Side Panels Cut and Scarfing Plan

 With this plan I cut both sides and both sheer-strakes from 5 sheets of plywood.

cut plan

 

sheet 5 cut plan

My cut plan aligns the pieces slightly different.  If lofted directly from the plans the pieces fit, but allow little room if I decide to raise the top of the sheer line of the sheer strake.  By rotating the side a few degrees and rotating the sheer strake 180, I gain a wide space in between the two.  I've drawn the possible rise of the sheer strake top with extra lines in the bottom drawing..

 

Sanding my scarf joint

One of the purposes of a scarf joint is to maintain the plywood's thickness.  When sanding down the first of my scarf joints I came up with an idea for a "leveling" sanding block.

 A found a good flat piece of red oak scrap in my shop and checked it's flatness with a metal straight edge.  I then affixed sand paper to the center of it, using a 6 inch peel-n-stick sand paper intended for a random orbital sander.  I don't know why I had this laying around my shop as I don't own a 6 inch random orbital sander (mine's a 5 inch model).  Using a digital caliper I measured the thickness of the board and sand-paper together and then added layers of tape at both ends of the board to achieve the same thickness (approximately).  In my case I used three layers of an aluminum metal duct tape.

 On the scarf joint not only did the epoxy need sanding, but the thin edge of the scarf was pushed up or curled up a little in places.  I used the random orbital sander to take down the bulk of the high areas and then used the sanding block to finish.

Using a regular sanding block to level a surface would require periodically stopping to check progress using a straight edge.  This new block checks the flatness during the sanding with not one, but two methods.  First when the block is over a high spot, the ends of the block will see-saw up and down.  The smaller the amount of see-sawing the closer you are to being flat.  Second, when actively sanding you can feel the bite of the sand-paper.  When the high spot is sanded away, the sand-paper no longer bites and the block slides more easily with less friction (being then supported mainly by the tape on the ends).

Now you might say a really long sanding block will also flatten a surface.  But I think that the ends of such a sanding block can't help but sand areas other than the high spots.  This block only has sand-paper in the middle of it to concentrate the sanding on the high spot while 'leveling' to a much longer area.

 

 

The second Scarf Joint and The Process explained

I had two worries when it came to gluing up a scarf joint.  One was to keep the alignment of the two pieces of plywood parallel (within reason) and the second was to prevent one taper from 'climbing up' the other taper by being pushed too far (making the joint thicker than the plywood).  The "stepped-scarf" method would have easily dealt with both these issues, but the tapered scarf has both these possibilities.  

After some consideration I came up with this process.  The first piece is turned taper down and secured tightly to the table with screws.  This makes it such that pushing the second piece against it, the tapers cannot climb up (not without tearing the screws securing the first piece out of the table) and the two pieces align parallel simply by being pushed together until they can go no further.

During gluing up the second scarf (another 8-footer) I took some photos to document this alignment and gluing process.

Step one was to cover the area of the table with plastic.  I was concerned that when I push the scarf together that I may push the plastic also and have a fold of plastic pushed into the scarf joint.  To prevent this I taped the full edge of the plastic to the table top. 

Step two: With the two pieces scarf-taper up, I wet out the wood with straight epoxy.  The board in the picture acts like a paint roller tray.  I spoon some epoxy out of the mixing bowl onto the tray, wet the roller up well, and then roll it out on the tapers.

The wet-out is completed.

Step Three: The smaller top-piece of plywood is then flipped over, taper down, and screwed down to the table with the clamping blocks.  The clamp blocks have plastic tape on the bottom to prevent being permanently glued down.  The blocks are about 16 inches apart, and in fact use the same screw holes from when the scarf was cut.  The screw in question is the one about in the middle of the blocks.  It looks far from the edge, but is just beyond the taper edge underneath.  The blocks are extra long on the right side to provided leverage to hold the outer edge of the taper down better during the process.

Here is the thickened epoxy glue and the tools I'll use.

Step Four:  Gluing up the taper.  Using the putty-knife I put some beads of glue across the taper and then spread them with the notched trowel.  Okay... I didn't get enough down and not close enough together.

That's better!

Completed

 Step Five:  Before pushing the joint together, I first pulled the plywood back to clean the excess off the plastic.  Don't want a smear underneath.

Step Six:  I push the plywood to within an inch of closing up the joint.  Then I set up two ratchet straps to help with the final squeeze.

Step Seven:  Working the ratchet straps carefully, I close the joint up until I get the joint edges looking to be a proper distance.  I had previously dry fit the joint and knew what the distance should be without a glue layer.  I also knew from the taper angle that a 1mm glue layer would mean the distance would be 6mm wider than a dry fit.  I was also rewarded with seeing a nice amount of glue squeezed out of the joint.  Little to no glue squeezed out of yesterday's scarf joint.  I made the glue less thick than yesterdays and put more of it on the joint today.

 Step Eight:  I screw down the further end of the clamping blocks and remove the ratchet straps.  I also scraped away the excess glue so I will have less to sand down later. 

 

 

Gluing the first Scarf joint

 I completed gluing up the first two 8-foot long scarf joints this week.  The first on Wednesday and the second on Thursday.

On Wednesday the first seemed to go okay, far from perfect, but maybe good enough or adequate.  I think I may have forced the tapers too far together, but I kept hoping some epoxy would squish out the top to show that I had the joint fully filled with glue and closed up well enough.  There was little to no epoxy squished out.

 On Thursday, I removed the clamps and cleaned up and sanded the joint flat.  I don't have x-ray eyes so I can't be certain about the results, but I got the feeling that it actually turned out better than I had thought the previous day.  I think this first scarf joint is not only 'good-enough' or adequate, but probably 'good'.

 

table side of the scarf, after cleaning and sanding.

top side results after cleaning and sanding.

top side end  

 The last picture looks wide, but that was because the taper was cut to such a thinness that it broke away.

Basic Hull pieces / The sheer strake

 Here's my computer drawing.  Many of the pieces are not drawn exactly, but it lets me view it in three dimensions to see what changes might look like.

 Here's the basic hull pieces.  The frames, sides, and first bottom panel.  These are the pieces that will be 'stitched' together when the hull first gets assembled.

 This is a simplified drawing of the basic hull pieces.  The frames in brown.  The two bottom panel layers in blue, and the sides in yellow.  There is also the 'sheer strake' in green.

The sheer strake goes along the top of the sides and visually is what gives the boat's profile view its graceful look.  In this construction it also makes the top 6 inches of the side panels a double thickness.

 

Bottom Panels Cut and Scarfing Plan

To minimize the number of sheets of plywood I'm using, I will scarf my sheets together as shown here.  Yielding both bottom layers from 5 sheets.

Two bottom panels.

Cut plan for sheet 5

The fore and aft scarf joints will be placed one to port and the other to starboard.  The side to side (beam to beam) scarf joints will be on top of each other, but I will mitigate that situation by preventing the scarfs from being contiguous.  If a scarf fails and begins to crack, that crack should not continue into the scarf of the other layer.  My current cut plan allows for at least the 'good' alignment.  Whether I'll be able to shift one layer's cut an inch or two to achieve the 'best' alignment I'll find out.
 

Aligning scarfs of the bottom two layers.

 

 

Scarf Cutting Completed (for now)

 Last weekend I managed to complete the four 8-foot long scarf cuts.  By the end of this weekend I had completed the eight 4-foot scarf cuts.  This completes all the cutting that can be done at this time.  The last two scarfs to cut are the side-to-side scarfs of the bottom panel layers.  They can't be cut until the panels are first widened by gluing up those four 8-foot long scarfs. 

a 4-foot scarf ready to cut.