Tuesday, May 4, 2010

Lining Off

With the stem in place and a full head of steam, we are excited to be thinking about moving into the planking. But first, we have to line off the boat…a job that everyone says is more feel than science.

Willy calls for five planks and although they are drawn onto the plan on the front page we realize upon inspection that the lines shown have no reference to reality. We think that the planks will look best if they appear to all be about the same size. For the middle planks that will be no problem. But the garboard and sheer strake planks present their own issues. Optically the garboard plank will include the thickness of the flooring, so this plank needs to be a little smaller than the others to appear the same size. Whereas the sheer strake plank will be partially covered by the outwale so this plank needs to be a little bigger than the middle ones.

So there you have the theory, in reality we ended up making all the middle planks the same width, the garboard about ½” smaller and the sheer strake about ¼” bigger. As it turned out our planks are not wide enough to accommodate a sheer any wider so we compromised.

We had real problems with getting good battens for the lining out. At first we ripped up a spruce 2 x 4 in to 3/8” strips and even though the board was straight to start out with it had some incredible internal forces that warped these thin strip something fierce. For stability we decided to use plywood. The 3/8” ply was ripped into ¾” wide strips (the width of our overlap) and scarfed together to make 16’ battens. We encountered some difficulties with battens where there was a gap in the 3 ply, plywood—this was solved quickly by brad nailing a section of reinforcing plywood over the bad piece. It was amazing how visual this task really is, there is lots of looking at the battens from different angles in order to determine what a “fair line” really is. Here is was we have decided to run with:

Oh, and did I mention that we needed to plane off the chines before lining off?  Probably not so here is a short of that process using old fashioned hand tools--a delightful job actually until you get right up tight to the stem where the whole process gets a little more trying.  Simply plane until a board laid across the chines lies flat on both chines.  Here is junior at work:

Our planks were purchased off a Kijiji listing for “magogany boards”. The mahogany boards are approximately 8’ long and 5 ½” wide and were used to panel a rec room for the past 20 years or so. Willy is ~14’ long and since we couldn’t find an inexpensive board stretcher we decided to scarf the boards to get the desired lengths.

Scarfing has been a huge pain in the neck, first we built a scarfing jig for a router—basically a ramp at a 12:1 ratio. Unhappy with the resulting feathered edges of the scarf we experimented with a table saw scarfing jig. This jig worked really well for the narrow chines but it is limited by the height of the blade to about 2 ½”. I tried to come up with a fool-proof way to run the board through a 2nd time to get the other half of the cut but eventually decided to wasn’t very repeatable or accurate. So I went back to the router jig and played around until I started getting nice square looking edges on the scarfs.

Router Scarfing Jig Tricks

1. As the wood gets thinner and thinner it has a tendency to start to lift up at the leading edge. Clamping it more aggressively will not stop this from happening. The result is a ragged leading edge if you just continue to finish the scarf. The trick is to elevate the back end of the board, this will keep downward pressure on the leading edge so that you can get a nice square finished edge.

2. Slowly advance the board along the scarfing jig taking medium depth passes at the beginning and lighter passes as you get close to finishing up.

3. Draw a line across the jig base to indicate the intersection between the base and the router bit. By doing this you will finish all of your scarfs in the same position and of course know when to stop (note: if you move the board beyond this point you will probably get a ragged edge cut again).

4. Another advantage of elevating the back end of the board is that you don’t need to clamp the board into position—instead I just used a small anvil as a weight to secure the board and had no troubles with the board moving during routering. Tip – check the location of the anvil by looking at the front edge of the plank, if it is too far back the leading edge of the plank will start to rise up off the base of the jig.

Using this method I found that scarfing can be a very rewarding and easy task with highly repeatable results. Although I will continue to use the table saw jig for smaller pieces of wood as it is much quicker and yields excellent results.

Gluing up the scarfed boards has been a long process that has been dictated by the speed at which our epoxy hardens. We purchased Industrial Formulators G-2 epoxy because it will cure in colder temperatures which has been a real blessing as there have been very few days so far this year when our “boat shed” (read garage here) has been above 70 F for much time. The downside to this epoxy is that it takes a long time to set up, generally 24 hrs. Consequently we have been gluing up 3-4 boards every day for the past few days and are just now ready to start the process of planking. But first we need to finish up the transom and get it installed—stay tuned!!!

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