Patching Head Through-Hulls

On Saturday the 23^rd of May, I began the process of patching the holes created by removing the original head through-hull fittings – one for the fresh water intake and one for the waste-out.  Since I will be sailing Froonie on the St. Johns River and along the coast, I can do without the head through-hulls – they would be points of potential failure while not being used. So I am going with a toilet that has a holding tank.  If I ever get the gumption to take this Alberg design into blue water, I will install proper through-hulls with seacocks for the head.

I began by roughing up the edges of the holes – both from the interior and from the exterior sides.  I then vacuumed all sanding debris from the inside, and thoroughly wiped the area with acetone to clean any residual dust from the work area.  Turning my attention to the exterior, I thoroughly wiped the repair area with acetone and generally prepared it for the patch.

I then taped a sheet of plastic to the exterior of the hull and began to trace the repair area with a sharpie.  I progressively traced smaller and smaller diameter circumferences – these tracings would later become templates for the fiberglass cloth cut-outs.  Once I had completed the tracings, I cut out the first template to be used to trim the initial fiberglass cloth patch.  I placed the template down onto a large piece of 6oz. fiberglass cloth, traced the circumference with the sharpie pen, and then cut the fiberglass to shape.  I then trimmed the plastic template down to the next smaller circumference, and repeated the process of outlining the shape onto the 6oz. cloth and cutting it out.  I followed these steps until I had my progressively smaller patches, all cut out of the fiberglass cloth.

Since I could not just begin applying thickened epoxy to an open hole, I prepared a backing surface from inside the cabin.  I placed a sheet of release fabric over the holes, and taped it in place as it had a tendency to slide down the interior of  the hull.  Since this was my first time working with the release fabric, and not being familiar with its performance, I placed a sheet of parchment paper on top of the release fabric – thinking the epoxy was going to bleed through the release fabric.  I then placed a couple layers of foam on top of the release fabric and parchment paper.  Finally, I placed a 2x4 over the foam, and then wedged a board over the 2x4 keeping everything solidly in place.  Biting my nails….I knew I was ready to begin the patch work.

I began by mixing ‘neat’ epoxy and brushing that over the prepared repair area – including the exposed release fabric.  Once the ‘neat’ epoxy began to kick (it was just tacky), I mixed 404 high-density filler into a batch of epoxy.  I worked the 404 in until I got a peanut butter consistency, and then spread this thickened epoxy into the old through-hull holes.  I worked the thickened epoxy in until it was just level with the inside bevel of the hole; I also spread a very thin layer across the remainder of the repair area.  I then immediately turned to the fiberglass cloth patches.  I placed the largest patch onto a clean work surface and used ‘neat’ epoxy to wet-out the patch.  Once I removed all excess epoxy, I placed the patch onto the repair area.  I repeated this process, working through all patches that I decided to use to fill the beveled surface.  Here is a picture of the fiberglass patches in place - you can see the 404 high-density filler at the center of the patches.

I say “decided to use” because as it turned out the beveled area was not as deep as to require all of the fiberglass cloth patches; if I would have used all of the prepared patches, my repair area would have stood proud to the surrounding hull surfaces and would have required a lot more sanding.  The process of wetting the patches out and then placing onto the repair area was a bit messy due to the size of the initial pactches.  In the future, I would plan to carefully place the patch onto the repair area and then fully wet-out with epoxy.

Once the patches were just tacky to touch, I mixed another batch of epoxy and thickened it with 407 micro-balloons to a spreadable consistency that would not sag.  I used a wide squeegee to work the thickened epoxy across the repair area – doing my best here to fair it even with the surrounding hull surface.  Finally, I placed a large piece of release fabric over the repair area, taping it to avoid the wind from grabbing it.  Working with the release fabric, I noticedthat the epoxy was not bleeding through as I worked the fabric up against the thickened epoxy.  I realized that the parchment paper was not needed in the interior backing.  …always learning!

The next day, I made a trip down to do some detail sanding on the cabin roof, and to check out the head through-hull patch work.  Here are a couple pics of the patched area with the release fabric removed and one of the interior showing through-hull holes filled with 404 high-density filler. I will sand the exterior, fill and fair until smooth with the surrounding hull surface; the interior will be finished with a layer of fiberglass, and faired smooth as well.