One sheet plywood boat(s).

I recently became intrigued with the thought of a small craft, kayak based, single person, that could be built from a single sheet of ply. Could there be any potential in such a design, I asked myself. What kind of stability and payload could such a boat offer?

I played around with a variety of ideas and prototyped a 7 1/2' kayak that helped prove the concept. Ultimately, a single sheet was used for the hull, but additional interior structure was built from another 1/2 sheet of ply. See this thread.

http://www.boatdesign.net/forums/wooden-boat-building-restoration/putz-floats-30448.html

Initially, there were stability issues due to my own eagerness to start cutting wood and not thoroughly investigating the design. Max righting moment of 5 ft.lbs. at 15 deg. of heel. It was actually challenging and fun AND moved though the water extremely easily. Modifications were made and stability was increased to around 15 ft.lbs. at 17 deg. of heel. I felt perfectly comfortable at the new stability numbers, but felt further improvements could be made.

The original plan was for dual chines flat a flat bottom panel. My thought was to keep panel widths to a minimum in an attempt to produce a monocoque hull design (1/8" ply, stitch and glue, glass sheathing). Investigating increased stability lead me to look at a v-bottom, single-chine design. This proved to be quite productive. My most stable multi-chime, to date, has 26 ft.lbs. righting moment at 24 deg. of heel. The single-chined, v-hull increased that to around 35 ft.lbs. at 30 deg. of heel. This higher level of stability, I suspect is more than is required for a simple kayak except that a novice kayaker might enjoy it, but I have a plan for the increased stability. :idea:

The added stability just might support a sailing rig. Ideally, all spars would ship inside the cockpit and all sail controls could be handle from a seated position in the cockpit. I opted for a sprit rig for it's short spars, light weight and reefing/scandalizing abilities. My plans are to modify the snotter arrangement to make it more cockpit friendly. My thoughts are to place a cheekblock on the mast and additional hardware as required to route a "snotter line" back to the cockpit. This way, the sprit could be withdrawn from the cockpit, inserted in the sail and attached to the snotter line, and finally, a single tug would pull the sprit into place at the mast. Tension could be adjusted through cleating at the cockpit.

I'm considering continuing the snotter line to the peak so that when scandalized, the peak can be tensioned down to the mast at the cheekblock. I final twist(literally) to the rig design would be to incorporate a furling sheave(?) into the base of the mast so that once scandalized, the main could also be furled by twisting the mast in it's step through a furling line. Perhaps, I've over engineered the whole design, but I would certainly open to input on these ideas. Also, I've never worked with a sprit rig before and would like input input on any aspects of the rig that I've overlooked.

 

Interesting! I got hooked on this path for a couple of years and it can be addictive. It’s a truly challenging task to design an effective AND attractive boat that can be got out of a single sheet of ply. I assume you’re speaking here of the 4 x 8' sheets not the bigger 5 x 10' size available in some places.

Here are some more links that might be of interest to you:

http://www.tdem.co.nz/boat/links/one-sheet.html
http://koti.kapsi.fi/hvartial/

I made a couple of One Sheet boats several years ago; they were flat-bottomed like Pirogues but did not have enough beam so I found they were not stable enough for me, and they did not paddle too well either. Then I made the 12 footer shown at post #94 of http://www.boatdesign.net/forums/projects-proposals/challenge-100-boat-12176-7.html which is actually a 1-1/4 sheet boat.

It is stable enough to handle the wake from “near miss” by a fast-moving powerboat, nice-looking IMHO, speedy, only 22 lb, and can accommodate my 6' 4" 220 lb paddling buddy although I’m a little bit lighter. I have great confidence in it for flat-water use (rivers and lakes) but would not venture far on one of the Great Lakes or the ocean!

You may notice it has a nice seat, which adjusts by sliding and can also be reclined. I use a double paddle, and when I need a rest I recline the seat, put the paddle athwartships and hook a leg over it for extra stability. I have actually fallen asleep like that, although I don’t recommend it in the middle of a lake with powerboats zipping around!

Generally I find it is not practical to get a kayak out of one sheet unless the decks are fabric, so my home-designed boats have all been canoes. More recently I made a 10.5 footer which is a true single-sheeter but I don’t have any pictures at present as it isn’t painted/varnished. It should come in around 16 lb. Here is an image from Free!Ship: I can send you the design file if you are interested.

One reason my boats are as light as they are is, I do not glass or epoxy them, just paint and varnish. I do not have to deal with rocks or fast currents where I paddle, and I “dry dock” my boats so the extra strength and water-resistance of epoxy/glass is not justified for me. I appreciate the light weight because I car top and it’s a long lift to the roof of my van at my age (70); I also have a long carry to reach the water at some of my favorite locations.

I find that many One Sheet boats tend to be somewhat odd looking, iconic would be more polite I suppose. I insist that my boats look like real boats not folded paper ones. Your kayak looks really nice in that respect, a proper kayak but too small for me I suspect.

I do not use the S&G technique. I developed another method of building using “chine logs” which are about 0.4 x 1" strips of cedar glued to the sheer and bottom planks while they are still flat. I bend these planks over a couple of forms and fasten them to the ply stems, then I plane bevels ready for gluing the bilge planks. This method produces a true monococque hull with no frames, just breasthooks and one thwart, and it is really stiff. The bilge plank seams are the only place I use epoxy, elsewhere I use Titebond III which sets up much quicker. As well as laziness, I also plead guilty to impatience!

I haven’t sailed my home-built canoes but a few years ago I sailed my (plastic) kayak which is only 9.4' but very stable. I plan on getting back to that this year. My last rig was destroyed in a garage fire; it had a 15 sq ft sail and used a Bruce Foil instead of the more common leeboard: the Bruce foil is inclined at 45 deg to the vertical and mounted on outriggers. The sideways force of the wind on the sail produces a vertical force from the foil that counteracts the heeling force of the sail, which is good in a kayak with a small cockpit because that does not allow you to hike out to balance the sail force. I also inclined the sail which was also offset from the center line: it must have looked rather odd from a distance as half the time it was heeling into the wind.

That rig worked very well, although with such a small sail it was not always possible to tack ans sailing upwind was very slow. That rig could be folded away from the cockpit in about 30 seconds and re-erected in about the same time. The sail had a kind of umbrella arrangement which instantly dowsed the sail, handy as my local lakes tend to generate sudden back winds and squalls; the rest of the time was required to collapse the foil and its outriggers against the side of the hull so I could paddle without obstruction.

 

Terry,

The ply sheets are the standard 4 x 8 variety. Thanks for the links. Some interesting offerings there. I'm afraid that one sheet boats are a bit of a gimick. Although, their size doesmake them very portable. I found your boat and it does look very nice.

Judging from comments in your postings on that thread, we are about the same size. You would fit in "Putz" just fine. I'm afraid though that my wifes size is more fitting than my own. As you can see from the pic, I float fairly low in the it. It is certainly interesting to float in a vessel that is barely longer than I am tall.

"Putz" was my first attempt at S&G and as such, I went the full route in sheathing and encapsulation to test strenghts and weights of the vessel. I like the technique and the challenge of creating an appealing boat from flat shapes. Putz's weight was very similar to your creation although slightly heavier; 23-25 lbs. I could shave some weight by using wooden stem and stern posts and being a little more discerning with the interior lay-up.

To save time, money and energy, with this build, I'll be using 1/4" ply with no sheathing except that the deck will be 1/8" to accomodate it's curvature. I'm thinking of calling it either "Man-O-Yak" or " Yak-O-War". I'm horrible at naming projects. I'm eager to try the thicker hull material. The 1/8" ply was a pain to keep aligned. One of your links showed a guy using fishing line to stitch his hull with a continuous line for each seam. The method looks worthy of invesigation.

The Bruce foil is an interesting idea. I like the concept. I would be interested to see a picture of it. How much rigging does it involve? I was toying with a simple centerboard arrangement. It complicates the build but keep the operation simple. Right now, my sail plan has 17'sq that will take me close to Force 4 by my calculation. Scandalizing drops the area to 9.5'sq. I may try to squeek a little may sail area, but I'm limited by my spar lengths.

Your Freeship image didn't post. I've attached a rendering of Putz's final configuation. I've renamed it The Adirondac Pack Yak. The idea being a person could build a harness and pack the little boat into secluded mountain lakes in the quest for solitude, fishing etc. It has a bulkheaded section behind the seat that would accommodate fishing tackle and so forth.

 

Here's the Free!Ship image again: not sure what went wrong last time.

There was no rigging at all on the last kayak sail rig: I even used a kind of tiller to control sail angle, instead of a proper mainsheet. Here is a pic of the first version which was only 12 sq ft. The "tag" hanging from the sail foot is a velcro wrap used when the sail was furled. The rig was all wood with a ply foil; even the rudder was home-made and all-wood.

I had plans to re-create it with an Aluminum outriggers and telescopic mast but I got distracted with building canoes instead. Short attention span!

Later I realized the flat sail and foil were inefficient, however it went quite well.

 

LP, here is a single sheet canoe I made to fit in my station wagon, All the best with yours from Jeff.

 

Interesting...pics when it is done please?!!