Outrigger construction

Discussion in 'Materials' started by Qmaran, Oct 13, 2019.

  1. Qmaran
    Joined: Oct 2019
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    Qmaran Junior Member

    I am playing around with construction ideas for a 40ft trimaran. I want to build the outriggers with a solid foam core but cannot find good information. Mostly I find info on retro-filling with liquid foam or info on building surfboards. My initial idea is as follows;

    I want to sculpt the hulls out of relatively light foam blocks. What is the most suitable foam for this taking into account weight, potential water ingress, offgassing, bonding strength to glue/resin, resistance to resins and cost?

    After the hull is shaped I want to cover it with a thin layer of stronger core foam and then fiberglass it with a not too heavy layup through vacuum infusion.

    It occurred to me that instead of gluing the outer foam sheet to the foam hull I could lay fiberglass, then core foam and then fiberglass again and then vacuum infuse both layers. Has that been done before? Maybe the resin can reach the inside glass layer by using perforated foam?

    Any thoughts and pointers are welcome.

  2. bajansailor
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    bajansailor Marine Surveyor

    I am thinking that if this was a good idea one of the professional multihull designers would have done it already.
    Have you got any sketches that you can post showing the outriggers (or the complete trimaran even) that you want to build?
  3. Qmaran
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    Qmaran Junior Member

    I am not that far into it yet. I have decided a while ago I want to start long distance sailing. I have to wait until my daughter finishes highschool in 2.5 years.

    I have weighed options of buying a good used boat, a cheap used boat that needs a lot of work, building from a plan or designing my own.

    I decided on designing and building myself mainly because I have built stuff all my life and feel I will enjoy sailing even more if I built the boat myself.

    I am new to boat building and have learned a lot in the past months.

    You say that any good idea that is not currently employed by professionals is probably not a good one. I doubt if that is true. There are a lot of things you can make yourself better and for less money than commercial offerings.....like an Ikea desk for example. Ikea has a lot of overhead and cannot spend much on the actual materials. Also they have to cater to the average conservative customer and have all kinds of regulatory constraints. I can build an amazing desk for the same price that will make their product look pathetic.

    Putting fiberglass on foam shapes has been done for decades. Foam core is a little more recent and vacuum infusion was adopted very slowly.

    Making a 30ft long outrigger entirely of a heavy foam seems wasteful and unnecessarily heavy. But light foam gives little support so requires a thick laminate.

    So covering a light foam hull shape with heavier foam seems the logical route to go. But then you have to glue the foams together. If instead of glue one could lay up dry fiberglass, then the outer foam layer and then the outer fiberglass and vacuum infuse you would end up with a light and massively strong piece.

    The only question is if perforated foam will be enough to cause proper resin flow at the back of the foam?

    If I cannot find the answer I will do a test myself once I get my hands on infusion equipment.
  4. bajansailor
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    bajansailor Marine Surveyor

    Have you seen this thread by OldMulti on the Multihulls forum here?
    Multihull Structure Thoughts https://www.boatdesign.net/threads/multihull-structure-thoughts.62361/

    It might be a good idea to post your thoughts above on the Multihulls forum as well, and / or send a private message to OldMulti to ask for his thoughts re your proposals. I am sure that he could give you some good advice. He has probably not seen this thread; I am sure that if he had seen it he would have responded.
    Re designing your trimaran yourself, these really are very complex beasts indeed, especially if you are trying to keep the weight down to a minimum. I can see why you want to build the boat yourself, but when you take into consideration the cost of a set of plans from a reputable designer vs the cost of building the vessel, it would (IMHO) be prudent to invest in plans where the designer has done all the ground work and has learnt by trial and error what works and what doesn't (rather than you having to learn the hard way).
  5. rxcomposite
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    rxcomposite Senior Member

    Qmaran- Do you think you can tackle this yourself? I mean besides the method of construction, the layup of that beam is very complex and would require at least 3 types of fibers.
  6. Rumars
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    Rumars Senior Member

    Qmaran the reason you don't see your method used is because it does not make sense. A production builder uses a female mold not a foam plug.
    An amateur without a mold has two choices either do a foam plug and lightly glass over it, or use a male mold and leave the interior hollow. The first method I have only seen employed on small outriggers.
    The lightest flotation is air and if you want to fill the ama with foam flotation its simple to just glue some in afterwards.
    If you want a solid foam ama the simplest way is to make a central wood/plywood spine that provides rigidity and atachement points for the crossbeams and glue some foam to it to define the shape. A light glass sheating will be needed for abrasion.

    As for the Ikea desk I will just say this: you can only make something better because labour, tools and overhead are free.

    Building and designing are not the same thing. Build if you like but buy a design. A boat is not just a funny shaped cabinet.
    fallguy and bajansailor like this.
  7. Qmaran
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    Qmaran Junior Member

    I do appreciate all the warnings but I have never been known to stick to plans. I know a boat is not as simple as a desk. I think it somewhere between an automobile and desk in terms of complexity.

    I have 2.5 years to do it so there is plenty of time to study, have some trial and error sessions with building techniques. I would also probably make a 1/10 scale model to get a feel for the balance of hull, mast, sails, keel and rudder.

    Here is the first bit of information that eludes to my idea. It comes from a Airex product brochure:

    3.1 Core preparation
    Grooving and perforation Before installation, foam sheets should be either grooved or perfora-
    ted. Grooving helps to evacuate air and - in the case of infusion
    processes – allows also the resin to flow.
    Perforation is used to equalize resin flow in vacuum infusion and to
    evacuate trapped air from the mould side.
    A typical grooving pattern is shown in the picture on the left.
    Cross-wise grooving is an additional option mostly used for vacuum
    infusion to prevent dry spots.
    For perforation, holes of approx. 2 to 3 mm diameter (1/16 to 1/8 in)
    at equal distance of 50 mm (2 in) or less are recommended. To get
    an accurate distribution of holes, it is highly recommended to use a
    pattern made of cardboard or plywood.
    Cores can be ordered with premade finishing options such as
    grooving and perforations.
  8. Rumars
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    Rumars Senior Member

    Designing a good boat is about as complex as designing a good airplane. You can take shortcuts, use proven forms and design solutions and end up with an average boat by performing only the most needed calculations, but for that you need enough experience to know what needs to be done in order to know where to compromise.

    Yes you can infuse both sides of a core at once from one side only, you can see it on youtube. Doing it on a light foam plug will be difficult, you either seal the plug or pump enough resin in a short time so as to not starve the skins. You also have to assure form stability under vacuum pressure. The end product will weigh more then doing it conventionally, that's a fact.

    Am I right thinking that you have no ideea what foam/resin/reinforcement system you want to use?
  9. fallguy
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    fallguy Senior Member


    The thing will be heavy.

    Rumars points this out.

    The method is difficult and the result not ideal.

    One thing that happens often on this forum is someone comes up with a reinvention and it really makes no sense. They are told so and some are stubborn and others adapt and change.
  10. fallguy
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    fallguy Senior Member

    The idea for solid foam amas works well for smaller amas for the time saving aspect as the plug is the part.

    Dierking's design is handy for outriggers on canoes.

    As the size increases; air becomes the cheap medium.

    The fastest way I can see to build a larger one would be in half shell moulds.
  11. MassimilianoPorta
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    MassimilianoPorta Junior Member

    Could you please share a link? Thanks
  12. upchurchmr
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    upchurchmr Senior Member

    The fastest way to make a mold is to strip plank it with a light coat of glass.
    Relatively cheap.
    If you just used the strip planking as the second heavy layer of foam, it will be a little heavier.
    If you strip plank but compare to the heavy and lighter foams, then it will be lighter.

    Since you are not making a natural finish wood surface, the strip planking can be faster than you might imagine, using epoxy/fillers to fill in gaps between the strips, before sanding to shape.
  13. Rumars
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    Rumars Senior Member

    There is a part two with the actual infusion and demolding. Perforated core is used. Most things done in a mold are done this way.
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  14. Dejay
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    Dejay Senior Newbie

    Hi Qmaran, welcome to the forum. Like you I also dream of building a trimaran but a powered one, not a sailing one, and powered by solar panels and batteries and a backup generator. So I will need to find a designer who design one (there are no plans for this) or adapt an existing design or design it myself. Like you I also don't have any experience and are trying to learn.

    But a sailboat is like an order of magnitude more complex than a powered boat, more forces working on it, more total number of systems to optimize, more structural requirements that require complex simulations, experience and/or knowledge of scantling size.
    The more I read and learn the more I am delighted by the absurd complexity of boat design. But for your requirements it's very unlikely that you can't just use or adapt an existing sailboat design that will be superior, will save you time and money and most of all will be safer.

    Like you I also started with crazy ideas and the old "Oh this is just like IKEA, I can do this better!" mentality ;) It's not wrong to try to think outside the box and try to reinvent the wheel. Just don't get defensive if you get shot down. For example I'd like to try out if you can vacuum infuse your own plywood in a mold using precisely CNC cut veneer pieces. Anyways, after looking into the different boat building methods my conclusion is:

    The cheapest build method in material cost you get with epoxy and fiberglass over a chined plywood hull. Stitch and glue or not. But it requires more work and lots of sanding. This is a good "beginner" video explaining a very simple building technique.

    The lightest and time effective build method is vacuum infusion in female molds using chined hulls. But structural foam is expensive. Look into the "intelligent infusion" approach by Rob Denney. His proa designs are optimized for an easy to build female mold that gets reused multiple times. If you like innovative, there are lots of ideas there. But the aesthetics of proas are seen as exotic and they don't sell well. I don't want to sail but his proa designs almost make me want to build one!

    Probably the cheapest way to get a sailing trimaran is to buy a used one in the right place. Even restoring a wrecked one after hurricane season is probably cheaper.

    And if you want to build, obviously build a small dingy from free or cheap plans first.
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  15. Blueknarr
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    Blueknarr Senior Member

    Dejay's advice is spot on. Exactly what the intelligent third of this forum's members wish to convey to you.

    Keep dreaming, thinking and exploring ideas. There are ways to innovate boat building. BUT it is wise to learn why wheels are round before trying to reinvent one.

    I often see complex solutions to non-problems. Dejay's example of mosaic veneers was just one. (Apologies to Dejay)

    A well designed boat is far closer to a car than even the most elaborate desk.
    BlueBell and Dejay like this.
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