Ontong Java is a large Ndura built in Africa by Hans Klaar. It is made of solid thick timbers and not epoxy coated. Cost was much less (a small fraction) of the equivalently sized modern high tech catamarans. Maybe it is not as refined, but it does work. Hans has sailed countless tens of thousands of miles in this boat. Boat life may be limited does to lack of epoxy, maybe only 30 or 40 years, however if your boat costs a fifth of that it does to build a 'modern' design then is that really bad economics, it sure sounds good to me.
There is some information on the Wharram owners website, but link changed and have had to build my own page. My understanding is that Hans built a Wharram inspired catamarn with two masts and crab claw sails, and then Ontong Java was built in west africa to a more traditional design but with a low aspect main and jib. Sealing of the planks (caulking) I think was done with rubber soaked in petrol to soften it, then hammered into the gaps between the planks then nailed on, simple but effective. Building the boat is west africa makes sense as the cost of labour is just so low, and high quality timber can be had for very low prices. The downside is that its not all shiny white and gleaming and may only last 40 years, but that cant be all bad, at least you get a great boat for relatively little money. My understaning is that Ontong Java was modelled on a Fijian Ndura based on sketches of a boat that sailed late in the nineteenth century.
Note that one hull is slighly smaller than the other, this reduces bending stresses on the crossbeams. Note that the rudders are lashed to the main hull and also there are trailing steering oars that work as rudders (dont know the name)
Clarification Looking at the above photos there are obviously two boats. I am going from memory here, but the first boat I think is a Wharram inspired catamaran built by Hans, and the second more traditional looking with much greater overhangs is his later boat called 'Ontong Java'. Ontong Java is a very impressive boat especially when you consider it probably cost a fifth of what a modern large catamaran would cost. There are a few videos floating around on YouTube of this boat, I have included one below though I know there is a much longer YouTube video of this boat sailing but cant recall where I saw it, apparently it can self steer by linking the rudders to the mainsheet somehow
There also seems to be a newer version of Ontong Java being built called Ontong Java 2. Boat now seems to be finished and sailing as of early 2013. It seems Hans was very happy with Ontong Java so he has built a new similar boat
Overview of Hans Klaar's boats
Hans Klaar's first boat was a ketch rigged Wharram cat in plywood/epoxy
In 2007 Hans built the first Ontong Java
Ontong Java was sold in New Zealand approx 2011, and now goes by the name Mareva
In 2012 Hans built Ontong Java II in Gambia in West Africa
Much more information can be found at the atom voyages website LINK 1
Lots of building photos at this LINK 2
More information here also LINK 3
Youtube video Sailing Ontong Java, 2 mins 30 seconds.