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Sheer Clamps and Strongbacks

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Installing Sheer Clamps and Strongbacks

After the paint hardened I recruited my friends again and we flipped the boat back on the cradle. It was now time to install the strongbacks and sheer clamp. The Scaup plans did not call for strongbacks. I studied the Black Brant plans, while waiting on the arrival of the Scaup plans, and saw that the Black Brant made use of a single strongback between the bow bulkhead and the storage bulkhead. I like the added strength a strongback provides and decided to add this feature to my Scaup. I wasn't able to go with a single strongback down the center due to interference with the gas tank. Instead I opted for two strongbacks.

Using 1" thick Mahogany I cut a bow transom. This piece was notched to accept the two 1"x3" strongbacks. The Mahogany bow was temporarily held into place with a c-clamp. The flotation bulkhead was notched to receive the strongbacks. To the storage bulkhead I mounted two Mahogany blocks that were notched to receive the strongbacks. I beveled these blocks so they didn't look as clunky. This really wasn't needed because they are in a location that isn't visible. These blocks were epoxied and screwed into place. The screws were countersunk in the face of the storage bulkhead and filled in with epoxy so they wouldn't show. Once the blocks were installed, notches were cut, and everything test fitted, I epoxied the Mahogany bow piece in. After it cured I screwed and epoxied the strongbacks in place. Once the epoxy cured the strongbacks were sanded. At over 2 1/2" thick the bow of my boat is very strong. Running over small saplings and brush is of no concern.

The sheer clamp's purpose is to add strength to the hull and provide an anchoring point for the decking. The clamp I used is different than what Sam showed in his plans. Borrowing from what Jeff Smith did on his Black Brant I incorporated a fluted or grooved clamp. The groove in the clamp serves two purposes. First of all it is esthetically pleasing compared to a flat board, and secondly the groove serves as an excellent place for a bungee cord to rest in. By incorporating bungee cord around the perimeter of the boat I can quickly add camouflage to hide the outline of the boat. During it's first season I did not use bungee cord. I plan to in the future. Below is a diagram of the clamp I created.

The groove was cut with a router and a guide. There are bits available on the market that can create a groove similar to the one in the diagram. I priced several and found them to be expensive. I came up with a cheap alternative by buying a $10 1/2" radius cove bit. A cove bit isn't designed to cut a semi-circle in the middle of stock, but rather a quarter circle on the edge of stock with the aid of a stud or bearing guide. The cove bit I bought came with a cheap stud guide on it, as opposed to the more expensive bearing guides. I used a grinder to remove the stud guide thereby creating the needed bit.

Before mounting the clamps on the boat I had to prepare the hull. This consisted of pre-drilling countersink holes at the sheer clamp line inside the boat. To make certain that the holes were drilled at the proper height I made a small drilling jig out of some scrap 1"x2". Essentially the jig was an "L" shaped piece with two holes drilled in it. The position of the holes was based on where the screws would bite into the thickest portions of the clamp. Countersink holes were drilled every six inches the entire length of the boat.

With all the countersink holes drilled it was time to epoxy and screw the clamp to the boat. Being a little apprehensive about bending the Mahogany I test fit the clamp with c-clamps. To my surprise the clamp bent easily into place. I had help from two others for mounting the clamp and it proved to go very smoothly. The first step was to paint both mounting surfaces with pure epoxy. Next, beginning at the bow, my father would spread epoxy, thickened with wood flour to the consistency of ketchup, to the mounting surfaces. My father-in-law would position the clamp and I would then drill the clamp and screw in #10 1" silicon bronze Frearson head screws. The process was used the entire length of the clamp and repeated for the other clamp. It took less than an hour to mount both clamps.

In addition to installing the strongbacks and sheer clamps I also installed two Mahogany 1"x3" pieces whose purpose was to provide an anchoring point during cockpit coaming installation. These two pieces were installed in the rear of the boat on each side of the motor well. By having a strong anchor point for the coaming I would be able to easily bend it into place. These two "coaming anchors" were mounted similarly to the front strongbacks. Pieces of Mahogany were notched and epoxied and screwed to the inside of each transom flush with the tops. The transom handles eventually bolted to these. The coaming anchors dropped into these notches, notches in the flotation compartment separators (rear flotation laterals) and fit flush against the motor bracket bulkhead. The coaming anchors were epoxied and screwed into place.

After the strongbacks, clamps, and coaming anchors were installed the clamp countersink screw holes were filled with epoxy, thickened to the consistency of peanut butter. Once this cured the filled screw holes were sanded smooth and flush and the entire interior of the hull received three coats of epoxy. It was time to begin decking the boat!!