A Canadian Canoes Information Sheet MAKING A STRONGBACK USING MANUFACTURED I-BEAMS BACKGROUND: We have worked with Ted Moores (author of CANOECRAFT and KAYAKCRAFT ) for 28 years. For most of that time, we have employed the plywood box beam style of strongback that Ted describes so well in his books. In the fall of 2001, we were involved in the construction of several 22 foot recreational rowing shells (the Dragonfly) designed by Steve Killing who has been instrumental in the many canoe and kayak designs found in Ted s books. We needed to make a long, straight and flat strongback upon which we could build this very narrow boat. The plywood box beam style of strongback did not seem to satisfy these requirements without a lot of fancy construction. By chance, we learned about the laminated I-beams being used in house construction to replace conventional 2 x 12 s for floor joists. A bit later, we discovered these are manufactured to be straight and flat (nice for a floor) and could have spans up to 45 feet long. Thus, we decided to make the strongback for the Dragonfly out of a pair of these I-beams with a flat plywood top. It turned out that making this style was simply faster and less costly than using plywood. Subsequent to that experience, we have made at least 30 of this style and will continue to do so. Of course, this strongback does have a drawback: it does not come apart into neat eight foot sections as will the plywood box beam style. So, if your canoe building is in a really restricted space, you might want to factor this fact in the decision making process. 1
THANKS TO MR. BOB IRELAND In the winter of 2002, Bob came to Canadian Canoes to build his own woodstrip canoe. Being recently retired, Bob was fulfilling one of his goals with this project. In fact, his plans included making several more canoes at his cottage property in eastern Ontario. Thus, he decided to make a strongback and then add on station molds then build his canoe on this new setup. So, our thanks to Bob for allowing me to take AND USE images of the process. The photo above is of his strongback all set up with station molds. Here, below is Bob s finished 15 RANGER -early summer 2002. This document follows the construction steps Bob used to complete his strongback. Note that for longer canoes/kayaks you will need to adjust the number of cross blocks to which the station molds are attached. A list of building materials is to found on the last page of this booklet. We have found at least five different manufacturers of these I-beams in our area. Although they all look about the same, the measurements are different. This will play a role when you are in the construction phase. The sketch at the right shows a typical beam. The I-beams vary in size-adjust measurements of gussets in particular to fit what you have. 2
CONSTRUCTION PROCEDURES: (A) Set up the two I-BEAMS on a pair of sawhorses. Place them side by side (not separated as in photo) and do the layout of the gusset lines as in the next diagram. Draw your lines on the TOP RAIL and along the vertical faces; this will make installing the gussets an easier task. Next, separate the beams as shown in this image; the separation distance will be about 7 inches or the width of your gussets. Next, make the I beams as level as possible from end to end and side to side. Use thin shims if necessary. (B) Along the top outside edge of the I-beams, lay out lines as shown in this diagram; these are the positions for the EIGHT notched LOCKING GUSSETS that act to keep the unit straight and square. 3
(C) The LOCKING GUSSETS (depending on the manufacturer) may be 7 x 9.5 or perhaps 8.5 x 9.0 with the corners notched to fit the size of the edge strip that forms the I beam. Take time to get these corners nice and square. You will notice there are two pairs of gussets which are only 10 apart starting 44 away from the midpoint of the beams. These will be the locations for the support legs. Once you are confident that the gussets are set vertically and are perpendicular to the I-beams, draw lines, predrill through the I-beam and into the gusset with a 1/8 bit then connect the I-beams and gussets with 2 #6 drywall screws; we use 3 screws at each location. It is also a good plan to use a small square to keep the gusset perpendicular to the I-beam. Here is a series of pictures that show the steps in this part of the procedure: FACE) 4
Now, you are ready to create the flat table-like working surface. These two TOP PLATES are made from either 5/8 or ¾ plywood which really must be Good One Side. This is important as all sorts of lines will be drawn on this surface. The two pieces are 12 wide and 8 feet long. To align the top plates and to create an overhang use a series of 1 wide blocks about 4 long and clamped(temporarily) to the underside to ensure that there will be a 1 overhang on both sides and that the plywood is evenly spaced along the sides of the I-beam. This overhang is used to position and screw the station cross blocks a bit later. After a dry fit tells you all is in readiness, remove the TOP PLATES and spread a line of yellow glue along both top rails of the I-beam. Reposition the two plates, hold with clamps then draw straight lines so you can develop a neat pattern as you screw the plates to the I-beams running along the mid point of the top of the I beam. We use a 5 spacing. Once again, 2 #6 drywall screws are employed to do the task. (D) The next step involves turning the partly completed box upside down then making the two SUPPORT LEGS that will be BOLTED in place. The two vertical legs are 2 x 6 x 24 long and the top piece seen in this photo happens to be 13 7/8 ( your measure may be a bit different depending on the beam you purchase.) The two 24 legs sit on the underside of the top plate. Each three part leg section is placed such that it is centered at a point 49 from the middle of the top plate. If you have your inverted box set nice and level on sawhorses, then it should be easy to set the legs so they are vertical (use a level to see that the legs are plumb). The legs are fastened in place with a total of 16 carriage bolts which are ¼ x 3 ½. The photo shows the bolts passing through the leg vertical member and through the upper and lower rail of the I-beam. The short top piece is glued and screwed with 3 ½ screws (deck screws work very well). 5
Now, the FLOOR SUPPORT BAR is prepared. Because shop floors are not necessarily level, we find it is prudent to insert some simple leveling feet. These are readily available at hardware stores. Usually, they come with a threaded T-nut which is inserted (by hammering) into a predrilled hole. The floor support is another piece of 2 x 6 stock 24 long. The holes for the T- nuts are drilled 3 in from the ends. Hammer the T- nuts in place, thread in the adjustable leveler leg then clamp this entire unit so it is horizontal (i.e. parallel to the strongback top plate).also note in the photo that this piece is set ¼ above the three part leg; this will help later when leveling off the strongback. It is also a good idea to completely screw down the 4 levelers. Use a total of 8 wood screws- 3 ½ #10- to connect the floor support bar to the vertical legs.be sure to center this piece before drilling and screwing it in place. At this point, the whole unit gets turned right-side-up. Move the strongback to the location where you will build your craft. Here, you can use one or more spirit levels to ensure that the whole strongback is level end-to-end and side to side. This is when you use the 4 leveling feet which are screwed into the floor support bar. You could choose to round the corners a bit before screwing these parts in place.. The process of drawing an accurate midline, attaching cross blocks to hold station molds and all the steps preparatory to building your craft are very clearly explained in Ted Moores CANOECRAFT (be sure to have the revised edition) or KAYAKCRAFT. 6
Here are a few photos of Bob Ireland s completed strongback with him attaching the station cross blocks and the actual CNC cut station molds. 7
MATERIALS LIST : STRONGBACK CONSTRUCTION 2 manufactured I-BEAMS 16 feet long and about 9.5 tall (take time to select two which show the best lines for being straight) 8 LOCKING GUSSETS of 3/4 plywood with very square corners; typically, these will measure 8.5 wide x 9.0 tall-but be sure to check if this will work with the I-beams you purchase. 2 plywood TOP PLATES GOOD ONE SIDE 5/8 or ¾ thick 12 wide and 8 feet long. 8 LEG PIECES all are made of straight 2 x 6 stock. SIX will be 24 long and 2 MAY be 13 7/8 this will depend on the dimensions of the I-beams. See notes above for an explanation. 200 DRYWALL SCREWS 2 #6 size 16 WOOD SCREWS 3 ½ # 10 size 16 CARRIAGE BOLTS ¼ x 3 ½ or 4 ½ -5 (depends on width of I- beam rail) 4 LEVELLING FEET complete with locking T-nuts Ron Frenette Canadian Canoes February 2011 8