Lightweight void filler for aluminium hulls

Discussion in 'Materials' started by GRD, Sep 4, 2019.

  1. GRD
    Joined: Apr 2019
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    GRD New Member

    Does anyone know of a suitable product that can be used to fill a keel void in an aluminium motor boat. The hull has a box keel (open to the inside of the hull) that also has a centreline structural keel bar which prevents the bilge suction from being located at the lowest point of the box keel. Hence we are looking at filling the keel void up to a certain level (about 200 mm deep), sloping the top of the filling compound to drain to a more forward strum box suction. I thought of using a resin / talc mix but as it would be exposed to bilge water I'm not sure that's a good idea and I dont know if we would be able to create a slope on top of it either. Other thought was expanded perlite / resin mix. Any ideas or suggestions would be welcome.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Is it painted, or raw metal ? I wouldn't try any filling without a suitable paint job, first, or poultice corrosion could bite you. Then you have to think about the difficulties of repairs, if welding becomes necessary down the track. Welding could start a fire, not to mention you won't be able to get at it from the inside.
     
  3. GRD
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    GRD New Member

    The surface is coated with Nyalic
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    What is the amount of volume involved ?
     
  5. GRD
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    GRD New Member

    The volume is quite small , about 35 litres. Depth of filler material would be 200mm aft and 85 mm forward
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I think I'd use PU pouring foam in a higher density than the standard product, at least 2kg/cubic foot, even higher, that makes water absorption much less likely, but you can still dig it out if needs be. I wouldn't use any resin based fillers that will be hard to remove in the event you need to. Save weight and money as well. Just my idea, others may have better ones.
     
  7. Deering
    Joined: Feb 2005
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    Deering Senior Member

    I faced exactly the same issue. I ended up using an epoxy/micro-balloon slurry to reduce weight but retain water resistance and make it possible to chisel out if need be. Though given the tight location, I think I would have to cut plate to access it in any event if welding or repair was necessary. Welding on the outside above any filler material will be a problem.

    I was reluctant to use foam in that location due to it being constantly inundated in the bilge. Perhaps you could use foam with a final cap of epoxy. Or shove chunks of foam board into the space and then encapsulate it all with thickened epoxy.

    Could you just plate over the top of the void area to seal it up from the inside? Put an inspection/drain plug on the outside.

    If you elect to go the epoxy route, be very careful about heat buildup. Add it in small portions at a time. I bubbled off some of my hull paint in that area even though I thought I was going slowly.
     

  8. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Two cents, but 200mm is a bit..

    I would fill it with corelite or coosa board bedded in epoxy thixo on aluminum prepped well.

    It comes in 20mm chunks, so you could run 4-5 pieces and then piece is up bigger.

    Obviously there are corrosion concerns, but you are past ideal already..

    You can build and shape and mold the corelite by spot hotgluing it on the edges only, then knife cut it apart after getting the pieces close.

    The beauty of using core is it won't exotherm in a single go.
     
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