March, 2013

 Marking The Planks

I laid the port and starboard plank pairs over the full size drawings and marked the station lines, the aft and forward space frame lines, the aft and forward faces of the apron and the transom. I used a simple compass to slide the pencil tip along the edge of the planks to draw the 19 mm plank overlap line.


On plank #8 I marked the location of the sheerline. This step is important to determine which edges should be rounded off, and in what direction, so that the port planks mirror the starboard planks.

Rounding Off The Edges

Construction note #11 provided by Keith Callaghan reads: Rule 4.m(i) states “The exposed edges, whether inside or outside the hull, may be rounded off to a radius not exceeding the plank thickness.”

Construction note #12 reads: "Forward of +550, each pair of overlapping planks is progressively beveled together,so that at the stem there is no plank overlap. (Rule 4.m.(i)) ." This means one should not round the forward 550 mm of each plank edge until creating the final bevel to merge the plank overlap towards the stem.

I used a 3/16" radius carbide router bit with a bearing to round off all exposed edges per drawing specifications and according to several pictures seen on Keith Callaghan's and the MROA's websites. This consisted of rounding off the outside of planks #2 through #8, and the inside of planks #3, #5, #6 and #7. The excluded plank edges are beveled to accept the next plank.

For rounding off the exposed edges of the 12 mm plywood parts, I simply used a 3/16" radius carbide router bit with a bearing.  A couple of tests using scrap pieces of plywood were very helpful for setting the proper router bit depth. I secured my router over the portable work bench and worked the different pieces.

To the left is a closeup of the results on the transom openings. I applied the same process to round off the exposed edges of the centerboard case ears, jib cleats, main space frames, the thwart, and the transom knee.    

Rounding off the 6 mm plywood planks presented a different challenge. The router bit radius is almost as long as the plywood thickness and the bearing does not have where to stop the router bit from cutting into the plywood. To solve for this, I added a router fence attachment.

  Coating The Planks With Epoxy

The Gougeon Brothers book on Boat Construction has a great guide in Chapter 15 on how to apply epoxy. I followed the recommended steps of applying 3 layers of epoxy in a single day as much as possible. Significant temperature drops required me to switch from West System 206 to 205 hardener, which also helped speed up the curing process.

Establishing a cadence is important to obtaining consistent, repeatable and timely results. I performed this process at least 96 times (16 planks x 3 coats x 2 sides).

The tools I used for applying the epoxy were sand paper to prep the plywood, an epoxy spreader, a West System foam roller (cut in half) to even out the epoxy and a foam brush to give it a smooth finish look.

I worked on 4 planks at a time and took the opportunity to coat smaller parts with the epoxy impregnated foam roller, thus using most of the epoxy mix. This helped speed up the process. After the epoxy curing was complete, I hanged the finished planks from the ladders.

The Apron, The Hog & The Bow Knee

Using the full size forward frames drawing I plotted the shape of the 18 mm thick apron (aka stem) I laminated from 12 mm and 6 mm marine plywood. 

Before bonding the forward and aft sections of the hog, I set up the aft section of the hog as a rip fence extension for the table saw.This helped me align the forward section right in front of the saw blade and slide it over to cut the slot.

Next, I cut a 6 mm wide slot on the forward section of the hog, long enough to accept the bow knee. 

I repeat the same process for cutting a slot on the hog doubler and the apron. Here is a picture of the hog doubler already laminated on the hog, and the hog/apron knee slotted into the hog and apron.

Next step was to bond the forward and aft pieces of the hog using the same scarf joint bonding method used on the planks. In preparation, I made several marks along the middle of the hog and shot a laser line down the middle of the hog to align the sections. I also used a string line along one side and marked the edges of the hog on the table to have a better  reference once bonding and clamping takes place.

I then applied 3 coats of epoxy to both sides of the apron, just like I did with the planks.

Afterwards, I applied 3 coats of epoxy to both sides of the apron, just like I did with the planks.

Here is a picture of the hog's scarf joint after coating the entire hog with epoxy.

A look at the hog and the doubler after finishing the epoxy coating
















Next month I'll probably set up the jig, mount the building frames and start planking.