Examples of traditional frame-first boat construction in Asian cultures are rare. Throughout the Far East, Middle East and east Africa, shell-first construction of planked boats is the norm, where it is used for everything from sampans and junks to dhows. One of the few exceptions is the vattai, an open, sail-powered, flush-planked (carvel) fishing boat common in the state of Tamil Nadu, in India’s southeast.
The vattai is described by Lucy Blue in “The Historical Context of the Construction of the Vattai Fishing Boat and Related Frame-First Vessels of Tamil Nadu and Beyond,” published in Ships and the Development of Maritime Technology in the Indian Ocean (David Parkin and Ruth Barnes, editors; Routledge, 2016). The information and images in this post are from that article.
A vattai in Tamil Nadu.
To quote Dr. Blue:
"Vattai, are flat-bottomed, have a box-like transverse section and are near wall-sided over much of their length. They range in size from around 13.72m long, with a beam of 2.13m and a depth of 1.37m, to the smallest vessels of c. 5.18m x 1.07m x 0.76m. However, irrespective of their size, they are all similar in shape with very high bows, and two or three masts each with a settee-lateen sail, a balance board, and, uniquely on this coast, leeboards."
The design process is of much interest. A single mould form or template is used to lay out most of the frames on a scrieve board, the form being flipped to draw the port and starboard half-breadths. (Forms for different boats differ from one another, apparently, only in the radius of the curve that joins their two straight, right-angled legs.) Since the boat’s cross-section (half-breadth shape) is constant across its entire midbody, a single shape drawn on the scrieve board suffices to define most of the frames, and this follows the exact shape of the form laid square to the edges of the scrieve board.
Use of the mould form and scrieve board (A) to create the shapes of the
"equal" frames for the midbody (B,C,D), and the progressively narrower
frames toward the ends (E, F, G).
Fore and aft of the “equal” frames that constitute the midbody, each of the next three progressively narrower frames at the bow has an identical counterpart in the stern. These frames that define the ends are derived from the same mould form according to a formula that defines how far in from the scrieve board’s upper edge and how far up along the diagonal the form is placed. By rotating and raising the form, different frame shapes may be drawn to create the narrowing and flare of the hull’s ends. The final three frames in the very bow and stern, however, are not drawn or gotten out at this time.
In the boat recorded by Blue, there were 15 “equal” frames for the midbody plus 12 “unequal” ones, evenly divided between the bow and stern. The midsection always consists of an odd number of frames – the central master frame, and equal numbers of identical frames fore and aft of it. The design can be readily made longer by the addition of more equal frames in the midbody with no changes to the ends, and made wider starting with a wider scrieve board but using the same mould form. Rules of thumb establish ratios between length, breadth, depth, and frame spacing, so the builder’s discretion to make changes is limited mainly to his choice of the mould form and number of frames.
Vattai construction drawing
Frames are built up from floor timbers and futtocks, which are assembled with “a complex dovetail joint” that “extends right through the turn of the bilge.” The vattai has no backbone, so apparently the frames are set up on the straight, flat bottom planking, which must be laid down first. Stem and sternpost are butted with a lap joint against the ends of the central bottom plank. The article states variously that the shapes of the very ends are determined by battens (ribbands) or by laid planking between the midbody frames and the end posts. Whichever is truly the case, these define the shapes of the three final pairs of half-frames at each end. Only in these final three sets of frames do the shapes of the vattai’s bow and stern differ. They are installed without floors, their lower ends overlapping fore-and-aft where they land on top of, or are notched onto, the stem and sternpost. (This detail can’t be determined from the drawing.)
Thanks: www.indigenousboats.blogspot.com
