Scarfing Weekender Rubrails

By Frank S. Hagan

The Gaff Rig recognizes that boat building involves inherently dangerous activities, and each builder must be responsible for his own safety. The Gaff Rig encourages all builders to read manufacturer’s instructions, follow all safety precautions, and be pro-active in seeking out more information on reducing the risk of injury or illness. Information presented here is general in nature and not intended to replace the safety instructions provided with products or tools.

      A common complaint is finding clear, nice looking wood long enough for use as rub rails. An alternative to that elusive long, clear stock is to join two shorter pieces using a "scarf" joint.
     Why a specialized joint for boat building? In order to make a good, strong joint in wood, you have to maximize the amount of glue surface. The scarf joint is often used in boat building because it produces a strong joint. Other methods may do the same, including a long lap joint combined with fasteners, finger joints, etc., but the scarf has several advantages: it makes a nearly invisible joint, is easy to align and glue, and will take a bend just as well as the wood it is a part of ... which is important for our rub rails.
     The scarf joint is a long angled joint using a 7:1 or longer angle. For every inch of the thickness of the wood, you need at least 7 inches in joint length. Because we bend our rub rails, I recommend a longer scarf joint of at least 8:1, and preferably 12:1 if using douglas fir, pine, or other coarser grained woods. For the purposes of this article, I'll use the 12:1 scarf. The math in making this joint in our rub rails is simplified since we'll be using 1 x 2 materials, but the same methods can be adapted for thicker stock.

     Three Scarf Joint Methods

     In this article, I'll outline three methods to produce a scarf joint: using a table saw, a hand plane (or router) and a circular saw. I have used the first two in the past. The circular saw jig is one I have seen, but I have never used. It looks like it would work fine.
     My rub rails turned out six inches longer than the 16’ I thought I would need. At first, I lamented the fact that I could not scarf two 8’ boards together to get the right length. But In a scarf joint, you overlap the stock by the length of the scarf. For our 12:1 scarf, we will "lose" 12" of the combined length of the two boards. If you used two 8' 1 x 2s, you would end up with 15', as the scarf joint "overlaps" the boards by 1'. So, even with just 16’ rub rails, I would need stock longer than 8’ to scarf together.

     Materials Needed

      If you are buying finished 1 x 2s, you should be able to buy 10' or longer pieces. Buy any combination of pieces that will give you at least 18' total before scarfing. For the standard plans, there are 4 rub rails, so you need 4 of each length to finish this project. An example would be to buy four 10’ 1 x 2s, and four 8’ 1 x 2s.
     You also need glue ... either epoxy, Weldwood Plastic Resin Glue or something like "Gorilla Glue," one of the new waterproof polyurethane glues available at most hardware stores. Two c-clamps, some plastic wrap stolen from the kitchen, and some scraps of plywood round out the materials list (except for screws and miscellaneous supplies needed to make the jigs, which I'll cover in each section.)

     Easy Table Saw Scarfing

     I used the table saw to make my scarf joints on Aslan. A common jig in a woodshop is a tapering jig to make angled cuts. Using a few scraps of lumber you can easily make a temporary one for your scarf joints. For this temporary jig, you need 2 1 x 2 scraps at least 14" long, some shorter pieces of scrap wood (plywood, lath or even more 1 x 2), and some 1" drywall or other screws.
     Start with the 2 1 x 2 pieces and place their 1" sides down on a flat surface with the 2" faces aligned together. Take a pencil and mark them 12" down from one end. While holding the opposite end together, spread the other end apart by moving only one piece so that your rub rail material, resting on the 1" edge, will just fit between the two at the mark. The piece you moved is now the "angled piece" and the other is the "straight piece." Now, place a piece of scrap over each end and screw the scrap onto the top of both 1 x 2s (you'll need two screws in each end.) This will fix the two 1 x 2 pieces into position. You don't want the edge of the scrap to protrude over the edge of the "straight piece," since that piece will need to ride flush against your rip fence on the table saw (you can trim it off if it does overhang.) Excess protruding over the angled piece is perfectly fine, unless your angle cutting jig is not as tall as your rub rail stock, in which case it will need to be trimmed also. (An easy way to trim it is to turn the jig upside down, use your miter gauge and adjust the angle to carefully trim off the excess.)
     Now you've created a right triangle out of wood that is 1" wider 12" from the top. To use the jig, position the straight piece against the table saw fence with the narrow end towards the blade. Place the rub rail stock next to the angled piece, aligning the end with the narrow end of the jig. Adjust the table saw fence so that the blade is at the outer edge of the rub rail stock. Sight down the assembly to make sure that when you turn on the saw, and advance the jig and rub rail stock together, the blade will cut through the rub rail on an angle and cut into the jig at the 12" mark you made earlier. If all looks like it will work, place another piece of scrap well in front of the mark made at 12", and screw it down too. This will keep your angle jig at the same angle should the excitement of making your first scarf joint cut cause you to cut completely through the jig.
     I use a small finishing nail in the piece of scrap that overhangs the narrow end of the jig to keep the rub rail stock from moving as I push it into the blade. Remember to keep your hands and fingers toward the back of the jig, well to the side of the spinning blade (you'll need all those fingers when it comes time to sail.) And while we're talking about safety, remember to support the long end of the rub rail stock with something stationary, lest your helper think the ringing phone more important than the expensive rub rail stock. Been there, done that, and had to buy more wood.

     An Even Easier Table Saw Jig

      By now, you may realize that you can also make a taper jig by simply cutting a piece of plywood into a right triangle, with the triangle 1" wider 12" from the top. You can tack a small stop onto the narrow end for the rub rail stock to push against. Easy enough to do, but you do lose some of the ease of use the wider jig gives you, especially if you secure the stock with the finishing nail. But the choice is up to the builder and his or her own level of confidence in using the table saw.
     Because the table saw and this jig make repeatable cuts, you can use it the same way each time by orientating the stock correctly. If you have a particular side of the rub rail you want facing out, cut the first piece with that side facing out towards the blade, and then the second piece with the preferred side facing in towards the jig (see Gluing it Up later in this article.)

     Scarfing with a Hand Plane or Router

     This second method is a common one, and has been used for centuries. It is covered well in the book "The Sailor's Sketchbook" by Bruce Bingham, published by International Marine (ISBN 0-07-155096-8.) I've adapted his formulas to our 12:1 scarf to simplify things.
     You will need a piece of plywood scrap 4" wide by 18" long, and at least 1 1 x 2 scrap 12" long. Mark a line along the 2" wide face of the 1 x 2 from 1" up from one corner along one end to the point of the opposite corner, forming a triangle 1" wide at one end diminishing to nothing at the other. You need two of these, so depending on your cutting ability, you may be able to get another piece out of the same 1 x 2 stock. If not, cut another one out. Clamp both together with the factory cut edges lined up, and make sure the tops are identical in slope by sanding or planing them. Now, place them on top of the plywood and position them so the rub rail stock just fits between them, as shown in the diagram above (note that I have the triangular "rails" screwed to the top of the plywood -- this simplifies measurement and uses the scraps of plywood we already have.) Turn the assembly upside down and glue and screw the rails to the plywood.
     To use this jig, you set the rub rail stock in the jig so the end lines up with the end of the jig, clamp it down, and guide the plane along the triangular rails to remove all the stock that doesn't look like a scarf joint, as shown in Bingham's diagram. After planing in this manner, use 100 grit sandpaper cut as wide as the rub rail stock but wrapped around a block of wood large enough to ride on the rails to finish up the surface. As in the table saw jig, you need to think about the side of the rub rail you want facing out, and plane the first piece with that side facing up, and the second piece with the preferred side facing down (see Gluing it Up later in this article.)

     To adapt this for use with a router, screw strips of 1/4" plywood on top of the rails. Use a bushing in the router and a straight cutting bit set at 1/4" depth. Guide the router on top of the rails, removing the waste (you'll be "freehand" where the rub rail stock is higher than the plywood strips, so take some care here.)

     A Circular Saw Scarf Jig

      If you've read the other two scarfing methods, you realize that two things are important: getting a repeatable angle, and being able to do it securely. That is even more important when using a circular saw.
     Because a circular saw is hand held, you need a sturdy jig that can support the weight of the saw as you use it. And there's a lot of variation in circular saws out there. This jig will work with a 7 1/4" blade. For this jig, you need 3 pieces of 2 x 4 24" long, some scrap plywood about 18" long and at least 6" wide, and a piece of scrap wood that is thin and at least 12" long (a piece of molding works well, a batten, or a strip of 1/4" plywood). You'll need some fasteners too, 8 2" long drywall or other screws and 20 or so screws long enough to go through your plywood scrap (3/4" or 1" will work.)
     First, unplug your circular saw and set it for the deepest cut possible. If you have a 7 1/4" circular saw, you should get about 3" total depth of cut. For this jig to work, you need at least 2" plus the thickness of the scrap plywood you're using. If you have one of those small 5" blades, you'll have to adapt the construction of the jig to suit the smaller blade.
     This jig is basically a u-shaped box that is built like the proverbial brick "land-based head." It is overbuilt to make it secure and safe to use with a hand held circular saw.
     Start by setting one of the 2 x 4s on edge, with the narrow part down, and place another one next to it with the edge butted against its face. The first 2 x 4 we'll call the "upright" one, and the second one the "flat" one. The two form an "L" when placed this way. Measure the inside of the upright 2 x 4 above the flat 2 x 4 ... you want to have enough room here so that the rub rail stock will fit on top of the flat 2 x 4 and not protrude above the edge of the upright 2 x 4. Most 2 x 4s are actually 1 1/2 by 3 1/2" and these instructions assume that. Most finished 1 x 2 rub rail stock will also be 1 1/2 to 1 3/4" wide. So, if you have the "normal" dimensions given, you can fit the rub rail stock, on its edge, on top of the flat 2 x 4 without it protruding above the upright 2 x 4. If not, place some 1/4" plywood scraps under the edge of the first 2 x 4. Glue and screw the 2 x 4s together with the long screws. Then, put the remaining 2 x 4 on edge, with the flat 2 x 4's free edge butted up against it, making a u-shaped assembly. If you had to use 1/4 plywood spacers in the step above to allow the rub rail stock to fit on top of the flat 2 x 4, then do so here too. Glue and screw this final 2 x 4 to the flat 2 x 4.

     With the open side of the channel facing up, make a mark 6" from one end of the assembly, and attach the piece of plywood to the upright 2 x 4s, aligning the front edge with this mark. Be sure to allow enough overlap onto each of the upright 2 x 4s to securely screw the plywood in place. Place a straight edge along the plywood, aligned with the inner edge of the first upright 2 x 4, and mark a line along it. This line shows the inside edge of the upright 2 x 4.

Measure back 14" from the front of the plywood, and make a mark 1" out from the upright 2 x 4 line. This mark indicates where the circular saw will begin to cut into your rub rail stock, so now we need to figure out how to put a guide-batten on the jig to guide the saw. Measure the foot of your circular saw, from the narrowest side of the foot to the blade. On my circular saw, it is 7/16". Measure back in from the mark made back toward the upright 2 x 4 line by this amount. Tack one end of the thin piece of wood, which is our guide-batten, at this point. Measure in from the front edge of the plywood 2", and make a mark the width of the narrowest side of the foot on your circular saw on the outboard side of the line indicating the edge of the upright 2 x 4 (in other words, over the edge of the 2 x 4 itself). Tack the other end of the guide-batten at this mark. You should now have a guide-batten that angles from over the channel formed by the 2 x 4s to about the middle of the first upright 2 x 4. Unplug your saw and raise the blade all the way. Guide it along the guide-batten on top of the jig to see if the blade will cut through a 1 x 2 placed inside the jig, forming an angled cut over about 12" (if you’re off by an inch or so, it doesn’t matter.) If it looks good, draw a line along the side of the guide-batten, remove it, and use glue and screws to reattach it securely.
     Set your circular saw depth so that you barely cut the surface of the flat 2 x 4 when guiding it along the thin piece of wood just attached (normally, about 2 ¼" deep if you used ¼" plywood for the top of the jig.) Check to see that you won't saw through any of the screws holding the plywood in place, and guide the saw along the guide-batten, cutting completely through the upright 2 x 4 as you begin and finish the cut. To use this jig, you feed the rub rail stock in from either end, always keeping the face side of the rub rail facing away from the first upright 2 x 4. This means for each rub rail, you will feed the first piece in from the front with the appearance side facing out, and the second piece in from the rear with the appearance side facing out. Unlike the table saw angle jig and the hand plane jig, this jig relies on the fact that any variation in the cutting should cancel itself out when both pieces are cut the same way.

     Gluing It Up

     Gluing a scarf joint is not hard, but does take some planning. You need enough support under the glued up assembly so that the hanging sides don’t pull the joint apart. I found the beam of the Weekender to work fine. Apply a generous amount of Weldwood Plastic Resin Glue, epoxy, or Gorilla Glue to both surfaces and align them. I used pieces of plastic wrap on top and bottom, then small scraps of plywood, and a c-clamp or two to hold everything together. Allow to dry at least 24 hours before trying to bend the stock (check your glue label for "fully cured" time and abide by it as a minimum.)