Thursday, August 18

Epoxying between block (which were installed the previous day)

 We started with the rails, the outwales (gunwales) and associated spacer blocks. During the whole process it's important to keep the parts correctly labeled (e.g. port inwale, arrow toward bow). There were three outwale pieces on each side. The cuts, ie, eventual scarf location should be located so that a) they are in the same location on the port and starboard pieces and b) the inwale and outwale pieces have scarfs at different locations from each other (but same to their corresponding part on the other side.

The bow outwale pieces are fitted first. They require a compound bevel; cut with handsaw, refit, adjust, etc.   See photos here.    Once satisfied, dry clamp the pieces. Repeat with stern pieces. With bow and stern pieces clamped, mark where the scarfs will fall on the spacer blocks, which had been glued in place yesterday.  Dry fitted wales can be seen here.

Note: Our spacer blocks were glued even with the top of the sheer plank. If you prefer, you can glue them slightly proud. Thus the out/inwales must also sit proud. This allows for a narrow wood strip to be fitted to the gap, covering the plywood end grain of the sheer plank.

Scarfs in plywood are generally 8:1; in natural wood they are 10 or 12:1; we used 10:1. Thus the scarf length of a 7/8” outwale is 8 3/4”; so measure out 4 3/8” from center of scarfs. The inwale scarfs are on 5/8” stock, therefore the scarf is 6 1/4”. The scarfs should be drawn so they fall on spacer blocks to facilitate clamping. [Note: Geoff uses a jig for 12:1 scarfs at home]. Sketch in the angle of the scarfs and cut with a bandsaw and finish with a plane. The scarf direction should use the same principle as the plank scarfs. For example, the bow wale section should be undercut so it rides over in undercut scarf at the forward end of the middle piece.

Next Geoff talked about and demonstrated casting lead for the centerboard weight. A propane powered heater (the kind used for deep frying turkeys) is used. The melting point of lead is 621.4 degrees F. A cast iron pot or even a coffee can may be used. There are various sources of lead, including balancing weights from tire dealers. The size of the hole in the CB into which the lead will be poured can be calculated. Since we know the density of lead (0.41 pounds/cubic inch) and the thickness of the CB, and we want a 10# weight, the calculation is straightforward: 10# divided by .41#/cu in = 24.4 cu inches of lead. For purpose of the calculation, I'm assuming (perhaps not correctly) a CB thickness of 3/4”.

Πr² x t = 24.4

r² = 24.4/Π x 0.75

r = 3.22 or approximately 3 1/4” radius.

As the lead is heated, most contaminants float to the surface and can be skimmed off with a slotted spoon. The lead is poured into a leveled CB with a plywood backer board covering the bottom of the hole.  The casting process photographs can be found here.

Next, Ed and I created blanks for the breasthooks (12” and 15” equilateral triangles). The 2+” thicknesses was laminated from plywood. The breasthook is a complex shape. It is roughly triangular in plan view, but the sides curve along the inwale. In cross section, it has angled sides corresponding to the inwale angles, and the top surface is convex and the bottom surface slightly concave.

We then turned to mast/spar building. The main (fore) mast is made of douglas fir, and of hollow construction, as mentioned earlier. Other spars on this boat are solid and made of spruce. 

The mainmast starts off as 8 staves. One stave is precisely cut and serves as the template for the rest of them. Stave width equals 40% of mast diameter at each point. The points are marked on the stave, faired with a batten, and cut freehand on a tablesaw.

Both the hollow mast and solid spars were glued up (epoxy).  Hose clamps held the 8 sided hollow mast together.  It rested in several holders on the bench top.  A drill with socket was used to tighten the clamps.

Asides: the Bevel Boss and 3” bevel gauge that Geoff uses are from Southerland Tools  http://www.sutherlandtool.com/.   The 3" bevel Geoff uses is no longer available, but the 2" and 4" are.  The batten we used throughout the process measures 3/8” x 3/4”.

All photos of the Ness Yawl 2011 class may be viewed at: http://www.flickr.com/photos/21597525@N00/collections/72157627358772597/