Thursday, February 1, 2007

Now you see it... Now you don't!

After finishing the fillets and sealing the entire hull interior with a coat of epoxy. I turned it over to prepare for adding a layer of fiberglass cloth and several coats of epoxy to the exterior of the hull. The first thing to do after giving the fillets a few days to fully harden, is to cut off the copper wires. I cut these as closely as possible to the hull's exterior surface. Then I carefully sanded the chines (edges where the sides meet the bottom), and the stern corners and stem, with a belt sander set on low speed. Using a very light touch, I was able to round over the edges to the correct profile and remove the soft copper wire nubs that remained after cutting the wires. If you attempt to sand over the cut wires with a orbital or pad sander, you will likely be frustrated by the sandpaper getting shredded by the sharp end of the wire. This did not pose a problem for the belt sander, because the belt is more durable than the other types of sandpaper.

After the 'sculpting' work was done, I mixed up some epoxy with wood flour filler and used it to fill any holes, scratches, or low spots. While I was still in the planning stage, I had made the decision to paint the majority of the boat and only use varnish on the trim. This choice was based on two facts: first, polyurethane marine paint is more durable than varnish, and second, I would not need to worry about how I was going to fill holes, scratches, or low spots in a way that would not show beneath clear epoxy and varnish. It is possible to mix the filler in combinations that pretty closely match the color of the epoxy soaked okoume wood, but this would take much more time to perfect than it did to simply mix in the wood flour after mixing a batch of epoxy resin and hardener.

Fiberglass cloth is pretty amazing stuff. Even after I have used it on several projects over the years, I am still mystified by the way it becomes transparent, or at least translucent, when epoxy is added. I bought 9 yards of 60" wide, 6 oz. fiberglass cloth from The Newfound Woodworks, a boat building shop located in Bristol NH. I appreciated the way that they packed the fiberglass cloth for shipping. They rolled it on a full length cardboard tube, then wrapped it in brown kraft paper and sealed the roll in a long cardboard box. Why does this matter? I'm glad you asked. When you unwrap the fiberglass cloth from this thoughtful packaging, there are no creases, wrinkles or dirt to deal with. It made rolling out the cloth on the overturned hull a very easy thing to do.

The plans actually call for 50" wide cloth, not 60", but that was the width available, and I was happy to have the extra width. Since this is not wide enough to fully cover the hull in one pass, two lengths of cloth are required, with at least a three inch overlap at the keel line (center). I had about eight inches of overlap, and wrapped the stem from both sides. The cloth followed the shape of the chines and stem quite nicely.

After getting the first side of cloth positioned where I wanted it, I used some push pins to hold it in place while I began the wet out the cloth with unthickened epoxy. The System Three Silvertip Laminating Epoxy is indeed wonderful stuff. With the 'slow' hardener, I had ample time to mix, spread, and smooth the epoxy with my shop heated to 70° F. When I ordered the fiberglass and epoxy materials from The Newfound Woodworks, I also ordered their instructional Fiberglassing DVD, which I found to be very helpful.

The picture on the right shows how well the fiberglass cloth disappears in the epoxy. The wood looked so nice at this point, I was starting to question my decision to paint rather than varnish. I know it was the right choice, and since I used the lighter colored wood filler over the scarf joints, there was no turning back anyway. If you look closely, or click on the photo to see a larger view, you can see that I had also layered on two layers of the 4" wide fiberglass tape over the chines, stem, and stern edges.

After the epoxy dried over night, I sanded the entire outer hull with 80 grit paper on a random orbital sander. This did a pretty good job of smoothing the edges of the fiberglass tape, but I mixed up some light weight filler to completely fair out the edges of the fiberglass tape and where the cloth overlapped. Since the epoxy and wood flour mix is pretty difficult to get perfectly smooth and is hard to sand, I decided to try mixing the epoxy with West System brand #410 Microlight Fairing Filler. I found this filler at Dover Marine.

After the filler cured, I sanded again with 80 and then 100 grit sandpaper. Then I applied four more coats of unthickend epoxy, allowing each to dry for not more than 48 hours, and lightly hand sanded with 100 grit paper on a rubber sanding block. The reason for not allowing the epoxy to fully cure, and lightly sanding, was to encourage a chemical as well as mechanical bond between each layer.

5 comments:

Jim said...

Nice looking boat Ron! I need to build another one so I can correct all my mistakes on my present boat. :)
Great work and documentation. I wish you had this blog going when I was building.

Ron Paro said...

Thanks Jim! I had a lot of fun building the boat and writing the blog. Now I'm having a great time sailing and rowing!

Jim said...

I am in the faring painting stage. It rained for two months strait here and I had to put it on the back burner. Hopefully I will be able to get back to her soon.

Scott Sabin said...

Dear Ron,

I have very much enjoyed reading your blog. I have a more detailed question about how you faired the tape on the chines and in the places where it overlaps. It look like you got it to the point where the raised portions barely show.

If you are still keeping up with this blog can you e-mail at sabinsontheroad@hotmail.com?

Thanks!

Ron Paro said...

Thanks Scott.
A key point that I did not think to mention in my blog text was that I did not use the fiberglass tape with the selvage woven edges, which are comparatively thick. Rather, I cut 4" wide strips on a 45 degree bias from the flat cloth. If you are unfamiliar with bias cutting, it is just cutting at an angle to the weave direction in the cloth. This makes it so that the strips will easily lay flat over a contour, such as the edges and bow (chine and stem). The other advantage is that you get a thinner edge than you would have with the pre-made fiberglass tape. The disadvantage is that the edges of the cut cloth tend to unravel some, but this is not really a problem in the end. I used a rotary cutting wheel that I bought at a fabric store. This makes getting a clean straight cut a little easier.

If you click on the third picture from the bottom in this page, you will see that the edge looks pretty rough at first. After the epoxy hardened, I sanded the entire bottom, including the edges of the glass 'tape'. I did not really sand into the fibers, as they were tight against the hull. The rough looking edge is more from an accumulation of excess epoxy, which is what I did sand smooth with the surrounding surface. Even if you do sand into the edge of the fiberglass tape a little, it's not a problem, as long as you don't sand through the fiberglass cloth under the tape.

Next I added the epoxy with microlight filler. This is done in much the same way as taping and mudding drywall. You fill any low spots and spread the filler along the glass tape edge and seams. As you can see from the last picture on that page, most of the filler gets sanded off after it hardens, leaving just the low spots filled.

Whenever I am nervous about a step that I have not done before, I generally try to practice the procedure on scrap materials. This way, I build confidence and if it goes wrong, no big deal, I did not ruin anything. I just try again until I get it. Another consideration is that while it is nice to produce the finest results you are capable of, keep in mind that this is a boat that will very likely get many scratches in use. The good news is that since you built it, you know you can fix it!