Introduction The idea of tranverse planking originated in a discussion on the Boat Design Forum http://www.boatdesign.net/
The planks for most wooden boat construction are laid longitudinally or fore-and-aft, although some are laid diagonally in several layers. A builder and contributor to the boat forum had a supply of short planks on hand and wondered if it was practical to lay them across the boat, i.e., transversely, or thwart-wise as a Nautical Architect would probably prefer to call it. As far as I know the builder did not proceed with the idea although it seemed to have some merits. However it stuck in my mind and I have been developing the idea further for about 3 years.
I'll describe how it works and how I hope to do it. I have a canoe design I wish to build using this method but the transverse planking method is not limited to canoes. In fact earlier I worked for some time on a design for a small sailboat that would have used the building method; but I decided I didn't need one of those.
A Related Building Method
The concept is related to radius chine construction used for larger boats in which ply sheets are bent around the turn of the bilge to connect the longitudinally laid sheer and bottom plank(s). It is, I believe, more commonly used in the construction of steel and aluminium boats than plywood ones, as shown here.
However, for transverse planking as described here the planks go all the way from the gunnel to the keel, in fact for a very narrow boat like a racing skull the planks could go across the hull from gunnel to gunnel. A racing skull, in fact, would probably be an ideal test case for this concept, but as for the sailboat, I don't need one.
Initial Study This preliminary canoe design attempts to show the effect of transverse planking on the shape of the boat. As with longitudinal planking the joints between the planks can be seen as vertical chines or which show faintly in the image. Although concerns were raised by several boat forum contributors over the possibility of turbulence from these edges, they get rapidly smaller as the plank count increases and become negligible without requiring the use of very narrow planks. They also get less apparent around the turn of the bilge and disappear on the bottom. The amount of wood that had to be removed from the jewel-like "facets" is a fraction of the outer veneer of typical plywood.
Plank Developments This image shows sample plank developments for the trial canoe design pictured above. Because the boat is identical at each end and both sides only a quarter of the planks are shown, so there will be 4x as many planks needed for a boat build.
The plank developments will look a little strange to a boat builder; for a conventional boat the plank length would be that of the boat, about 7x as long as these planks, and there would be far less of them, perhaps 12 instead of 36. However, the plank widths are similar and therefore total length of planks, and plank-to-plank seams, is similar to a conventionally planked boat. The amount of cutting out for the planks is the same, although I expect cutting will be much easier for several reasons, including the shorter length of each plank.
Because the planks are almost rectangular there is very little waste material. The short planks will be easier to handle than thin, floppy longitudinally-laid planks. Interestingly, it is possible to design the boat so that the planks other than the ones at the ends are identical; which would make measuring and cutting the planks extremely simple.
A Classic Canoe for Comparison
This elegant canoe is my design take on the Wee Lassie, a classic canoe of the late 19th century by John Henry Rushton. It is constructed with 6 planks per side.
Rushton built canoes for an inveterate paddler called George W. Sears, a tiny man with health problems who required an ultra-light boat. The Sairy Gamp (named for a Dickens character) weighed a mere 5 Kg.
These are the plank developments for the Wee Lassie, as they would be for a stitch and glue build.
Although they can be re-arranged on the plywood sheet for minimum waste, a fair bit of wastage will still occur, and the planks require careful measurement, accurate marking is crucial to a good result and the long, delicate planks need careful handling.
A Design for Transverse Planking This canoe will be a little longer than the ones I have built so far, almost 16 feet or 4.8 meters. I like the idea of most of the planks being identical so I will add that objective.
The first step in the design process is to make the curve of the gunnel - viewed from above - into a perfectly circular arc; this is not unusual in boat designs, many boats have very nearly that shape anyway and it makes for a nice looking, symmetrical canoe. The next step is to make the curve of the bilge a circular arc, as was done for the Rose Lee canoe design. The rationale for the circular bilge profile is to get the bilges as small as possible without breaking the plywood; a curve with a constant radius is the most efficient way of doing this. The use of mathematically created shapes also simplifies the task of generating plank developments. That is not usually a problem when it is done with hull design software such as Free!Ship but those programs are intended for use with longitudinal planked boat designs. Entering a design that accurately enough to obtain usable plank developments is much more difficult for a transverse plank design. So This design will be created in detail using mathematical methods and conventional drawing rather than software. However, hull design software is still useful for hydrostatic and hydrodynamic analysis.
The gunnel curve radius together with the hull length will mostly determine the beam of the boat about 31" (79 cm), although that may change depending on how the hydrostatics and hydrodynamics work out. The beam also depends on the shape of the gunnel curve approaching the stems; the radius can continue up to the stems or be a straight line approaching the stems or any curve between those extremes. A transition to even sharper curves at the stems is often found in canoe designs intended for significant load hauling, like the Voyageur canoes that opened up much of North America to fur hunters and traders, but that's not what I want from this boat.