Building a kayak: Hull

This is a foto-documentary about my handicrafts and experiences, separated into 3 sections. It is not meant to be a complete instruction replacing a reference book, but I hope it’ll give you a clear overview. The order of things is, more or less, chronologically.

• Methods
• Preparations
• Hull
• Deck
• Finish
• Literature
• Pictures

Bevel plywood boards

The plywood boards are usually too short. To get them sufficiently long, they need to be extended by glueing boards together. For doing that, the edges are bevelled to enlarge the area of overlap. A ratio of the bevel of 1:10 (4 mm thickness of board : 40 mm slope length) is common, 1:5 has worked fine for me. For this purpose, a belt grinder is very useful.

On the pictures you see 4 boards on top of each other, the edges spaced at 20 mm in a step-like fashion. Hold the belt grinder in an acute angle and grind the steps down until a smooth slope is achieved, exposing the individual layers of the plywood (lower picture). Afterwards, the boards are glued
TIP: my boards have a manufacturer print on one side, hence it’s important to watch the orientation of inside and outside.

Draw the shape of the panels onto the extended boards. In doing so, watch the straight alignment of the parts (taut string as a guide), paper easily warps over a length of 5 m.The mirro-like left and right panels can be cut together, place the boards accordingly.

TIPS: Secure boards well with clamps against slipping. A jig saw cuts while lifting, hence the plywood get torn a bit on the upper surface. Therefore place the good face down, and cut with someseam allowance. Afterwards, sand the edges smooth

Stitch the panels & align the hull

To do that, drill holes into the panels: in pairs close to the edges at a distance of about 30-50 cm, closer near bow and aft. Place the panels into the mounts and align them with the help of the construction aids. Tie the panels together loosly, either with cable ties or copper wire. And already it looks like a boat!

Align the boat, make sure the panels butt evenly at the edges. Tighten cable ties. Fix panels in place with tape to stop them from slipping. The seams and the keel must not be wavy – reason for that: a couple of mm inexact cutting and uneven tightening of the ties, resp. Rather fill in a little gap later.

On the large picture the inner construction aids and outher mounts stabilizing the panels are clearly visible. The little picture shows the cable ties, which give the hull the appearance of a hedgehog. The hull is still very wobbly.

Plug up inner seams & and laminate with fibre glas band

Lay the inner side seams with 25 mm fibre glass band and the keel with 50 mm. Laminate with epoxy resin.

After curing, cut the ties on the outside.You can laminate either over the cable ties, or just the sections in between. The first option is faster, but doesn’t look so professionally.

Thickened epoxy & fillet

The runny epoxy resin can be thickened with cotton fluffs, hollow micro-balls or grinding dust (from the belt grinder)

With this stuff seams, or more generally two parts adjoining at an angle, can be glued in a very stable fasion. To do so, the inner side of the angle is filled with the thickened epoxy, a so-called fillet. It should form a nice smooth concave curve.

Glue in bulkheads

The bulkheads close off the cockpit from the compartments. Their distance is adjusted to the length of the paddlers legs.

Install the bulkheads well with ambient thickened epoxy, you may re-enforce the fillets with fibre glass band.

For the forward bulkhead I have used thicker birch plywood, because it has to take the pressure of the feet (stem block). In the rear, the 4 mm plywood used for the hull I decided to be sufficient.

Glass cockpit & bulkheads

The cockpit area and the sides bulkhead facing inwards into the cockpit are more exposed to wear and tear, and therefore should be re-enfored. These areas are glassed with fibre glass cloth.
The front and rear sections of the hull, i.e. the area of the compartments, are varnished only.

Fill outside seams & sand

The hull gains enormously in stability by filling in the outer seams with thickened epoxy. Also, the cable tie holes are closed.

Afterwards, smooth and round off the plywood edges along the seams, because the fibre cloth doesn not lay well along sharp bends.

Skeg & Skegbox

After quite some brain gymnastics a skeg and its housing was constructed, see drawing. The skeg is approx. 30 cm long, plywood and covered with fibre cloth. The wire, 4 mm, is firmly glued into the skeg.

The left picture shows the hull from below. The skegbox is inserted through and glued into a large opening cut into the hull. It is stabilized from the inside with generous fillets.

WIMPORTANT: Laminate or varnish well all sides of the box which are exposed to the water to avoid deterioration. Later, access to the box is rather difficult.

A plastic tube runs from the box below the (future) deck to the rear bulkhead, through the bulkhead and up to about the area where the thigh sits later, on the chocolate side of the paddler.

The tube, here glued in with grinding dust-epoxy, should have as little bends as possible to avoid friction of the wire. More about the skeg-system on the page Finish.

Reenforcement strips bow and aft

Bow and aft as well as the keel suffer from wear and tear. Here are additional xxx useful. Ash, planed to a thin veneer, bends well around the curvatures.

For the keel, an additional keel strip of 5 mm wide glass band might be a good idea, laid over the whole length of the boat.

Sand & glass outer side

Sand the timber, dust well. Place glass cloth (163 g/m2) diagonally to the fibre direction over the hull. This way, the cloth can adjust well to the shape of the hull, and you get better use of the width of the fabric.Glass

After curing, cut the extra bits and sand. Watch out, don’t sand into the glass fibre.

Hull is ready !!