Friday, September 14, 2007

Scarf

video
Tonight begins the building process. As with almost all kits from Chesapeake Light Craft, the building process begins with the scarfing of some parts. Scarfing refers to the joining together of small parts to make larger ones. In this case, the side panels of the 16-foot-long boat must be comprised of smaller parts cut from 8-foot-long plywood sheets. The plywood can be joined with epoxy to which silica powder has been added to increase strength. In researching the building of a Mill Creek kayak, I read WoodenBoat magazine #136 (May/June 1997), the first in a two part series focusing on building the Mill Creek. By happy coincidence, the same issue contains an article by Greg Rössel on scarf joints.

I started by wrapping the area adjacent the beveled ends of the panels with clear packing tape, which will protect from epoxy spreading outside the joint. The bevelled ends come in the kit pre-cut, which is very convenient. These are cut at an 8:1 ratio, meaning the bevel surface is 8 times as long as the thickness of the plywood. This falls within the recommended range of the WoodenBoat article which suggests going even to 12:1. To epoxy the ends, I coated each surface with unthickened epoxy, allowing it to soak into the end grain. I then coated each joint with epoxy thickened with silica to mustard consistency. Using a sheet of plastic to separate each panel and prevent them sticking together, I stacked corresponding bilge and sheer panels on each other, and weighted down the joint. To get the correct alignment of the panel, a string was run from one end to the other, and the panels adjusted until the specified distance to the arch of the panel was achieved. The scarfing process was also repeated with the sheerclamps, which will form the attachment point for the joint between the deck and the hull. The epoxy will be allowed to cure overnight, in a shop that is now at about 80 degrees F. (Total hours: 2.00)

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