Duck Punt - with a twist

Discussion in 'Boat Design' started by Jeremy Harris, Mar 29, 2012.

  1. Boston

    Boston Previous Member

    OK its this stuff

    http://foamular.com/foam/products/

    the link you provided ( thanks by the way ) was for a UK supplier, cheap on price but huge on shipping ;-)

    They list a whole line of different types and densities, as well as the laminated stuff I found at the local place. I might just go with the 5mil ply I found and actually frame it out like the real deal, just smaller. The foam is more expensive and I've got all the framing sticks I could ever want at the shop already. Will probably go through the tools easier anyway. The foams a great idea though. Going to have to remember this stuff. Its supposed to be impervious to water. So it will make a great insulation/buoyancy material. I'm just building a model and thinking about what to build it out of.

    Cheers
    B
     
  2. Jeremy Harris
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    Jeremy Harris Senior Member

    Yes, that's the stuff. The foam is really just an experiment. I had a feeling that if I'd asked here before trying it I'd have had a bunch of experts tell me it was crazy and to use an established composite core material (at a heck of a price), which is why I just went ahead without having a public debate about it first!

    You're right, it is impervious to water. In building codes/regulations the stuff is certified for continuous use in wet soil, I believe. Sunlight damages it though. I was completely blown away by the stiffness of the test sections I made up before starting the hull, with just a single very thin layer of glass either side (the epoxy glass skins are maybe 20 to 30 thou thick). I can't bend or break a bit that's about a foot square by hand, yet it's as light as a feather.

    The original punts were massively over-built, probably because they were working boats, plus they had to take the recoil of the bow mounted duck cannon! The current fun racing boats (http://www.duckpunt.org.uk/) are still built from pretty thick ply, 9mm (about 3/8") which seems far heavier than needed.

    Good luck with your project.
     
  3. portacruise
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    portacruise Senior Member

    Hi, Jeremy:

    Thanks for posting on the foam. You got me wondering how much support the foam really supplies. What if a solvent that doesn't affect the glass skin was used to dissolve the foam within? That would make for an even lighter shell if the foam is liquified and poured out. I think similar things were done with CF structural parts on aluminum substrate which was dissolved in acid for the pedal planes...

    Porta



     
  4. Jeremy Harris
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    Jeremy Harris Senior Member

    I'm sure the foam is playing a big part in stopping the very thin epoxy glass skins either side from buckling, so I'm pretty certain that melting it out wouldn't be a good idea. It adds very little weight overall, anyway. The duck punt hull is about 16ft long, 3ft wide and a foot high, yet has less than 3kg (~6.6lbs) of foam in it. The glass lay up is just a single layer of 300g/m² cloth on either side, so pretty thin. I haven't measured the layup thickness, but would guess that each skin is less than 0.5mm/20 thou.
     
  5. portacruise
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    portacruise Senior Member

    Yes, that seems to make sense, as there may be a lot of difference between glass and CF thin layer strength. You have come up with a creative method of building.

    I have also wondered if the liquid type expanding foam could be injected into inflatable boat hulls to create more permanent rigid structures. Take the plastic skin off and put some kind of coating on to finish if necessary. Might be hard to control the expansion, so there are no voids, though.

    Is there a safety inspection on this cordless tool competition? We have HP kinetic sculpture races in the USA, where a panel carefully inspects for hazards such as unshielded belts, shafts seaworthyness, etc...

    Porta

     
  6. Jeremy Harris
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    Jeremy Harris Senior Member

    There wasn't at last years event, but there may be this year, as there are a couple of safety-related changes to the rules (like needing a quick means of turning the power off and they've mandated that no craft be left with batteries fitted when not being raced).

    Some of the craft in last years competition were a bit iffy with regard to safety, with several with long-tail drives that could have done nasty damage if they got out of control. This year there's at least one twin propeller air boat driven canoe running, but he's fitted shrouds around his props for safety reasons. My drive should be pretty safe, as the prop is under the hull through the outboard well, so is pretty well protected from accidental contact with anyone. I have way over 200kg of built in buoyancy, too, although the race is run on a fairly shallow and well sheltered lake, fed from the river Thames.
     
  7. DCockey
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    DCockey Senior Member

    The foam between thin glass/resin skins has two important structural functions:

    1) As Jeremy already mentioned it provides local stability and buckling resistance to the individual skins.

    2) The foam provides provides shear resistance between the skins which greatly increases bending stiffness. Without the foam the bending stiffness would be the sum of the two individual skins.
     
  8. philSweet
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    philSweet Senior Member

    Jeremy, the race must be soon. Good luck to you. The new battery rule sounds like a prudent bit of business. I wonder who inspired that:D
     
  9. Jeremy Harris
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    Jeremy Harris Senior Member

    Thanks for the good wishes, the race is run over next weekend, 9th/10th June at Beale Park, near Pangbourne, Berkshire, UK. You're right, it was my misadventure last year that inspired the "no battery" rule, I'm sure!
     
  10. philSweet
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    philSweet Senior Member

  11. Jeremy Harris
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    Jeremy Harris Senior Member

    Bit of a last minute rush, but Quackers the foam core composite Duck Punt was finally finished and loaded on to her trailer an hour ago (the race is tomorrow morning........). The weather here turned pretty nasty and really slowed the final stages of the build. I was varnishing the gunwales under a tarpaulin last evening, not ideal.

    Anyway, in case something dire happens at the competition at Beale Park tomorrow, here are a few photos of her for posterity:
     

    Attached Files:

  12. DCockey
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    DCockey Senior Member

    Very nice. Good luck!
     
  13. paddilack
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    paddilack Junior Member

    Best of luck tomorrow!

    And thank you for sharing your facinating ideas. I would really like to see some close-ups of your cordless outboard when convenient.

    Regards,

    Paddilack
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Race

    ================
    Good luck, Jeremy!
     

  15. hoytedow
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    hoytedow Carbon Based Life Form

    Ditto!
     
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