centerboard shaping

The Centerboard has been roughed out to its approximate final shape and I have become a tad obsessive compulsive regarding the final shape.  The photo shows the NACA 0008 shape as it seemed to fit the final shape of the tip of the foil the best.  the NACA 0009 might be better.  My plan is to set a dado router bit to the depth indicated by the template and then  set a guide for the router to follow.  I will set the guides as expanded lines up the foil at several stations as the template can be expanded to fit the width at each point.  I used the plotter at http://airfoiltools.com/plotter/index  be sure to select "no margins" on the printer or things get compressed.  I can generate a NACA foil for several points along the board and then connect the points to expand the lines through the taper.  The router would then follow the lines to cut the lines to be planed to.

 Area that will be inside the trunk is clearly marked.  router will be used to go vertically up and strike marks to plane to.

 I have no idea how I will shape the tip, other than just rounding it off.

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3 9 13 centerboard

I took the plunge today and bought a few board feet of 2X6 fir to start laminating the centerboard.

After an hour on the saw including set up, I have a pile of nice strips to glue up to the basic shape.

The logic to start on this part of the boat was that the garage is still too cluttered and cold for serious building and these parts can be done with the glueing indoors and the shaping outdoors.  The centerboard trunk will be determined by the final shape of this part, so there it is.

Plywood will be ordered next week so it arrives when Im home to receive it!

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The Utility part 3 Stem and floor battens

The Utility’s stem, as with the Squirt, Zip, and I assume several other Glen-L designs, is made of 2 laminations of 3/4” plywood. Fortunately, I had enough 3/4” marine-grade Douglas Fir plywood left over from Lusitania 13’s second transom to build both the transom and the stem for the Utility. 

The laminations are glued together with marine epoxy, (I used Poxy-Shield thickened with #2 silica), and bronze screws. The breasthook is basically made the same way, although the mating pieces are shaped differently: The top piece fits over the stem, and the bottom supporting piece fits around the stem. The breasthook is then epoxied onto the stem. I clearly marked all my centerlines, and tried to make the pieces fit as precisely as possible.

With the centerline on the keel clearly marked, I clamped the Utility’s stem/breasthook assembly into position. Next, using twine and a plumb bob, I worked carefully to make sure the whole assembly was aligned with the centerline of the keel. As a one-person job, this is rather tricky. If you have someone to help, it should be much easier.

With the assembly clamped into position, I drilled two 1/4” holes vertically through the forward part of the keel and aft section of the stem, countersinking the carriage bolts. After applying copious amounts of thickened epoxy, I bolted the stem to the keel with 5” long, 1/4” bronze carriage bolts. After tightening them, I filled the extra space from the countersunk carriage bolts with thickened epoxy.

Stem clamped and bolted onto forward end of keel.

Stem-to-keel joint after epoxy. Glue blocks added for reinforcement.

Having now learned my lesson from having to build up the keel thickness, I turned to the floor battens. As I mentioned before, the frame notches for these were cut to 1” deep. “1-inch” lumber off-the-shelf is typically only 3/4” thick. So, for the floor battens, I purchased an 8-foot, “5/4” mahogany board. (After they plane 1/4” off it at the lumber yard, you’re left with an actual 1-inch thick board.) The cuts for the floor battens were straight cuts, producing four 2” wide battens. Cutting the battens produces a lot, I mean a lot, of red sawdust. I decided to sweep up & collect most of it to use as wood flour to thicken epoxy later on. This turned out to work quite well.

The floor battens had to be fitted into the transom frame notches the same as the keel. The battens were fastened on with thickened epoxy and 2” bronze screws.

Transom knees attached to keel & transom. I put these on before adding the floor battens.

A note about bronze screws

Bronze screw heads are rather soft, and will strip out on you easily. This is particularly true when using a power drill as a screwdriver. Below is the method I used to remove a stripped screw during the fitting process for the floor battens:

Totally stripped-out bronze screw head.

I cut a slot in it with my Dremel.

Removal was then easy with a flat-head screwdriver.

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