Thursday, February 22, 2007

Two seats, a skeg and a mast spar

I added SiteMeter to this blog a few weeks ago, and I would like to thank all of you for your interest in my wooden skiff building project. So far there have been over 150 visitors from a dozen different countries all around the world, stretching from Alaska to Australia. I was aware that Chesapeake Light Craft has a very widespread appeal and a global customer base, but I am very pleased to see the interest in this simple yet elegant sailing skiff. I remember seeing a post on CLC's Builder's Forum some time ago wherein the person was asking if anyone has built a Jimmy Skiff ™, and questioned the Jimmy Skiff's ™ popularity. Here was CLC's response:

"We've sold more Jimmy Skiffs over the years than Skerries and Passagemaker Dinghies combined; it's one of our most popular non-paddling boats. (Blogs and forums aren't a reliable measure of the number of boats out there.)

It's an excellent all-round skiff, very easy to build. Rows really well; you can row it all day if you wanted. Fast and weatherly under sail. Just a good old skiff, nothing flash or fancy."

I wonder if Jimmy Skiff ™ 'fans' may tend to be more conservative than those drawn to other designs. This may explain the lack of other Jimmy Skiff ™ blogs. Or, maybe other Jimmy Skiff ™ builders were just having too much fun building and then sailing their boats that they simply did not take time to share in this way. As for me, I am thoroughly enjoying the entire experience, including writing this blog.

I closed my previous post by saying that I would be installing the seats and bulkheads next. When it came time to get to work on the boat, I realized that I was getting a little ahead of myself again. I had cut out the seat parts at the same time as I cut most of the other parts, but I still needed to assemble the seats before I could install them in the hull. Since the seat parts had been coated with unthickened epoxy earlier, I started by tacking on some temporary glue blocks with a 18 gauge pneumatic brad nailer. I only nailed through the sides where it will be easy to fill and hide the holes if I choose to varnish the seats vs painting them. The blocks were cut in the shape of an 'L' so that they would not become permanently glued to the bottom of the seats. Click on the photo for a better look. My purpose in using the blocks was to ensure the squareness of the supports to the seat tops. This was not something that was shown in the plans or building guide, but I found that it did help keep everything in place until the glue was dry.

After using an epoxy and silica mix to glue the seat supports to the tops, and allowing them to cure while clamped, I removed the temporary blocks and pulled out the steel brads. Next, I mixed the epoxy and wood flour to form small fillets on the insides where the seat supports meet the tops. This is what really gives strength to the joint.

This is the blank I glued up for the skeg. I ripped a relatively straight-grained oak board into 1½" widths, and then alternated the grain before gluing it back together. This should keep it from warping. I figure that having a warped skeg would be like having the wheels of my car pointing in different directions. That would be bad, right?

After the skeg epoxy cured, I marked the final shape on the blank by holding it in place against the bottom of the skiff and tracing the curve with a pencil compass and the assistance of my lovely wife. I then cut out the skeg and fastened it in place on the bottom of the boat with thickened epoxy and eight bronze screws driven in from the inside of the hull. I then formed a fillet around the skeg.

In order to support the bottom of the boat without putting undue stress on the skeg while it cured, I added a 'Y' shaped support to the rear saw horse which holds the hull from tipping and placing lateral pressure on the skeg.

Since I was in 'part making mode', I decided to go ahead and mill the parts for the mast and boom spars. I used this sliding scarf jig that I built when I needed to cut scarfs for the inwales last week. The toggle clamp holds the board while I slide the jig along the saw's fence. This is set up to cut 12:1 scarf joints. This means that for every inch of board thickness, the joint will be twelve inches long.

The spars for the mast and sprit boom will be made with pieces ripped from 4" x 4" x 8' Douglas Fir beams. I dug through two pallets of beams at Home Depot to pull out the best four specimens with regard to straightness, tight knots, and lack of splits. I knew that when I ripped these, there would pieces that would not be suitable for the spars, so that is why I bought four. As it turned out, I only needed to rip three of the beams to get all the very good pieces I needed for the mast and boom. The 1½" x 1½" x 10' long blank for the sprit boom is shown on the right side of the photo. This was glued up from pieces that were ripped to 1½" x ¾".

The mast spar blank will be 2¼" x 2¼" x 16'5". Note that as I cut the pieces and fit them together, I marked each joint to indicate orientation. In case anyone is wondering, the white 'paper' I used to protect my shop floor while gluing is Tyvek. I know that some people like to make sails out of this very durable material, but I think that this is a much better use of the extra I had from an earlier building project. Thanks again for bearing with me, and hopefully next time I'll show you the seat and bulkhead installation.

Sunday, February 11, 2007

Inwales a.k.a. Sheer Clamps

In the Jimmy Skiff ™ building instruction book which accompanied the plans, the solid wood strips that run along the inside of the top of both sides of the boat hull are referred to as 'sheer clamps'. Since the side of the hull is the 'sheer', and the wood strips serve to help hold the shape of the sheer, I can see how this term would be descriptive, especially when a deck is attached to the top of the sheer clamp. More frequently, I have seen these parts referred to as 'inwales', when discussing an open hull. According to a wikipedia article, "The gunwale, pronounced 'gunnel' to rhyme with 'tunnel', is a nautical term describing the top edge of the side of a boat." The gunwale typically consists of the inwale on the inside, and the outwale or rub rail on the outside of the hull.

Since the temperature climbed up out of the single digits to about 30° here yesterday, I decided that it was time to once again crank up my tiny portable electric space heater and resume work on the Jimmy Skiff ™ project. My workshop is insulated pretty well, so I just use the portable unit. It will hold the temperature in the shop at about 70°, even when it is very cold outside, but when it is less than 25°, the heater has to run constantly to maintain the shop temperature at a level warm enough for curing the epoxy. Since my shop has been unheated for a couple of weeks, it took all day for the temperature to rise to 70°. Not only does the air need to be heated, it is even more important that the wood and epoxy are warm before attempting to glue or saturate with epoxy.

After the scarf joints on the inwale pieces have cured, the next thing to do is to cut the inwales to length. Since there will be a deck over the bow which will hide the miter joint where the two sides meet at the stem, I started by cutting the stern end so that I would get as near perfect fit as possible where it would show. This is a compound angle cut because the sheers and stern are angled out toward the top. I left the inwale slightly proud of the hull, and I will trim it flush after the epoxy cures. When using 'c'clamps, it is a good idea to protect the wood with a small piece of scrap material.

After I fit the stern ends, I marked and mitered the ends where they meet at the stem. Again, these where compound miter cuts due to the flare of the sheers. Since the deck will have a bit of camber, leaving the inwales slightly raised will allow me to trim them with an angle that will match the underside of the deck for a nice tight fit.

Since I needed a clamp about every six inches, I used every clamp I had in the shop, except for the long bar and pipe clamps.

I didn't have quite enough clamps, and I am going to be adding rub rails or outwales later, so I used 1" drywall screws to temporarily hold things snug in a few spots. I drilled pilot holes before driving the screws. I will remove these screws at the same time as I remove the clamps.

Next I will add the bulkheads and seats. I will leave the top off the rear seat until after I turn the hull over again to add the skeg. This is because the skeg is screwed on from the inside and the rear seat top would be in the way.

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.