80 foot cargo harryproa

Discussion in 'Multihulls' started by lucdekeyser, Nov 15, 2020.

  1. Eric ruttan
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    Eric ruttan Senior Member

    whats your best price on polyester
    For 1@ 50 gal drum?

    Run the economics of a box beam. Now do a truss. Now you see.
     
  2. Eric ruttan
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    Eric ruttan Senior Member

    Can you even read? It will never be a successful commercial operation. That is literally not a goal.
     
  3. Rumars
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    Rumars Senior Member

    3.7/kg for the 58usgal drum, hardener included, +50/drum delivery. I can go lower, ~2.x if I arrange my own delivery. I can't find any epoxy under 9/kg.

    I don't see, the truss beam has to be able to take the same torsion loads as box beam (the two hulls try to move independently), it won't have signficantly less material and is more labour intensive since it can't be infused in one shot.
     
  4. rob denney
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    rob denney Senior Member

    Good questions, thanks.
    There was no polyester infusion resin available here last time I looked.
    Ve ages, epoxy doesn't, which could be a problem in the tropics with left over build material.
    Infusion vinylester costs $Aus11/$US8 per kg. Epoxy $Aus14/10.22 per kg, so significant, but not huge.
    Ve takes longer to cure enough to not distort so has to stay on the table longer. Probably not a big problem now the ambient temperature has risen.
    Secondary bonding to Ve should be done with epoxy or csm backed cloth. Takes at least a week before epoxy sticks to it properly.
    Ve stinks and styrene rots your brain, epoxy 'only' destroys your skin. Neither is a huge deal with infusion.
    Ve is flammable. OHS on a university site is pretty stringent, we would need sprinklers and god knows what else.
    I am more experienced and comfortable with epoxy.
    Gel coat needs a perfect mould. Our mould doubles as a work bench, gets abused and is repaired with a quick application of epoxy. The first layer in the stack is thin plastic sheet, so there is no polishing required. Applying gel coat post mould to joins and repairs is hard work. Paint 'only' needs peel ply. House paint can be applied with a broom and look OK from 10' away.

    The truss for the beams has to support the mast, so it is 1.2m deep at the leeward end, so windage for a box would be higher. The prototype lee hull is 800mm high, so spray drag is also an issue.
    The truss does not require expensive foam, uses cheap tow/roving instead of expensive knitted fabric and has no need for bulkheads.
    It may be deep enough not to need carbon, which would be a big cost saving.
    I've proved I can build boxes, trusses are still a challenge, ;-) With a lot of potential once you start thinking about it. With the techniques we are developing, there will be a lot more uses for them. The uni guys are talking about a patent. We shall see.
    Truss beams are easier to attach to the masts than box beams.
    A truss in the lee hull means it can have (triangular) hatches, which allows access to the inside, which makes the build process much easier. Hatches in a structural box would need a lot of reinforcing.
    It is easier to join two trusses together (I think, samples of the joins will be built soon and tested. The pics will tell the story), allowing the lee hull to be built in 3 pieces (1 x 12m, 2 x 6m) for easier transport and fitting the stub masts which hold the beams in place until the masts are installed.

    A truss works reasonably well in torsion. The hulls will pitch independently, but this does not result in the beams twisting. Think of the hulls and beams as one structure. When it twists, the beams need to be stiff in bending, not torsion. If there was only one beam, torque would be an issue. see page 5 in Changing Catamaran Beams from Wood to Composite. https://www.boatdesign.net/threads/changing-catamaran-beams-from-wood-to-composite.64278/page-5 for a discussion on this.

    Keep the questions etc coming, please. Makes me think about what I am doing and why.
     
    bajansailor likes this.
  5. gonzo
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    gonzo Senior Member

    Can you show any example to back up your claim?
     
  6. Gringles
    Joined: Nov 2020
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    Gringles Junior Member

    There's a patent which discusses using foam core to make structural members of this type for powerboats.

    I suspect adding stiffness without using core as a structural member means going back to stringers and bulkheads. Compound curves also adds stiffness.
     
  7. Rumars
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    Rumars Senior Member

    I understand the constraints of building the prototype, but if and when you envision a series production you should adapt it. Island reality will be that some chinese made polyester will be the cheapest and what the builders will want to use. If first world donors are to pay for it all, then it is no problem, the difference is not going to break the bank.

    Are you glueing the trusses to the deck and the deck to the hulls? I am curious how the trusses work when constrained on one side.
     
  8. Gringles
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    Gringles Junior Member

    When I'm modeling integrated structural members in a composite, I usually run FEAs in solid works before building a prototype.

    I suspect more of a ladder looking configuration would be optimal for your application.

    I can see how getting rid of the core could make infusion easier, but wouldn't the structure have to be heavier to achieve the same strength as a cored composite?
     
  9. Eric ruttan
    Joined: Jul 2018
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    Eric ruttan Senior Member

    It's like you cannot read.
    I really like Rob's innovation. But I am also a tad worried this kind of early work is missing. But I am just an observer. He would probably be open to input.
    I think the lack of core is about cost savings. Running the $/m², foam is expensive, glass tow is cheap. So, if you can develop a boat building tech to exploit that, you can build boats cheaper. It is what I enjoy about Robs work.
     
  10. Gringles
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    Gringles Junior Member

    Makes sense about the cost. That extra weight won't have a real world impact on sailing performance.
     
  11. gonzo
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    gonzo Senior Member

    Have you ever compared the sailing performance of an overloaded boat vs a light boat?
     
  12. Eric ruttan
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    Eric ruttan Senior Member

    Yep. As you probably know Rob's designs are very light and fast to build. Sacrificing a bit of weight, to even further reduce cost makes boat building more afforable and reachable.
     
  13. Alik
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    Alik Senior Member

    This thread comes to another 'parallel universe' where proas are the most important boats... ;)
     
  14. Eric ruttan
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    Eric ruttan Senior Member

    Have nothing to add, yet posts anyway.

    Poor form
     

  15. Gringles
    Joined: Nov 2020
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    Gringles Junior Member

    I was just trying to play along.
     
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