Prepping To Cover the Boat's Bottom

Fig 1.  Marking board that is the same width as the frame and is notched
to clear
the protruding chine and plywood edge.  The darker board is there to help hold it in alignment.

Now that the sides are finished, it's time to prepare those sides for the bottom ply sheathing.  Because the chine and plywood edges are 90 degree edges. We have to trim those edges at an angle to match the boat sides so that the bottom plywood will lie flat.  We also need for the plywood sides to assume a nice, close fit to the bottom and not have humps and bumps that keep them from lying tightly on the frame bottoms.  Just as the frames created a nice fair curve for the plywood sides, we need for those same frames to create a nice fair curve on the bottom.  How to accomplish this?...


Figure 2. Frame bottom transferred to outside surface of side.

To prepare, we need to mark the outside plywood surface with the frame's bottom edge, basically extending that edge through the plywood.  This was accomplished as seen in Figure 1.  Once finished we will end up with a series of marks that look like the ones shown in Figure 2.  One thing to note is that the bottom of this boat is a continuous curve from front to back.  This creates rocker.  In a boat's design it provides maneuverability.  You can spot this gradual arc by the horizontal frame pencil line in comparison to the edge of the plywood. See how the left side is closer to the edge of the ply than the right edge of the line?  And obviously the bottom is sloping from left to right.  That bottom ply will contact that left edge of the frame.  When the boat is flipped upright, we will fill in that gap with epoxy creating a structural joint, as well as, using screws to hold the bottom to the frames.


Now that we have all of the lines drawn we will place one screw at the end of the line closest to the plywood edge. (in figure 2 taht would have been at the left edge of the pencil line).  Again, this represents the edge of the frame closest to the bottom and the one that the bottom ply will come into contact with when screwed and glued down tight.



Fig 3. Screws driven along pencil line temporarily to rest the batten on to drawn a fair curve.

Figure 3 shows this.  This particular screw is located in the middle of the line as it represents the Station 12 frame, the middle and flattest part of the boat's bottom.  What this picture also shows is the spline or batten strip resting on top, not attached.  We prepared this by ripping a 1/4" thick strip out of some scrap 3/4" pine, 12' long.  When bent along the tops of the screws, the spline gives us a nice fair curve that gets us much closer to what the finished boat's bottom will be.  We will used thickened epoxy along this joint which is gap filling but the closer the better.

Figure 4. Line marked along top edge.

Now that we have a line to follow its is time to chose a way to cut down the edge protruding above the frame level to that line.  It's a good bit of material to remove and we wanted to get it as cut as quickly and accurately as possible.  We eliminated a power planer since the amount of waste to be removed varies and might be hard to keep level. We eliminated the jig saw because it was such a gentle curve and decided on the circular saw.  It can handle gentle curves easily and has a foot that can be adjusted at an appropriate angle to handle most of the cut.  Things get steeper near the stem so we will have to use the planer to level down to the frame.  We used a bevel gauge to establish the angle and transfer that to the circular saw foot.  Unplug the saw first.  We used a clamp to keep the guard back while we transferred the angle to the saw.  See figures 5 & 6.


Fig. 5  Getting the angle using the bevel gauge



Fig 6  Transferring to the saw to set the angle.

 Now its a matter of carefully cutting along the line and getting used to the flavor of marine plywood with a hint of epoxy.  By the way, wait till the epoxy is fully cured. Green epoxy will gum up your tools and is still unhealthy to breath when not fully cured.  Here (final few pictures below) is the result with some minor hand planing to finish off.  Note that it is fairly level now and ready to provide a fair surface for glue and screws.  This wide edge will provide a nice glue surface for the bottom ply.