There appears to be a big difference in the approach to workmanship between Western (i.e., European/North American) boatbuilding and that of the dhow world. While the design of traditional Western working boats may have varied, from "workmanlike" to pure grace, workmanship tended to be quite high. Good enough was rarely good enough, and even the simplest and most pragmatic of working craft -- Banks dories come to mind -- tended to be built with cleanly-cut frames, nicely lined-off planks, and in general, evident pride of workmanship.
This doesn't seem to have been the case among dhow builders. Dhow designs are often lovely, sometimes elegant: as shown in the photo of a boom above, their hollow entries tend to merge beautifully along the waterlines into rather wide, square bilges, and there's an ineffable grace to the settee sail in its great variety of rigs. But workmanship tended toward -- no, that's too kind -- let's say favored -- the crude.
Construction began with the backbone (keel, stem and sternpost). Most had their planks assembled before frames were installed, being held together temporarily with external blocks or battens. No forms or moulds were used, so achieving the proper hull form required a really sophisticated understanding of plank shapes -- all the more impressive given the total absence of drawn plans. Contrary to popular belief, however, frame-first construction did occur in in many cases, with the frames being set up on the backbone, Western-fashion, before planking began. Scantlings were quite light by Western standards, but then again, the Indian Ocean isn't the North Atlantic.
In either case, only the outboard surfaces of the frames were flattened or squared up with an adze -- and that done rather roughly. All three inboard surfaces of the frames were left "natural" -- i.e., in the round, with the bark still attached. A look at the interior of a dhow's hull looks positively primitive. (Framing was often done with what was called "jungle wood" which, I believe, was mangrove.) In the picture below, showing a small boom under construction, every other frame butts against the keel, while those in between use natural curves to pass over the keel from one side to the other.
As late as the 1970s, dhows were being built with hand tools, sawing being done by hand, and drilling with bow drills. Plank fastenings were typically iron nails, driven in from the outside and clenched over into the inboard surface of the frames. Construction often occurred on a beach with no proper shipbuilding facilities whatsoever.
Launching from the beach was a strange procedure. As shown in the drawing below, logs were placed beneath the keel, and these were lashed tightly to lengths of timber laid across the gunwales, so that the dhow was held upright inside a vertical square framework at each end. The lower logs rested on skids. Baulks of timber were suspended by ropes from the upper timbers. Shipbuilders would pull back on these baulks and then release them; they would swing forward and strike the transverse logs with a great "thunk," inching the dhow forward over the skids. The procedure was repeated as many times as needed until the dhow reached the sea. A windlass was also used to pull the vessel along.
(All information and photos from The Dhow: an illustrated history of the Dhow and its World, by Clifford W. Hawkins, Nautical Publishing Co. Ltd., 1977.)