This is (probably) the last post that I'll derive from Outrigger Canoes of Bali and Madura, Indonesia, by Adrian Horridge.
The "five-part" hull typical of the outrigger canoes of Oceania is an interesting construction unlike any Western design. As shown in the illustration (from Horridge), the five parts consist of the hull bottom, two upper planks that form raised gunwales, and fore and aft "crotches" that form the ends of the raised gunwales and serve somewhat like a stem and sternpost. Fastening methods differ, with the pieces either pegged or sewn together (pegged in Bali and Madura). In either case, the outrigger booms, which rest atop the raised gunwales, are typically lashed to cleats inside the hull bottom which are left standing proud when the hull is carved. These lashings therefore tend to hold the raised gunwales down against the hull bottom.
Indonesian canoe builders start building on ceremonially auspicious days, and some take care to launch on such days as well. "Like other cultures in the Austronesian tradition, the Balinese have a deep belief in the cyclical nature of life and the world," writes Horridge. "(An) aspect of the cyclical nature...is the flow of generations. The son becomes the father and generates another son, and every child in Bali is considered to be the same person as an ancestor. This means, in our context, that changes in the design of canoes are not acknowledged," even though the brief historical record shows significant changes, even since the introduction of photography.
"Another Malayo-Polynesian belief is that objects such as canoes must be made exactly in a specified way," he writes. "If a man should adjust the design of his fishing canoe and gain an advantage, it would be attributed to evil magic and he would expect to have to repay the evil spirits in retribution later, possibly by drowning at sea. There are strong forces, therefore, ensuring that all canoes are the same within the village and strengthening the local view that the designs have always been the same."
As to the source of those supposedly immutable design principles, Horridge writes, "The Balinese believe that ideal proportions are represented in the human body. Therefore, an outrigger canoe, being a creation of its maker and having a soul of its own, must always be constructed with every dimension calculated according to a simple rule of numbers." There are elaborate rules of thumb concerning the proper dimensions of every feature on the canoe, and these rules are invariably based on proportions to the builder's anatomy -- for example, his height, the span between his thumb and forefinger, etc. Such rules are based on the belief that the human form is perfect in its proportions (not unlike the belief by Renaissance European artists in the Vitruvian Man).
The association between the human form and the canoe goes deeper yet. The hull bottom is held to be female, while the crotch pieces are held to be male. During construction, the builder bores a hole in the joint between the two (not clear if it's at the bow or the stern), and deposits in it a minute quantity of gold, which Horridge states is symbolic of semen. Put it all together -- man, woman, a bit of jizz -- and you've got that wonderful living thing, a canoe.