Flapdoodle Hacks – Part One

By Tom Hruby - Olympia, Washington – USA

I got going on the flapdoodle, and as I go along I have many comments and ideas I would like to share with your audience.

This project is not for the novice boatbuilder because the plans as found on Duckworks leave much to be desired.  Some information critical to the construction is lacking and the major decisions that need to be made are not identified up front (sailing, rowing, where to put the seat, etc.).  A discussion of the benefits and problems of the different options would also be very helpful for the novice.

  1. The series of instructions for building the sailing version have you putting the mast step behind the dagger box.  It is only later that you find the option for putting it up front.  However, a position behind the dagger box will not work with the sail plan proposed.  The center of effort of the balanced lug sail proposed is way behind the center of resistance of the hull and dagger board if it were placed in this location.  Also, it would be very cumbersome to try and sail with the mast pretty much in the center of the boat – no place to sit without being either too far forward or aft.
  1. The dimensions of the plywood needed to rough out the dagger box are not correct. The directions say to use a piece 14″ by 17″ but then the drawing shows that the base in only 13″ and at angle.  If you built the box as proposed the box would be too big. Luckily, I started by first cutting out the sides using the angles and distances in the drawing and found the discrepancy before I glued everything together.
  1. More detailed information on how to cut out and attach the PVC cloth would be helpful.  I found that I could use the protecting strips as a pattern for cutting out the PVC.  Also, I was able to limit the amount of glue excess by first marking the edge of the strip on the hull panels, and then using this mark as the boundary of where I applied the glue.  Since I am using pigmented epoxy on the boat sides I used E-6000 glue rather than pvc glue since the latter did not bond well to epoxy.
  1. I found that the stainless hinges were quite rough on the outside of the hinge and I was concerned the might wear through the PVC.  I added an additional  small strip of the PVC fabric over the top of the hinge before I folded glued the fabric to the other side.

  1. I did not look forward to cutting 24 hinges with a little dremel tool as suggested, so I splurged and bought a 5 inch sheet metal plate shears (on Amazon) to do the cutting.  This worked great and let me add a nice toy to my tool collection.  I pulled out the pin of the 6 ft long SS piano hinge and cut each side separately.  I then used a nail cutter to cut the pins to the correct length.




The stainless steel hinges are a great idea and really increase the stability of the system.  However, the instructions on how to install them are somewhat lacking and misleading.

  1. The instructions for drilling the holes for the hinges connecting the keel to the bottom are misleading.  Since the bottom panel is curved one needs to measure the distance along the curve, not the flat perpendicular as drawn.  The keel will bend along the line of the bottom sheet and if one starts attaching the hinge in the middle there will be a discrepancy of about 1/4 inch by the time you reach the bow or stern if the location of the holes is determined by the horizontal distance along the bottom. I measured this difference, luckily before I drilled the holes for the hinges.
  1. The hinge itself can be used as the template for drilling the holes.  By laying the hinge upside down along the edge and drilling through the hole in the hinge one can achieve a gap of about 1/4 inch between panels as suggested.  This way all the gaps will be of the same size.

The hinges between the bottom and the side panels require one to drill additional holes in the hinges so the panels will lay flat.  Since it is almost impossible to drill the holes in exactly the same position in each hinge, they have to be numbered and each used as a separate template for drilling the holes in the one panel that will have two holes per hinge.

  1. There is very little flexibility in attaching the hinges so making accurate measurements and holes is imperative.  Any discrepancies will force one to increase the size of the hole to make the machine screws fit. The side panels will not really bend adequately to force the screws into the holes if they are misaligned.

I have found that the best screw size is #10-32 stainless flathead screws with a length of 7/16 inch. This will avoid the need to grind down the top of the screw.


Two bottom panels after two coats of pigmented epoxy. The strips are first primed with pigmented Titebond III and then the outside is sprayed with Rustoleum paint. The strip on the right in the picture below shows what the pigmented Titebond looks like.


​Bottom panel with pvc hinge attached.  I used a spray paint of a slightly different color on the strips to add interest. Note also the push pin in the top end of the strip.  I used this to identify the bow since the curve of the strip is not  uniform​.

The small piece of fabric used to reduce wear at the hinge.

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