Boat Hull model materials

Discussion in 'Boat Design' started by KristyP, Jan 14, 2013.

  1. midnitmike
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    midnitmike Senior Member

    Since the assignment is based around hull design there is an added benefit to working with paper. Computer programs like FreeShip or DelftShip could be used during the design phase and the results can then be printed on some form of stock for construction and testing.

  2. moTthediesel
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    moTthediesel Junior Member

    You could have them print the body plan sections on paper, then glue them onto foam poster board with photo adhesive. Cut the molds out, mount them on a strongback, them plank with balsa or soft pine strips. Like this --


    A little more work perhaps, but much more like real boat building, and with a nice shapely result.
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  3. Landlubber
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    Landlubber Senior Member

    "A little more work perhaps, but much more like real boat building, and with a nice shapely result."...not so silly really when you think about the project cos this way they learn a lot of the boatbuilding skills (good NAs are always boatbuilders)...and they get to keep a family heirloom if they do it right......
    The foam is not really all that messy cos it is done inside, no wind, and the foam itself is the only tool needed, as it rubs itself on itself.
  4. hoytedow
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    hoytedow Carbon Based Life Form

  5. Earl Boebert
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    Earl Boebert Senior Member

    The first decision you have to make is whether the hull is to be hard-chined (sharpie) or have smooth curves overall. Hard chined hulls can be made from a variety of sheet material, but the hull must be "developable," that is, capable of being formed from sections of a cone (no compound curves). This restriction may give you an opportunity to slip in a little solid geometry :)

    Suitable sheet materials vary from construction-grade cardboard (called strathmore board in the US) through sheet balsa, 1-3mm aircraft ply to expanded styrene sheets called Depron and Sentra in the US. Cardboard and wood are not inherently waterproof and have to be sealed with something like varnish or epoxy, which would add to the cost and mess.

    Depron is a lightweight sheet used primarily for those molded takeout containers and other food packaging. It is extensively used by model airplane builders and there is a lot of information on working with it on the Internet. Sentra is a heavier and more durable sheet material used in the sign industry. Both these materials can be used to make prototype hulls by taping seams together with good quality duct tape.

    If you choose to construct hulls with compound curves, your options are molding, planking, or carving. Molding is more suited for production runs than "one-off" hulls. Planking, as others have noted, is a great way to learn the way a hull is formed but may require more effort than your student's time budget allows -- I'm assuming the primary goal is to produce hull, not teach a secondary skill no matter how interesting it may be.

    That leaves carving. Florist foam is, as you noted, pretty awful stuff to work with. Not only does it leave a big mess, but the holes require a lot of work to fill. A good alternative is construction insulating foam, called "blue foam" in the US. This can be cut and with a little practice carved with "hot wire" cutters. Again, there's information on this on the Net. The real secret to carving a hull is to laminate it up in layers so that the carving part just involves smoothing the corners off. Model yachtsmen call this the "bread and butter method." The best approach is to build up the hull on the "buttock lines" or vertical slices. This saves material if the hull is to be hollow and makes it easier to make the hull symmetric.

    Pictures of bread and butter construction can be seen at:

    Hope this helps.


  6. KristyP
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    KristyP New Member

    The assignment looks at a boat of the students choice, so if they want to design a boat for speed, or one for carrying heavier weight then its their choice. It is a marine aquatics (non-academic) group so we focus more on the general picture, and give them small ideas about the industry. Students have opportunities to use a design program, however most simply prefer to just sketch, their design which is ok as well so long as its fairly accurate to their final design. Other than foam we tried creating ribing from wire similar to tyre wire and "skinning" the boat with thick caterers foil, which was ok but didn't create a high quality finish like the foam did, and we've also tried using Overhead transparencies and hot glue guns to create panels and welds. The overhead transparencies worked ok, but needed to be cut perfectly and were fiddly to "weld". Thanks so much for the suggestions. I'm going to give a couple a go at home to see which one yields the best results compared to price and take them to my Head of Department when we head back to school :)
  7. midnitmike
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    midnitmike Senior Member

    Please come back and let us know what method you chose and why.

  8. Ad Hoc
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    Ad Hoc Naval Architect


    I used to do exactly this with a local school when I was based in the UK. We would give the kids (ages around 10years old) a brief chat about boat design..and then the kids all had exactly the same batteries, same props, water or air props, and the same brief…design a boat. And held a competition at the end of the science project, which is the fastest, best course keeping etc..and of course funniest!

    The kids were given a maximum dimension LxBxD, as it was to be taken into a hot plastic mould...and they could make their hull(s) out of foam or wood. But the shape was then moulded with the hot sheet of thin plastic using a special forming plastic press. (I can’t recall the exact make/name of press they used, but it would have been easy to source and cheap being a school!, and it was over 10years ago now). The result being a thin plastic empty hull, to their shape, which they then “fitted out” with batteries, motors, switches, or anything else they wanted.

    Was great fun at the end when everyone tested their hulls....from monohull to catamarans to trimarans..all great fun to see.
  9. Katoh
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    Katoh Senior Member

    Hi Kirsty
    Coming from a different background I have to agree that foam as you put it is the way to go, but not just any foam. What you want is eps basically a high density styrene, comes in sheets.
    We use this in the CNC world (computer controlled machining) and it works extremely fine indeed, a friend makes 2m long RC helicopters from it, so it cant be that bad. It can be machined easily by hand, or machine, best way without mess is to use a hot knife,at least threes no dust, just offcuts. Or for a little mess use a dremel on low speed.
    Hope this helps.
    Personally I believe to go into printing or cutting out frames and plates and putting them together is to much for the little dears, plus you may need some high powered software to generate the patterns.
    Just do a quick Google on "cnc foam carving" to see how well this foam works, but you need the right foam.

  10. michael pierzga
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    michael pierzga Senior Member

    If you live near a shipyard with boats hauled out of the water, a good way to stimulate young folks progress on their foam shipmodels is with a camera .

    Tell the kids to take pictures of a boat that interests them.... side on, stern on and bow on.

    Take these pictured and blow them up to " model size" on a photocopier .

    With scissors chop the profiles out and use these profiles as a beginning shape and reference for the model building.


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