Wednesday, December 20, 2006

Layout and Cutting (Measure twice, cut once)

The hull is drawn in scale on one sheet of the plans and it is necessary to transfer the measurements from the plans to the plywood. This is what is referred to as 'layout'. Working from plans with the exact dimensions indicated as 'offsets' is much easier and faster than just working with line drawings that would require lofting to get the offset measurements.

The bottom of the Jimmy Skiff ™ hull is drawn on the plans with offset dimensions, which are indicated at right angles to a center line. I started by using a chalk line to mark the center line about 20 inches in from one side of the 9mm panel. Next was marking off the stations or intervals for each offset. On the Jimmy Skiff ™, there are six, 24 inch sections beginning from the bow, and then a four-and-a-half inch section at the stern. I marked off the the stations along the center line, then used a large carpenters square to mark the offsets out from the center line. The square ensures that the offsets are all at right angles to the center line. After the offset points are marked out, I used a 14' long, 1/2" pine quarter-round as a batten. I temporarily drove 2" finish nails in where the offset marks where, then used the spring clamps to hold the batten with the flat side against the nails. Then simply drew a line along the flat side of the batten. The side panels were done in a similar manner, except that the offsets are measured from a baseline rather than a center line.

I used my cordless jigsaw to cut out the panels, bulkhead, seats and stern. I cut about 1/8 to 1/4 inch outside the line, and then used a sharp block plane to plane to the line. This makes a very clean and 'fair' edge. The seat supports have inside curves, so I used a spokeshave to plane this to the final line. The CLC plans for the Jimmy Skiff ™ have full size templates for most of the parts other than the hull itself.

I used an awl to poke through the template lines about every half-inch, then 'connect-the-dots' with a pencil prior to cutting. Cut out all of the panels and parts before moving on to assembly. Note in the photo that the seats are wider than the bottom. The bottom is about 40" wide at the widest point, whereas the beam (overall widest point on a boat) is 50". This is because the sides will flare out from the bottom.

I built a couple of very stable saw horses for the boat construction. Then I padded them with some egg crate foam I had left over from when I 'sound proofed' my dust collection closet. The foam will keep the hull from getting scratched and dented during construction. Next post will show the stitching of the hull...

Saturday, December 16, 2006

Not so scary scarf joints

The one thing about building from plans vs buying the kit that I was most apprehensive about was cutting and gluing the scarf joints. These are used to join two sheets of plywood end-to-end so that a boat longer than seven or eight feet is possible. I was encouraged by chapter nine, Scarf Joints in Chris Kulczycki's book, which I mentioned in my initial post. He explained the process in a way that almost made it sound as easy and enjoyable as it actually was.

The 9mm sheets are marked, stacked and lined up for a 3" ramp (scarf) to be cut with a very sharp block plane. The edge of the bottom sheet needs to be supported on the edge of the work bench to prevent the plywood from breaking off when it gets thin. I also clamped a couple of pieces of MDF on top to prevent the panels from shifting or bowing while I planed across the width of the plywood. Keep the plywood veneer bands parallel, and cut with smooth, long strokes. The 6mm sheets are done in the same way, except that a 2" scarf is cut. I did attempt to practice cutting scarfs on some scrap luan and found that the luan was much more prone to tear-out than the okoume was. I had similar difficulty with some scrap fir plywood I practiced on.

After the scarfs are cut, the sheets are glued end-to-end with epoxy thickened with Silica. The 9mm and the 6mm panels can be stacked and glued at the same time if you lay plastic wrap between the sheets where the joints are. In retrospect, I think I would not have tried to stack them, and only glued one at a time. This is because it is much more difficult to perfectly align four sheets on two different planes than two sheets on the same plane.

I placed another layer of plastic wrap on the top, and then placed a 4x4 beam across to use as a clamping bar. It is very good advice not to apply too much clamping pressure. All you need, is to tighten until you begin to see the epoxy squeeze out. Again, this would be much easier to determine if you only glue one set of panels at a time.

Thursday, December 14, 2006

In the beginning...

If we are to begin in the beginning, which seems like a pretty good place to start a journey of any sort, my boat building project began last summer when I read Stitch-And-Glue Boatbuilding by Chris Kulczycki. This is when I finally settled on a boat building method and design, and then ordered the plans for the Jimmy Skiff ™ from Chesapeake Light Craft. Mr. Kulczycki was the founder of CLC and the designer of the elegantly simple skiff I chose as my first boat building project.

Even though the book has an entire chapter on building the Jimmy Skiff ™, including scaled-down drawings, Mr. Kulczycki recommends purchasing the plans or a kit from CLC, and I heartily agree that this is the way to go. Quality materials and time are too valuable to waste on trying to cut a corner by not buying the full size plans and building guide. See the CLC website for pricing and availability. I also recommend getting a copy of Chris Kulczycki's Stitch-And-Glue Boatbuilding to supplement the plans and building guide for anyone who has not built a stitch & glue boat before.

My project started to move from a dream toward reality when I bought the Okoume plywood from Maine Coast Lumber. The Okoume I bought is grown in managed forests in Gabon Africa and then milled in Greece by Shelman.

The Lloyds Register sticker and the B.S.1088 stamps on the plywood sheets indicate that this is a high quality material specifically manufactured for use in building small boats. The Jimmy Skiff ™ plans call for two sheets of 9mm and two sheets of 6mm plywood.