Monday, January 14, 2008

Finishing Inside Keel Fiberglassing

Since building the starboard hull is practically exactly the same as building the port hull, which I started first and detailed in photos and descriptions here in previous months, I have been reluctant to bore readers with the same details again as I go through the process the second time. There have been some comments and questions however, about certain techniques and procedures I used, and I try to answer those either in replies to the comments or in direct emails, but I can also use this opportunity while building the second hull to elaborate if I can remember to.

One technique in particular that I find useful and some other Wharram builders have been interested in is the method I use for laminating fiberglass in areas like the inside of the keel. This method allows for a clean, almost invisible transition from the fiberglassed area to the other epoxy-coated but not glassed sections of the panels, and is especially useful for areas that will be finished bright with the natural wood grain showing, as I have chosen to do for all of the interior parts of my boat.

In the Tiki 26 plans and in most stitch and glue boatbuilding instructions I've seen the use of prefinished fiberglass tape is suggested for applications such as this, and it is available in various widths such as 2-inch, 6-inch and so on. Such tape is convenient and easy to use, but there are two disadvantages to it in my view: one is the extra cost, and two is the fact that the finished edges are thicker and are almost impossible to fair in to a surrounding surface. If you are painting, this is no problem, fairing compound can make the edges disappear; but for a bright finish, the tape does not work well.

A better solution is to cut your own strips of glass cloth from the same 6-oz. fabric used to sheath the hull. I roll mine out on a flat piece of scrap ply, and slice with a razor knife it into strips cut on the bias, so that it will easiely bend into curved areas and not unravel before you can wet it out. The trick to getting the invisible edge is to first tape off the perimeter of the area to be glassed with masking tape, after sanding and cleaning all surfaces, and then lay the cloth on top of the tape so that it overlaps the inside edges - see below:

The cloth is then saturated with epoxy resin, making sure it is completely wetted out even over the edge of the tape. After it has a few minutes to soak into the weave, I then squee-gee out the excess to keep from building up puddles in the keel.

It's important not to get too far away from the project after doing this, as you have to catch the epoxy at just the right stage of cure in order to cut it and pull the tape before it gets too hard. This timing is dependant on the temperature and the speed of the hardener you are using. If you try to cut the cloth too soon, it will pull away even in the areas where you want it. Usually it's about right when it's still sticky to the touch, but the overlapping excess areas require a firm tug to peel away from the wood. Use a sharp razor knife to cut just inside the perimeter of the tape, and pull the tape and excess cloth away all together.

The next step is to go ahead and second coat the remaining fiberglass while the first coat is still tacky. Then it can wait until full cure, when you can then lightly sand it and and apply a third coat. The finished fiberglass job should be come out neat and the cloth will be nearly invisible.

This method of glassing small areas is so much neater that I also use it on the exterior that will be later painted. It is especially useful for glassing in limited areas like the extra reinforcing layers added to the exterior of the keel, skeg, and stem post.

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