W22 Building Header Building the W22 Trimaran

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July 19, 2013

W22 Build INDEX

Building the W22—Article #2

Article #1 covered the basic hulls for the amas; so let's now look at how the akas (cross beams) will fit to the amas, how shroud chainplates might be made and attached, and also look at one way of attaching the important trampolines.

Aka Sleeves

The akas (or cross beams) will either be of aluminum mast section or can also be built of carbon fiber—details of which are in the Build Manual. As these will slide into sockets or sleeves mounted into the ama deck, you will first need to find the beams you wish to use and then build a short sleeve in fiberglass around that section. In order to provide a little clearance, it's good to first wrap the beam end with a thin plastic—say 0.5 to 1. mm thick and then add the fiberglass—making enough turns around the beam end to create about 3 mm of thickness. See photo 2.

Building a W22

As the sleeve will lay 'into' the deck, the outer ¾ of the deck will need a hole cut out the width of your beam. To compensate for this, the plans call for a strip of UNI carbon fiber (~750 × 100) to be added along each sheer—tapered off at the ends. The sleeve will fit directly over two bulkheads in the ama—see Pic 1—and both the outer and inner ends of the sleeve will be attached with tows of UNI carbon fiber, that pass over the sleeve, go down through the deck and are then either spread over an inside bulkhead or fanned out over the exterior inboard surface of the ama prior to fairing—see Pic‑4. The sleeve will also need to be located at 10° to the ama deck in order to give the correct ama inclination. See Pic‑3. Also, as there is a little toe-in on each ama, there will be a slight angle to the sleeve in plan view. See Manual for more detail on this.

Trampoline attachment to the ama

There are many potential attachments to the ama deck. One option is to fit a small CF or FG tube in a pocket at the outer edge of the trampoline and strap this to S/S D-rings, bolted to the deck. Another is to create retaining hooks in CF that will hold the tube and these are detailed in these photos. The design is somewhat like a question-mark—"?"—and initially, only the top 'hook' is molded solid.

Building a W22

In Pic‑5, several layers of CF are compressed between wood boards and then rolled over a PVC tube to create the hook (Pic‑5 & Pic‑6). The lower part is left dry for the moment. Once cured, the strip so‑formed, is cut into lengths of about 38 mm (1.5"). These are slotted down through the deck at intervals of about 400 mm and then, the dry tows of CF at the bottom are spread out and epoxied to the inside surface of the ama side, with a light cloth covering them. The 'hooks' are further reinforced with short tapes added both inboard and outboard of the hook (Pic‑8).

The shroud 'chainplates' can be traditional S/S bolted straps but preferably made of carbon-fibre. The Manual suggests one way, but this builder create his by laminating a 1000 (40") length of UNI about 4 mm thick and then cutting this into 4 strips. Pic‑7. Each strip was then slotted down through the deck, one each side of the slightly inclined shroud bulkhead, and then bonded in place with a couple of good through-bolts, after checking the angular alignment given in the Manual. Between the straps that will extend about 50 mm above the deck, the space was filled with bars of CF running parallel to the deck and well bonded to both the deck and the straps. Once cured, 5–6 holes can be drilled through the completed 'block' of CF, with each well‑countersunk and rounded, so that a rope (spectra/dyneema) lanyard attachment can be used with many parts. This is strong, light and infinitely adjustable.

Pic‑9 shows an experimental fairing procedure of first adding filler to a hull in strips and then filling the space between with more filler. But finally, this proved more work than just laying on thin layers of filler over the whole surface and shaving it fair with a long board equipped with some form of grip or handle. Add a little different color to each coat so you can see what you are sanding.

Pic‑10 shows the added sharp corners to the transom bottom and sides that will enhance water flow and also shows the mounting of a rudder blade holder—these coming from a retired beach cat of 18 to 20 ft. Even if slightly larger blades may be needed, using the holders can save work.

Pic‑11 gives an overall view of two amas after completion, painted with their first coat of primer.

Building a W22

The next W22 build article will cover a little about the cross beams (akas) and also show how the centerboard case is put together, prior to starting the main hull. Look for it sometime in August.


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