Thursday, March 31, 2011

Beams

Back in the days when we were planning this project, we had imagined building first one hull per year, then in year three building the beams and deck structure.

That's not what happened. Because we finished the boat-shop a bit later than we had intended, plus took time off in the summer to go sailing, winter arrived before we had completed our first hull. And a cold winter it was, too! Much too cold to keep working on the hull in our boat-shop. We can heat the shop, but to heat it adequately would be $20 plus per day for propane -- neither ecologically nor financially sensible.

So -- we decided to move to Trevor's heated shop for the winter and work on the beams we had planned to build a couple of years from now.

Our beams are not standard Narai beams. We bought the design improvement package from Wharram, which is based on the Tiki 38, and hence we are building Tiki-style beams which will be lashed rather than bolted.

Assembling the beams has been a long and painstaking process. Each beam is essentially an I-beam with a curved top. The "I" -- the web -- is made from four layers of 3/8" ply, glued together. (The plans called for two layers of 3/4" ply, but we did not have any of that.) The top and bottom of the I are fir -- two layers. Flanges connect the web with the top and bottom pieces; they are also fir.

All the pieces are glued together with epoxy, and held together with bronze ring-nails. The top edge of each beam will be glassed.

In addition to the basic I-beam shape, there are solid mahogany inserts in six locations on each side of each beam. This is a total of 48 mahogany blocks.

Although we'd already bought the wood for the boat based on the cutting list included in the original Narai plans, we had to go shopping again when it came to beam-building time. This was both for the mahogany inserts, and for the top and bottom wide boards on each beam.

2 comments:

  1. Hi, I just found your blog and am enjoying following your build. There are many other building blogs on my website. http://wharramcatamaransforsale.blogspot.com/
    I would recommend that you sheath your beams entirely. Beams are very common places to find rot in the Wharram boats.I would also suggest xynole polyester fabric instead of glass. The xynole will drape easier, doesn't itch when sanded and has better peel strength, abrasion and impact resistance. I like to wet out the wood, then apply the fabric with just enough epoxy to saturate the fabric. The fabric will float if flooded with epoxy. Once the epoxy starts to kick I roll on another coat of pure epoxy to fill the weave and then roll on one more coat that is thickened with micro balloons.
    This way I don't have to sand between coats or worry about blushing and am sanding micro balloons rather than pure epoxy which is much harde. Maybe you know all of this stuff, and maybe you don't. Peace, David

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  2. David, thank you so much for your comments -- much appreciated, and they will indeed be mulled over!

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