A New Old Classic – Part 2: The Hull is Laid Up
29 09 2008The hull is the biggest single piece of the project, and arguably the most important part of the boat. For this project I’m using a four-layer hull: 2 layers of 6-oz. s-glass on the outside and 2 layers of 5-oz. kevlar on the inside. In addition, there are multiple layers of extra kevlar in the bow and stern and under the seat, as well as strips of additional kevlar to serve as longitudinal ribs for extra stiffness. Finally, in the foot area there is an additional pad of diolen to protect the kevlar from abrasion from the paddlers shoes.
Kayak in a Can. It may not look like it, but there’s a whitewater boat hidden in these cans, waiting to be released.
The boat-building process is 90% preparation. Epoxy is a very good glue, so the first responsibility of the boat-builder is to make sure that, when the layup is complete, the hardened boat part and the mold separate cleanly. So, after the cleaning the mold the next crucial step is waxing. Five coats of hand -rubbed carnauba wax seals pinholes and rough areas in the mold and forms the foundation for the mold release, a liquid plastic film that is painted onto the mold after the waxing is finished. It may seem like over-kill at times, but this is a critical steps, as a stuck part means both the part and the mold are trashed, and thousands of dollars are down the drain.
Cutting the cloth. The layers that go in to the boat must be carefully planned, with an eye toward constructability, strength, weight, and cost. Each layer is cut to fit the mold before any resin is mixed. Kevlar is fun to work with, as it’s soft, pliant, and one of the few ingredients of the entire boat-building process that isn’t toxic, carcinogenic, allergenic, or something.
The first layers are laid up. For this boat I’m using a purple pigment with silver metal flake accents. The purple contrasts strongly with the yellow kevlar. Note that the layers are carefully trimmed along the edge as they are laid up. This saves a dreadful chore of trying to trim a fully cured kevlar and glass part. This stuff is tough, and will ruin saws and knives quickly.
The hull is finished. The stern rib reinforcements are seen in the foreground, the seat reinforcement in the middle and the diolen foot pad in the distance. The white fabric along the edges is peel-ply, a material that can be peeled off the part after the resin has hardened, leaving a surface ready for application of the inside seam without the extensive sanding that is usually required.
It doesn’t look glamorous from this angle, but the exterior will be beautiful when we pop it out of the mold in a couple of days. I hope.
Nice! I’m anxious to see how it looks (and slices through the water) when you’re done! The mold looks nice. Do you happen to know the dimentions of the potential finished model (i.e. length, width, depth)?
Hi Adam,
It’s an old slalom boat, so it’s 4 meters by 60 centimeters, by ICF rules. I think the depth is about 13 inches. Not sure about the volume, but it should be in the neighborhood of 90-100 gallons.
When I get it on the water we’ll give is some trials. It should be faster than any plastic boat, but not as fast as your Isere. OTOH, it fits in the slalom boat category.
It’s always fun to look at someone else’s build pictures! I hope it looks great when finished!
I’m curious–I know that you’re not vacuum bagging, but are you using an epoxy squeegee after you wet out each layer? The reason I ask is because your pictures make it look like the fabric was wet out but not smoothly bonded to the layers under it, as if you only used a foam brush. It could just be the pics, or the fact I’ve never built a boat from a female mold.
Also, while this might not work with kevlar, I generally like wetting the glass out, letting it kick for about three or four hours, and then coming back with a box cutter and slicing the “leftovers” off. At least with fiberglass, it cuts like butter, and you get extremely crisp, clean edges.
Bill – this is very interesting. I’ve never seen this process – excited to see how it turns out
Gary
Hi Chris,
There are certainly some areas where the laminate isn’t perfect. It’s tough to get uniform results in a hand lay-up, and you only get a few passes with the squeegee until you get air in the resin and you have to stop. I tend to err on the side of excess resin rather than not enough, as a resin-starved or air-entrained laminate is pretty much unpaddle-able.
Mostly what you see in the photos, though, are areas where the purple-pigmented resin is bleeding through to the top layer. I didn’t use pigment in the top layers as it isn’t necessary for UV protection and it reduces the resin strength slightly. Areas where the purple resin bled through to the top layers give the surface a mottled look.
The box-cutter technique doesn’t work on kevlar. The only ways to cut kevlar are to use heavy duty shears when it’s still dry or wet, or use a Sawzall after it’s set up, using up many blades in the process. The box-cutter method is also somewhat dangerous, as a single slip can cause damage to the mold that will take weeks to repair. The general rule is No Sharp Tools In or Around the Mold.
Thanks for the info! It’s really interesting to see the differences between mold construction and wood-core composite construction. I really appreciate you taking the time to post this.
I can definitely see why you don’t want sharp tools around the mold! I made minor mistakes when trimming my edges, but it didn’t really matter because it could be trivially fixed when the halves were joined.