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From a Bare Hull:  Sheer Clamp

Installing the Sheer Clamp
Once I was satisfied with the location of the temporarily-installed sheer clamp section on the port side of the bow, I prepared to install it permanently.  After double-checking its location, I marked the outline of the board on the hull to make realignment later easier and to show me where to apply the adhesive during installation.  

I planned to install the clamp sections in a thick bed of 5200 (polyurethane adhesive), with bronze through bolts securing it to the hull.  To mark for the bolt hole locations, I drew a line halfway (1-1/2") down the width of the board, and then marked off 6" centers on that line.  I drilled from the inside out, through the two clamp boards and the hull.  Then, outside the hull, I milled countersinks in the fiberglass so that the bugle head (flat head) bronze bolts would sit in a slight recess in the hull, for later covering with putty.  I used a 5/8" 3-flute countersink with a standard 82° angle.  There were about 20 boltholes in this section.

With the holes drilled, I unclamped the boards and vacuumed away the dust, then cleaned all mating and surrounding surfaces with acetone.  When everything was clean and ready, I opened a cartridge of 5200 and applied it to the hull inside the marked area.  It took two full cartridges to cover the 10' area.  I applied the adhesive heaviest around the boltholes and near the top edge, since I knew that it would run down a bit while I prepared the boards for installation.  5200 has a long open time, so I wasn't worried about it curing prematurely; still, I didn't dawdle through the next steps.

I chose to apply some thickened epoxy resin between the two boards so that they would effectively become one piece when installed.  I mixed a batch of resin thickened somewhat with cabosil, and brushed it onto the mating surfaces of the boards.  Now, working as quickly as possible, I carried the board back to the boat and got them roughly aligned.  I used a couple clamps to start bending the boards into the curvature of the hull and as soon as I could I lined up the first bolt hole and installed one of the 5/16" x 3" silicone bronze bolts to help align and hold the boards in place while I moved forward.  After a couple minutes and some juggling, I managed to get both boards aligned and pulled tightly against the hull with the wooden screw clamps, and then installed the remaining bolts from the outside.  Still moving fast, I installed a flat washer, lock washer, and nut on every other bolt, and then tightened these down with a ratchet.  When these first bolts were tightened, it pulled the two boards tightly together along their length, squeezing epoxy out from the joint--just what I wanted.  I removed the wooden clamps, and continued by installing the washers and nuts on the remaining bolts and tightening them, before going back and tightening each bolt just a bit more in turn.  The bolts pressed the boards tightly into the bed of adhesive beneath, helping to make up for the undulations in the fiberglass hull interior.

There was a substantial amount of 5200 and epoxy oozing down the hull beneath the tightly-installed sheer clamp, so I spent 20 or so minutes cleaning it up with putty knives and acetone.  I tried to clean off as much spillout as possible, but didn't fret too much about its ultimate end appearance since the whole area will eventually be covered and out of site when the boat is finished.  But I still wanted the installation to be neat and clean.

With the port bow section of the sheer clamp securely bolted in place, I continued with the opposite section, following the same process described above.  By the end of the afternoon, the second section was in place.

Over the next two days, I completed installing the remaining sections of the sheer clamp, following the same basic technique described above.  Each side needed three total sections.  The second and third sections went more smoothly, partly because of my gained experience and partly because the hull was straighter and less flared in these sections.  The final section on each side was about seven feet in length and ran nearly to the transom.  To complete the job, I ran a bead of sealant along the seam between wooden clamp and hull, just to provide an additional barrier should any moisture end up in that area.  

Work remaining:  cut off the protruding bolts, and fill the countersinks on the hull with epoxy putty.

Continue with the Deck Framing>