Replacing Cold moulded Panels with Corecell Foam - Advice Please?

Discussion in 'Fiberglass and Composite Boat Building' started by dbstormchild, Jan 28, 2014.

  1. dbstormchild
    Joined: Jan 2010
    Posts: 4
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: South Africa

    dbstormchild New Member

    Hi Guys,

    I have a friend who due to family issues has given up on his 95% completed 37ft Woods Flika build and has offered it to me free as long as I can remove it from his property (house is being sold).

    Build history - Started about 15 years ago and completed all structural works, installed tanks engines hatches plumbing and started wiring.

    Hull 3mm x 3 diagonal strip cold moulded (**not epoxy coated/ laminated, he used a type of glue)
    Deck - 9mm ply

    Boat has been sitting for 5 years now and has been effected by 2 things.

    1. Some damage to the outer Port hull just below the water line along 40% of the hull. During house build the builders drove TLB past and gouged through the wood. mostly hull skin damage 150-200mm wide (nothing Deep).

    2. Rainwater has in the 5 years gathered up in the bilge, mostly in the port hull and caused havoc to the cold moulded skin. 95% of stringers and bulkheads are still perfect (these were coated with saturation epoxy). however almost the complete Port hull lower section is effected by wood rot. localised areas in the SB hull also effected by water in the bilge. Hull still feels solid as it is glassed below the waterline but inspection shows rot.

    Now for the query.

    I have built many fishing boats and replaced decks, bulkheads etc with Corecell Foam. 10-21ft boats. I have helped a friend replace the complete outer skin on his bridge deck bottom 40ft Cat. but nothing this large of a project.

    I am interested in replacing the complete hull skin and lower bridge deck with Corecell Foam, it is best priced I can find for the purpose otherwise I have thermo-bonded honeycomb core at half the price - but I dont know this product.

    Now there are a few ways in which this can be achieved that I have thought of. Please chip in if you know any other ways!!

    1. Use the existing hull outer as a mould, and mould a new skin Glass/Foam/Glass. this can be done one hull half at a time with vacum plastic sheeting and peel ply sheeting.

    2. Use the plans and bulkheads to create female plug similar to F-boat type build and create full half hull skin glass/foam/glass.

    Both the options above use the existing boat hull (once repaired enough to take mould) to reproduce the outer skins. I shall be using 20mm foam, I realise that this will increase the beam of each hull by almost 11mm. After new skin is made, strip the existing ply off the hull and clean stringers etc and offer up..

    3. Strip complete half hull outer of one hull (cold moulding skin) and repair the stringers, bulkheads where needed. In so creating a skeletal frame onto which I can vertical strip plank the Corecell directly to the stringers and bulkheads. after corecell is mounted and fair (epoxy join lines etc) then I shall glass the outside. Self-tapping screws will hold the foam to stringers and bulkheads internally. small tabs can be temporarily fixed on bulkheads and stringers to assist in the foam forming.

    Once outer skin is glassed then whole panel will be released and inside epoxy filled (join lines and screw holes) and then glassed.

    I have developed a bolt and flexi-board system to ensure that when the new full half panel is offered up to the stringers and bulkheads it is pulled up securely to ensure best bond. all stringers and bulkheads shall then be filleted to add to the panel/frame bonding. Followed by glassing in all bulkheads and half bulkheads.

    same procedure shall then be done for hull inner and half bridge-deck bottom skin, then move across to the SB Hull. I am not concerned with supporting the hull while this work is being done. the boat has many pre-made supports so that one hull may be lifted at a time.

    This boat is sparsely fitted out internally as the original builder wanted to keep it light so there is very minimal parts that will restrict my access to the whole process internally. maybe a few furniture fixings shall be temporarily removed to gain access to the stringers and bulkheads.

    I have 2 full-time laminators who work 6 days out of 7 for me on my fishing boat projects and Land Cruiser Rebuilds. I am not trying to pinch pennies to the extent that i have a dogs breakfast of a boat. I dont mind spending the money on materials. I have time and a place to do the work at minimal cost. The boat will be used for cruising.

    Now the question is does anyone have any advice on this topic?? I really dont want to replace with plywood (personal choice). I realise that at the end of the day I will probably be creating a slightly heavier boat.

    Is there a simpler way in which i could replace the skin in smaller stages? So far I see that trying to do complete smaller panels and bonding to stringers and BH would leave the inner skins a non-continuous skin, could i just epoxy fill the join line and glass in 3-4 layers to join area? bearing in mind that I could have the outer skin complete in continuous laminates. this is attractive to me as 3-4m sections shall be much simpler to handle.

    or go with solid glass below the WL and core above? (save time?)

    engine is central outboard linked to tiller system. (no interior engines to worry about)

    Long winded query but I hope i got the idea across right Smile

    Decks shall later be replaced with corecell as well.. If i ever get through the hull process..

    Any constructive Ideas would be most Welcome. At the end of the day I am not trying to re-invent the wheel but getting a VERY fair 37ft mostly complete boat is a great opportunity and I would like to do this right. I shall have all the existing plans as sold to my friend by Woods.

    Thanks in advance
  2. nimblemotors
    Joined: Jun 2009
    Posts: 244
    Likes: 3, Points: 0, Legacy Rep: 4
    Location: Sacramento

    nimblemotors Senior Member

    do you have any pics?

    I would suggest number 1, use an existing hull to make a female mold, and just make two new hulls.

    I am considering the same, using wall plaster to get fair surface, and then paint/polish.
  3. groper
    Joined: Jun 2011
    Posts: 2,467
    Likes: 123, Points: 73, Legacy Rep: 693
    Location: australia

    groper Senior Member

    Seems like a hell of alot of work just so you dont have ply hulls and decks... if the existing hull is very fair, then id just repair the damaged part and your 97% complete boat is still 97% complete...

    If you want to use the original hull exterior as a male mold, the entire system of bulkheads and stringers will be short by the thickness of the ply hull skin once you strip it, and the beam of each hull will be 42mm wider than designed using 20mm foam. 20mm foam seems overkill on a 37ft boat, dont usually see this thickness foam used on boats unless well over 40ft. Plus you have a network of stiffeners which was designed for the 9mm ply which means you will have ample support for lower stiffness panels than the 20mm provides. Consider using 15mm instead.

    If your looking to use the existing hull as a plug and make a new mold from it, then layup the hulls in your newly made mold - im not sure if the flika has symetrical hulls or not? If not, then your up for 2 molds instead of 1. Either case, your finished hull ends up slightly smaller in internal dimension due to the increased core thickness - so all of the bulkheads and stringers would have to be cut down slightly for it to fit.

    Male or female, you still have fairing on 1 side of the skin unless you want to cover up the non tool side with something to hide the glass texture.

    So either option, is alot of work considering you already have a very fair hull...

    Methods 2 and 3 seem like more work again compared to 1...

  4. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 494, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Agreed, you have a nearly finished project, that needs repairs. Make the appropriate repairs and try not to make more work then you have to. It's a bit like having a house, that has a need for a new bathroom floor, but you're thinking about building a new house. Stand back, access your needs and address them.
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