Designing a New Hull Shape

 The initial boat type, pictured in my mind, was of a slender canoe which could be paddled with a double-bladed paddle.  Speed was not a goal, reduced weight (partial deck) and slightly more forgiving stability were the goals.  The first thing was to picture the midships cross section; a bottom slightly wider and flatter.  I 'played with numbers' in an equation, used to define the major chine.  I could alter the coefficients of X, Y, Z in parabolic equations to get the right length (X), width (Y), and upsweep (Z) that I was seeking.

Next, I needed to decide the X:Y:Z ratio in the bottom projection; get the midships deadrise desired with progressively steeper deadrise approaching the stems.  In order to achieve this, the major chine needed to be reconsidered.  Position and spacing of frames needed to be included as well as width of the keel.  The Y:Z ratio is determined by the desired deadrise angle amidships.  The X:Y ratio is determined by the bow half angle of the major chine.  

Creating the topsides is perhaps most critical.  At this point, I had to start over with all new numbers for the equation for the major chine; however, there were multiple choices/combinations to pick from.  Incorporating three more projections to create a more rounded topsides shape, I discovered, would result in a hull that was wider than desired.  I used a paper sketch to help decide the coefficients for my topside projections.  I had to choose a major chine equation with less beam (Y).  Iterative process, but I was making progress.

When I started to achieve harmony between all the equations and coefficients, I had more aspects to consider.  Just how slender do I want this hull to be?  What should the overall length be?  What should the sheer look like?  How much depth amidships?   Height at the stems?  Should I consider creating a transom at one end; should the hull shape be symmetrical or should one end be slightly more tapered?  But those factors are not requirements- they are choices to create the specific boat you want.

With the offsets already generated, I needed to make two more projections: first to see a lateral view of the stems and secondly to see the shape of the plank keel.  All offsets need to be charted on paper before I can visualize the result.  (Hey, all I use is a TI pocket calculator: no computer screen.)

Full-size paper patterns for the frames, stems, and keel are complete, a little drafting practice.  Not sure they are interesting enough to post (pencil on rosin paper), but the cross-section shape is satisfyingly rounded.  I plan to add some partial decking at the ends.  The major dimensions will be 156" (13 feet) long, 30" wide, and 12" deep.

Thus far, my description has only been in generalities, should I post a table of numbers?  It will be some time before I can start building.  I do already have the plank keel lumber on hand.  Next task will be designing the frames and developing a list of materials.