Location: Belgium

    SV Pororoca New Member

    Hi Smart boat engineers

    First let me announce that I am building a proa in Alu based on plans for madness by John C. Harris.
    Those plans are obviously not for an alu boat so I'm doing some changes but not allot to the boatdesign to compensate for this. Biggest change is the size
    It's going to be a wopping 45ft long!

    some of the other hanges are:
    Some sort of viewing portal or a light bridge in the living compartment
    Widening of the pod to accomodate for a regular 140cm wide matress.
    Sliding hatch instead of hinging like the original plans call for.
    many many more to come

    Second of all I made a video explaining how a proa works and why I chose this design instead of any other conventional boat:


    Go subscribe if you are eager to see me fail or succeed. entertaining in both ways.
    I also have an instagram account , you can find me under the same name as my channel: Kingherog

    I am not a boatbuilder, nor a welder for profession nor do I have any experience in this practice but I'm a person who likes to dive headfirst into challenges with full knowledge that I might fail and I'm ok with that.

    I'm open for critique but if you're going to be a fatalist then know that I'm not inclined to listen too you because I'm not arrogant and 100 percent sure this will work and I am in no need for more insecurities with this project.
    Just ask questions and make suggestions. Diving head first doesn't mean I don't think things through but I haven't thought of everything in advance off course!

    I have certain specific questions I will ask in the future but this is basically announcing my plans and letting everybody who's interested know what I'm doing!

    Wish me luck!
    I probably need it!

    Ps
    I attached some pictures showing at what stage I am at this specific moment
    IMG_20200103_181623_6.jpg IMG_20200103_181605_6.jpg IMG_20200103_181553_5.jpg IMG_20200101_163439_5.jpg IMG_20200101_163433_3.jpg IMG_20200101_163342_6.jpg IMG_20191231_143427_2.jpg IMG_20191231_143416_6.jpg IMG_20191231_143413_8.jpg IMG_20191230_000306_2.jpg
     
    BrissoDamo likes this.
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 6,610
    Likes: 617, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Firstly - well done and good luck....and welcome to the forum.

    However, secondly and should be firstly - you need to go learn how to weld aluminium. The welds you show, are shocking!
    Too much shoot, implies so much, - basic QA for set up, gas settings, volts/amps etc etc
    No prep's
    No returns..
    and craters/cold blobs...localised over heating
    etc etc

    I understand this is your first time....and to be expected.
    However, if you wish to sail, in safety, you need to get someone else to weld. It takes many years to produce good quality aluminium welds consistently and with quality.
     
    BrissoDamo likes this.
  3. SV Pororoca
    Joined: Jan 2020
    Posts: 4
    Likes: 1, Points: 3
    Location: Belgium

    SV Pororoca New Member

    First of all. Thank you for your concern!

    Here is all of my knowledge and thoughts about my welds and practice:

    Gas flow is 16L a min
    Using an esab 235ic weld machine with the voltage settings I start with using the chart inside the welding machine and then fine-tune too the hissing sound.

    My research in papers from Miller and Lincoln etc learned me that sooth isn't that uncommon with high magnesium content weld wire like 5356. As long as the weld bead itself is nice and shiny.
    I clean with acetone and wirebrush with a stainless wire brush either by hand or on the grinder when doing bigger longer pieces.

    At the end of every weld bead I return a little bit to fill in the crater and I design most of the weld joint to be lapjoints since looking up welding aluminum shows that the weld itself isn't as strong as the original material and coldcracking is common and a lap weld is a good way to avoid that. Even though 5356 is less prone to cracking.

    Most of the pieces are welded in with mostly Tack welds. Leaving the longer beads for when all the nesecary pieces are in place to check that the form is within reasonable bounds.

    I've set this piece up in a cradle which I will tumble to make it easier for me to get into an easier weld position when doing the big longer beads.
    Not too long to avoid distortion.

    I'm willing to learn but I learn by doing. Ideally some welder comes over to help and shows me the tricks.

    Both the hull are designed with watertight bulkheads.

    I do share your concern for good welding quality and therefore have purchased a better machine.

    I hope this information shows that I've done my research and don't do all of this blindly.
    I'm taking my time to learn and improve! No need to hurry with this project. I've got the time!

    But again
    Thanks for the concern!
     
  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

  5. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    I am curious, did Harris designed you a 45 Harry or did you just multiplied his offsets by 1.5?
    What thickness Al plate are you using?
     
  6. SV Pororoca
    Joined: Jan 2020
    Posts: 4
    Likes: 1, Points: 3
    Location: Belgium

    SV Pororoca New Member

    Ama hull
    6mm on the bottom
    4mm on the top
    Vaka hull
    10mm on the flas bottom plate
    6mm on the bottom side
    4mm on the top sides

    I've done a basic volume calculation with the vaka hull alone. And the waterline seems pretty close too the original plans if I use the weight of all the aluminum I bought for the project as a reference

    But this then is pretending use 100% of the aluminum
    That the ama is flying so that all the weight and buoyancy needs to
     
  7. SV Pororoca
    Joined: Jan 2020
    Posts: 4
    Likes: 1, Points: 3
    Location: Belgium

    SV Pororoca New Member

    I multiplied the patterns of the hull plates and most of the parts by 1.5 times.
    Just getting the right patterns shapes and changing certain ways of building due to the different material and building style
     
  8. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    I bet Harris is thrilled.

    IMHO getting a profesional welder to weld it up after you tacked it to shape is your only chance to get her floating.
    Keep us posted and in pictures.
     
    ALL AT SEA likes this.
  9. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Multiplying by 1.5 does not give you correct dimensions. The volume, and therefore the hull loading, increases faster than the surface. How did you calculate the structure? I see widely spaced bulkheads and a light angle at the seam. By the way, the welds are awful.
     
  10. Ad Hoc
    Joined: Oct 2008
    Posts: 6,610
    Likes: 617, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    There is so much there...im not sure where to start. It would simply take too long!

    I would recommend reading the article about basic fabrication and sequencing "Order of Assembly" in Proboat Magazine issue 151 Oct/Nov 2014.

    But good luck ...
     
  11. Bruce Woods
    Joined: Sep 2007
    Posts: 132
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    Location: perth

    Bruce Woods Senior Member

    Good to see someone hopping out of their arm chair and having a go.

    A friend built an alloy 29 foot cat, round bilge, seat of the pants design, with almost no internal structure except for the three beam bulkheads.
    He had access to an English wheel so played around with full size sheets till he had a great looking shape. 30 years of hard racing and cruising later its still going strong.

    On the back of this success his mate built a 45 footer similar method and its still going strong.



    So Pororoca, don't listen to the neh sayers, good luck and keep posting.

    Ps, 3 tons displacement seems about right for a mini minimalist boat. :)
     
  12. BrissoDamo
    Joined: Dec 2019
    Posts: 49
    Likes: 7, Points: 8
    Location: Brisbane

    BrissoDamo Junior Member

    It will be too late then! - this boat is so narrow you must finish the welds on inside on the way up to the gunnels. The other thing I don't like is how hes brought 2 sheets together to form the bow without making a joint surface between them(how do you weld the backside of the joint being so narrow?), is it done the same down the keel line?

    He should start by buying a bottle of 100% argon. He's is using co2 the black around the weld gives that away, even on steel I use would speed shield(25%argon).

    Love his idea, but he is doomed by lack of technical skills and finance. Get some tech assistance before you wreck a bunch of alloy plate..........
     
    Last edited: Jan 11, 2020
    ALL AT SEA likes this.

  13. BrissoDamo
    Joined: Dec 2019
    Posts: 49
    Likes: 7, Points: 8
    Location: Brisbane

    BrissoDamo Junior Member

    It needs stringers between the bulkheads. You need an engineer. Like the concept is great idea for liveaboard coastal hopper. Put an outboard on it, it will need it to navigate in ports and rivers.
     
    Last edited: Jan 11, 2020
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