How to fill carbon dagger boards with foam

Discussion in 'Multihulls' started by MichaelRoberts, Dec 8, 2020.

  1. MichaelRoberts
    Joined: Sep 2015
    Posts: 40
    Likes: 5, Points: 8, Legacy Rep: 16
    Location: Australia

    MichaelRoberts Archimedes

    Recently I made two carbon fibre dagger boards for this catamaran I am building.
    The method used was wet layup carbon and epoxy into female forms and vacuum bag the lot.
    The forms were 3D machined from thick slabs of craft wood/MDF, then fine sanded and waxed.
    Worked a treat. Two shells, left and right hand, beautiful finish (NACA63010)
    I glued them together with wodges of epoxy soaked glass pulled snug against the inside of the joint.
    Also added a glass and foam centre rib to give shear strength.
    20200711_100510.jpg
    Then it rained and somehow water got sucked in - or maybe it was humidity and condensation.

    So I want to fill the hollow centre with pouring foam. I haven't used pouring foam but understand it sets very quickly,

    Maybe I could suck it in with my vacuum pump, but that would froth it up?
    Or maybe I could blast it in with air pressure on the foam mixing vessel.

    Any suggestions?
    Thank you
    Michael
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,340
    Likes: 712, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    You do realise this will exert pressure that could bulge the thing, unless it can escape while expanding ? Even with escape holes, you will still get pressure to some degree. What is the volume to be filled ?
     
  3. redreuben
    Joined: Jan 2009
    Posts: 1,747
    Likes: 103, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Sorry but imho pouring foam is rubbish, use pvc foam bonded to the laminate and sand it flat so the two surfaces mate when you bond the halves together. Leave the foam shy of the edge to make way for your bonding mix. most commercial type rudder moulds I used had a rebate on the leading edge for some biaxial tape to toughen up the connection.
    Metal rudder shafts are a pain in the arse as they leak eventually due to the different expansion coefficients of metal/composite. Carbon shafts are the bomb as they bond properly and the don’t leak. 2c
     
    bajansailor likes this.
  4. Doug Halsey
    Joined: Feb 2007
    Posts: 484
    Likes: 136, Points: 53, Legacy Rep: 160
    Location: California, USA

    Doug Halsey Senior Member

    Too late for that, isn't it?
     
  5. Doug Halsey
    Joined: Feb 2007
    Posts: 484
    Likes: 136, Points: 53, Legacy Rep: 160
    Location: California, USA

    Doug Halsey Senior Member

    A cautionary note: If you end up trying to pour the foam, make sure you orient the pieces so the foam expands sideways - not vertically.

    When I was a kid, I tried pouring foam into a mast (an untapered aluminum extrusion), while standing on the roof of our house. (My parents must not have been home at the time.) When the amount I had mixed didn't rise to the top, I kept mixing more & pouring, until I finally gave up with a grossly overweight mess.
     
  6. redreuben
    Joined: Jan 2009
    Posts: 1,747
    Likes: 103, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Maybe for the OP, but not for anyone else who might read the thread.
     
    Doug Halsey likes this.
  7. Doug Halsey
    Joined: Feb 2007
    Posts: 484
    Likes: 136, Points: 53, Legacy Rep: 160
    Location: California, USA

    Doug Halsey Senior Member

    Instead of foam, you might consider using a mixture of epoxy & microballoons, which I think can be similar in density to the foam & put in place with syringes or possibly just a trowel.
     
  8. trip the light fandango
    Joined: Apr 2018
    Posts: 421
    Likes: 77, Points: 28
    Location: Rhyll Phillip Island Victoria Australia

    trip the light fandango Senior Member

    How about an icing piping bag approach for the microballoons , one hole for the nozzle another for the air to escape.
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,340
    Likes: 712, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    This is why I enquired what the volume was, I was going to suggest just filling it with a fluffy mix of resin and lightweight filler like Q-cell, which is going to be heavier than foam, but if the volume is not that great, tolerable. Pouring foam in confined spaces is a ticklish problem, both as regards pressure exerted, the degree of expansion achieved (which may vary according to temperature) and whether to pour in stages. The expansion of PU foam products to advertised density, as I understand it, is calculated as if there is no impediment to the expansion. In a very confined space, the density ends up being higher, depending on the degree of confinement.
     
  10. redreuben
    Joined: Jan 2009
    Posts: 1,747
    Likes: 103, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Any filler/resin mix that qualifies as “light” is not going to be very fluid.
     
  11. MichaelRoberts
    Joined: Sep 2015
    Posts: 40
    Likes: 5, Points: 8, Legacy Rep: 16
    Location: Australia

    MichaelRoberts Archimedes

    Thank you all very much for your interest in my project and your valuable advice.

    1. Mr Efficiency - you are right, unpredictable expansion pressure is too risky.
    The volume of the immersed part is 100 litres, measured weight is 38 kg. Curiously, to push it fully down will require a force of about 60kg / 600 N.

    2. Red Reuben - yes I have been told pouring foam is rubbish - what am I thinking. I considered a rebate in the mould but I felt that the undercut would prevent the part from coming out of the mould. Instead I made long sausages of resin soaked glass with threads tied every 100 mm. The sausages were laid inside along the peripheral joint and the threads led outside. Then I lowered the top half onto the lower half (which was still in the mould to control the shape). Then the threads were pulled tight to draw the sausage against the inside of the joint joint. Hope that makes sense.

    3. Doug Halsey and Trip the Light - I like syringes - bought some big ones on eBay recently to squirt black epoxy into CNC cut slots in beautiful birch ply - floorboards - a bit faux but they look great

    Conclusion: No foam, instead suck some micro balloon or Q-cell filled resin along the leading edge (facing down) with light vacuum. Then later do the same with the trailing edge.

    PS and I won't fiddle around trying to foam fill the wing mast either. If anyone is interested I could start a thread on the wing mast
    Mast ribs assembly enhanced and cropped.jpg Mast white enhanced March 2020.jpg
     
    redreuben likes this.
  12. Russell Brown
    Joined: Jul 2012
    Posts: 127
    Likes: 32, Points: 28, Legacy Rep: 25
    Location: washington state

    Russell Brown Senior Member

    Yes please on the wing mast thread. One product that might interest you is Pro-Set epoxy pour foam. It will exotherm and it's still scary, but it's very strong and has high compression strength. People do use if for cores on foils, but done in-mold.
     
  13. MichaelRoberts
    Joined: Sep 2015
    Posts: 40
    Likes: 5, Points: 8, Legacy Rep: 16
    Location: Australia

    MichaelRoberts Archimedes

    Thanks you Russell
    The data sheet for Pro-Set indicates it is a Gougeon Brothers product - their distributor here is looking for it - seems like the right stuff
    Meanwhile, encouraged by your suggestion I have started a new thread on our carbon wing mast
     

  14. Eric ruttan
    Joined: Jul 2018
    Posts: 188
    Likes: 26, Points: 28
    Location: usa

    Eric ruttan Senior Member

    perhaps low pressure expanding spray foam?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.