Lofting, Part 1

After two months of fiddling around with paddles and outrigger timber, I finally had a good opportunity to begin the work on the hull.  The first step is "lofting," which is the process of transferring the shape of the various hull panels from the plans to the plywood itself.

Because the plans are smaller than boat they depict, the panels can't just be traced from them.  Instead, you draw a number of reference lines ("stations") at measured intervals along the plywood, and then mark precise points at each station according to the plans.  These points are then joined in a continuous, curved line and traced using a flexible straight edge from your scrap lumber pile - a "batten". 

Lofting in progress. The longitudinal
chalk line is the center line for the
bottom panel; dimly visible are the
transverse station lines.

The Wharram Melanesia is a narrow, low-cut, 16-foot boat, made from two sheets of plywood laid end-to-end.  To loft the patterns onto the plywood, you lay the two sheets out together, mark the stations and the centerline of the bottom panel, and then get your battens and scribe the lines.  These lines become your guides for cutting the patterns out.  Both side panels and the bottom panel fit in the 4-foot width of the plywood, along with several miscellaneous parts like the stem and stern posts, the bow and stern decking, and various butt plates and lashing pads.

Lofting has to be done right or you'll be buying new plywood and starting over.  One reason is that it's a tight fit, squeezing all of these shapes into two sheets of plywood.  If a cut wanders much, it will probably end up in the next panel.  But the most important reason the lofting and cutting have to be precise is that these shapes will be "tortured" into a hull shape by joining the curved panels along their edges.  If you get the curves wrong, the hull formed by joining the faulty curves together will be skewed.  So lofting is where it all starts.  Get it right, and you've laid a solid foundation for the rest of the project.

This is the aft end of the bottom
panel. It has a "swallowtail" cutout
shape; the interior edges of this
cutout are stitched together
to form a flattish, curved
bottom in the stern.  The
last 4-5" of the tips are
traced from a full-sized
pattern included in the plans.

For these reasons, I'm taking this step nice and slowly.  My eldest son (12) helped me chalk the stations and the bottom panel's centerline in.  The only error I found so far came when I mismarked one end of the centerline - I had it off by an inch!  The error became obvious as I drew the center panel in, and we redid that part.

We stopped short of actually drawing the curves in, because it was getting to be past everyone else's bedtime.  It's nearly impossible to hold a batten in a complex curve and trace it faithfully when you only have two hands for the job.  So I contented myself with making all the marks necessary to draw the curves when people wake up tomorrow.  We'll take care of that in the morning, then I'll be ready to start cutting pieces out whenever time permits.

More news as it happens.