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Shaping and Glassing the Hull

As I have progressed with the construction of the Mud Peep, I have recommended the application of fiberglass in specific areas and in varying weights and number of layers. All of this glassing was done to strengthen and reinforce the various weaknesses in a plywood hull. In most cases, the glassing made the weak areas stronger than the surrounding wood. The gusset created by adding two layers of glass to a fillet adds incredible strength to a joint, but you will not get near the same benefit from adding two layers of glass to a large flat area. This does not make glassing the large areas of the hull and decks any less important than the structural glassing done inside the hull. The life span of a stitch and glue boat is more dependent on how well the hull is protected than how strong it is. Throughout the construction of this boat, I have emphasized epoxy sealing all parts at least two times to protect the wood from moisture. Protecting the exterior of the hull is more problematic because of the constant physical abuse it will sustain. Even a relatively small gouge on an epoxy-sealed piece of wood can compromise the structural integrity of it over time. The big benefit of glassing the exterior of the hull and the decks is for abrasion resistance, but there is also a structural benefit from the glass wrapping around corners that also acts as a gusset much like glassing a fillet. Because of the varying shape of a hull, it is difficult to just lay one piece of glass over it and wet it out with epoxy. Whenever I lay glass over a hull, I try to lap it at least several inches past a joint, be it a chine, stem, keel or transom joint. The next layer I will lap several inches over the other side of the joint. I apply glass to the exterior of a hull with two goals in mind, the first is to cover all wood for abrasion protection, and the second is to double up at all the joints for a structural benefit. Adding extra glass to the joints not only strengthens the joint, it also adds extra protection to the end grain of the plywood. As you shape the corners of the hull, you will find that the individual plies of the plywood will widen creating more end grain, which can be a problem area if not properly protected. At the bow and transom I will end up with four or more layers of glass overlapping the joints four to six inches, staggering the layers to make the fairing easier.

The three main tools for fairing a hull are a low angle block plane, an eight-inch grinder with a hard pad and 36 grit paper, and a "blaster board" which is a 2 3/4" x 16" piece of wood with a 36 grit piece of self-adhesive sandpaper. This sandpaper can be purchased at any auto body store. The first step in fairing the hull is to grind or plane off any overhanging plywood or epoxy such as at the stern where the plywood may have run beyond the transom and at the chine where the side panels dropped below the bottom panels. The objective is to get all the corners sharp. There will be some areas where the joints will not grind to a sharp edge because of a lack of material, don't over grind to get a sharp edge everywhere if it creates an unfair line. At the bow I will plane the ends of the side panels to get a flat area that runs from the sheer to the chine. The transom should have sharp straight lines, and the chine and keel lines should be a fair curve. Any high areas of the hull should be taken out now.

When the hull has been faired all the joints can be rounded over. Because the corners are rarely at 90 a router will not work, so a block plane is the best tool to use.

Stitch And Glue Plywood Epoxy Boat Construction

I will start by putting 3/8" facet on the sharp edge with a block plane. If your chine was fair, the lines created by the facet will also be. Use the plies in the wood as your guide as you start rounding the chine. You should end up with straight parallel lines that run the length of the joint. Wherever you had to fair the hull, you cannot use the plies as your guide, so keep this in mind as work to get the corners round. In Fig 2 you can see the final shape of the bow. In order to give the bottom corner of the bow a soft look, I had to take quite a bit of material off. I went completely through the 1/4" plywood on the side and bottom panels when shaping, but stopped at the interior glass. This will not weaken the area because of the mast step that was installed on the inside, which reinforces this area.

Epoxy Plywood Stitch And Glue Boat Construction

There is no specific radius to use on the corners, but I prefer to use larger radiuses on sailboats giving a softer look. After the rough shaping is done I use the blaster board to even everything out. I will finish with a palm sander and 80 grit sand paper.

I glassed the decks earlier, but will go over it in more detail here. In Fig. 3, I am wrapping up the glassing of the aft deck. The large areas are best wetted out with a plastic auto body squeegee. For the corners a foam roller cover works best to wet out the glass, and a bristle brush for any inside corners and for touching up any dry areas. Notice that all corners were wrapped with glass. When the hull is flipped to glass the bottom, the corners will be wrapped again. After the epoxy has cured, the corners and edges of the glass may be a little rough. The blaster board makes quick work of smoothing these areas out.

Stitch And Glue Plywood Boat Construction

The bottom and transom can be glassed all at once, or in several stages if you are more comfortable doing it that way. Don't worry about using continuous pieces of glass to cover the whole side panels or bottom panels at once. There is no harm in overlapping the glass if you feel more comfortable working small areas at a time. If you want to glass the whole length of the hull at once it will probably take two runs of glass, one for each side. If the glass overlaps way past the keel line, let it. The extra glass on the bottom will only help. With the glass laid out on the boat, and I prefer to lay the glass over a dry hull and work the epoxy through. Start in the middle and work your way out. I will mix about a quart of epoxy at a time and pour it over the glass, working it outward with a squeegee. The large areas are easy, but the bow and transom areas will require a bit of work. When I get to the transom, I will use a razor blade or scissors to cut the glass at the chine joint and wrap the glass from the bottom panel over the transom, and then I will wrap the glass from the side panel over the transom. Use the same method forward. The sheer clamp area will require a bit of work with a bristle brush. The sheer clamps on my boat are tapered at the bottoms and come to sharp point at the hull so I can wrap the glass over the sheer onto the decks. If you went with a 3/4" sheer clamp with a round over, you will need to fillet the clamp in order to get the glass to wrap around it, or just cut the glass at the bottom of the clamp. If you find trouble areas where the glass won't stay down, use a razor blade to cut the bubble.

One problem area that we will need to address is the dagger board trunk hole. I think it will be easiest to not glass it or several inches around it when the bottom is glassed. Come back later and sand the rough glass around the dagger board trunk hole. Use a router or hand sand the opening with a 1/4" or larger radius so the glass will wrap around inside of the trunk. I would use only use one layer of glass that wraps about an inch inside the hole.

Whenever glassing avoid using too much epoxy. As I said earlier, I just pour the epoxy over the glass, which is not a problem to initially wet out the glass, but as I work outward I scrape the excess away. You want a thick epoxy layer, but whenever the glass looks smooth and shiny you have applied too much. The glass will float on the epoxy making later fairing more difficult. The glass should be wet, but the weave pattern should also be readily visible. Later sanding and flow coats will fill the rough pattern and make it smooth.

Now that the exterior of the hull has been glassed, it needs to be shaped and sealed several times. Use the blaster board to knock of any rough glass, runs or drips and sand with 80 grit All overlapping glass needs to be faired smooth and the blaster board will work best. You want to avoid using anything with a soft pad because it will remove material everywhere, not just the overlap. It does not have to be completely flat but you will want to get out about 90% of the unfairness. Future flow coats and fills will finish the fairing. The same approach can be taken with the large areas of glass, just sand out the bulk of the weave pattern and flow coats will fill the rest. In particularly uneven areas, such as where many layers of glass are overlapping, you can used thickened epoxy and trowel the rough areas. When it has cured, use the blaster board to fair it out.

The skeg can be added after the hull has been glassed. It is easiest to attach it by applying a thick layer of peanut butter and using masking tape to hold it in place until the epoxy has cured. Add a fillet around the skeg and apply a couple of layers of glass over it.

Stitch And Glue Plywood Boat Construction

After the hull has been sanded, faired and sealed as many times as necessary to get the quality you are after, add one more thin coat of epoxy to seal any exposed glassed and sand with 150 grit sand paper to get ready for primer. Any areas that are to be varnished should be sanded with 220 grit.



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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