Thursday, March 31, 2011

Backbone and Bulkhead set-up

After the backbone and bulkheads are built, we assembled them -- ready for stringers and, eventually, planking.

The process was amazing, and we loved having the first of many work crews (thanks, Pollen and Lisa!) join us for the task.

Note to self (Mary): You're just not tall enough to hold the backbone as far off the ground as it needs to get
to be on top of the bulkheads.


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.


Planking a hull is just fun. It's like putting up the framing for a house -- fast,relatively straightforward, and visually a quick trip from, "Oh, what are you building?" to "Wow! A boat!"
Planking in the plywood-and-epoxy world is particularly engaging, since it happens 32 square feet at a time. Take that, mahogany hand-craftedness!

We did the planking over three
days -- a total of 44 people-hours, with one person mostly mixing epoxy, two nailing, and all three scraping excess glue off. Very satisfying.

"Alpaca side?"

Well, we have alpacas too. And their pasture is on this side of the boat.

The other side is "house side."

This labelling system is not in the original plans.


We made one somewhat unusual decision with the stringers -- and thanks to Trevor, completed one step in the plans that should be done in this early stage, but would be really easy to miss.

The frequent mis-step has to do with shaping the stringers. The plans call for the stringers to be bevelled before they are installed, so that their top edge is level once they're installed inside the hull. This gives a straight, flat surface for cabin furniture to land on.
Its obvious once you've seen the hull right way u
p (or even upside down), but it's not obvious
when you are laying out the stringers.

Trevor built a jig for bevelling the stringers, to keep them all at the same angle. Here it is, partly loaded.

The decision we made was to scarf the stringers, instead of joining them with butt blocks. Trevor's background is in traditional boat-building. Scarf joints are commonplace to him, and he felt that it would give the hulls a cleaner look inside.

We tried a few different ways of cutting the scarf joints, but ended up going something quite simple: stacking the stringers, and planing the 12:1 angle for the scarf joints.

We glued them up on a long (40 foot) bench that runs down the side of our boat-shop. Each piece was assembled from three pieces -- two 16s and an 8.