Sunday, February 17, 2008

Crossbeam Fairings and Reinforcements

There are still many details to finish on the crossbeams, mainly the exterior fillets and the fairings. Before installing the fairings I wanted to shape all the edges of the Doug Fir stringer sections to a consistent radius. This was done using a router with a 3/8" radius roundover bit. In the photo below you can see the radius on every corner, including all four corners of the top plates and the exposed corners of the bottom plates. This radius will help protect the beams from damage by eliminating sharp corners that can be easily cracked or broken if something hits them. It will also allow for easier fiberglass sheathing, as I plan to glass over all the exposed surfaces of the beams.

The transition between the plywood webs and floors of the beams is also eased with a concave radius formed by a nice, wide fillet that is both cosmetic and structural. It takes a surprising amount of thickened epoxy to make all these fillets on the beams, as there are so many exposed corners that require them. All in all, building the beams for the Tiki 26 is a substantial project; even more time consuming than building the mast. It would be quicker to skip the fiberglassing step, with all this preparation it involves, but for maximum longevity this is important. One thing I don't want to have to do is replace major components like the beams sometime in the future because of rot or damage that could be prevented by these extra steps.

Below: All corners have been rounded and exterior fillets started.

At this stage before the fairing goes on, there are also extra reinforcing parts that must be installed on the mast beam, which will bear a much greater load than the other two. Here you can see the top plate doublers that have been glued on in the area of the inner hull gunwales, and the vertical compression struts that connect the top and bottom plates in these areas and at the beam center point, under the mast step.

After the epoxy cured and clamps were removed from these parts, the fillet under the aft edge of the top plate was made. All these fillets will be sanded and touched up as needed until they are smooth. When glassed, faired and painted, the beam parts will hardly be recognizable as wood, but will instead look molded out of fiberglass or plastic. The smoother they are, the less the possibility for moisture to hang around and cause rot.

I did the cutting and fitting of all the beam front fairings this morning. When they are installed the bottom edge will be shaped to match the leading edge of the beam floors. This corner will be filled with thickened epoxy and then rounded off to match the radius of the other corners.

The first step in preparing the fairings for installation is to coat the inside with two coats of epoxy. Here the first coat is drying while the parts are spread across the beams, which also have fresh epoxy fillets curing. This is where I left things at the garage shop this afternoon. The weather is supposed to be good for the next three days or so, and I will be back at the boat shed working on the hulls as much as possible.


tsunamichaser said...

Hi Scott, Your beams are looking good. You're on the right track glassing the outside of the beams. As you saw in my last post I've sufferred a small amount of wear on my aft beam. Right through the glass too. I'll be interested in seeing how you attach cleats, tramps and all the other stuff. It's painstaking work if you plan to plug every hole with epoxy. I drilled every hole, pre attached everything, took it all apart and then syringed epoxy into the holes and then bedded all the fasteners in 5200. I think that in the long run beams made of aluminum would be the way to go. They carry such a significant load


Scott B. Williams said...

Hi Thomas,

The beams are always a problem because of the wear points where they land on the deck, the attachment of the cockpit tray, etc. I plan to add extra layers of glass at these points, and try to keep the holes drilled to a minimum. The hardware mounting holes will be drilled oversized, filled with epoxy, then drilled the correct size. For the trampoline lacings I'll attach seperate teak rails with lacing holes to the beams to eliminate the need to drill through the beams themselves. Aluminum beams would be less trouble, but they sure wouldn't look as nice. It's also neat how the beam design incorporates the hanging attachment for the cockpit tray.