Creating fair curves with batten

I am going to start building a CLC sport tandem from plans in the next few weeks.  In the meantime, I have been practicing some basic woodworking techniques with some cheap luan plywood.  I cut out a set of 12 inch blanks, scarfed them with a hand plane, glued them together, and traced the side panel cut-out using offsets.  The one area where I am still a bit uncomfortable is making fair curves with a batten.  I basically hammered a thin nail into the plywood at the exact point described in the table of offsets, then took a long thin strip of plywood to connect the dots.  I noticed that a lot of factors can influence how I draw the line: the angle of the nails in the plywood, how I am holding the pencil and any warp that might be in the table.

I think I've identified some solutions to this problem.  First, my table is 20ft long and held up by only two sawhorses. This causes it to sink a bit in the middle.  If I added some sawhorses and made it perfectly flat this might fix a large part of the problem.  Secondly, instead of hammering in the nails exactly where the offsets say, perhaps I should hammer them 1/4 inch past the actual offset so that the plywood batten, when placed inside the nails, traces the exact curve that needs to be cut.  Does anyone have any thoughts about this?  Thanks


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RE: Creating fair curves with batten

I'm a plans builder, too.

I've made a handful of long, straight-grained battens, usually with a couple scarfs to get them boat length plus some extra. Their thickness needs to relate to the amount of curvature, but for most kayak curves something like 3/4" x 1/2" seems to work well. I use them on the flat.

I use a all-in-one countersink and predrill- your big box store has some, or some of the nicer places carry the Fuller brand. Adjust it to suit your screws- for my battens I use 3/4" x #6 flat head wood sheet metal screws.

I lay out the points on the wood as accurately as I can with a sharp pencil, then I start somewher near the middle and pre-drill and screw the batten to the ply. I'll spring-clamp the ends to get them close to the final shape, then continue pre-drilling and drving screws at every other station exactly on the marks, sight the batten to be sure it is lying fair, tap one or two screwed stations to adjust, remove a screw and redrill and drive a screw next to where the bad one was, then fill in the remainder with screws on every station point. Sight the batten for fairness, and adjust as needed, adding/removing screws as needed.

I cut 1/8" away from the batten with a jigsaw, then use a pattern-following router bit (or flip the plywood so the batten is underneath and use a flush trim bit) and running the bearing along the batten the plywood is cut to the exact shape of the batten. No edge planing or sanding or "finessing" needed.

Since you have luan ply, you have the opportunity to make some full size patterns. Once you have those, you can use them as your router templates- just screw or clamp or double-sided tape them to your okoume ply and repeat the rough-cut-and-router routine.

Save your patterns, so that when your wife/child wants another boat like yours you can skip all the layout and batten work. (But remember to call CLC for an additional build license).

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