Lightest Building Material

Discussion in 'Materials' started by Mat-C, Jun 17, 2007.

  1. Mat-C
    Joined: May 2007
    Posts: 255
    Likes: 12, Points: 0, Legacy Rep: 141
    Location: Australia

    Mat-C Senior Member

    Leaving aside the 'exotics', what is likely to be the lightest building material?

    There seems to be a number of powerboat projects around 30ft long discussed hereabouts. So, using that as an example - a 30ft powerboat with a top speed of say 25 knots, to be built as a one-off boat - which would be lightest?
    Foam-core
    Wood-epoxy (glass over ply, strip plank, balsa core)
    Aluminium
    Soemthing else......
     
  2. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Not getting into exotics, probably glass over balsa core or foam core. this will give a stiff boat hull, though not as tough and puncture resistant as plywood, but stiffer and therefore stronger for the weight if top performance is the desired result.
    Then, quality of lay-up and vacuum-bagging count for a lot in terms of weight reduction.

    Alan
     
  3. Mat-C
    Joined: May 2007
    Posts: 255
    Likes: 12, Points: 0, Legacy Rep: 141
    Location: Australia

    Mat-C Senior Member

    That's what I would have tough too.
    In The Nature of Boats, Dave Gerr suggests that a wood core - he talks about strip plank - might actually be the lightest and easiest for a one-off.
     
  4. Willallison
    Joined: Oct 2001
    Posts: 3,590
    Likes: 130, Points: 0, Legacy Rep: 2369
    Location: Australia

    Willallison Senior Member

    There's a bit more to it than simply the lightest material. A strip plank boat will tend to have greater impact resistance than a balsa cored boat, which will in turn have greater impact resistance than a foam cored boat. And whilst the strip plank core itself is denser than either balso or foam, it requires thinner shins to give it strength and far less in the way of interior supporting structure - frames, bulkheads, stringers etc.
     
  5. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    How light?

    I tend to agree with Will on this one. You are not building a racing yacht so that practical considerations and costs are also important. This is not to say that light weight is not a worthwhile goal. It is, but it isn't the main thing for your project. My take on this is wood strip in cedar with biaxial glass both sides set in epoxy would be probably the best choice. It isn't the cheapest but it is much less than exotics and probably cheaper and more practical than a balsa core as well. Hey, it's your call, but consider all the important factors before deciding.
     
  6. Mat-C
    Joined: May 2007
    Posts: 255
    Likes: 12, Points: 0, Legacy Rep: 141
    Location: Australia

    Mat-C Senior Member

    Thanks Alan, Will, Frosh.
    I understand the differences between the materials and how they effect the overall structure. And yes - you are correct, the weight is not the only consideration (cost definitley comes into it...perhaps another thread...) But all else aside, I'm interested in the lightest overall structure for this (hypothetical btw) "project".
     
  7. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    Strip plank is an excellent all-around one-off method. A balsa or foam core will generally be layed up inside a mold, which eliminates a lot of time gluing and fairing, but such methods require a mold and so favor multiple copies.
    I don't know if foam or balsa core require more stringers or frames--- this may be debatable as strip-building might need frames more than stringers and cored may need stringers more than frames, and each design will be unique (for instance, certain furniture in a larger boat will provide both frames in the form of bulkheads and stringers in the form of berths, shelves, etc..
    In a small boat, cockpit seats make stringers and so a cored hull might be lighter for its strength, while a kayak usually has full bulkheads and no long interior pieces and so favors strip construction.
    Multi-chine plywood is another light and strong method, well suited to one-off. All of the methods mentioned use resin and cloth to achieve tensile strength, water-proofing, and bonding. In that sense, all are cored in principle. The exception would be plywood in cases where only the exterior is fully glassed.
    Every one of the methods will produce a light and strong hull if properly designed and carefully built. Barring using exotic materials, I would say that without knowing which particular design was being analyzed, there isn't a very significant difference between any of them that would make one better in every boat.
     
  8. Raggi_Thor
    Joined: Jan 2004
    Posts: 2,457
    Likes: 64, Points: 0, Legacy Rep: 711
    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    It's also a question of practicality.
    I think you can save some weights with lots of frames (cnc cut) and a very thin skin (plywood). But it's time consuming, it's hard to keep clean inside, the skin is so thin it will puncture if you hit a sharp stone or a corner.
     

  9. War Whoop
    Joined: Jun 2003
    Posts: 661
    Likes: 16, Points: 0, Legacy Rep: 84
    Location: Sunny Ft Lauderdale Fla

    War Whoop Senior Member

    Foam core by a mile!
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.