Is Inflatable Boat Design/Building a Black Art?

Discussion in 'Boat Design' started by Squidly-Diddly, Aug 12, 2009.

  1. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,896
    Likes: 156, Points: 63, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

    I've seen places that sell the glue and fabric, and even some rub strakes, valves and other accessories.

    I've yet to come across any info on the design practices.

    Do you just use a typical CAD program and use its tools to 'convert' boat shapes to flats with some overlap?

    Do you need to compensate for what happens when all that fabric you glued up becomes pressurized and starts to bulge in places.

    I thinking of that Structural Engineering principle that says a cylinder under pressure will bulge/burst in the middle, not the ends.

    I saw a TV show about an inflatable boat factory but they sure seemed to miss all the important parts that might help someone making their own design.

    Construction of a "hard boat" seems pretty straight forward, especially metal or molded.

    It seems that "in theory" an inflatable could be easily fabricated "in the living room" of a 2nd floor apt and then rolled up and carried downstairs (besides the noxious glue fumes riling the neighbors.

    Shouldn't there be some fairly simple parameters, and sequence of construction for this?

    Maybe I'll try a mock-up with some cheap airtight material, some day.
     
  2. kroberts
    Joined: Mar 2009
    Posts: 318
    Likes: 12, Points: 18, Legacy Rep: 210
    Location: Chicago area

    kroberts Senior Member

    I have never built an inflatable boat, or contemplated it.

    I have messed with inflatable shapes though.

    You need to look up these math topics:
    1. Cylindrical sections
    2. Conic sections
    3. Spherical Sections

    That covers most of your basics on making an inflatable shape. How to make those into a boat that works is for someone else to say.
     
  3. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,896
    Likes: 156, Points: 63, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

    As far as I can tell, fabric inflatables DO bugle out a little

    on the cylindrical sections, just not that much due to strength of the fabric and low pressure.

    The fact that most 'speed boat' types with transoms also have larger diameter tubes towards the stern and smaller towards the bow sort of masks that, I think.

    I'm wondering if they also have a slight built in narrowing in the middle of cylindrical or mildly conical sections.

    I'm thinking a 2' dia. X 3' long section might have a 3' x 1/2" sliver cut-out of each edge before gluing.

    I'd love to see how they glue these boats up in the factory.

    Do they use a bunch of fancy gigs and supporting frames until the final envelope is sealed?
     
  4. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,896
    Likes: 156, Points: 63, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

  5. kroberts
    Joined: Mar 2009
    Posts: 318
    Likes: 12, Points: 18, Legacy Rep: 210
    Location: Chicago area

    kroberts Senior Member

    AFAIK, the fabrics used in inflatable boats is not really very elastic. So no, I don't think they bulge in any noticeable fashion. I seriously doubt that they change the shape of their tube to compensate for whatever stretching is there.

    I've built hovercraft skirts, and there is no provision in there for a stretching fabric.

    The frames in that video seem to be only to facilitate gluing a baffle to the inside of the tube. I can't imagine that they leave it in there long enough to get the second baffle in there.
     
  6. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member

    Some of the older inflatables might bulge out a little bit in the middle of compartments. It is my understanding that most of the manufacturers are currently using fabrics consisting of a fairly inelastic weave (Dacron, etc.) laminated with various layers of Hypalon, PVC, maybe some neoprene, etc. to provide airtightness and scratch/cut resistance. These fabrics are pretty stiff in tension, and the pressures in an inflatable's tubes really aren't all that high. Except for air floors like Zodiac's H2P, the pressures involved are rarely more than 10 psi.

    Someone with sewing/tailoring skill could probably do a simple inflatable boat on their own. (The boats are glued, not sewn, but a dressmaker's skill for 3D-to-2D pattern making would be a big asset.) But by the time you factor in all the components- fabric, adhesives, valves, bulkheads, rubrails, handles, transom mounts, floorboards, etc.- I'm not sure you'd be ahead, cost-wise. These boats are built on elaborate, partially-automated production lines, with economies of scale weighing heavily in production decisions. Buying fabric and glue by the railroad car is a lot cheaper per boat than buying it by the roll or quart jar. By the time you add up the cost of all the parts, does it still look worthwhile?
     

  7. Squidly-Diddly
    Joined: Sep 2007
    Posts: 1,896
    Likes: 156, Points: 63, Legacy Rep: 304
    Location: SF bay

    Squidly-Diddly Senior Member

    MM, no, it wouldn't be 'worth it' and I wouldn't take a homebuilt

    inflatable out farther than I can swim by itself, but it might be a niffy way to quickly produce a custom boat for nich uses, like maybe a stowable yacht tender that has some special ability, or is some how "just right".

    Also, the materials could all be shipped in a normal postal box to any location. Try that with plywood. Also, "in theory" all you need for tools is a pair of scissors and paint bush.

    I'd also be even more interested in a existing inflatable maker being able to wipe out a custom with your parameters and ship it. Again something that is nearly impossible for a ridge boat of any size.

    One thing that strikes me about the manufacture of inflatables is "in theory" their is no big "time frame" as material COULD be cut and glued very quickly. My understanding is the glue works is a few minutes, not even hours like fiberglass resin or epoxy. I see them rubbing down the joints then handling the piece with no special care. I figure by the time your new custom arrives via OverNight it would be ready for use.

    I don't see why the same tech that uses lazers and computer plotting to cut super fast and accurate fabric for garments and even sheet metal couldn't be used. Plus all that CAD 'parametric' stuff could scale the pieces up or down as needed without further human work.

    What exactly do I have in mind that isn't already for sale? Not sure, I'm working on a solution that would be then searching for problem.
     
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.