W22 Building Header Building the W22 Trimaran

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September 19, 2013

W22 Build INDEX

Building the W22—Article #4

Starting the lower Main Hull

In Build Article #3, we briefly covered how the CB case was built, using fiberglass 'logs' to create a very strong connection to the main hull. We will now start to create the main hull and at some point, we will be dropping in that CB case and setting the logs into the lower strip bottom.

The Build CD for the W22 includes numerous full size PDF template files for building the main hull, as well as DXF files for CNC cutting. If you have no access to CNC cutting, then the PDF sheets will permit you to print out the same full-size stations as given in the DXF files.

As the lower part of the W22 hull is very contoured and has a built-in flare and knuckle to keep the boat dry, this shapely part is most easily created using narrow strips. These can be of light wood (cedar, kirri etc) or medium to hi-density foam such as DIAB®, Divinycell®, or Corecell®. The boat shown here used Corecell, which gives a strong but light weight result, together with low maintenance predicted for the future. The core strips near the centerline should be of wood or hi-density foam, or plan to add more glass to the skins in this highly loaded area.

Here are the main hull building stations for the lower solepiece as well as most of the permanent foam core bulkheads—all cut with precision.

Building a W22

Pic-1 shows the lower main hull stations being cut in plywood by a numerically controlled router (CNC). Pic-2 shows them all done (except one is missing in the photo). The bulkheads (in ply or foam core) can also be cut using CNC and Pic-3 shows them in Corecell.

PLATFORM

The first step in the construction assembly is to build a platform.

This builder was smart to build his building frame well up off the floor so that there is the minimum of back bending once the work begins.

Building a W22

Pic-4 shows a strong, rigid base and also the required sloped centerline mount for the stations. (This slope matches the drainage slope for the self-draining cockpit, as well as the sheer of the knuckle line, in order to keep the build stations vertical.)

Pic-5 shows the first station being set up nice and square. Note the use of a large steel square as well as a spirit level. Pic-6 shows a number of the stations on the platform—each well braced to stay vertical and horizontal.

FRAMES SET

Building a W22

Once the stations are set up, it's most advisable to check both the keel profile and the sheer of the knuckle line, before attempting to add any strips. Pic-7 shows the knuckle line sheer being checked and Pic-8 shows a check being made of the keel profile using a long, stiff straight edge (from offsets given on the plans).

Pic-9, shows that the builder made a keel template early, so that he could fabricate and mold his fiberglass logs with exactly the same keel curvature and so ensure a good fit when the CB box is installed. (see Article-3)

STARTING to STRIP

Building a W22

If you are using wood for your strips, then you will probably purchase them already cut. It's also doable yourself but requires patience and care to make them well enough to match properly and if they do not, you will waste much time and use far too much filling. In Pic-10, this builder decided to strip in Corecell (a lighter solution), and he made his own strips from a large sheet. The Build Manual recommends to cover one side of the foam with glass and then lay a flat sheet over the glass (with a release film over it) and apply a fair amount of pressure. Even just 0.5 lb/in² over the whole sheet will amount to about 2300 lbs (~1050 kg), so you can see how little a few concrete blocks would compress the panel so make sure your work bench is flat and strong!

Pic-11 shows a flat, cured sheet and the small electric saw (4" blade) used to cut the strips, using a side guide to stay parallel. Pic-12 shows a bunch of strips already cut and 3 of these will then be joined together to create strips of ~23 ft (7 m) length. (Each scarf will be at least 100 mm long.) It's best to clamp each 3 lengths against a long straight rail, so that they line up straight while bonding the joint. Overlap the ends and cut through both pieces together to get a well-aligned joint.

In Build Article #5, we will start the actual stripping and show how the lower main hull will look.


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