: Hi,

: I recently discovered foldable canoes (watching a Larrs Monson
: program) and immediately wanted one for camping and fishing
: trips. When I saw the price I wished I never discovered them.
: Then I found Tom Yosts site and thought I would look into
: building one.

: For the last couple of weeks I have been putting some ideas
: together and thought I would post it on a few message boards to
: get some feedback before I finalized the plans and bought the
: materials. The yostwerks site is fantastic, there are loads of
: great ideas and techniques for building kayaks which I will try
: to apply to this canoe.

: . . . To make matters worse I live in the UK so I couldn't
: even use the Yostwerks links for my materials and have had to
: source them from elsewhere.

If you have a source for the aluminum tubing at a reasonable price then go for it. Otherwise, you can use Ash, or a similar hardwood and make your chines for far less money.

: Basically it will be a 4m aluminum frame with HDPE cross sections,
: Inflatable sponsons in the flanks, and a 18oz. (HH-66 glued) PVC
: hull.

I see no reason for inflatable sponsons. Save yourself the trouble of making them. If you want greater beam to increase stability simply push the gunwales further apart. This not only gives you the greater displacement and stability, but it crease interior volume making more room for the paddlers and greater comfort. You lose the weight of the sponsons, the annoyance of inflating them, and gain displacement and capacity. If you really want to have wide, squishy cushions on the sides of the boat, buy some cheap plastic "pool noodles" from a toy store.

: I would appreciate any feedback on my plans (which are attached to
: this post). I have a few questions too that I have struggled to
: find good answers for, like:
: 1.) Is there an easy way to work out the Gunwale length (before it
: is bent) or is it a case of trial, error and adjustment?

Traditionally the length of the canoe was determined by how long the gunwales were, not the other way around. Thus if you were working with 16-foot-long material for the gunwales, after bending it to shape you found that the canoe had an overall length of about 15 1/2 feet.

If you are committed to absolutely a certain overall length, then I'd just allow about 20cm more for the gunwales and trim off the excess. Or, I'd go with the longer boat and make the nose a bit more pointy.

Another tradition was to build the boats with "found" materials. If you found a longer piece of wood, and some bigger pieces of birchbark you could build a longer boat. These traditions go back before the arrival of Europeans in the New World, and the arrival of rulers and tape measures. If you are not producing many canoes in a factory-like setting you don't need to worry if your gunwales are a certain length, or if the canoe ends up a certain length. This is not going to be a state-of-the-art raceboat, so do like the original designers did, and allow yourself some flexibility on exact measurements.

The basic rules will still apply. If you go longer and wider you will get greater displacement. With an unstretchable skin like birchbark, rocker is built in by the building process, to accommodate the opening of the birchbark "pouch" as the gunwales are stretched apart and the center thwart is inserted.

Try this simple experiment to see this. Take a standard business envelope (something in the realm of 100mm by 325mm I guess) and pull it open in the center. The folded bottom edge can not shorten, but as you pull the envelope wider and wider the top corners move in toward the center. As they come in, the bottom edge curves upward just a slight bit.
If you don't have an envelope handy, take a sheet of standard writing or typing paper, fold it in half lengthwise, and use tape or glue to close the ends. Set the fold flat on your table, in front of you, and you will marvel at the subtle effects you can achieve by the simple process of opening that up a bit, and then opening it a bit more.

If you were building a canoe with an "envelope" of birchbark you'd get the same effect. Trim the envelope so that it is not a perfect rectangle --extend the top edges so the top is about 24 inches, or about 60 cm longer than the bottom, or about 30 cm at each end-- and when you open up this pouch to insert the other parts of the canoe you'll find the ends draw in about 4 to 6 inches (about 10 to 15 cm), and the middle drops down (or the ends come up--it is all in how you look at it) by a few inches, or 5 to 8 cm. That is our rocker.

It is getting harder and harder to find good birchbark, so, well over a century ago it was replaced with fabric. You are following in that path. Instead of using canvas you are using a plastic-coated polyester fabric.

For a simple design, lay out your fabric, fold over a hem in which you can insert the gunwale tubes and sew or glue this. Trim the ends and sew or glue them or both. Slide in the gunwale tubes and secure them to the stem and stern posts with a bolt, or a short rope. Insert the keel. Insert the center thwart to establish the width of the boat. Add thwarts near each end to give you the desired fullness and shaping. Now add ribs to link the gunwales to the keel so that all stresses are shared by the three main structural elements. You can use a few yards of inexpensive fabric to make several 1:5 or 1:8 scale models of your canoe. Sprayed with paint they'll float for a while as you tinker with them.

Or, you can get an off-the-shelf design and play with that. Percy Blandford designed several folding kayaks made from wood. You can get copies of the plans from Clark-Craft (www.clarkcraft.com) and modify them as you wish.

Another thought is to build a folding flat-bottomed canoe called a pirogue. Google "Uncle John's pirogue plans" to get a look at the design on these. The building information--minus the measurements--are online. The plans call for bending plywood around a few frames, but the same frames can be connected at the gunwale and bottom with chines, and that skeletonized frame can be wrapped in your strong fabric.

To convert from kayak to canoe you take off the deck. I guess in England they would say that would be converting from canoe to Indian canoe. With no deck to keep the water out you increase the sides to add freeboard and raise the gunwales higher above the waterline. The deckbeams on a kayak structurally connect the gunwales in the same way that thwarts do in a canoe. Canoes, though, suspend their seats from the gunwales, and the seat supports actually serve as thwarts, too.

: 2.) Is the recommended load of the commercially available canoes
: dependent on the strength of the craft, overall buoyancy or a
: combination of the two?

Those two and more. If you wanted to boil it down to just one spec, then the recommended load would be related to the strength of the craft--but that really says nothing. Your are saysuing that a boat which is strong enough to hold x pounds also displaces x pounds, or less.

Displacement is a factor of the length and width of the boat, as well as how deep it sinks into the water. If we were working with straight lines it would be a snap to figure the volume of a shape. Boats, confound it, are built with curved lines and make the math a bit more complicated. Generally, if you want to carry a greater load you get a longer boat rather than a wider one, or a deeper one. You are going for the deeper one. I'd go for a longer one: easier paddling, less waterpressure on the skin (per square inch of exposed fabric); with a simple gunwale curve, a longer boat also gives proportionately greater width at the beam for greater stability.

What you need to play with are the elements that create the strength of the craft. Basically everything you do has to fight waterpressure. On a canoe all the waterpressure is on the skin of the boat, and transmitted to the keel and gunwales. The gunwales and keel share these loads because they are connected by the ribs, frames or triangular bracing between the gunwales and keel, and the thwarts connecting the gunwales. Sometimes the thwarts also are connected to the keel. For a light boat, I suggest that.

If the boat sinks deeper in the water then you have to have more strength on the inside of the boat to resist the outside pressure of the water, which wants to squeeze the boat shut. If you sit on the thwarts, or use the seats as thwarts, they need to hold your weight. They also need to be strong enough to take the pressure of the water trying to squeeze in on them.

A wider boat has longer thwarts, and those need to be thicker or wider or both so they don't collapse. Or, you use more thwarts to get enough strength. A skin-covered kayak has several deck beams which are tied to a center chine which supports the center ridge of the deck fabric. The greatest unsupported length of any of these deck beams is a bit over half the width of the boat at that spot. Being tied together by the deck chines helps to keep those deck beams from flexing--and as long as they are straight they can resist the crushing forces of waterpressure on the sides of the hull.

If the boat is displace 450 pounds, or about 200 kilograms, and you have a single thwart it needs to be able to withstand that pressure. A piece of wood the size of a cane or walking stick does that job easily. But if you have 5 frames along the length of the kayak, then the top of each frame--corresponding to a deck beam or thwart-- only has to handle about 1/5th that pressure. That is about 40 Kilos, or about 90 pounds. A piece of 1/2" HDPE (about 12mm) such as Tom Yost uses can take that lighter load. Particularly since it is practically cross braced with the deck ridge chine, and about 1 1/2 inches wide (about 4 cm).

If you go for a wider boat, and eliminate the deck, and all that would support a deck, you will need much stronger and less flexible thwarts. Or, you can go with stronger and less flexible frames. Or both.

I'd eliminate the plastic frames completely and replace them with aluminum tubes. You can get a tool for bending electrical conduit (thinwall steel tubing) and use that to fabricate 6 or 7 ribs from your aluminum tubing. Rivet blocks of HDPE to these, and drill the HDPE blocks so the aluminum chine tubes snap in. You get greater strength with lighter weight, and retain the ease of assembly you would have with solid plastic frames. The cost is much less, too.

I'd also look at canoe plans rather than trying to adapt a kayak plan. Yost's kayaks are great designs for kayaks. They can roll, and are easily recoverable. That's great when you have a completely covered deck and your butt is sitting low and close to the bottom of the boat. But, add additional weight, double the displacement, double the draft, raise the center of gravity with the paddler on a seat, and remove the deck--and you don't have anything like the conditions that this kayak was designed for. Were you thinking the sponsons would help with stability? Plenty of cheap or free canoe plans kicking around. Or design one yourself around a fabric envelope, as I describe.

You can get all the plastic you need for a canoe from one or two kitchen cutting boards. Cut them into blocks 5 x 7.5 cm (about 2x3 inches) and drill your tube holes in these blocks. File open the ends of the tube holes so these block snap over your chine materials. Position the chines and blocks along the ribs, clamp in place, then drill through the block and rib and fasten them with rivets or stainless steel bolts.

Since I'm suggesting you dump the plastic frames, I'm going to propose some other way to hang your seats, too. Your idea of adding a hole to the frames, and another aluminum tube for hanging a cloth seat is redundant. You might just as well hang the seats from the gunwales. For two seats that would be 4 less pieces of tubing to buy and pack. If the gunwales are supported well by the frames then you can do this. Remember that here we will have the force of waterpressure on the outside of the hull squeezing in, added to the weight of the paddler puling in the gunwale. It is a double whammy against you.

Or, you can go the other way, and have the seats support the gunwales. Make rigid seats from aluminum tubing. Cover them with mesh strapping and they will look like the foldable aluminum chairs that are so popular at summer picnics. The seat frames serve as two thwarts. They can be hung from the gunwales with long bolts and wingnuts. This is a fairly standard method of attaching canoe seats, so you can find silicon bronze seat bolts at places that sell canoe parts. Or try Clark-Craft. I think I got mine from them.

If you add a leg or two to the center of each seat you can transfer some of the paddler's weight down to the keel, and at the same time transfer some of the upward force of water pressure from the keel to the gunwales. Use a block of your HDPE under the seat as a mount for the leg. Bolt the leg loosely to it, and it can fold out of the way. Another block of HDPE on the keel connects to the bottom of this leg with a removable bolt when you assemble the canoe frame.
You can make surprisingly strong boats out of very small pieces of wood, bamboo, plastic or metal. Take a look at the Geodesic Aerolite line of boats designed by Platt Monfort. (Not sure if he is related to the Monfort whose program you saw) www.gaboats.com.

A canoe is usually wider than a kayak, so you need to be concerned with thwart strength and stiffness. For a boat with the length you are thinking of, you can usually get by with a single center thwart. Add in the thwart-like effect of the seats and you effectively have 5 thwarts. Plenty of strength for a boat up to 15 or 16 feet--about 5 meters.-- with a beam of up to 90 cm. You can even use 2 pieces of tubing side by side for your center thwart. Make a "D" shaped part consisting of the center thwart and the center rib and you'll have most of the structural strength needed for your boat in one place.

You don't want more 6 to 8 inches (15 to 20 cm) of unsupported fabric. If you have more then you'll have some durability issues with light fabrics, or with heavy loads. You are talking about a heavy load. So, once you have the ribs or frames designed, you'll space chines (aluminum or wood) around them, keeping these no more than 20 cm apart. If you have them closer then you'll need more materials, and increase the weight, but have a stronger supprt under the skin. If you space them further apart, you'll have a lighter, less expensive boat, and just keep an eye out for wear and tear.

3/8 inch (roughly 9mm) aluminum rods make fine chine strips on multi chine designs. nest those inside the larger diameter rods for packing. You can also use 3/8 inch hardwood strips. They are cheaper and lighter. Let's say you have wood strips which are 18mm wide, 9mm thick, and 1 m long. That would be about 3/4 inch wide, 3/8 inch thick, and 40 inches long. Round the ends of these strips. Drill a hole about 2.5 cm (an inch) from each end of each strip and loosely bolt these together using 6 short bolts and 3 similarly dimensioned pieces of wood strip which are just 10 cm (4 inches) long. You'll be able to fold these 4 m strips in a fan fashion for travel, and unfold them for use as chine strips. It is going to be much easier to find a source for such wood strips than for aluminum tubes. And price? You can probably make these from wood for less than the shipping costs alone on aluminum tubing.

If you go with fewer chines--say just those at the intersection of the bottom of the boat and the side-- then you'll need thicker tubes, and you have wider areas of unsupported fabric over a large area of the boat. Water pressure will cause this to sag in, and tug more at where the fabric is fastened at the gunwales. The heavier the weight per square foot of footprint in the water the more pressure on that fabric. Help it out with some added support.

As for using your 3/4" aluminum tubing for paddles. I think you'll find you want something with a slightly greater diameter so you can get a good grip on it. Depending on your hand size you night want a diameter anywhere from 7/8" to 1.25" (21 to 32mm). If you have the 3/4" tubing on hand, though, try to find some heavy foam you can wrap around the tube so you can get a good grip. The foam will give the paddle some flotation so (hopefully) it won't disappear if you set it down on the water. A wood plug at each end of the tube helps to trap air inside to aid in flotation, too. The plugs don't have to be airtight, or even watertight. Seal the top one, or put a handle at that end of the tube. At the bottom leave a 1/16" (about 1.5mm) hole in the plug and any water that gets in can drain out, yet it won't fill with water, and the trapped air will provide flotation.

Just some ideas here. Before you rush out to buy some expensive materials, you might want to try making some large scale models to test attachment methods and structural support. They are fast to build and not expensive. It is easier to see if the 1/8th sized model holds together with 1/8 the expected weight of the full sized boat. And they make great kids toys (or tow them behind to hold the beer if your friends are all adults)

Hope this helps. Good luck with your project.

PGJ