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Making the Curved Outer Beams for the W17

BeamBefore showing how the Outer Beam ends are assembled, let me say that because the beams of the W17 have been designed to give very high strength for relatively low weight whilst using relatively inexpensive materials like plywood, timber and glass, they will take more time to build than one might first estimate. But although these are perhaps the trickiest part of the whole boat, they are also the most rewarding once done, giving the W17 important wave clearance as well as its distinctive look.

Work preparation
To clamp the beam parts together, you will need a good number of large 6–8" clamps—sometimes called 'F' clamps, typically using a sliding arm to quickly adjust in opening. Figure on 14 clamps if you're ready to do one side at a time or 28 if not. But such clamps need a little 'preparation' if you don't want to be challenged with cleaning off rock-hard epoxy from the main stems. It's virtually impossible to avoid the occasional epoxy drip on them and once in place, it's very hard to wipe off this excess.
So first, make sure they are clean and the adjusting bar slides easily over the entire length (best when new), and then wipe the main stem with an oily rag or light grease film. The reason for this is to prevent epoxy drips from bonding to it—making them very easy to clean afterwards. Otherwise the essential little teeth that stop the adjustable arm from slipping, will soon become clogged with epoxy and difficult to clean.

Building the curved W17 Outer Beam
BeamFor the Outer beam ends, first cut out the four pairs of plywood webs. Personally, for any shape that will be repeated three times or more, I always make a template of it first and then, trace around that. In this case you'll need 8, so even a good plywood template makes sense. Then cover the interior of each web with 6oz cloth laid as shown in the sketch under Task 9 of the Build Manual.

You then need to put together a few simple assemblies. The core framework that will take the hinge load is the first of these. For the top and underside of each beam, you need to bond a 600 mm length of clear timber between two side rails (sized as per plans) —see pic. The after beams will require similar frames, but be of 20 mm less width. Once these frames are cured, bond on a rectangular plywood 'hinge plate' to the inner end of the inside, as was done for the main central beams.
Then cut out the center as shown on Plan W17–10 to optimize weight relative to strength. (A small bridge has been left to maintain constant width). In the meantime, glue up four end blocks from several thick pieces to create a 3" total thickness that will serve as the solid end-block through which the BeamBeam attachment bolt will eventually pass. You can use lightweight cedar for this as, with a tube bonded in to limit its compression, there will not be much load on this block (see Plan W17–12). Once rough-shaped, you can drill the sides with six 25 mm holes about 30 mm deep, to lighten it. Leave the center solid for the shroud eyebolts. See pic.
BeamUsing the side webs to guide location, clamp the end block and core framework in place. Make certain that the top, sides and underside are all square to each other. You can then cut, shape and fit the small link pieces to connect the core frames with the end block, both above and under.

Check repeatedly with your square to make sure the two webs stay parallel to each other. Now, ideally with your router (or a small grinder), create a small recess in the end surface—say about 0.04" (1 mm) deep. If you used a router to make your scarfs, then clamp on two temporary side rails to the outer-beam sides and use the same router box to make a neat recess. Then lay in a 24oz bias cloth with light mat and level it flush by temporarily clamping a ply over it.


An isolating sheet of plastic or wax paper will prevent it bonding in place. Repeat this on the underside also for all four outer beams (see pic).

BeamThen pre-form the thin inner ply sheets by making them wet on both sides and then slowly clamping them into the inside curve of the beam webs. By the next morning, they will be ready to use. First of all epoxy-coat the outside curved surface of each piece. This will become the inside once bonded in place.

Then lay a 6oz UNI cloth between the two ply layers and wet out. Finally, sandwich this in place and clamp the two plies with glass sandwiched in between, to the inside of the web curve. See pic. Clean up the edges after it's cured and put a radius (equal to ply thickness) on the corner.
Beam Beam Then pre-form the external ply to shape, again using a wet towel if necessary. When dry, epoxy the inside curved surface and when cured, bond in place. Note that you'll need to screw a small block (cut diagonally from a 4" length of 2" × 2") to provide a good grip for the end clamps that will do most of the work. After cleaning up, bond another light UNI cloth to the top and bottom surface and over-sheath the complete assembly with 6oz (200g) boatcloth.

BeamIt then only remains to fill the cloth weave with filler and sand smooth, before the hinges are mounted. See full details in the Manual for this.

The forward beam fairing will be added after the beams are installed on the main hull.

See here for Main Beam construction.

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