At the start of this post, the state of the boat is it’s upside down (stem is pointing downward) and the chines are attached to the stem and the transom.
The boat needs to be prepared for eventual flipping at this point as access to adjustable blocks will be impossible once the bottom is on. To do this preparation, the adjustable blocks at the 1/3 and 2/3 stations were removed and replaced with temporary solid pieces (with the correct angles) that spanned the boat’s width. This was done because we want to retain the chines shape after the boat is flipped from upside down to right-side up. The temporary solid pieces were attached with screws through the transom.
The chines “Bottom” need to be trimmed up so the plywood fits flush on the chine (i.e. the chine bottom is still square). We found the easiest way to do this is to lightly clamp a batten board along the chine so the tops of the chine and batten are relatively flush. Aside: a batten board is a long narrow strip of board that flexes easily, and for this trick, the batten board and chine thickness need to be the same.
Next, we put a straight edge across the beam and lowered the batten until the straight edge touched both board’s edges. This process was done at about 10 locations along the boat, adjusting the batten board along the way. When complete, we had a batten board that was slightly lower than the chine. Then we scribed a “trim line” along the batten. The batten was then removed, and the excess wood removed with an orbital sander (a plane could be used but a sander worked good for us)
After the chine is all trimmed down,the plywood is ready to be put on. We got this plywood from Dysons Lumber.
The aft piece of plywood was first placed on top of the chines, lined up with the stern, secured with clamps, then the chine outline was traced on the plywood. You may notice on the pictures in this blog that clamps have water bottles on them and that is to prevent running into them with your head or eyes. After tracing, the plywood was then removed and the outline cut out with a jigsaw, having the cut stay on the outside of the pencil line. At this point it is understood that the jigsaw cut is vertical, but we will shape it after permanent attachment with the orbital sander.
The plywood was placed back on the chines and the screw locations were marked at every 6” to the chine. The “inboard” screw location was marked using a custom homemade tool that skirted around the small amount overhanging plywood and placed the marking point in the center of the chine’s width. The screw holes were then drilled using a taper bit with countersink (aka Fuller Bit) sized for using a #8 x 1-5/8” screw.
Homemade Screw Hole Marker
The plywood was then removed and good amount of PL Premium placed on the chine surface. The plywood then replaced and the screws were attached in a manner to go from the stern to the front. As a note: temptation would have it to secure the “4 corners” but that is not a good habit to get into in boat building as securing should be done sequentially, one after the other, to capture curvature firmly. The screws used were 1-5/8” stainless steel obtained from the hardware store. Although the screw’s packaging didn’t denote what “kind” of stainless it was, but these hardware store screws are typically 305 SS which is probably OK as none of these fasteners will be inside the fiberglass, and not see the galvanic action that would make 316 SS necessary. After all the screws were fastened, the PL Premium was allowed 2–hours to firm up (but not harden), and then the excess was easily and cleanly scraped away.
The same process was performed on the front piece of plywood. The seam between the 2 sheets is a butt joint and we used Glen-L instructions for reference (http://www.glen-l.com/wood-plywood/scarf-butt.html) and we used thickened epoxy between the 2 butting surfaces.