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Stitching The Hull

Once the panels have been lofted and you are happy with the lines, you can begin cutting out the panels. If you are cutting the panels out of two scarfed sheets of plywood, it is a good idea to screw the panels together. A screw placed every four feet along the inside edges of the panels will hold the panels together for cutting and fairing. A skill saw will make this cut quite easily. With the panels cut out and still screwed together, use a block plane to clean up the saw cut and do any fairing that is needed along the entire edge. It is important that you take the time to do it carefully, as any high or low areas along the edges of the panels will have a dramatic effect on the boat's lines.

A line needs to be scribed along the keel run of the bottom panels so holes can be drilled to stitch the panels together. The line for drilling the holes should be 5/16" from the edge of the panel. The holes should be placed a few inches apart on the first foot of each end about eight to ten inches apart along the rest of the run. After these holes have been drilled, wires can be put in the holes and twisted snug. Plastic wire ties will also work if you prefer. The screws holding the bottom panels together can be removed at this point. Set the bottom panels upright on the keel edge and slowly pull apart the panels. A temporary spreader may be needed to hold the bottom panels apart while the side panels are stitched in place.

Holes can now be drilled in the lower edge of the side panels. Use the same method as with the bottom panels for hole placement. Another pair of hands will be needed to stitch the side panels to the bottom panels. It is generally best to start stitching forward and work aft. The side panel can now be held up against the bottom panel, making sure the side panel is against the edge of the bottom panel and not sitting on top of it. You will need to drill holes in the bottom panel that are opposite to those already drilled in the side panel. Start by only drilling the first few holes and wire together. These are the most difficult stitches to make, but they are the most important because they determine where the panel will be located. Don't worry so much about getting the stitches tight, but rather where the side panel sits fore and aft. Any gaps in the stitching can be tightened later. When you're happy with the side panel position, continue drilling holes several at a time and stitching as you go. It gets easier as you work your way aft. As you stitch the side panel on, try to keep the bottom edge of the side panel fairly even with the bottom face of the bottom panel. After the hull is stitched, you can fine-tune all the stitched joints. When the other side panel has been stitched in place, holes can be drilled along the forward edge of both side panels so the bow can be stitched together. The hull shape will start to be defined now.

Stitch and Glue plywood epoxy construction

Fitting in the transom (made out of 1/2" to 3/4" thick plywood) can be tricky and may take a couple of tries to get the proper fit. Screws work best for holding the transom in place and should be tightened just enough for the panels and transom to touch, then backed off 1/2 turn. Over tightening the panels to the transom can create uneven lines in the hull. The screws are temporary and will be pulled later; they are only used as a clamp until the boat is glassed.

Plywod Epoxy Stitch And Glue Construction

Stitch And Glue Plywood Epoxy Construction

Three temporary spreaders need to be installed and will give the hull the desired shape. Start with the forward one and work your way aft. A screw through the sheer will hold them in place. Remember not to over tighten. The top view line drawing will give you the proper beam width for three stations. The first station (fwd) and the third station (aft) also happen to be the location for two bulkheads. It is not important that the spreaders be installed exactly at the three stations, but make sure they are below the sheer a bit. Use a straight edge at each station and check to make sure to the diagonal measurement from the stem to the sheer is equal on each side. This will make the straight edge perpendicular to the fore and aft center line. Mark the top of the side panels at each station; you will be referring back to these stations later.

Stitch And Glue Construction

The next step in construction is called tabbing or tacking the hull. Epoxy is mixed with a wood flour filler until it becomes the consistency of peanut butter and is applied with a tongue depressor to the inside corners to create a small cove. This is called a fillet. Tabbing is the first of many steps that will make the boat rigid and give it its strength, so care must be given to ensure the hull is "straight" to avoid gluing a twist in it. Every time you add fillets, fiberglass, or a structural member, you will need to make sure the boat is "straight" before you walk away from it for the day. Getting the hull straight for the initial tabbing is the critically important. All the stitched joints need to be checked: the bottom panels along the keel run need to be butted up evenly and the bottom edge of the side panels should be flush with the bottom face of the bottom panels. The hull should not be sitting on the keel, but suspended by blocks under the side panels, two at station 1 and two at station 3. The hull does not need to be level with respect to the water line, but each station and the sheer line at the transom need to be level side to side.

Plywood Epoxy Stitch And Glue Construction

When the hull is straight you can begin tabbing, and try to avoid getting epoxy on the wires if possible. It is good practice to brush on a little clear epoxy wherever a fillet will be made. Fillets should be placed between all wires on the three bottom joints and the stem, as well as the transom. Depending on the type of epoxy used and the temperature, the fillets should cure over night.

After the epoxy has cured, the wires can be snipped on the inside of the hull and easily removed from the outside. The inside will need to be sanded and excess "peanut butter" removed with a chisel or scraper. Cured epoxy must always be sanded prior to adding more or poor adhesion can occur. Sanding is best done with 80 grit sandpaper and a dual action sander. It is good practice to start each day of boat building by sanding the previous day's epoxy and glasswork. There are two things that are always assumed as I explain the construction process: cured epoxy work is sanded before any more epoxy is used and the boat is always straightened and/or leveled after new structure is added.

All interior joints will be glassed with two layers of 6 or 8 oz. cloth. I don't use pre-cut fiberglass tape so I have to cut it off a large roll; a new razor blade on a clean sheet of plywood works the best. Cut the glass in 5" or 6" strips and lay down two of them, one on top of the other, over lapping the strips about an inch, I will refer to this as a "lay-up". Cut enough lay-ups to do all the inside joints. You can pre-cut the lay-ups to the proper lengths, or cut them after the glass is wetted out with epoxy. When you are ready to start glassing, make up some "peanut butter" and fillet the joints prior to laying down glass. I find it easier to wet out the lay-ups with epoxy on a piece of plywood using an auto body plastic squeegee, rather than trying to saturate the glass in the boat with a brush. Lay the glass in place over the fillet and work out the air bubbles with a bristle brush or with your fingers (using latex gloves of course). If you have any left over glass, add it to the stem and transom. Make sure the hull is straight and let the glass cure.

The gunnels can easily be built with a 1"x2" piece of lumber as shown in figure A. I wanted a softer look at the sheer so I went with a "x2" piece of mahogany, but that left the sheer a little thin to screw the decks to, so I also put in 1'x1" piece of cedar to beef it up a bit as shown in detail B. To attach the gunnel, use epoxy thickened with wood flour to a thick honey-like consistency and screw it on from the inside. Before actually applying any epoxy, it is worth the time to completely fit the gunnel in place (dryfit). Ideally you will want the epoxy to squeeze out everywhere ensuring there are no voids. When the epoxy is cured the spreaders can be taken out. The sides may spring in a little requiring a temporary spreader.

In order to put the bulkheads (made out of 1/2" to 3/4" thick plywood) in, the boat now needs to be level fore and aft as well as side-to-side. The sheer at the bow is 1'4" above water line and the sheer at the transom is 1' above waterline. Put a 4" wide board on edge just in front of the transom then put strait edge or run a string from the bow extending back to the transom. Get the string level and the hull is level. Also check for level side-to-side to take any twist out of the hull. Drop a plumb bob from stations 1 and 3 to get a placement for the two bulkheads. You can easily make patterns from 1/4" plywood. Rip it into 4" wide strips and break off a piece large enough to span the bottom panels. Scribe and trim to get it to fit then break off two more pieces that will span the sides. Screw them together in place with 1/2" screws and your template is done. I notched the inside sheer clamp on my boat to make installation easier. To install the bulkheads, wet out the end grain with clear epoxy and spread a thick bead of "peanut butter" on it and set in place. A few screws on each side of the bulkheads will wedge them in place until the epoxy cures at which time they can be filleted and glassed like the rest of the interior hull was.

Stitch And Glue Construction

Now is a good time to seal the interior of the hull with epoxy, which I will refer to as a "flowcoat". Applying epoxy over large areas is best done with a paint roller and a 1/4" foam roller cover. The flowcoat should be "tipped off" with a bristle brush by lightly brushing over the rolled area to get any bubbles or runs out. It is a common error to apply too much epoxy during a flowcoat that will require extra hours of sanding later. When bare wood has been flowcoated, the grain of the wood will raise requiring it to be sanded and re-sealed. A properly sealed piece of wood will require no less than two flowcoats.



This is the Devlin design "Mud Peep", for more information on this design and others offered by Devlin Boat, go to devlinboat.com

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