Boat Design for Dummies

(No, not the book, if there is one.)

I have been invited by a kind pastor to run a summer program for upper elementary kids at her church.  Since I have pretty much free rein, I have decided to make it "the Boat Science Experience": we will investigate floating and sinking, buoyancy, stability and the like, building and testing paper models along the way, and finishing with the building of a real paddling boat (maybe even more than one).  To this end, I have been investigating designs for boats that would hold two kids or one kid and one adult, be a good enough performer not to be frustrating, and be simple and cheap to build.  A Michael Storer (Aussie) design called the Quick Canoe 150 seemed to fit the bill, and I bought a set of plans.  The plans--all metric--require a good deal of meticulous measuring and drawing of curves, which might be good practice for using metric units and doing careful work.  Or not, with kids this age.

Then I started asking around on-line for advice on building boats with kids and got a lot of good responses--some of it related to the ins and outs of doing this kind of class (keep it SIMPLE), some of it related to the choice of designs.  I was impressed by the simplicity of the designs suggested: some are made of two perfectly straight-cut sides attached to a trapezoidal center frame and bend around to form the ends of the canoe/kayak.  Though the wood is straight, the boat develops lovely curves because the sides are held at an slight angle (called "flare").  This makes the boat wider at the top than at the bottom (as most boats are) so that the ends curve gently upward both at bottom and sheer (top edge).  (The fore-and-aft curve of the bottom is called "rocker.")  The ends of the sides are cut at an angle to accommodate this flare and giving the boat more or less pointy ends as the designer wishes.  The greater the flare, the more the ends would curve upward--that is, the more the rocker and curve of the sheer.  Gunwales, sometimes inwales, and one internal frame and maybe seats give the hull enough stiffness to hold its shape.  The bottom could be experimented with to establish a shape and measurements for pre-cutting, or simply cut to fit the sides.  The designers of these "straight cuts" boats--all amateurs--could alter beam and length independently or scale the whole hull up or down as desired without altering the drawings that much.

This was a revelation.  Here were nice-looking hulls very simply drawn and built.  You could play with such designs easily with pencil, ruler, cardboard and scissors.

Top ("plan") view: from the right, the first two boats are  the published designs Wacky Lassie and Lazy Weekend Canoe, the others are my modifications.  Actual lengths are about 13 feet for most.

Except for Wacky Lassie, all the designs have a similar amount of "flare" (angle of sides from the vertical)--

--which gives them a similar "rocker" and sheer line (curve of bottom and gunwale)

Now-- I have always been of the opinion that boat design was for pros and really experienced amateurs.  I would never trust my money and time to a design of my own--I would want to be sure the thing would GO once I had spent all that money for materials and put in the months of labor.  But for a simple boat like this, I'm beginning to change my mind.  You see, the designs I've looked at aren't quite what I want: good capacity but not too much length, wide enough at the chine (bottom edge) not to be too tiddly but narrow enough at the sheer for a child to use a double paddle, and light enough for a couple of pre-teens to handle and car-top.  Hmmm...