Foam Core Shiplap

Discussion in 'Fiberglass and Composite Boat Building' started by Doran M. Oster, Apr 29, 2021.

  1. Doran M. Oster
    Joined: Apr 2021
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    Location: Gainesville, FL

    Doran M. Oster Junior Member

    I have decided to use the following option: Cover the inside of both the port and starboard foam hulls with a composite (either glass or carbon fiber). Make a foam shiplap with a CNC router or by hand (gray in the image below). Cover (at least) the mating surface of the shiplap foam with the composite. Glue the shiplap to one of the hulls with thickened epoxy. After the epoxy sets, glue the other hull to the assembly. Then fair and add a composite to the outside of the hull.

    shiplap_view1.jpg
     
  2. fallguy
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    fallguy Senior Member

    You mean add a skin or tab at the end?
     
  3. Doran M. Oster
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    Doran M. Oster Junior Member

    Sorry, but I don't understand your question. Please clarify.
     
  4. fallguy
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    fallguy Senior Member

    composite?
     
  5. Doran M. Oster
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    Doran M. Oster Junior Member

    By composite, I mean a hard skin made of fiberglass, carbon fiber, or a similar cloth, with epoxy. I have not made a final decision about which cloth I'm going to use.
     
  6. wet feet
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    wet feet Senior Member

    Does this project actually exist beyond the renderings posted here?I'm finding it a bit difficult to imagine the practicalities of getting inside these hulls to laminate any kind of material and it makes me wonder whether we are being questioned about adding a lateral bonding flange for fastening two hull halves together by somebody without too much knowledge of hull manufacturing.I have never had more than a very distant connection with multihulls and I believe they are likely to need local reinforcement for cross-beams,rigging and rudder fittings at the very least.I haven't seen any mention of the type of propulsion intended for the vessel and it may impose local loads that need to be dealt with.Can somebody please explain how it will be possible to bond bulkheads in place or even get to the back of any bolts to fit the nuts that hold fittings in place?I am as keen as anyone to ensure that our collective knowledge base is preserved and passed on and what I'm seeing here is a project that needs to absorb a lot of it before proceeding too far.
     
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  7. Scuff
    Joined: Nov 2016
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    Location: Richmond VA

    Scuff Senior Member

    Many hulls have been built using the half female mold method are they using this shiplap approach? Make sure there is a rebate for the outside of the hull otherwise you'll have to try and fair the resulting bulge.
     
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  8. Doran M. Oster
    Joined: Apr 2021
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    Location: Gainesville, FL

    Doran M. Oster Junior Member

    Wet Feet: The forms are already cut on a CNC machine and the strongback is built. I have enough bead and cove foam cut for the first half of a hull. The strongback in the picture below is set up to build the port side of an ama. I had originally planned to align the forms with the wooden frame of the strongback, but I found that it is difficult to get the frame straight enough. If the frame is curved only 1/16 of an inch over its 20-foot length, the hulls will be misaligned by 1/8 of an inch when they are mated together. I believe I can reduce the alignment error between forms to a negligible amount by routing a notch in the forms and laying a straight edge in the notch. It would have been trivial to cut the notches when the forms were originally made on the CNC. Now, I will have to cut it on my table router, or carry the forms back to the CNC router. (In the rendering below, the 2" x 48" gold and yellow straight edges are laid in the notches and overlapped to make a 20' straight edge. I am using straight edges from Home Depot that are made for a table saw. They cost about $30 apices. Their width tolerance measures +/- 0.003", and I can't see light though the seam when I hold the sides together.)

    As for your question about reinforcements: 1. I plan to add reinforcements before the halves are joined together. 2. A access port can be added later, if necessary. 3. An access hole can be cut in the hull and repaired later, if necessary.

    Scuff: I'm new to boat building, so I don't know how many others have used the shiplap approach I am using. I posted the question in hopes of learning a better method, or to be talked out of needing an inside shiplap all together. After the hulls are glued together, the foam outside surface will be sanded fair and true before glassing. I plan to use two layers of cloth over the outside hull. Will I be able to sand the two layers smooth, or will I need a rebate? If so, where do I put it?

    upload_2021-5-2_10-49-52.png

    upload_2021-5-2_11-39-0.png
     

    Attached Files:

  9. Scuff
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    Scuff Senior Member

    I see so the outside of your hulls would be joined before any glass is applied no need for a rebate then.
     
  10. fallguy
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    fallguy Senior Member

    Nearly impossible to laminate the outside of that without an overlap at least or a seam. So, a rebate still reduces fairing.
     
  11. wet feet
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    wet feet Senior Member

    I rather expected the "new to boatbuilding" admission.Had the OP sought advice at an earlier stage,we might have steered him in a different direction as I fear there will be more time and effort expended on this project than might have been totally necessary.I wouldn't like to be too dependent on the quality of the joint at the bow as it will be extremely hard to get in there and prudence would dictate a watertight bulkhead in there somewhere.
     
  12. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    It's hard to give good advice when people are so tight lipped about what they are doing.
    Anyway, in the interest of "next time":
    The cnc cut strongback is made self-aligning by using distance pieces between the frames. Mortise and tenon joints keep everything in place in all directions.
    Bows are made as separate pieces glued to a bulkhead, this avoids the need of laminating into tight, hard to reach places.
    There is no need for the foam backed "shiplap". All the work is done by the glass, and the easy way is to just laminate it wet onto the joint. Long handled rollers and access points trough the deck make this possible. There are alternatives, like stripping past the jointline and removing the foam, solid glass keellines, etc.

    Cutting the rolling bevel into the foam backing strip will be very demanding, it's not something you want to do.
     

  13. Doran M. Oster
    Joined: Apr 2021
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    Location: Gainesville, FL

    Doran M. Oster Junior Member

    Thanks for all the advice, everybody. I think I have enough information to move forward.

    Please consider this thread closed.
     
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