My Merlin Rocket: June, 2013

Shaving The Garboards

A good idea is not always the best solution...

I stood for several minutes pondering the best way to shave the extra material left on the garboards forward of the centerboard case opening. Still not comfortable with using the block plane and the spokeshave, I looked around the garage and there it was... the router sled of the scarfing jig. I figured I could mount two rails on the building frames and mount the router sled across and at a slight downward angle towards the apron. Then, I would proceed to slide the router back and forth while adjusting the plunge router depth as needed. I loved the idea. Actually, I still do. The building frames provide the perfect base to brace the rails. The with of the jig was perfect for the job. The problem was I didn't have a pair of stiff enough and strong enough rails to execute. Can't say I could justify the time and expense to do it.

To the left a picture of the concept. Maybe some day, just not today.

So about the block plane and the spokeshave. Nifty little tools that do a great job when the blades are properly adjusted. Small shaving increments, long strokes, a lot of patience and a good dose of 70's rock and roll. I used the forward and aft frame full size drawings and the building frames as reference. The hog is the best reference for removing the excess material. I'd marked the shape of the hog at each station and in between based on the dimensions provided in the construction drawings.

Slowly but surely, got into a rhythm and I worked my way from the transom to the bow, beveling the lands for plank #2. The building frames provide excellent bevel angle references and make it easier to transition from one angle to the next.

To the left a picture of the garboards after the first round of shavings.

After a couple of hours of carefully shaving off the extra material off the garboards the hog marks appeared. These marks were scored when the hog was shaped according to the drawings for station's #0a through #4

The Keel

The 18 mm x 98 mm keel is shaped from Western Red Cedar stock. I was able to find a 16 foot long board at my local cedar supplier, just right for the keel. A couple of knots on the board were removed. I used a rotary tool with a wire brush head and sander drum to remove the next couple of layers of wood next to the knots and clean up the openings. I then filled the holes with an epoxy and colloidal silica filling mix based on the West Systems recommendation.

I then proceeded to rip the keel stock on my table saw to 98 mm in width, as specified on the drawings.

I laid the board over the hog and clamped it aligned to the center line running from the bow to transom.

Forward of station #2, I marked the narrowing shape of the garboards under the keel board to remove the excess material.

Here is a top view of the keel board after tracing the shape of the garboards. Notice the garboards contour around the hog forward of station #2.

While still clamped to the hog and the garboards, I marked the center line and the precise location of the centerboard slot on the keel stock. Then, I marked the location of the keel band along the board. When finished, I had three-dimensional references for shaping the keel.

Next, I cut off the excess material towards the bow and mounted the keel stock over the hog using 24 mm thick plywood spacers. This gave me enough spacing to start beveling the keel edges with the block plane and the spokeshave.

Side view of the setup to shape the keel. The spacers allowed me to handle the block plane and spokeshave comfortably.

It is a messy process but much easier to manage than saw dust. I swept the shavings and saved them in a disposal bag for later use.

A photo of the keel after the initial shaving and sanding. The shape of the keel at the transom was still more rounded than straight. It was important for me to take time shaving a bit and sanding a bit to achieve the required shape.

To the right, the shape of the keel at the bow after the initial shaving and sanding. I figured I would only be able to shape the keel so far before bonding it to the hog and the garboards. I would have to get down to shaping the precise details afterwards.

To the left is a photo of the keel's shape changes between the centerboard opening section and the aft section towards the transom.

Next, I laid the keel over a sacrificial sheet of plywood over sawhorses and cut the long sides of the centerboard opening with my circular saw. I drilled four 3/8" holes on the opening corners where I used my jigsaw to cut the short sides.

The keel after cutting out the centerboard opening.

The keel back on the hog and the garboards after sanding and for final alignment before bonding.

Closeup of the centerboard opening shape after sanding.

The method I used for bonding the keel to the hog and the garboards is the one recommended on page 109 of the Gougeon Brothers' book on boat construction. I used the West System 105 epoxy resin with the 209 Hardener to wet the scarfed area. After bonding, I performed the necessary shaving and sanding required to shape the final contours of the keel based on the drawings. The photo to the right shows a triangular shaped keel at the transom, as specified.

A top view of the keel at the bow. Forward of 800 mm the keel's width diminishes while following the contour of the garboards towards the apron. A bit hard to see the details on this photo. I'll try to take a better picture and add it to the next update.

Planking

The Construction Notes provided by designer Keith Callaghan and the National Merlin Rocket Class Rules provide invaluable information with regards to the planks and planking. I spent considerable amount of time reading these documents and recommend doing so to ensure adherence to the Class Rules and design specifications.

While coating the keel with epoxy, I laid planks #2 on their construction frame landings and, more importantly, on their beveled garboard landing to ensure the proper angle was shaved at each station. Class Rule 4.m.(i) requires that "The angles at the lands on the outside of the hull shall not be filled to a radius greater than 4 mm."

A view from the transom as I align planks #2 at each station against the beveled landing on the garboards.

One thing I really love about the precision CNC cuts and the construction drawings is the three-dimensional alignment I am achieving at each station. It is very self-assuring. I couldn't be happier. Thank you Keith! Well done!

Construction Note #12 says "Forward of +550, each pair of overlapping planks is progressively bevelled together, so that at the stem there is no plank overlap. (Rule 4.m.(i)) ."

To the left is a photo of the progressive inner bevel on the incoming plank forward of +550. I used the hand block plan and spokeshave to accomplish this.

It took a couple of tries to make the final shavings on both the garboard and plank #2 to get it just right. While clamping the planks I noticed the torque exerted by the deep throat clamps. To counter this effect, I drilled holes in the building frames to clamp down the new plank against it and ensure the plank laid flat over the building frame landing.

Photo of planks #2 after bonding.

Some shaving will have to be done after bonding to take advantage of the additional strength and rigidity of the planks over the construction frames. This is also necessary to comply with Class Rule 4.m.(i) so that at the stem there is no plank overlap.

Forward photo of the same.

With every plank I learn something new. Clamping is a little bit different at every station and there are a few differences between the starboard and port planks, depending which one I installed first. As the apron widens towards the sheer line, the plank landing takes a different angle and required using different clamp types to achieve a good grip.

From plank #2 onward I first installed counter torque clamps on the Hazardous to ensure the previous planks remained flat on their landing when installing a new plank on the opposite side of the hull. Then I aligned and clamped the new plank against the building frames. Lastly, I added the deep throat clamps to secure the new plank tightly onto their landing.