by Bill Meier
During the lofting and construction I made a few minor changes to the boat as designed and built by John DeLapp. I also ran into a few complications that I wanted to document. I lofted the keel as a 1x6 timber – wider than John specified - using the cross sections to develop the fore and aft curve that would transition smoothly into the stems. I'm hoping that it will provide a wider, flat surface for feet when I'm moving about in the boat, avoiding the need for floor boards or other additional complications. I also increased the height of the chine log a bit so I could bevel the top surface to avoid having water collect against the sheer strake. The hull is made from 6mm bruynzeel plywood, which I think is a good choice in spite of some issues I encountered.
First, the sheets I was able to buy locally were only 48 1/4 inches wide, not the 49 1/4 inches I was expecting. I don't know if the standard size changed over the years but that was what was available to me, so I went with it. I made a full size pattern of the bottom piece using cheap door skin plywood and carefully laid it out on the bruynzeel so I could just squeeze two 10 5/8" sheer strake pieces. Because the tolerances were so tight, I had to glue the scarfs in place to get the angle perfect. Actually this worked out very well. I used plywood backer pieces and wax paper to keep the joint fair when it was clamped up. When the epoxy had cured I removed the sheer pieces and sanded the joints smooth. The inside joint was close to perfect and the outside just needed a bit of ultralight fairing compound and epoxy to make it (almost) invisible. The sheer at the middle station was maybe 1/16" below the design height but I can't see that being a problem.
The larger issue I had with the plywood was in bending the bottom pieces. It took a great deal of clamping to get the ends to lie flat on the stems and when I had it clamped down the chine log pulled out of the #4 molds about 1/2" - even though they were screwed down tightly - and the chine log to stem joints cracked even though they were epoxied and screwed. Of course, all this happened not when I was dry fitting the pieces but when the glue was already on!
In addition, the plywood fractured at the point where the keel transitions into the stem. I drove some additional sheet rock screws on either side of the fracture to keep it flat and decided to deal with the chine-stem joint with epoxy filler when the hull was turned over. If or when I build another Natoma I'd be inclined to widen the #4 mold slightly to reduce that stress. I don't think it would change the looks and the somewhat wider section forward would provide a bit more buoyancy and dryness in the kind of chop we get in Fishers Island Sound.
A boatbuilder friend told me that applying boiling water to the plywood while bending it makes it more pliable but I was reluctant to pour water on my wooden shop floor and I didn't want to wait another day for the plywood to dry before gluing it down. That was a bad decision, although not a fatal one, fortunately.
Due to the thicker plywood, I ended up needing 1/2" half oval trim at
the ends. I ground down a bit at the lower 12" so it would transition smoothly
into the bottom and I did a little grinding at the top where it bends over the
breasthooks to improve the look a bit.
The only other change I made was to move the aft thwart forward about 9 inches to improve the trim when two large adults are in the boat. It was my impression that the boat was a bit low in the stern with two full sized adults aboard.
In spite of these few challenges, the construction went very smoothly. The transition between the bottom piece and sheer strake as they overlap at the ends was exactly as you had drawn them and adds substantially to the beauty of the boat. The riggers as designed are both elegant and functional. I built a form and laminated them from thin (0.1") honduras mahogany veneers. Even at 0.1" the veneers needed to be steamed avoid splitting but with 10 minutes in the steam box I had only one failure in twelve attempts. The thwart knees were made from laminated douglas fir, scraps from the stem material. Fortunately I was able to bend them dry with no problem. The foot stretcher (I only made one for the primary rowing station) was made out of some red oak I had lying around the shop. I glued it and screwed it through he bottom, so I hope I got the positioning right.
Besides the vertical grain douglas fir I used for the stems, I used cypress for the keel, chine log, breasthooks and thwarts. It is almost as light as Eastern white pine and has better rot resistance. It was also available locally - although it was not cheap. - and I like the look of it. The interior finish is Interlux Bristol Beige for the bottom and Petit Captain's varnish for the top. The outside is two coats of Petit EZPoxy.