W22 Building Header Building the W22 Trimaran

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June 20, 2013

W22 Build INDEX

Building the W22—Article #1

As most readers will have noticed, plans for the W22 are finally ready for distribution. So in this first build article, I can now share with you some pictures of the first boat taking shape.

Just one of several unique aspects of the W22, is that she combines several different boat building methods, with the best method being used to construct the part it is most suited for. It's hard to believe that someone will be bored building a boat like this, as there is something new and interesting going on all the time.


Typically, a builder will start with the amas. Particularly with a demountable boat that is designed with enough ama buoyancy to carry a powerful rig and even lift a main hull on occasion, it will be advantageous for each ama to be as light as possible—just for the ease of handling ashore. And as amas seldom have to scrape across the river or sea bed, the use of a semi-rigid foam core makes sense. So ama build-stations are supplied in full size format and in female format—meaning that the ama sides are to be built 'inside' them as you'll soon see. Using strip-cedar is another option. See below.

So for this W22 Build Article #1, let's take a look at how these amas are built. First the female stations (spaced an even distance apart) are to be cut out. This can be done in two ways; either by taking the DXF file (on the supplied CD) and having the parts cut by a numerically controlled cutter, or by printing out the print tiles on regular letter paper and laying them on a grid board that you have pre-inscribed with accurate rectangles, all as clearly defined in the Manual.

There are two construction options for the ama. One is to use vertical foam strips as the core and the other is to use strip cedar (or kiri/paulownia). The vertical foam strips will need to lay in against longitudinal battens for support, so the female stations have a line 19 mm back from the outer foam surface, to give space for those 19mm battens. In the case of using strip cedar strips, these can be laid directly against the stations, so the latter should be cut to the inner line, not needing the 19 mm extra space. (Strip cedar has the potential to make a more rugged ama but will be about 10–12 kg heavier—see note below.)

Most builders already have a good idea about building with wood strips and as even more information and links are given in the Manual, let's concentrate here on building with a foam core.

We need a foam that is not too rigid or brittle but neither too soft or rubbery. Corecell™, Divinycell™, or Airex™ are ones that I would rank as most suitable. While I recommend 38" or 10mm for the amas, the first builder had such a good deal offered to him for 15mm Corecell™ that he decided to 'go for it', despite the weight increase. Personally, I'd not go over 12mm but 15mm can still work.

(One can roughly figure on 4 cuft of foam per ama, so say 20 lbs for 38" (9.5mm) foam. So using 15mm will add about 5 kg. Strip cedar would appear to add about 32 kg but roughly 20 kg of this will be offset by the use of thinner FG skins.)

Building a W22

Pic-1 show the female stations set and the first strip of foam being laid in. Notice that 50mm (2") packing tape is placed around each batten under the edge of each foam strip (about 300 mm wide), so that epoxy at the joint does not stick to the mould. At the gunwale, there's an option. One can either heat the foam locally to make the sharp radius to continue over the deck, or one can run it to the deck gunwale height, stop there, and later, drop in a flat plywood deck with foam laid over it. Either will work, with the former meaning less work to complete the deck. However, the latter was part of the original design as it gives easy access to seal the keel joint on the inside, without the need to make a number of temporary openings in the deck. (See later.)

Pic-2, shows the foam being heated using the fan head of a heat gun. After first heating the outside, the foam will then curve into place. (Experiment with a piece of scrap to see what area must be heated and by how much, and then mark that location in both sides of the foam.)

Pic-3 shows all the vertical foam strips fitted in place, and Pic‑4 shows the joints lightly grooved out and then filled with thickened epoxy.

Before the interior glass is laid in, a foam stringer is added from near the bow, back to about ⅓ ama length, with its sides well beveled to allow cloth to roll over it without bubbles or folds.

Going to the next picture block, Pic-6 shows the bias cloth being laid-in prior to rolling on resin and Pic‑5, shows one ama half, almost complete, with the specified cloths laid neatly over the internal stiffen. Pic‑7 shows the first ama half being removed from the mold. After two such halves have been made (one for each ama), the battens need to be unscrewed and then stations rotated 180 degrees. Once the battens are re-installed, two more halves will be created so that you will have 2 rightside and 2 leftside half-ama hulls. Into the 2nd ama halves, you will need to fit, bond and tape-in the bulkheads and transom, plus a couple of partial bulkheads where the beam sleeves will sit. See Pic‑8.

Building a W22

Once the interiors are finished, the matching halves can be fitted and bonded together. You might find it easier to fit the trampoline attachments and the shroud chainplate before closing the halves, though these can also be done through deck openings. (See later.)

Once the butting deck edge has been trimmed straight and mating keel surface matched (Pic‑9), the two halves are bonded and strapped together, making sure you use a length of flexible timber to press against the outer hull sides to avoid deforming their shape.

The exterior is then given a fairing with a long board, after which a light recess is made in the exterior of both hulls to take an additional reinforcement where the ama may later nudge against a dock (Pic‑11). This is best done with a router as is shown in Pic‑15 and need only be 1 mm at most, Just enough to lay the next full layer over a flush surface.

The hulls are then sheathed with the final layers (as per plans)—see Pic‑12.

Building a W22

During the covering of the hulls, the aft transom corner is left rounded, so that the cloth stays tight to the foam surface. But once complete and cured, the transom side corners are then squared off with added epoxy filler as this is more efficient for a cleaner water flow at speed. See Pic‑16. Interior stiffening is added for the transom rudder pintles.

It's then time to make two sets of solid supports for the amas, preferably fitting these at the bulkhead locations and also adding foam liners to treat the hulls gently, as per Pic‑13.

Once turned over, it will depend on which deck solution was chosen. If of foam extending around the deck and gunwale as per the example shown here, then you will need at least 5 temporary openings in the deck (see Pic‑14) in order to fair-in the keel inside and to lay in at least two tapes. You will also need this access to complete the sleeve mounting for the akas as well as for the trampoline connections and deck cleats. These details will be shown in Build Article #2. If you choose to use a drop-in pre-sheathed ply deck, then you will need to bond in a gunwale to support this, making sure the deck widths are correct at each station. But keel and reinforcing access will be easy. Once the ply is in place, then two layers of 10-12mm foam will be laid on and bonded to the ply, before the upper corners are rounded and at least two layers of cloth are added. But this deck closure is best done after the aka sleeves are in place and these will also be shown in Build Article #2.

(Keep in mind that these Articles are only supplementary to the official 70‑page Build Manual and do not replace it. They are published freely however to explain the various steps and add further photo illustration. More coming soon ;-)

Building a W22

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