That is a very fine smack that you are proposing to build - however with all due respect, are you absolutely sure that an Essex smack is the most suitable type of vessel for carrying cargo around the islands of PNG, and trading with Australia?
The Essex smacks evolved to suit their particular working conditions in Britain which are probably rather different to those in PNG (?).
I would humbly suggest that there are many other designs available for small commercial working craft which would probably be more suitable for the intended purpose - and be able to carry more cargo for the same overall hull dimensions as well.
But if you really want to build this type of craft, Ed Burnett is probably the person to speak to - here is a 40' gaff cutter from his drawing board (or computer rather!)
http://www.burnettyachtdesign.co.uk/134.html
I am in complete agreement re building the vessel in timber using traditional methods -assuming that there is a plentiful supply of timber available at a reasonable price.
But if there is not, then there could be an argument for teaching the local folk how to build fibreglass working craft. Pretty much any keen enthusiast can become a competent fibreglass laminator in a week or so, but it takes a lot longer to become a reasonable shipwright using timber.
You could even consider the pros and cons of building the hulls in ferro-cement (cement is almost universally available everywhere - in PNG as well?) or even steel.
I am writing this from Barbados in the West Indies, where up until relatively recently much of the inter island cargo trade was carried under sail, in schooners and (later) sloops with auxiliary engines which evolved very well to suit the local conditions - I would suggest that the types of trading sloops still sailing in the Lower Caribbean might be more suitable for your purpose than an Essex Smack.
For a comprehensive review of the working sailing craft of the Caribbean, may I commend to you this excellent book 'Clean Sweet Wind' available from Amazon :
http://www.amazon.co.uk/Clean-Sweet-...7304278&sr=1-1
And here are some interesting designs for sailing cargo vessels from the board of Tom Colvin -
http://thomasecolvin.com/designs.htm
Although most of them are designed for steel construction.
PS - Here are a couple of web pages which might be of background interest :
MacAlister Elliott are Fisheries Consultants in Lymington who work all over the world on all sorts of fisheries projects -
http://www.macalister-elliott.com/
Working Boats have built various vessels for relief work in Indonesia -
http://www.working-boats.co.uk/