Rachel wrote:Tool-wise, I see that Peter mentions using a 5" grinder. I don't (yet) have a grinder or a Porter Cable DA sander -- I've had the sander on my wish-list though, so I would rather buy one of those first. Could it be used with the flap wheel for this sort of repair?
You can accomplish all the grinding on your boat with the DA sander and heavy duty paper. I have an angle grinder, but I virtually never use it for actual grinding. I get better results and have more predictable control with the DA.
If you want to buy both, go for it. But if you buy only one, it needs to be the DA. I'd give up my angle grinder 10 times over before I let go of my DA.
There's a lot of confusion surrounding the proper way to fill clean round holes in a hull. I have frequently avoided addressing this issue because I've had trouble figuring out a way to express what I mean without sounding as if I'm somehow recommending an easier or less sound way out.
I guess at this point, I'll have to hope that you, dear reader, will take for granted that I wouldn't recommend anything that wasn't a sound, strong, and professional way to accomplish the task, and press onward. I hope that my past writings might support this notion.
While it's not wrong to go to the extent of filling an entire 3/4"deep round hole with solid fiberglass, it's not necessary. In addition, frequently only one side of the hole need be ground at all (or at least not severely ground), since if one is not going for a completely flush, hidden repair (such as inside a bilge locker), new material can simply be layered over the existing hull without the need to grind tapers and neat concentric rings. This doesn't mean the interior work need be sloppy or ugly, but the need to make a completely flush and invisible repair, such as that on the exterior, is not there.
Here is how I address round through hull holes in a hull like that of a Triton or Alberg 30, or boat of similar construction. Since that's what this thread is about, that's what my description will cover. Other types of repairs, of course, may require a completely different approach.
- 1. Tape over the bottom (exterior) of the hole and fill from the inside with thickened epoxy--usually a plain cabosil and resin mix. Allow this to cure.
2. From the exterior, grind a circular depression equal in depth at the center to the thickness of the new material you plan to apply, or just a bit deeper. Roughly gauge about a 12:1 bevel and taper the grinding out concentrecally from this center point. 3 layers of 1708 biax is adequate to repair something like a filled through hull, no matter how thick the original hull is. I usually like to install one layer of light-ish cloth (normally 8 oz. or 10 oz.) over the top of the repair, since it makes for a cleaner, smoother finish. I often install this dry to help soak up the inevitable excess resin in any hand layup, then only wet additionally as needed.
That said, one can install as many layers as they wish. No harm, no foul. But it's truly unnecessary. Remember that a cleanly-cut round hole is structurally insignificant to the boat, and that truly the only reason a patch is required is to (obviously) prevent water from coming through that big hole after you remove the fitting.
3. Cut concentric circles of your chosen fiberglass material for the exterior of the repair, each slightly larger than the next. Laminate these in place beginning with the largest, and working back to the smallest on the outside. While this seems backwards at first glance, remember that when grinding and fairing the repair, some material will be removed, and with the largest piece on the inside (bottom) of the repair, the largest bearing surface of the new material will remain intact.
4. Clean, grind, and fair as necessary.
5. On the inside, assuming you don't see a need for the repair to be completely flush, install fiberglass over the inside of the plugged hole. You should clean and lightly grind this area first to ensure good bonding, but you need not remove material from the hull as on the outside. Here, install a smaller piece first, overlapping the round hole by a sound margin--an inch or so-and then install larger overlapping layers.
6. I always clean and grind all fiberglass repairs. You always end up with pooled resin, sharp spots, etc., and it makes for a clean job if you take the time to grind it later on.
There are lots of step-by-step pictures of this very sort of repair to be found in the Kaholee project logs, if you need a visual reference. For now, I won't try and copy them here.
