This is Instructable number 4 in the Build a Greenland kayak series.
In this Instructable we will be installing the keelson and the stem and stern boards.

Step 1: Materials

In this section we will need a keelson board, 3/4 inches x 1 inch in cross section and 16 feet long. The wood needs to be knot free and straight grained.

A board for making the stem and stern, 3/4 inch x 5-1/2 inch x 8 foot long. Some knots acceptable as long as they are small and tight.

1/4 inch dowel rod 24 inch total length

lashing string (nylon mason's twine)

Step 2: Tools

We will need a saw for cutting and trimming the keelson,
a plane to shape the keelson
a jigsaw and handsaw to cut the stem and stern boards
a drill with a 15/64 bit for drilling dowel holes
a 3/16 inch bit for drilling lashing holes
a wire lashing needle

Step 3: Make the Keelson

Cut the keelson from a 16 foot board that is 3/4 inches thick.
Cut it 1 inch wide.
When you install the keelson, it will sit on one of the 3/4 inch wide edges. In other words, it will be taller than wide.
Plane the corners on one of the 3/4 inch wide edges. The rounded off corners will sit up against the skin. The edge with the unrounded corners will sit on the ribs.

Step 4: Cut Spacers to Shim Up the Keelson

The keelson establishes the line of the kayak's bottom when viewed in profile.
The kayak will be deepest at the bow and get more shallow toward the stern.

With the deck inverted on the saw horses, shim up the keelson so that the distance from the top of the keelson to the bottom of the gunwales is 10 inches at the bow, 7 inches in the middle and 6 inches at the stern.

For spacers, I use sections of two by fours cut to the appropriate length with holes drilled at either end to run the lashing string through.

Install the spacers at deck beams 1, 7 and 11. You will have to do some math to figure out how tall the shims need to be. But assuming that the deck beams and keelson take up two inches of the depth, your spacers should be roughly 4 inches, 5 inches and 8 inches tall.

Step 5: Install the Keelson and Spacers

Lash the spacers to the deck beams and lash the keelson to the spacers.
Check line of the keelson. Rocker, that is curvature of the keelson should be 1 to 2 inches. To measure rocker, set the kayak on the ground, keelson down so the keelson touches ground at the center. Prop up the frame so both ends of the keelson are the same distance from the ground. Measure the clearance off the ground at either end. This is your rocker.

Rocker should be 1 to 2 inches. The straighter the keelson the better your boat will track, but it will also be harder to turn.

You can adjust the curvature of the keelson by re-cutting the spacers or more simply by adding some shims between the spacers and keelson.

Also make sure that your keelson is centered on the deck.

Step 6: Fit Your Stem and Stern Boards

You will be cutting the stem and stern boards from a board that is 5-1/2 inches wide and 8 foot long.

The job of fitting will be easier if you cut the long board in two. However, you don't want to cut it right in the middle because the stem board will need to be longer than the stern board. Hold the board up against the stem to see how much you will need and cut appropriately.

Once you have a manageable size board for your stem, lay it up against the bow and keelson and mark where the underside of the keelson and the bow intersect it.
Trim to your marks and check the fit. Make adjustments as necessary.

Repeat the procedure for the stern. The stern board will be considerably shorter.

Step 7: Dowel the Stem and Stern Boards to the Keelson

Clamp the stem board to the keelson and mark it for four dowels.

Dowels will be 1/4 inch. Dowel holes will be 15/64 inch.

Drill a vertical hole first and dowel that, then drill the remaining angled dowels.

Dowel the stern.

Step 8: Trim and Round the Keelson

Trim off excess keelson in line with the edge of the stem and stern boards.
Use a hand plane to round the corner of the keelson.

Step 9: Drill Lashing Holes for Lashing the Stem and Stern Boards to the Keelson

Drill lashing holes in groups of 3 at the junction of the gunwale and the stem and stern boards.

Try not to drill through any of the dowels that hold the gunwales together.

Step 10: Lash the Stem and Stern Boards to the Gunwales

In triangular lashings you do a few loops on each of two legs of your triangle, then lash around the two legs with a series of half hitches to pull the two legs together and tighten the whole thing up.