By Jeff Mueller
Upgrading our sailboat’s navigation instruments called for eliminating one thru-hull fitting and reducing the diameter of another by 1/8″. Takara, a 1974 Irwin 30 Competition, has a one-piece molded fiberglass and polyester hull with alternating layers of hand-laid mat and 24 oz. woven roving. Her original instrument set included a pair of 2 1/8″-diameter transducer thru-hulls in the bow. Upgrading to modern instrumentation standards required installing an NMEA 2000 network instrument that was 2″ diameter.
The project, while simple in scope, posed a few complications:
- The two original thru-hulls were quite close together.
- These thru-hulls were close to the centerline of the bow.
- From the inside, the thru-hulls were near some laminated stiffening for the bow as well as some tabbing to the inside liner.
We reached out to Gougeon Brothers, Inc. and were connected with Technical Advisor Don Gutzmer. We sent some pictures over and he assessed our situation. This was truly the best thing we could have done. Don’s technical expertise was evident throughout our discussions.
He recommended we start by reinforcing the inside area with two layers of biaxial fiberglass cloth before making the repair from the outside. On the outside, to eliminate the obsolete thru-hull, we needed to taper the fiberglass at 12:1. Repairing this unneeded hole required eight layers of 17 oz. biaxial fabric with mat. The resized thru-hull would need a couple of layers on the outside as well. Since it only had to be 1/8″ smaller, it could be filled with a “puck” of thickened epoxy, covered with two layers of glass, and re-drilled.
Prepping the Repair
With our game plan in place, we gathered the tools, materials, and West System® Epoxy for the job. We easily removed the old thru-hull transducers. Next, we began grinding to prepare the inside of the hull for proper adhesion of two layers of 17 oz. biaxial fabric.
To make a clear area for applying the reinforcing layers of fiberglass on the inside of the boat, we removed an original piece of fiberglass tabbing. We then used a piece of clear plastic sheet to make a template for cutting the two layers of fiberglass cloth to be applied inside the hull. The template made it a breeze to cut the fabric to the correct shape.
With the inside prepped and ready for new fiberglass, we moved to the outside of the boat to begin the more significant elements of the repair. On the exterior, we marked a circle for the proper 12:1 taper required to eliminate the unneeded thru-hull. We made a template for the new glass cloth as we had done on the inside of the boat.
Don recommended a layup schedule of eight layers of 17 oz. biaxial fiberglass fabric to match the thickness of Takara’s hull. This was the perfect thickness and left us with very little sanding and fairing to do. Nice to have experts working with you!
Our next step was to prepare the unneeded hole. We tapered the hole to the full thickness of the laminate, at a 12:1 bevel. We used a straightedge to ensure that we were not “dishing” the taper. This kept all the layers of cloth in plane for the best possible repair. The taper was a little tricky because it wrapped around the centerline of the boat, but we did our best to keep it consistent.
We followed the same process for the resizing hole, but instead of grinding the bevel all the way down to the inside of the hull, we only tapered the hole to a depth of approximately two layers of 17 oz. biaxial fiberglass, at a 12:1 bevel. We roughed up the inside edges of the resizing hole to prep it for filling with thickened epoxy.
Fiberglassing the Old Thru-Hulls
With the holes properly tapered and prepped on the outside, we were ready to apply fiberglass inside the hull. Using 300 Mini Pumps, we mixed West System 105 Resin® and 206 Slow Hardener® for applying two layers of 17 oz. biaxial fiberglass cloth on the inside.
After this cured, we mixed a batch of 105/206 thickened to a peanut butter consistency with 406 Colloidal Silica Filler. The mixture didn’t run or sag when we used it to fill the resizing hole. We allowed this to cure.
Next, we moved to fiberglassing the thru-hulls from the outside. Using the template we had created earlier, we cut the layers of fiberglass cloth for each thru-hull—two layers for the resized thru-hull and eight for the unneeded thru-hull. With our cloth cut and the repair area masked off to keep things neat, we mixed additional resin and hardener to wet out the biaxial cloth patches and applied them from largest to smallest. We used rollers to ensure there were no voids or air bubbles in the layup. The resulting repairs were beautiful and precisely matched the hull thickness.
After the epoxy cured, we moved on to the final step: fairing the repair area. We mixed some resin and hardener then added 407 Low-Density Fairing Filler. We applied this fairing compound to the repair area. Because of the precision of our work up to this point, the repair needed very little fairing compound or sanding.
We applied new tabbing from the hull to the inside liner where we had removed it earlier. Then we carefully marked the center point in the resized thru-hull, drilled it out, and installed the new thru-hull fitting for the updated navigation instruments.
Our last step was to apply a fresh coat of anti-fouling bottom paint. Finally, Takara was ready to splash! With our plans to take the boat from the Great Lakes out to bluewater, we could not have been more pleased that we’d executed an extremely structurally sound thru-hull repair and resizing. Don’s expert advice and direction was invaluable. West System materials are top-notch and formulated to be easy to work with. Takara is moving into the exciting realm of modern-day navigation and instrumentation. Her hull is strong, fast, and ready for upcoming bluewater cruising!