Kingspan sandwich construction

Discussion in 'Boat Design' started by congellous, Sep 23, 2013.

  1. congellous
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    congellous Junior Member

    Hi, I'm concerned with insulation in my build and I'm specing up a sandwich construction. The core will be 100mm closed cell Kingspan insulation which has increased strength for going under concrete slabs. I'm allowing for 2 layers of 600gm cloth /side on a 41ft hull in my costings for a canal cruiser - do I need any more thickness ??
     
  2. FAST FRED
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    FAST FRED Senior Member

    >do I need any more thickness ??<

    You will need to do some testing to see if the insulation has any sheer strength at all.

    The core needs to be a structural member ,like the center web in an I beam, it is not just a spacer.

    I would not experiment with a hull , real structural foam for boat construction does not carry the risk of hull failure .
     
  3. congellous
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    congellous Junior Member

    sandwich

    Hi thanks, I have seen a range of foams used on here ? it's on of the stronger closed cell, I think it's Polyurethane ?? If it is strong enough what kind of build up of the GRP
     
  4. philSweet
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    philSweet Senior Member

    I can't think of any more benign environment than under a concrete slab. If that's what it's for, then build a four inch thick ferrocement hull and insulate it with the stuff. Evidently it needs an extraordinary amount of protection from physical abuse.
     
  5. congellous
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    congellous Junior Member

    Yeah will do thanks
     
  6. FAST FRED
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    FAST FRED Senior Member

    Even if you used the best foam in the world , to me its AIREX , the cost of a 41 ft boat would change only by a percent or two.

    There is nothing wrong with solid glass boats and fire proof insulating foam installed inside.

    Sure a fan$y foam core might make the boat a few % lighter , but on a non competative cruiser , why bother?
     
  7. congellous
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    congellous Junior Member

    Well it gives me an insulated core and the stiffness of a sandwich member, it has massive strength gains for weight. I'm building it as Monocoque panels with any joints becoming flitch beams, also the interior face will be on show so both sides of the sandwich will come out of a mould. A 100mm sandwich polyurethane and say 5mm either side is better then just 10mm single skin GRP, no ?
     
  8. keith66
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    keith66 Senior Member

    Kingspan insulation foam comes with a warning printed on it not to walk on it. It has bugger all strength & is very soft & friable. I use it occasionally for making cheap plugs for parts that will be thrown away after one shot.
    There is a version that has glass strands in it but even that is hardly structural.
    Plus if it gets wet it will absorb water. No use as a core in a boat.
     
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  9. congellous
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    congellous Junior Member

    They have 30 products and I was thinking of using the one with high compression strength and with closed cell in case it wasn't fit for the purpose.... the HD duty one has 700 Kpa and has decent shear strength.
     
  10. congellous
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    congellous Junior Member

    The strength of the composite material is dependent largely on two factors:
    The outer skins: If the sandwich is supported on both sides, and then stressed by means of a force in the middle of the beam, then the bending moment will introduce shear forces in the material. The shear forces result in the bottom skin in tension and the top skin in compression. The core material spaces these two skins apart. The thicker the core material the stronger the composite. This principle works in much the same way as an I-beam does.[4]
    The interface between the core and the skin: Because the shear stresses in the composite material change rapidly between the core and the skin, the adhesive layer also sees some degree of shear force. If the adhesive bond between the two layers is too weak, the most probable result will be delamination.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    The foam i have seen using in concreting raised slabs is polystyrene so far as I know. Not going to be any use as a boat core.
     
  12. SamSam
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    SamSam Senior Member

    I'm going to use some kind of foam, some glass and some kind of resin to make a boat. Please confirm my plan.

    And yet some ***** when others want to discuss politics or religion.
     
  13. Willallison
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    Willallison Senior Member

    Setting aside whether the Kingspan is an appropriate core material - from the comments of others, it certainly doesn't sound like it would be - there is no simple answer to your question. The thickness / density / strength / type of core material, as well as the thickness / type / strength of the skins of a cored structure are dependent on a number of things which have to be calculated as part of the design of the structure. The span between supports, the field of operation of the craft, speed, puncture resistance, etc, etc all have to be taken into account. That's what naval architects do....I would strongly suggest that you employ the services of one and have the boat designed properly...it will be a lot less costly in the long run.

    Having said all that, if it were me, I would want rather more than 1200 GSM of glass on the outer skin of any boat that is likely to come into regular rough contact with locks etc.....
     
  14. congellous
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    congellous Junior Member

    I think it's a bit beyond the scope here to be honest but thanks. Uretha core or polyurethane has been used in sandwich construction as core as has cardboard honeycomb in a door. It was more the Grp shell I was after as I'm OK with the core contrary to advice. I have used pro balsa, and expanded hex cell aluminium and polyurethane, the dense stuff is now being used in construction sips panels and it has had lots of testing.
    So it's down to puncturing, in that case would a couple of layers of diolen or a kevlar layer in the build up not do the trick ?
     

  15. keith66
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    keith66 Senior Member

    A 41ft canal cruiser is going to meet narrowboats made of iron. Puncture resistance is relavant, best make her from steel.
     
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