These drawings come from a document called 'Development of Outrigger Canoes in Sri Lanka' by Norwegian consulting Naval Architect Dr Ovyind Gulbrendsen. The full document can be found HERE (file size=1.1MB). The source of this document is the OneFish program and in particular the Bay of Bengal programme. This resource is packed with information regrading traditional boats and sustainable fishing methods. To see more of this resource, please follow this link HERE
The above diagrams show the traditional Bala Oru (Oru means canoe I think) also called sometimes an Oruwa. This is a very successful shunting fishing boat found on the Southern and Western coats of Sri Lanka. To understand this boat it is first important to note that the winds in Sri Lanka come from a predictable direction. Thus a fishing boat can go straight out from the beach, at right angles to the wind, and then straight back in. The boats are large and heavy though very fast. Because the wind is from a predictable direction there is no requirement for the boat to point very high into the wind. Thus the shunting sail, which is simple, cost effective and practical.
Over 4000 of these large sailing craft are still plying their trade. The problem now is a shortage of the large trees that are required to make these boats. Thus there has been an attempt to develop a lighter boat that can work with an auxillary motor that uses sawn timber. In response to this need canoes such as the SLR-18 were developed. The boats are sailed when the wind is favourable. In the notes a gunter rig is shown as an option but the lug sail was preferred as it was simpler and more suitable for an auxillary source of power for a fishing boat.
More information on these large Oruwas and other proas can be found at the following links
Indigenous Sails website, as found HERE
Thomas De Mejer's links of proa craft HERE
The pacific proa website by Joseph Oster HERE
Michael Schact's proafile.com website HERE