Building folding boats is a great way to show off your creative muscle. Collapsible boats in particular are useful, because you can often get away with not having to buy a trailer to haul it around, and after it dries out, it stores well in a compact space like your trunk. Your best bet as a first-time boat builder is to start simple by making a boat for one person.
Create a small rowboat design that is simple and portable. Make sure that you carefully design and plan your boat with the ends in mind. You need it yo be watertight, stable and strong enough to hold whatever cargo will be in it. You need a place to rest the oars and to brace them against while rowing on the edges of the boat. Use the appropriate materials and make sure that the boat is large enough for the purposes for which you are going to use it.
Make sure the keel of the boat runs up and down the boat, since it is the spine of the boat that rests lower in the water. It should be made of a wood that is traditionally used in boat building for strength and beauty, but you can also use plywood in a glue-up to make an appropriately strong keel. Several lengths of wood planks should be designed to go parallel to the keel and are attached at the ends of the keel in a set of hinges so that either end of the boat resembles a tripod when they fan out. You then need removable braces that hold these in place when they fan out, including a board or set of boards that provides a place to step. These boards help to brace the keel outward against the water it is pushing towards once the skin is on so that it doesn't fold back on you when you take it out into the water. These two pieces should be latched securely in place so that they don't come undone inadvertently as you move around in the boat. Make sure that the latches are sufficiently strong and are screwed into the wood so that it doesn't come out. To save weight, some people use lightweight, non-corroding cordage.
Do a glue-up by taking pieces of wood to glue together and coating the sides to stick together with a thin layer of wood glue (make sure it is the water-proof variety). Put the pieces together so that there are no air bubbles and tightly clamp the pieces of wood tightly together so that they stay that way at all contact points until the glue is dry. Give it about 12 to 24 hours to dry, depending on what your bottle says to do. Make sure that you do not cut parts too small, making them flimsy. Test your boat repeatedly before you go out in it. The bow supports (ribs) can be cut out of plywood to the shape that you want. Make a system that allows you to install and remove the ribs with ease. It might help if the shape of the boat is the same on both sides so that you can make the supports in pairs. Making a templates out of some scrap wood or cardboard as a guide. This will also see how the pieces fit together in the final project. These templates can be used to cut several pieces and saved in case you want to make more boats or repair the one you have. The ribs and other supporting parts should be fashioned by gluing several pieces side by side to make it strong enough to withstand all of the pressure that will be on it. For cosmetic purposes and to help keep out water, you can glue a veneer on the end. Use your waterproof wood glue and clamp it. If you don't have clamps and are willing to experiment, you can possibly secure your two pieces with some extra wood blocks and tie them together on ether side of the two pieces with rope. Do not glue your wood to the blocks or the rope. Then you can insert a sturdy stick under the rope and twist it so that the rope is wrapped around it. By twisting further, you can increase the tension on the rope, and you can secure the stick in place by tying it to the rope that it is twisted around. Make the ribs like the keel but with a different shape to them. Many of the smaller ribs pieces can be made with light and inexpensive 1x1 pieces of wood.
Use a fabric skin but make sure that you attach it so that you can replace it or tighten it periodically. Any tightly woven sailcloth that you buy used should do the trick for covering the boat's skeleton. The cloths come in a variety of styles and colors. Make sure that the cloth/skin is attached to the boat in a way that makes it tightly drawn when the boat is assembled. You can use brass washers and screws to attach the skin to the boat, but it gets rather expensive. You can avoid tear-outs by sandwiching cloth between pieces of wood that are screwed together so that the contact area spreads out any stress on the cloth when it feels a push or pull. Canvas is a good and heavy cloth that can be used and can stand up better than other cloths to accidentally being stepped on. Sailcloths are supposed to be waterproof. You can use a brush to apply hot wax to the cloth on both sides, working it into the cloth. Let it cool. Another way to waterproof your boat is to coat it with a water-tight adhesive or paint. Make sure that all of the wood is waterproofed and that any hinges or other fittings are in working order.
Put the heaviest part of the boat in the middle of the boat and down low to help the boat balance. Design a boat that has a heavier keel to add stability. Do a couple of test runs near the shore and troubleshoot any problems. After a little tweaking, begin to build up your confidence by trying out the boat in controlled conditions. After every run, make sure to let the boat dry out before storing it.
