Monday, July 4, 2011

Hello and stitching a hull

Dear blogosphere,

This will be my modest attempt to share my latest fun project, building a high performance pedal powered boat.  It will be my second "hpb" and third stitch and glue craft altogether (including my kit canoe you will see hanging in the garage).  You will see where the name "stitch and glue" comes from in the photos.   I apologize in advance for not consistently using proper maritime terminology, I'm still a cyclist who wants to bike on water rather than a boater who wants efficient human power.

If imitation is flattery, I should point out that I am borrowing heavily from a boat and drivetrain design by Rick Willoughby and getting inspiration for a blog from Michael Lampi.  You can see very similar creations by both enthusiasts.  Mine will be slightly different in ways easiest to explain when we get to that point.

The boat is made from 4mm okoume marine plywood and was cut to exact shape by CNC router according to CAD files created by DelftShip design software.  The hull length is 20 feet, limited by my garage, and the first step is to glue multiple pieces cut from 8 ft plywood end to end to make long enough panels.

The butt joints are glued and reinforced with 2 inch fiberglass tape on top of 4 inch tape.  It was done in one step and covered in semi-rigid plastic (scrapbook cover sheets) and wood and weights to ensure a smooth surface.  I am leaving the exterior side without tape reinforcement as this will be laminated in a full sheet, and the glass will already be 4 layers thick at the joints.  You can see faint lines from the tape even in my best fiberglass attempts.

The hull is formed from 3 panels, two sides and one bottom.  The sides I designed included integrated seat back forms to avoid additional seams.  Altogether the panels went together pretty well with just one joint that had a few air bubbles.

 I tried something new on this build, which was to glass the inside ends of each panel before stitching and avoid cramped quarters trying to laminate the inside after assembly.  The hull is so narrow, it will be hard to work close to the ends.

Once the panels are complete, I drill 1/16" holes every 12 inches along the edges joining the three pieces.  This is wider spacing than usual but the panels have very little bend, so it seemed appropriate and worked fine.  These holes are used to stitch panels together with wire.  The stainless wire I ordered turned out to be too rigid, so I picked up some .8mm copper wire at the hardware store and, while more expensive, it is far easier to work with than any other type I have used.  It is also much less likely to break when tightening.

Most of the stitches have the "twist" on the inside.  This makes it easier to glue the seams on the outside without getting scratched constantly.  On the end, the twist in on the outside due to space constraints.  Loosely stitch everything first, then tighten by pulling slack out and then twisting until there is enough friction between panels that they do not easily move against each other.

I used one forward bulkhead, and one rear.  I also decided to stitch the seat back on at this point to help provide some rigidity.  Lastly, I taped the rear deck on temporarily to create the proper taper of the hull sides.  I also noticed a slight amount of twist at the stern, I'm not sure why.  I think I corrected this with some tape anchored to the workbench.

Next up, gluing the seams - as in stitch and glue.

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