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
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
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
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!!