Preparations

Latest updated Friday, September 18, 2020, 26 comments

station molds | the inner stems | cut strips | the strongback | attach the molds | attach the inner stems

Station molds

Trace the station molds onto a 12 mm particle board or plywood. This can be done in many ways - this is one: cut a small hole (3x3 mm) in the drawing where the centerline and waterline meets and small holes on the waterline extreme left and right. Draw a waterline and a centerline on the board, using the edge of the board as baseline. Position the plan correctly over these lines and mark the station perimeter with an owl. Flip the plan over, center it over the lines and mark the other half of the station. Remove the plan and draw the station by connecting the marks. Draw the centerline and waterline. Mark the sheer. Draw a new centerline on the board and continue with the next station, until all molds are done. Cut the molds with a saber saw or bandsaw - following the vertical lines to the baseline (leave the deck for now).

Inner stems

Draw the stems in a similar way, marking the waterline. As with the molds leave material to the baseline - it is easier to attach the stems if the can rest on the strongback.

Cut strips

There are in principle two ways to strip a kayak or canoe: using bead-and-cove strips, gluing the strips one at a time with carpenters glue, and using square cut strips, working epoxy into the seams afterwards. The end result is functionally the same with slightly less visible seams with the bead-and-cove method. For the first method buy milled and routed strips - doing this yourself is a tremendous waste of time, unless you have a fully equipped professional shop. For the second you only need a handheld circular saw with a fine-toothed furniture grade blade.

The strips should be approx 18-20mm x 5mm. Wider they resist bending, narrower there are more seams to fit, which takes time. The length is not important since scarphing is very easy and quickly done. Look for boards with as few knots as possible and reasonably strait grained. But above all - look for low density.

When you calculate boards, remember the blade takes 2-3 mm for every strip. Check the adjustment of the saw: 4,7 mm is OK but 5,5 is unnecessary thick. Moisture content is not critical - when the strips are cut, a day or two in the shop will have them dry enough for building.

The number of strips required depends on hull type, length, beam etc but approx 75 strips for a kayak and 60 for a canoe is a reasonable approximation. Some 30% of the strips are full length (as is or scarfed), the rest is decreasing length.

I prefer using a handheld saw instead of a table saw. Moving a small saw along a stationary board is easier than moving a 5-meter board over a stationary saw, with less risk of breaking the thin strips.

Attach the board with thin nails to a couple of saw horses, adjust the fence, put the earplugs in and get ready for a couple of rather boring hours. The odd strip may be waste when the saw wobbles because you happen to stand on the cable. But it doesn´t matter much - you will need a lot of short strip pieces before the kayak is done.

Planing?

Do not bother planing the strips. First, it is unnecessary work as you will have sanded every square inch before the hull is done and secondly: there is a risk of smashing the strips when the blade hits knots or other imperfections in the strips. Especially fir is notorious for deceptively hard knots.

Routing?

As stated above I do not think routing is a good idea. Too much work compared to the expected advantages, and with normal amateur shop equipment it is hard to maintain the precision needed - and without perfect precision, you are far worse off than with square-cut strips. So my recommendation is: cut and start building - or buy professionally milled and routed strips.

Bead-and-cove strips may result in almost invisible seams ("may", since the odd imperfection will show up against an otherwise perfect surface like the proverbial sore thumb). Square cut strips will show seams as thin (typically 0,1-0,2 mm) slightly darker lines. Not unattractive since they are even in thickness and follow the sheer like on a carvel-built yacht. An alternative way to invisible seams is to use a small plane to adjust the angle of each strip.

Is routing an unavoidable temptation? Visit One Ocean Kayaks web site for instruction.

Strongback

Time to prepare a strongback. This can be done in many ways. The only requirement is that it provides a stable surface for attaching molds and stems. This is my favorite: two long 1x6" boards with ends nailed together, a spreader inserted in the middle and the hole construction positioned on a couple of saw horses. The length approx the hull length and the width a couple of inches narrower than the hull is optimal. A string tensioned along the strongback will be a reference line for attaching the molds. Check the strongback using a spirit level - it is easier to get the molds correct if the strongback is horizontal both ways.

Set up the station molds

This is one of the two critical tasks, where a little extra care will pay off (the other being sanding). Measure and mark the mold positions on the strongback. Attach short crosspieces of 1x2" at the marks like this: stations 1-6 with the aft edge against the mark, stations 7-12 with the front edge against the mark (the reason for this is to avoid having to plane the outer edges of the molds to an angle).

Attach one mold at a time with a clamp against the crosspiece: mold 1-6 aft of the 1x2", 7-12 forward of them (like this). Adjust them vertically and horizontally and make sure they are positioned exactly over the reference string. One neat way of doing this is to drill a small hole (4-5 mm) in all molds where the centerline and waterline meets - then a lamp at one end showing through all the holes will have all molds positioned in a straight line.

Normally the edges of the molds are taped to prevent excess glue to stick to the molds, but lately, I have come to regard this as an advantage: the strips are held perfectly to the molds with no risk of staples becoming loose during the work. When the hull is finished it is easy to tap the molds lose and to sand away the small pieces of particle board that may adhere to the inside of the hull.

Precision

Every mold is adjusted in three dimensions - sideways (left-right), height (up-down) and angle (vertical-horizontal).

I start with a spirit level to ensure the waterline is horizontal. Then I tap the mold sideways to position it exactly above the reference string. A precision of +/- 1 mm is enough since more accuracy takes unproportionally long time, and this is within the tolerance of a normal draw and cut job. Make sure that any small inaccuracies are divided randomly to both sides - consistent curves in the spine of the kayak may lead to paddling in circles.

At last I check the height, adjusting the molds so the keel is a smooth and even curve without bumps. Check with a batten or strip, held at different positions along the bottom of the hull.

When you are satisfied, fix the molds with a couple of screws into the crosspieces.

Inner stems

The inner stems are there to give the correct shape to the stems - they do not contribute much to the strength in the finished hull. The dimensions are therefore not critical.

• Sawn stems (most kayaks): cut the stems (fx from fir or plywood, 8-12 mm thick) and attach them in the position given by the plans and the waterline mark on the stem. On most hulls the stems terminate at mold 1 and 12, but on kayaks with long overhangs, the inner stems may be let into mold 1 and 12.
• Laminated stems (Canoes and a few kayaks with short stems): cut thin (approx 3 mm) strips 1 meter long. Laminate four of these (glue with thickened epoxy) over a particleboard mold.

Shape the stems, creating a large gluing surface for the strips. Draw a centerline along the stem. Hold a strip to mold 2, 1, and the stem and mark the angle. Plane to the mark, leaving the centerline intact (it is your reference that the profile remains correct). The stem will be pointed at the sheer but open towards the keel.